A brief review on factors affecting flow and pool boiling

Renewable and Sustainable Energy Reviews 112 (2019) 607–625

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Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser

A brief review on factors affecting flow and pool boiling ∗

T

Manish Dadhich , Om Shankar Prajapati Department of Mechanical Engineering, Rajasthan Technical University, Kota, India

A R T I C LE I N FO

A B S T R A C T

Keywords: Critical heat flux Thermal transport properties Heat transfer coefficient Nanofluid Surface modification

Boiling is a phenomenon in which heat transfer causes liquid evaporation. Boiling phenomenon; when the liquid is imposed by a forced flow is termed as flow boiling and in pool boiling heating surface is submerged in stagnant liquid. Suspended nanoparticles of small size and concentration dispersed in liquids like oil, water etc. are called nanofluid and are heat transfer carrier due to their thermo physical properties. CHF and HTC in boiling are affected by enhanced surface, nanoparticles size, nanofluids concentration and its development, thermo physical properties, like density, specific heat, thermal conductivity and viscosity of nanofluids. Goal of this paper is to review critical heat flux and heat transfer in nanofluid in flow and pool boiling and to understand in better way. Compilation of equations for estimation of thermal conductivity, viscosity etc. from past research has been briefly shown. These equations have adaptability for determination of nanofluid properties for various working parameters. Different experimental procedures of pool and flow boiling, multiphase computational schemes, computational modeling of bubble nucleation, growth and departure has been discussed. One and two stage techniques for nanofluid formulation and approvals of numerical simulation against experimental data have been represented. Current advances in flow and pool boiling of nanofluid to determine HT and CHF has been discussed. CHF enhancement process by surface modifications in pool and flow boiling is accomplished. Finally, for CHF enhancement in flow and pool boiling concluding remarks are given followed by future studies.

1. Introduction In numerous engineering applications boiling phenomenon is most critical to understand. In case of heat exchange various scientists purposefully look for procedure to enhance boiling heat transfer implementation as far as practical applications and fundamental science, the main logical and purposeful investigations regarding boiling can be observed from 1960s [1]. In different segments like refrigeration and air circulation and cooling, atomic reactors, synthetic building and space ship makes heat transfer (HT) an important part. The heat transfer coefficient (HTC) measures the HT force [2]. To make boiling systems more capable; enhancement in boiling HTC is essential to achieve significant decrease in energy consumption. Critical heat flux (CHF) is an important issue in boiling heat transfer. Improvement in basic critical heat flux (CHF) is necessary for system safety. CHF is also called boiling crises, deteriorate heat flux, dry out, dependent upon the condition it follows [3]. As far as possible thermal limit is shown by CHF. After the CHF point, the controlled overheating of the heated surface takes place and the HT productivity all of a sudden decreases. The physical burn out of the materials of the heated surface is the most significant thing which is

∗

called boiling obstacle. Utilization of nanofluid is attractive scheme for the enhancement of CHF and boiling HT [4,5]. Almost half century back the pool boiling and hydrodynamic hypothesis of burnout crises [6] were developed, but due to conditions of burnout, there is restriction to maximum heat flux. When heat flux reaches its critical point, immediate contact between the fluid and heated surface is reduced as the rapid formation of vapor bubbles covers the surfaces which are heated up. This causes extreme increase in the temperature of the heater surface, bringing about burnout of the material. Therefore, for the efficient management of thermal system it is required to enhance the critical flux (CHF). Utilization of nanofluid is attractive technique for the enhancement of CHF and boiling HT. Choi and Eastman [7] carried out a detailed nanofluid test in later 90s. It was a liquid designed with the help of scattering nano particles of size varying from 1 to 100 nm in liquids like water; oil etc. boiling of nano fluids came into notice in later 2000 and turned into a critical research territory of nanofluids. The principle subjects of boiling of nanofluid incorporate flow and pool boiling. Dhir et al. [8] did numerical simulation on pool boiling and results were compared with some of the previously done experimental tests. From numerical simulations the concepts of single and multiple

Corresponding author. Department of Mechanical Engineering, Rajasthan Technical University, Kota, India. E-mail address: [email protected] (M. Dadhich).

https://doi.org/10.1016/j.rser.2019.06.016 Received 1 January 2018; Received in revised form 19 May 2019; Accepted 10 June 2019 Available online 15 June 2019 1364-0321/ © 2019 Elsevier Ltd. All rights reserved.

Renewable and Sustainable Energy Reviews 112 (2019) 607–625

M. Dadhich and O.S. Prajapati

Nomenclature

γ ε λ μ ν П ρ σ ϕ

General Symbols Aa Ar Bo C Cp d dp Dn Dr Ea e G Ga g h hlv He hfg k L M nf Nu P p Δp Pr q Re Ra Su T To ΔT x We

Actual micro fin tube surface area, m2 πDrL, m2 Bond number Concentration of nanoparticles Specific heat at constant pressure (J/Kg K or J/mol K) Tube diameter, mm Nano particle diameter size, nm Dean number Fin root diameter of micro fin tube, m Area enhancement factor Aa/Ar Fin height, m Mass flux, kg/m2s Galileo number Gravitational acceleration,m/s2 Heat transfer coefficient, W/m2K Latent heat of vaporization, J/kg Helical coil number Latent heat of evaporation, kJ/kg Thermal Conductivity, W/mK Heated length of micro fin tube, m Molecular mass, kg/kmol Number of micro fins Nusselt number Pressure, Pa Pitch ratio Axial pressure drop, Pa Prandtl number Wall heat flux, W/m2 Reynolds number Roughness, μm Suratman number Operating temperature, K Reference temperature, K Liquid subcooling temperature, K Vapor quality Weber number

Subscripts bf H2 l nf p r s sub tp v w

Base fluid Hydrogen Liquid Nanofluid Particle Fin root Suspension Subcooling Two phase Vapor Water

Abbreviations CHF DNA DIW DW EDM EG FCNT HEG HTC HT MWCNT OBE ONB pHEMA rGO RSM SANSS SDBS SST TSP

Greek symbols Δρ α β

Fin apex angle, deg Dissipation energy, m2/s3 Thermal conductivity, W/m⋅K Viscosity, Pa.s Kinematic viscosity, m2/s Dimensionless variables used to develop new correlation Density, kg/m3 Liquid vapor interface tension, Jm−2 Nanoparticles volume fraction

ρl − ρv , kg/m3 Polymorph of silicon carbide Micro fin helix angle, deg

bubbles, film and nucleate boiling with their significance were explained. Ciloglu and Bolukbasi [2] did the observations on pool boiling of nanofluids and displayed how the improvement of nanofluids can be done and later it was discussed how the different parameters effect the pool boiling of nanofluids. A correlation was built up by Kandlikar [9] for exchange of heat in vertical as well as horizontal tubes. The correlation was developed for two phase saturated flow boiling utilizing an extensive variety of experimental information and ten clear liquids. Kamatchi and Venkatachalapathy [10] led an examination by including parameters such as the material type, type of surfactant, nanoparticle concentration and size, pressure of system, deposition of nanoparticle and thermal properties of transport to see the effect of nanofluids on enhancement of CHF during pool boiling. Gorenflo et al. [11] simply compared the previously experimental results of 55 individual liquids with semi-empirical and empirical predicted technique for nucleate pool boiling. It was declared that exact test information for thermo-physical explanation was identified by

Critical heat flux Deoxy ribo nucleic acid De-ionized water Distilled water Electrical discharge machining Ethylene glycol Functional carbon nano tubes Hydrogen exfoliated graphene Heat transfer coefficient Heat transfer Multi walled carbon nano tubes Onset of bubble elongation Onset of nucleate boiling Poly hydroxyl ethyl meth acrylate reduced Graphene oxide Reynolds stress model Submerged arc nanoparticle synthesis system Sodium dodecyl benzene sulfonate Shear stress transport Tri sodium phosphate

surface tension; moreover heaters effect played a major role. Celen et al. [12] executed nano refrigerants related review in which the boiling phenomenon of the flow and pool was included. Nanofluid in which the refrigerant acts as a base fluid is called a nano refrigerant. A magnetic nanofluids investigation was conducted by Bahiraei and Hangi [5]. A magnetic nanofluid is composed of magnetic nanoparticles in nonmagnetic liquid and subjecting the fluids to magnetic field. The process of particle movement, liquid stream and heat transfer process can be controlled in the magnetic nanofluid. You et al. [13]conducted an experimental study in sub-atmospheric condition by using SiO2 and Al2O3 with water nanofluids. The copper plate was submerged into the hotter nanofluids to carry out pool boiling and the phenomenon of heat transfer was studied. The outcomes showed inclusion of Al2O3 with water nanofluid enhanced CHF on round and hollow cylinder. Milanova and Kumar [14] utilized SiO2 with water nanofluid having 0.5 vol. % and achieved a greatest improvement of 300% in CHF. Main reasons for CHF improvement was mainly because of technique for 608

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CHF expanded by 200% when compared with water. Blast and Chang [25] researched the features of pool boiling on horizontal flat surface with Al2O3 nanoparticles in water having various concentration by volume was used during experiments. Outcomes indicated when compared with pure water; Al2O3 nanofluid presented a lower heat transfer as the concentration of particles increased; CHF improvement of about 13% and 32% was observed for vertical and horizontal surface respectively during pool boiling. As the concentration of particle increases the roughness of surface also increases. It was cleared that nano-particle deposition caused increased CHF and HTC was decreased in case of pure water. Due to deposition; nucleation site density were decreased and due to this conduction became low because of various values of roughness of surface. Coursey and Kim [26] performed a process of pool boiling using nanofluids to analyze CHF. The process was carried out on different surfaces. It was found that performance was dependent on concentration of nanoparticles and wettability of surface; additionally it was shown that regime of nucleate boiling remains unaltered. With 0.5 g/L or more concentration CHF was improved to 37%. Chopkar et al. [27] did an experimental investigation using a tube made of borosilicate having diameter 150 mm and length 300 mm. A copper plate was located inside a tube in which the nanofluid made up of ZrO2 and water was taken and the process of nucleate pool boiling was done. It was observed that at lower concentrations of nanoparticles improvement in HTC of pool boiling and get decreased as concentration of nano particles increases and lastly HTC becomes so less, even lesser from pure water because of smooth coating. Additionally it was revealed that heat transfer rate was increased by adding surfactant, but significant heat transfer decrease was noticed in nucleate boiling when surfactant were added to nanofluid. The point of this investigation is to present significant findings of boiling phenomenon of flow and pool which affects the performance of heat transfer and these effects needs to be understood in a better way.

nanofluids stable formation and nanoparticle size. Nanofluids stability of dispersion can be enhanced by the use of surfactant in nanofluid preparation. But most of the time it was forwarded that degradation of CHF was observed by surfactant addition to nanofluids. Kathiravan et al. [15] used a nanofluid which was made by copper and water combination and further added surfactant into it and observed a decrease in the value of CHF by 75%, when results were compared with de-ionized water (DIW). With the help of wetting features Kim et al. [16] recognized that deposition of nanoparticle on the heated surface was due to mechanism of evaporating micro layer. As the thickness of deposited layer increases, corresponding to it increase in surface wettability also takes place which also brings about up enhancement in CHF. Stutz et al. [17] investigated the enhancement of CHF for two wetting liquid pentane and water respectively; the fluid outcome indicated that increase in CHF was observed for water when compared with pentane. Reduction in contact angle of deposition over heated surface, which enhances the surface wettability due to which CHF was improved, moreover it was seen that reduction in contact angle increases CHF and decrease in CHF was due to reduction of surface tension. Magnificent effect was observed more for contact angle rather than surface tension which is the main reason for enhancement in CHF for Tri Sodium Phosphate (TSP) and nanofluids. With a goal to understand the surface roughness, Harish et al. [18] utilized two types of heater to carry out tests i.e. rough and smooth. Outcomes demonstrated for similar concentration of volume; rough surface executed a superior execution mainly because of development of many nucleation sites though deterioration happened for heater which was smoother. In addition, average diameter of particles and surface roughness relative size are the qualities of stable nanofluid boiling. For CHF enhancement effects of concentration of particles, size of particles and roughness of surface have been examined. As the value of contact angle becomes zero the wettability of surface enhances. For this Kim et al. [19] clarified that there were some difficulties to investigate the major component which was responsible for the enhancement of CHF. It was further demonstrated that in nano porous layer the fluid can be accessed by the capillary action. Ho Seon Ahn et al. [20] used nanofluids made of grapheme oxide for the test and showed that improvement in CHF was observed. This improvement was due to capillary action. However it didn't appear to be satisfactory to investigate the mechanism of observed 320% CHF improvement. In this way, it was concluded that factors which were responsible for the improvement of CHF was capillary action of nanoparticle which were deposited on the surface. Barber et al. [21] summarized about the variables that influenced heat transfer in pool boiling using nanofluids. It was realized that utilization of nanofluids improves CHF in pool boiling. However, the outcomes were scattered mostly because of different variables. Hence this study tell about the details of the variables which improves CHF from the recent literature outcomes in view of parameters like surfactants, pressure of system, deposition layers of nanoparticles, thermal properties of transport, nano-particle material, size and concentration and additional information about relevance on these parameters towards the CHF enhancement. In saturated FC-72 Chang and You [22] analyzed heat transfer in pool boiling occurring on diamond particle surface coating. Uniform porous coatings are characterized into two groups, i.e. micro porous coatings and porous coatings, as per the superheated fluid layer thickness, which is evaluated to be 100 μm for FC-72. A huge increment in CHF was seen over the micro porous surface area. Thome et al. [23] did a review of heat transfer in flow boiling, pressure drop in two phase and different pattern of flow for hydro carbons and ammonia which are frequently used in heat pumps, refrigeration and air conditioning systems. Vassallo et al. [24] played out an experiment under atmospheric condition of 1 bar. The apparatus of experiment was made up of a Pyrex dish in which the silica nanoparticles were arranged and wire made of Ni–Cr which was submerged into the arrangement. For this experiment

2. Research process In this section the procedure adopted for literature review is described. For the completion of the review process, the research technique adopted is literature review. By exploring the contributions which are already done in the relevant field helped many researchers to find the answers to many questions. Basically literature review is a assembly of contribution of appropriate work in the relevant field. Literature review is also research plan which picks, judges, examine, arrange and reveals the existing studies within the range of framed questions. The main point is to clear everything about the existing study i.e. what is hidden and what is known about the studies by refining the clarity, simplicity and validity. The scope of this research is to focus on nanofluid heat transfer coefficient and critical heat flux in flow and pool boiling. This review is carried out because boiling process plays a major role in many industrial applications. Enhancement in boiling HTC plays an important role in making boiling system efficient and decreasing the consumption of energy. CHF enhancement makes the industrial system safe which are running on critical heat flux. Addition of nanofluid is one of the best methods to enhance HTC and CHF. In this study a brief summary of results obtained from previous research is presented. Denyer and Tranfield [28] developed a method which ensures that literature review is clear and well examined. Steps adopted for the review are mentioned below: 1. Formulation of research questions. 2. Locating the studies i.e. methods used to find out the studies from database and other sources. 3. To select and evaluate the studies i.e. the formulation of criteria for including or excluding papers to refine the research. 4. Process of analysis and synthesis is carried out to extract the results from collected data and analyze them.

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formulated to retrieve the most relevant literature. These criteria are applied for the selection of significant studies which can answer the questions related to research of literature review. Inclusion and exclusion criteria acts like boundaries which separates the relevant and irrelevant studies. For the current review the inclusion and exclusion criteria selected are mentioned below:

2.1. Formulation of research questions The main inspiration of this literature review is to collect, examine and inspect existing studies of pool and flow boiling all over the world. The information obtained from this review is summarized to develop some effective methods which can enhance the HTC and CHF in pool and flow boiling. This review also gives the information about the methods which are followed in existing studies which enhances HTC and CHF in pool and flow boiling. A set of research questions is framed to be followed during his literature review to achieve the objectives. During the course of finding the answers to the framed research questions, many weakness in the existing research will be highlighted. For finding, exploring and analyzing the available literature some questions are framed which are mentioned below:

2.3.1. Exclusion criteria

• Articles not related to boiling phenomena. • Articles not written in English. • Articles published before 2000 (5–7 relevant articles are included). • Articles which are published as a short paper. 2.3.2. Inclusion criteria

1. What are the main factors that affects thermal transport properties of nanofluids? 2. What are the different investigations carried out on boiling of nanofluids? 3. What are the different methods for the preparation of stable nanofluids? 4. What is the effect on Heat Transfer Coefficient and Critical Heat Flux during pool and flow boiling of nanofluids? 5. What is the effect of surface change on pool and flow boiling heat transfer?

• An article that provides thermal transport properties of nanofluid. • An article that provides method of nanofluid preparation. • An article that provides different investigations (experimental and numerical) carried out on boiling of nanofluids. • An article that provides the effect on Heat Transfer Coefficient and Critical Heat Flux during boiling of nanofluids.

On the basis of discussion on above mentioned two criteria's. Articles were removed from the final list that meet the exclusion criteria and articles that met any one of the inclusion criteria were included in the final list to get the desired information.

2.2. Locating the studies The study reported that this topic is not present in some specified journals. This topic is discussed in variety of journals such as heat transfer journals, nanofluids journals, thermal engineering journals and applied physics journals. So the papers cannot be selected on the basis of journal titles. In order to find the desired papers keyword search was done in major science publishers such as ScienceDirect, Taylor & Francis, Wiley, American Society of Mechanical Engineers, SpringerLink and Google scholar. The majority of the papers related to research were found in ScienceDirect, American Society of Mechanical Engineers, SpringerLink and Google scholar. Boiling is considered to be a very common term in this research. Very limited papers were found using this term. So in order to complete the selection process of the papers a wide range of the search terms were included. The below mentioned keywords were used for selecting the papers: Nanofluid, Pool boiling, Heat transfer coefficient, Critical heat flux, Nanoparticles, Flow boiling, Experimental, Numerical, Thermo physical properties, Thermal Conductivity, Density, Viscosity, Specific heat, Surface Tension, Preparation, Two phase, Concentration, Heat transfer, Correlation and Bubble. The search was done using all feasible combinations of above mentioned keywords in titles, abstracts, keywords and all text.

2.4. Process of analysis and synthesis When the selection of relevant literature is completed, the first aim is to split every included paper into components. A data extraction form was framed in the first step and papers were grouped on the basis of criteria shown in Table 1. Synthesizing of findings is the second step. The process of synthesis, groups the results of every paper and makes accurate arrangement which is suitable to the fundamental point of the study with the goal that it gives a comprehensive and distinctive view to the readers. 3. Thermal transport properties of nanofluids In the heat transfer various thermal transport properties of nano fluids like viscosity, thermal conductivity, surface tension etc assume a significant part. In this section thermal properties of nanofluids have been presented. 3.1. Thermal conductivity Thermal conductivity enhancement is the primary goal by utilizing nano particles and mixing them into the standard liquid. Different studies showed that even when the concentration of nano particles in the base liquid is low, higher value of thermal conductivity is displayed. Philip et al. [29] founded that there was enhancement of about 25%

2.3. To select and evaluate the studies For the refinement of the search inclusion and exclusion criteria are Table 1 Quantitative analysis criteria of the articles. Grouping

Details

Year Source of publication Name of database Boiling type Method of research Type of Data Research interest Aim of research

Publication year Journals in which the papers published Collections of online journals that publish thermo physical properties of nanofluid, nanofluid preparation, nanofluid boiling related studies The type of boiling investigated (Pool and Flow) Categorization of methods used (experimental, numerical, case study, literature review) Categorization of type of data (qualitative and quantitative) The main centre of attention of the study The objective of the paper

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in the value of thermal conductivity of nano fluid made up of Fe3O4 nanoparticles in various base liquid having an average molecule size up to 6 nm. The outcomes revealed that the material of base liquid plays a least important part in determining thermal conductivity. Altan and Bucak [30] by using various base liquids tentatively examined the performance of thermal conductivity by effect of Fe3O4 nanoparticles. With increase in magnetic particle concentration in the mineral oil, heptanes and other non polar solvent, thermal conductivity of this type of nanofluids increases linearly straight. In the various base liquid outcomes of thermal conductivities of nanofluid comes out to be different, when nanofluids are made up of various base liquid and similar nanoparticles. The main cause is due to interaction of base liquid with particles having surfactants. Rizvi et al. [31] in comparison to Hamilton Crosser's model introduced another model that described the nano particles and surfactants interactions and their effect on each other. Outcomes revealed that the results of nanofluid thermal conductivity come out to be more precise from introduced model. Rarely any examinations indicate that the higher thermal conductivity of suspended nanoparticles shows larger improvement in the thermal conductivity of nanofluid. With use of nanoparticles like Al2O3 and CuO with base liquid like oil and ethylene glycol forms nanofluids which reveals that metallic nanofluids shows higher value of thermal conductivity when compared with oxide nanoparticles [32]. Gowda et al. [33] utilized nanoparticles of copper oxide and alumina dispersed in the base liquid of ethylene glycol and examined the thermal conductivity of both nanofluid and the results revealed that CuO nanofluids shows higher thermal conductivity value when compared with alumina nanofluids, whose thermal conductivity was noted to be lower. Zhu et al. [34] revealed the fact that the improvement in thermal conductivity of ferro liquids is not effected by nanoparticles thermal conductivity. An examination was conducted taking nanofluids like Al2O3, TiO2, CuO and Fe3O4 to determine the thermal conductivity. The outcome results revealed that Fe3O4 has higher thermal conductivity when compared with Al2O3, TiO2 and CuO nanofluids even though mass Fe3O4 has bring down thermal conductivity than the others. Ahmed et al. [35] noticed that the reason for enhancement of critical heat flux was nanofluid thermal conductivity rather than surface deposition rate of nanoparticle at very low concentration. This case needs advance investigation of nanofluid planning technique, nanofluid stability, nanoparticle shape and size for this type of enhancement in critical heat flux. Ho Seon Ahn et al. [36] notify that the critical heat flux enhancement was delayed due to little increment of rGO colloids thermal conductivity. Yang and Liu [37] for silica nanofluid noticed an immense increment in thermal conductivity. In any case, any effect on enhancement of critical heat flux was not indicated. Gavili et al. [38] applied electrically controlled magnetic field outside the coil and examined the ferro nanofluids thermal conductivity. Inspection of saturation time and reversibility was done after switching off the magnetic field. At 5% volume concentration ferro liquid indicated that the thermal conductivity enhancement over 200%. Outcomes likewise showed that after switching off magnetic field reversibility in thermal conductivity was seen.

ρnf = ∅ρnanoparticle + (1 − ∅) ρbf

(1)

(ρcp)nf = ∅ (ρcp)nanoparticle + (1 − ∅)(ρcp)bf

(2)

where. ρ and cp are density and specific heat. ϕ is the nanoparticles volume fraction. ‘nf’ stands for nanofluid ‘bf’ stands for base fluid Kedzierski [40] conditionally focused on the variety of density of CuO nano lubricant with various nano-particle mass divisions (2.9%, 5.6% and 39.2%) for a temperature variation of 288–318 K with circular nanoparticles of measurement of 30 nm diameter. Results displayed that the density of the CuO nano lubricant decreases with temperature increase at atmospheric pressure. The author likewise assumed that, density increases with an increase in the CuO mass fraction. Sekhar and Sharma [41] carried out the examinations by utilizing the combination of Al2O3 and water nanofluids with 47 nm nanoparticle diameter and working temperature variation from 25 °C to 45 °C. After the experiments an equation was developed for nanofluids which were water based and this equation determine the specific heat is mentioned below:

Tnf −0.3037 ⎛ dp ⎞0.4167 ∅ 2.272 ⎤ ⎛ ⎞ ⎛1 + ⎞ Cp, nf = ⎡ 1+ ⎥ ⎢0.8429 1 + 50 50 ⎠ 100 ⎠ ⎝ ⎝ ⎠ ⎝ ⎦ ⎣ ⎜

⎜

⎟

⎟

(3)

where: Ø = Nanoparticles volume fraction in per cent. Tnf = Temperature of nanofluids dp = Nano particle diameter size Vajjha and Das [42] determined the particular specific heat of Al2O3, ZnO2, and SiO2 nanoparticles. The nanoparticles of ZnO2 and Al2O3 were dispersed in liquid blend having 60 to 40 ratios of ethylene glycol and water and SiO2 was dispersed in de-ionized water. ZnO2 and Al2O3 have molecule size of 77 and 44; respectively. 315 K–363 K was the varying temperature range in which the evaluation was to be done. Volumetric concentration of nano molecule was taken up to a limit of 10%. The best conditions that fits test information of three nanofluids made from two kinds of base fluids is given as:

Cp, nf

⎡ (A × T ) + B × ⎢ =⎢ C+∅ ⎢ ⎣

( ) ⎤⎥ C Cp, p

Cp, bf

⎥ ⎥ ⎦

p, bf

(4)

The values of constant A, B and C for three nanofluids are given below: For ZnO the values are: A = 1.769*10−3; B = 1.1937; C = 8.021*10−1 For Al2O3 the values are: A = 8.911*10−4; B = 5.719*10−1; C = 4.250*10−1 For SiO2 the values are: A = 4.604*10−4; B = 9.855*10−1; C = 2.990*10−1

3.2. Specific heat and density An instant transformation was seen in specific heat and density by vast majority of examiners. By increasing concentration of nano particles a decrease in specific heat was observed. Still there was lack of disciplined examination which tells about the effect of specific heat and density towards critical heat flux improvement. Deep investigation on the effect of these parameters is required. Pantzali et al. [39] determined nanofluids density and specific heat. It was observed that the fluctuation of specific heat and density was 2% and 5% respectively, hence utilizing the below mentioned equations; nanofluids specific heat and density can be calculated:

Where: Cpbf = Specific heat of base fluid Cpnf = Specific heat of nanofluid Cpp = Specific heat of nano-particle Ø = Nanoparticles volume fraction in per cent T = Operating temperature Teng and Hung [43] in the concentration limit ranging from 0% to 1.5% investigated density of nanofluid composed of water and Al2O3. 611

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CuO nanoparticles and water as base liquid and observed the viscosity increase. Two CuO nanofluids were different in particle measurement. One was having particle measurement of 8 nm–14 nm size and other having 23 nm–37 nm size. Higher viscosity was observed for particle having size of 8 nm–14 nm. Consequently, possible reason behind viscosity rise was behavior of small size of particles which gathers the particles without a repulsive force. Timofeeva et al. [51] took α-SiC nanoparticles size varying from 16 nm to 90 nm and prepared the nanofluids of water and α-SiC, it was found that nanofluid viscosity increases as particle measure decreases working in temperature range of 15 °C–55 °C. Electrostatic attraction becomes higher due to smaller nanoparticles larger surface area, so it is supposed to be the main reason for viscosity increase of nanofluids containing smaller nanoparticles sizes. Kwark et al. [52] measured viscosity and found an insignificant difference among nanofluid and pure water. They reported this may be because of low concentration of nanofluid utilized as a part of their examination. For the shear rate Das et al. [53] analyzed water alumina nanofluid viscosity. Outcomes revealed as the concentration of particle increases viscosity also increase and with variation of temperature it decreases. Additionally viscosity increases along shear rate. Kulkarni et al. [54] analyzed to decide the rheological conduct of nanofluid composed of de-ionized water and nanoparticles of copper oxide (CuO) having diameter size measuring 29 nm, volume concentration variation in the vicinity of 5 and 15% and temperatures changing in the vicinity of 278 and 323 K. Their work yielded a fluid viscosity correlation ship mentioned below:

When the experimental values of density were compared with the calculated density value from Equation (1), a deviation in the range of 1.50%–0.06% was seen. With the increase in concentration of nanoparticles more significant density deviation pattern is observed. Mahian et al. [44] took nanoparticles of ZnO having a size of 20 nm and suspended them into base blend of water and ethylene glycol mixed together in ratio of 60 to 40 by weight working in 25 °C–40 °C temperature range for most extreme concentration of about 4%. Deviation of around 7% was observed in the density values when compared with Equation (1) density values. Maximum value for density at 25 °C was 1328.72 kg/m3 for volume concentration of 4%. Mariano et al. [45] carried out experiments using SnO2 nanoparticles and dispersing into ethylene glycol. The particle size was 17 nm. The whole experiment work was done in the 10 °C to 50 °C temperature range and volume concentration in the range of 1%–5%. At volume concentration of 5% and temperature 10.5 °C density at its maximum value was observed. When compared with base fluid the density of nanofluid was higher with concentration and decreases with the increase in temperature. Wang et al. [46] showed that the specific heat is affected by size of particles. For nanoparticles of CuO of size 50 nm the specific heat estimated values obtained from tests at temperature below 225 K were very close to the theoretical values of specific heat. In any case, when size of particles lowered from 50 nm to 10 nm and temperature rises over 225 K, at that time the specific heat theoretical values decreases. As the size of particles increases the value of specific heat also get increases. But this is possible only for particles below 10 nm. The supporting understanding can be produced using the examinations attempted on specific heat of nanofluid. When compared with base liquid the specific heat of nanofluid is found to be lower and decreases with increase in concentration, and does not shift altogether with temperature. The variation in nanofluids heat capacity value for nanoparticles size is insignificant as the volume concentration rises, because of base fluid heat capacity. This variation of capacity with volume concentration is steady.

1 ln μS = A ⎛ ⎞ − B ⎝T ⎠

(5)

where: μs is viscosity of suspension, A and B are polynomials acting as elements of volumetric concentrations of particle which can be calculated by below mentioned correlation ship:

A = 20587∅2 + 1587∅ + 1078.3∅3 B = −107.12∅2 + 53.548∅ + 2.8715

3.3. Viscosity

with value of R2 = 0.99 with value of R2 = 0.97

where:

As regularly observed viscosities of nanofluids are comparatively higher than the base liquid. Higher particle growth and collaboration causes enlarged viscous distribution which is the primary reasons for large viscosity in nanofluids. Accumulation of particle because of the attractive intermolecular forces brings about higher viscosity of the nanofluids. Kadzierski [47] observed the kinematic viscosity of Al2O3 which is utilized as a nano-grease. The author considered a temperature variation of 288–318 K with two different measurements of nanoparticles diameters: 60 and 10 nm, respectively. Utilization of surfactant keeps up appropriate dispersion of the nanoparticles which are circular in shape. Nanoparticles mass fractions and surfactant both were utilized as working factors. Furthermore, the author built up a model to predict the kinematic viscosity, considering the nano-particle blend viscosities, base liquid, surfactant utilized, component of mass fraction of nanoparticle, temperature, mass fraction of surfactant and diameter of nanoparticle. Ho and Gao [48] founded that paraffin emulsion with Al2O3 nanoparticle in various concentrations has nonlinear dynamic viscosity. Moreover, the dynamic viscosity decreases with an increase in temperature. Observations showed that the improvement of dynamic viscosity was significantly higher than thermal conductivity enhancement in similar condition. He et al. [49] clarified the reason of increasing viscosity of BaCl2 fluid solution with TiO2 nano particles. As the particle volume fraction grows, the separation between particles decreases. The frictional strength among nanoparticles and amongst nanoparticle and water molecule is enhanced rapidly. It shows the increase in viscosity. Gallego et al. [50] used two nanofluid composed of

Ø is the fraction of volume varying from 5*10−2 to 1.5*10−1. Values obtained from experiments were compared with the computed values obtained from above correlation ship. The variation among the values was about lower than 10%, except at temperature of 278 K for 15% suspension of CuO. Nguyen et al. [55] conducted examinations for the confirmation of viscosity of nanofluid composed of water with CuO and Al2O3 nanoparticles at various concentrations, 22 °C to 75 °C temperature range and finally the size of particles. Tests of CuO nanoparticles with size of 29 nm and Al2O3 nanoparticles with sizes of 47 nm and 36 nm; disclosed that nanofluid volume concentration and viscosity have a solid dependency. Viscosity altogether is not affected by size of molecule for below 4% concentration. For dynamic viscosity confirmation of Al2O3 and CuO nanofluid in light of concentration for 1.0 and 4.0%, respectively, an equation is exhibited as:

μr = μr =

μnf μw μnf μw

= (1.1250 − 0.0007T )

= (2.1275 − 0.0007T + 0.0002T 2)

where:

μr = Relative viscosity (ratio of nanofluid-to-water viscosities) μnf =Viscosity of nanofluid 612

(6)

(7)

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Temperature: 303 K < T < 343 K Particle concentration: 0.005 « 0.06 Diameter of nanoparticle: 15 nm < dp < 50 nm. And the values of constant are: a1 has the value of 1.02219 b1 has the value of 0.27706 c1 has the value of 0.00063558 Overall D has the value of = (a1+b1+c1) = 1.17344 γnf = nanofluid surface tension, N/m γbf = base fluid surface tension, N/m Ø particle volumetric concentration, % T = Measured absolute temperature, K To = reference room temperature, 26 °C (299 K) dp = Nano particle diameter size, nm dbf = molecule size of base fluid, nm

μ w = Viscosity of water T = Operating temperature Sundar et al. [56] carried out an examination to decide the effect of water/ethylene glycol based fluid blend on viscosity having percentage weight ratio of 60:40, 40:60, and 80:20 with nanoparticles of Al2O3 in 20 °C–60 °C temperature range. Maximum enhancement ratio observed was 2.58 and it was obtained with nanofluid concentration of 1.5% at 0 °C and ratio of 40:60% water/ethylene glycol when compared with base fluid. Presently, viscosity information from the boiling literature was observed to be of pure water for every single test concentrations of nanofluid. However, this requires extra investigations like experimental and theoretical to make nanofluid viscosity database, precise models utilization and finally building up new correlation ship for investigation of heat transfer in nanofluids.

M.H.U. Bhuiyan et al. [61] examined the effect of nanoparticles concentration and the effect of variety of nanoparticles alongside with the size of nanoparticles. Nanofluids were compared with distilled water (DW) and dispersing nanoparticles like TiO2, SiO2 and Al2O3. The varying size of nanoparticles was taken as TiO2 is of 21 nm, SiO2 varies from 5 nm to 20 nm and Al2O3 have 50 nm and 13 nm. Utilizing a programmed surface tensiometer and strategy called Du-Nouy ring nanofluid surface tension was calculated. Outcomes indicated that with the increase in size of particles and concentration; nanofluids surface tension also increases. When all three nanofluids water-SiO2, waterAl2O3 and water TiO2 were compared; higher surface tension is displayed by distilled water TiO2 nanofluid.

3.4. Surface tension For enhancement of critical heat flux of nanofluid, surface tension plays an essential part and received many considerations. It is mentioned in previous literature as the temperature and concentration of nanoparticles increases, decrease in surface tension occurs. Vafaei et al. [57] did an experimental investigation by taking Bi2Te3 (Bismuth Telluride) nanoparticles. Concentration of nanoparticles and the influence of their sizes were taken for successful study of surface tension. Results revealed that as the concentration was increased up to saturation point there was decrease in surface tension and after the saturation point a turnaround in the process was seen. In addition nano particle size of 10.4 nm shows higher surface tension when compared with 2.5 nm size of nanoparticle under similar mass concentration. Jeong et al. [58] indicated that as the concentration of water alumina nanofluids and tri phosphate solution increases, a sharp decrease in surface tension was observed. Actually, the decrease in surface tension lowers CHF value. However, the effect of nano-particle surface deposition causes increase in wettability and contact angle decrease. All these factors were responsible for critical heat flux enhancement in alumina water nanofluids and tri sodium phosphate. Interestingly, for every single tested concentration, nanofluids surface tension was practically similar to pure water. Kumar and Milanova [59] showed that surface tension of nanofluids becomes lower when compared with base liquid which was the main reason for delay in critical heat flux occurrence in carbon nano tubes nanofluids. Kathiravan et al. [15] showed that enhancement in critical heat flux was suppressed due to insertion of surfactants particles in nanofluids of water and copper which causes surface tension decrease. J. Chinnam et al. [60] took four types of nanofluids and measured their surface tension. Mainly three parameters like size of particle, particles volume concentration and temperature were taken into consideration. When compared with size of particle, temperature and volumetric concentration, surface tension showed more dependency on the temperature. For instance, a nanofluid having 1% concentration of Al2O3 nanoparticles and having a size of 45 nm, near about 12% lowering of surface tension was seen for around 13% of temperature increase. A decrease in surface tension of about 6.5% was observed for 0.5%–6% volumetric concentration increase for very same nanofluid. Along these lines as compared with two parameters the most effect was of temperature. A correlation ship was developed for calculating nanofluids surface tension using test results. The correlation ship is mentioned below:

4. Different investigations on boiling of nanofluids In the current section the review of the experimental and numerical studies has been carried out from the past research. In this various experimental and numerical methods to calculate heat transfer as well as critical heat flux of nanofluids in flow and pool boiling are explained. Various commercial and open source software's which helps in performing numerical based studies are explained. 4.1. Experimental investigations Under turbulent flow in plain and helically dimpled tube Suresh et al. [62] investigated the characteristics of friction factor as well as convective heat transfer. Thermal boundary condition used during the investigation was steady state heat flux. The working fluid that was considered for the complete process was nanofluid composed of CuO nanoparticles and water. By solgel technique CuO nano particles of 15.3 nm size were mixed. During examination the effects of dimples and concentration of particles were seen. Reynolds number worked in the range of 2500–6000 for the investigation. Outcomes revealed that for the tube with dimples and nanofluids was having higher Nusselt number when compared with tube without dimples and water, Nusselt number increases around 19% for 0.1% nanoparticle volume concentration, 27% for 0.2% nanoparticle volume concentration, 39% for 0.3% nanoparticle volume concentration. Similarly nanofluid pressure increases marginally when compared with distilled water. Finally for Nusselt number a correlation ship was proposed:

p 2.089 Nu = 0.00105Re 0.984Pr 0.4 (1 + ∅)−80.78 ⎛1 + ⎞ d⎠ ⎝ where: Φ volume concentration of nanoparticles p = pitch ratio d = diameter of tube (m) Re = Reynolds number Nu = Nusselt Number

γnf

dp T = a1 ∅ + b1 ⎛ o ⎞ + c1 ⎜⎛ ⎟⎞ + D d γbf T ⎝ ⎠ ⎝ bf ⎠

(8)

which works in the range of: 613

(9)

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information was utilized as a part of the Kutateladze correlation:

Pr = Prandtl Number

h λ

Kahani et al. [63] presented a report of nano powders of oxide of metals and nanofluid thermal qualities flowing in helical tubes. Boundary condition of constantly changing heat flux was applied. Al2O3 & TiO2 nanoparticles along with water with diameters of 35 nm and 50 nm respectively were utilized for working fluids. Experiments were done for Reynolds number in the range of 500–4500 and concentration of nanoparticles varying from 0.25 vol% to 1 vol%. Outcomes showed that as the concentration of nanoparticles increases; pressure drop and convective coefficient of heat transfer gets increases. Nanofluids composed of water with Al2O3 nanoparticles indicated better enhancement compared with nanofluid composed of water with TiO2 nanoparticles. At last for drop of pressure and Nusselt number two correlation ships were proposed: For nanofluids consisting of TiO2 nanoparticles and water correlation ship of Nusselt number was:

Nu = 0.5He 0.522Pr 0.613∅0.0815

⎡ q ×⎢ ⎣ ρv hfg υ1

Nu =

0.7

σ ⎤ g (ρ1 − ρv ) ⎥ ⎦

(13)

σ vapor-liquid interface tension ρl and ρv = fluid and vapor density νl = fluid kinematical viscosity P = pressure g = acceleration due to gravity λ liquid thermal conductivity hfg = latent heat of vaporization Prl = Saturated fluid Prandtl number h = coefficient of heat transfer q = heat flux of wall

(10)

Therefore, it was concluded that modification in the liquid thermo physical properties was the explanation behind HTC decrease in nanofluids. In first case, surface becomes rougher by nanoparticles deposition. Decrease of contact angle as well as roughness of surface causes increase in nanofluid critical heat flux and decrease in heat transfer coefficient. Sheikhbahai et al. [65] used a test pool of barrel shaped having diameter 130 mm and length 180 mm with wire of NiCr placed in horizontal way to examine boiling heat transfer under atmospheric pressure of nanofluid composed of ethylene glycol, water Fe3O4 nanoparticles. Outcomes showed the decrease in heat transfer coefficient with the increase in concentration of nanoparticles. For 0.1 vol% of concentration of nanofluid CHF improved around 100%. The principle purpose behind these outcomes was change of surface in pool boiling by deposition of nanoparticles. Improved roughness of surface as well as wettability causes enhancement in CHF because of delay in vapor film coating and HTC decreases because of a porous layer having poor surface thermal conduction. Nikkhah et al. [66] with nanoparticles concentrations of 0.001–0.004 wt% investigated heat transfer coefficient in flow boiling occurring in heat exchanger of vertical type using nanofluid composed of water and CuO2 nanoparticles. Results indicated that as mass fluxes and heat increase; heat transfer coefficient increases broadly in regions of nucleate boiling as well as single stage convective boiling. However increase in concentration increases heat transfer coefficient in convective area of single stage; however decreases in the region of nucleate boiling. It was shown that wettability as well as properties of surface is changed on the segment of heating by nanoparticles in the region of nucleate boiling. Dynamic nucleation sites and depressions cause decrease in heat transfer. Inside horizontal helically coiled pipe Hashemi and Akhavan-Behabadi [67] studied characteristics of heat transfer and drop of pressure. Boundary condition of heat flux was applied. As working liquid blend of copper oxide nanoparticles and oil was utilized, with variation in weight concentrations varying from 0.5% to 2% and Reynolds number in the range of 10–100 tests were performed for nanofluids. To locate the ideal work states of two upgraded procedures of heat transfer, a parameter called performance index was characterized using a pipe of helical shape and nanofluid. Outcomes revealed that nanofluids flowing in the helical tube have much better characteristics of heat transfer as compared with fluid flowing in straight tube. Nanofluid flowing in helical as well as straight tube with weight concentration of 2% has enhancement of heat transfer of about 30% and 18% respectively when compared with base oil flow. Another Nusselt number correlation ship was built up and given as:

(11)

Significant in the range: 0.25 % « 1% 115.3 < He < 1311.4 5.89 < Pr < 8.95 Correlation ship for pressure drop:

Δp = 5.584He1.36∅0.446dp0.163

0.7

σ ⎤ ⎡P ⎢ g (ρ1 − ρv ) ⎥ ⎦ ⎣σ

where:

For nanofluids consisting of Al2O3 nanoparticles and water correlation ship of Nusselt number was:

0.7068He 0.514Pr 0.563∅0.112

σ = 7.0 × 10−4Pr10.35 g (ρ1 − ρv )

(12)

Above correlation ship is valid for nanoparticles having spherical shape and are oxides of metals. With.

∅ < 1:0% 115.3 < He < 1311.4 35 nm < dp < 50 nm. Where: He = Helical coil number ∅ = nanoparticle volume fraction (%) Nu = Nusselt number Pr = Prandtl number Δp = drop of pressure axially (Pa) dp = Nano particle diameter size, nm Under different pressures and nanoparticles concentrations Liu et al. [64] performed a work to investigate heat transfer in nucleate boiling of CuO/water nanofluids. For thermal surface a grooved cut block of copper was used. For the nucleate boiling qualities; the working pressure plays an important role. It was additionally discovered that as the pressure decreases, the nanofluids heat transfer coefficient and critical heat flux increases when compared with pure water. Ideal values of concentration at every testing pressure come to be 1 wt%, which revealed that critical heat flux and heat transfer coefficient increases gradually. However, value of critical heat flux practically remains unchanged while values of heat transfer coefficient fall down for those values. For clarification of above results, the authors did two activities. Firstly is the effect of characteristics of surfaces which was changed, secondly is nanofluids thermo-physical properties. Values of nanofluid thermal conductivity, nanofluids surface tension and nanofluid viscosity were measured. When compared with water, 102%, 88% and 101% increment in the values for nanofluid was noted. This

Nu = 41.730Re 0.346Pr −0.286 (1 + ϕ)0.180 614

(14)

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coefficient decreases for roughness of surface at every stage. In case of aluminium, deterioration of heat transfer coefficient occurs for every level of roughness and concentration of particles. Nucleation site declination and thermal resistant enlargement occurring between liquid and heated surface are the cause of above mentioned deterioration. Aluminium showed better heat transfer coefficient than copper for e.g. at roughness 0.2 μm around 30% better. Then again as surface roughness for copper increases, 13% increase in heat transfer coefficient was obtained due to fact that rough surface incorporate many nucleation sites and pits. For boiling of pure refrigerants and their mixtures flowing in micro fin tubes Mehendale [72] developed a correlation which determines their heat transfer coefficient. Development of correlation was done in two steps, by taking thirty eight dimensionless parameters in first step followed by multi variable regression analysis in second step to recognize the important variable which affects the Nusselt number during flow boiling. It was found that new correlation was better than existing six correlations. So this correlation was reliable to use for many refrigerants under varying operating conditions. The correlation is mentioned below:

This works in range of: ϕ < 2:0% Re < 125 700 < Pr < 2050 ϕ = volume concentration of nanoparticles Nu = Nusselt number Pr = Prandtl number Re = Reynolds number Setoodeh et al. [68] focused on the effect of surface roughness in the phenomenon of flow boiling heat transfer of nanofluid composed of water and Al2O3 nanoparticles moving through the flat channel. The outcomes revealed that with increasing the surface roughness and mass flux the heat flux increases, and with including nanoparticles the flow boiling HTC was enhanced. In a heat exchanger consisting of double helical pipe Wu et al. [69] examined transfer of heat and drop of pressure. With 40 nm mean diameter of Al2O3 nanoparticles and water were utilized as working liquid. Examinations were performed on various weight concentrations of nanoparticles varying from 0.78% to 7% in laminar as well as turbulent flow. For steady velocity of flow in laminar and turbulent region enhancement in heat transfer was observed for nanofluids in the range of 0.37%–3.43% when compared with water. At last, another correlation ship in the laminar region of flow for Nusselt number is mentioned below:

Nu = 0.089Dn0.775Pr 0.4

Nutp =

htp Dr

C11 = C0. ΠC341 . ΠC352 . Π1C3 . ΠC264 . ΠC7 5 Π5C6 . ΠC247 . ΠC218 . ΠC6 9 . ΠC810 . Π33

kl

(16)

Π34 =

qDr hlv μl

(17)

Π35 =

q hlv1.5 Δρ

(18)

(15)

Working in the range:

2. e . nf ⎞ ⎛ ⎛ 1 γ γ ⎞ . Π1 = Ea = ⎛ ⎜ + tan 2 ⎛ ⎞ ⎞⎟ − tan ⎛ ⎞ + 1 2 ⎜ ⎝ 2 ⎠⎠ ⎝ 2 ⎠⎟ ⎝ πDr ⎠ ⎝ ⎝ cos β ⎠

100 < Dn < 1300 4.0 < Pr < 7.0 ϕ < 2:0%

⎜

Π26 =

Where: Φ volume concentration of nanoparticles Re = Reynolds number Pr = Prandtl number Dn = Dean number

Π7 =

Dr (G. ρv σ

Π24 = Su v =

Π21 = Wel =

(19)

x )2 (20)

1−x x

Π5 = Ga v =

Edel and Mukherjee [70] examined flow boiling in a single rectangular micro-channel using nanofluids made by composition of water and Al2O3 nanoparticle having 10−3 vol% concentration. As deposition of nanoparticle on surface of channel is increased, onset nucleate boiling i.e. ONB gets decreased. Reason for this was surface cooling of channel due to larger mass transfer into areas of thin film. This cooling raised the temperature of neighboring surface in flow of two phases. In case of nanofluids OBE (onset bubble elongation) location gradually advances in direction of upstream. Reason for this is wettability enhancement due to deposition of nanoparticle on the surface of channel and fluid wicking by capillary action in smaller scale layer region of evaporating concave meniscus, which causes a very slow rise in temperature of local wall. The process of evaporation was stabilized by very slow movement of area of OBE in upward direction and with the progress in transition of flow regime a very little fluctuation in temperature was observed. With nanoparticle addition bubble nucleation and finally its development was balanced, moreover in regions of the thin film heat transfer was increased. Suriyawong and Wongwises [71] carried out an investigation on heat transfer of nanofluids composed of water and TiO2 nanoparticles in the nucleate pool boiling. In the test round aluminium and copper plates were utilized as heating surfaces. The plates were flat placed in horizontal direction. When compared with pure water a 15% enhancement in heat transfer coefficient was obtained for 10−4 vol % concentration of particle and 0.2 μm roughness on surface of copper. However increasing of concentration after this level, heat transfer

⎟

(21)

ρv g ΔρDr3 μ v2

(22)

ρv σDr μ v2

(23)

G 2Dr ρl σ

(24)

Π6 =

Δρ ρl

(25)

Π8 =

M MH2

(26)

Π33 =

g ΔρeDr3 σnf

(27)

The calculated values exponents are: C0 = 0.03771, C1 = 1.459, C2 = −1.139, C3 = 0.6214, C4 = 0.2249, C5 = 0.2253, C6 = −0.1209, C7 = −0.6149, C8 = −0.04878, C9 = 1.661, C10 = −0.04224, C11 = 0.1121 The details of the above correlation are given in nomenclature. Anwar et al. [73] carried out the flow boiling experiments in a vertical stainless steel section to calculate pressure drop, boiling heat transfer and dry out characteristics of two refrigerants: R123yf and R134a respectively and later on thermal performance of two 615

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simulation on coiled pipes of helical shape to simulate the heat transfer and turbulent flow. For simulations Reynolds and Prandtl number were kept in the range of 14000–80000 and 0.7 to 5.6 respectively. The authors utilized various turbulence models, in particular (RSM) Reynolds stress model-ω, k-epsilon and shear stress transport (SST) k-ω. The outcomes revealed that the Reynolds stress model-ω and shear stress transport k-ω give practically identical outcomes for Nusselt number and friction coefficient. Profiles of temperature and velocity were marginally better than direct numerical simulation. Results of Nusselt number and friction factor were obtained using k-ε turbulent model, with wall treatment. Utilizing wall function predicted more serious results. Conté and Peng [79] numerically researched behavior of flow and heat transfer effects in coiled pipes of rectangular shape. Different straight tubes having inclination angle of 9°, 15°, 30° and 45° and Reynolds number working in range of 300, 700 and 14000 were taken for simulation on four coiled channel of rectangular shape. Results revealed that coil having small inclination angle for straight tube exhibits high heat transfer. Sasmito et al. [80] took four types of straight square, straight square helical spiral, straight square in plane spiral and straight square conical spiral tubes. Nanofluids flowing in these tubes were numerically examined. Al2O3 and CuO nanoparticles along with water having concentration of 3% and 1% respectively were utilized as working nanofluids. Outcomes showed that enhancement of heat transfer was due to nanoparticles concentration of 1% and these results were valid for above mentioned tubes. Heat transfer results of water with Al2O3 nanoparticle were better than water with CuO nanoparticles. Jayakumar et al. [81] investigated effect of different parameter of helical pipes like diameter of pipe, void fraction, pitch of coil, diameter of pitch circle etc. on drop of pressure and heat transfer utilizing FLUENT software. Results showed that diameter of pipe, measurement of pitch circle and void fraction has important effect on drop of pressure and heat transfer. Thus a correlation ship needs to be set up between the parameters, pressure drop and heat transfer. Lin et al. [82] utilized various turbulence models like low-Reynolds k-ε, realizable k-ε and Reynolds stress turbulence models along Navier's Stokes equation to numerically examine pattern of flow and qualities of heat transfer in heat exchangers having helical coils and varying number of turns. These heat exchangers are connected to gas reactors operating at high temperature. Straight tubes were converted into coiled tubes having turns and pitch varying 7 turns with 112 mm pitch, 10 turns with 78.5 mm pitch and 15 turns with 52 mm pitch respectively. Simulations were performed on heat exchangers in which helium was flowing in shell while water was flowing in tube. Mass flow rate and operating temperature for helium was 0.143 kg/s and 973 K while for water was 0.116 kg/s and 377 K. Operating Reynolds number for helium was 14800 while for water was 28–900. Outcomes showed that enhancement in heat transfer were observed for larger pitch value between coils in heat exchanger. In coil tubes, turbulence intensity was higher for low Reynolds model which upgrades thermal productivity strongly. Akbarinia and Behzadmehr [83] investigated numerically effects of concentration of nanoparticles on the thermodynamic and hydrodynamic parameters of nanofluid convection phenomena in curved tubes standing in horizontal manner. Nanofluid composed of Al2O3 (alumina) and water having volumetric concentration in the range of 1%–4% were utilized as working liquids. They assumed that increasing nanoparticles concentrations positively affected the heat transfer enhancement. Two phase method and scheme of control volume were used during numerical simulation. Akbarinia and Laur [84] investigated numerically effect of diameters of particles on nanofluid flowing through the curved tube in laminar pattern. Diameters of the particles considered were 30 μm, 3 μm, 10 nm, 80 nm and 300 nm. The outcomes showed that flow behavior was not affected by increasing nanoparticle diameter.

refrigerants were compared. The operating conditions of the experiments were: mass fluxes varying from 100 to 500 kg/ms2, heat flux in the range of 5–130 kW/m2 and saturation temperature of 27 °C and 32 °C. For measuring dry outs characteristics experiments were performed by increasing heat flux gradually till complete dry out. Results showed that operating pressure and heat flux significantly controlled boiling heat transfer rather than vapor quality and mass flux. R134yf demonstrated lower value for dry out heat flux and both refrigerants showed the same heat transfer performance. Increment was seen in pressure drop with increasing vapor quality and mass flux and decrement was seen as saturation temperature was increased. Results of experiments were compared with some popular correlations. 4.2. Numerical investigations Li et al. [74] utilizing rectangular shape cells in a computational domain of two dimensions carried out numerical investigation of nucleate pool boiling HT. The experimental results were in good validation with numerical model of two-fluid. Correlation ship for heat transfer, nucleate site density and bubble diameter during departure in pool boiling due to nanoparticle Brownian movement were taken into picture. Simulation based outcomes showed that precision in nucleate boiling procedure of nano based fluids is enhanced by nucleate site density, nanoparticle Brownian movement because of change in morphology of surface. Akbaridoust et al. [75] utilized dispersion numerical model to examine pressure drop and heat transfer through convection in helical tubes. Experiments were also performed to examine the both above given factors. Numerical studies were performed under steady condition with temperature at wall to be steady. Nanofluid composed of nanoparticle of CuO having 68 nm diameters dispersed into water with volume concentration of 0.1% and 0.2% were utilized for working. The results from numerical models recognizably showed a very little enhancement in heat transfer when compared with the results obtained from the experiments. So for numerical investigation in helical tubes a relevant model was chosen which gave the satisfactory results. It was observed as the concentration of particles increases the pressure drop and co-efficient of heat transfer increases. Wang and Wu [76] performed simulation for flow boiling of pure water and waterAl2O3 nanofluid. In the simulation the development & departure of bubbles were observed. For the same concentration of nanoparticles, an ideal measurement of nanoparticles was an important finding for improvement in heat transfer during flow boiling. Zachár [77] examined the effect of the different geometrical patterns on inward side of helical tube working in the range of 100–7000 Reynolds number. Rate of heat transfer in heat exchanger of helical tube was examined numerically. Pure water and blend of water and ethylene glycol with 50% by 50% volumetric ratio were used as working liquid. Outcomes revealed that spirally corrugated wall design in tubes of heat exchanger gives higher heat transfer when compared with smooth tube heat exchangers. Correlation ship for Nusselt number was built up during the examination and mentioned below:

h 0.166 p −0.192 ⎛ ⎞ Nu = 0.5855Dn0.6688Pr 0.408 ⎛ ⎞ d ⎝d⎠ ⎝ ⎠

(28)

Which is valid for 30 < Dn < 1400 and 3 < Pr < 30. Where: d = tube diameter (mm) p = pitch ratio h = coefficient of heat transfer of liquid (W/m2 K) Dn = Dean Number Nu = Nusselt number Pr= Prandtl number Utilizing the ANSYS CFX code Di Piazza and Ciofalo [78] performed 616

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5. Nano-fluids preparation methods

maximum researchers are attracted towards chemical techniques.

The maintenance of colloidal stability is the greatest challenge in nanofluid revolution. Due to the appealing Vander Waals forces nanomaterials tend to agglomerate when dispersed in fluids. A few devices utilize mechanical energy to disperse nanomaterials in fluids, for example, test probe ultrasonication, shower bath ultrasonication, mechanical mixing, magnetic blending and shear homogenization. Keeping in mind the final goal to limit particle–particle interactions and accomplish colloidal strength unique systems including surface chemistry, for example, electrostatic stabilization and steric/electrosteric stabilization. In electrostatic stabilization, by changing the dispersing pH; the surface charge of the nanomaterials are modified in such a way that forces of repulsion comes into play because of which surface charge of particles affect up the attractive forces existing between the molecules which bring about stability in dispersion. For keeping the steadiness of colloidal in the process of steric stabilization the atoms of surfactant which are added to dispersion gets adsorb on the surface of particles and causes a force which is of repulsive nature and is responsible for the complete process. In the process of electrosteric stabilization which gives higher surface charge to the particles, the surfactants added to the dispersion separate into particles and adsorb on the particles' surface. The formation of nanofluids includes two procedures: two stage technique also called top to down application which occurs through the decrease of size where as the other is bottom to up application in which synchronous generation of nano particle as well as dispersion takes place which is also called one stage technique. In two stage technique manufacturing of nano particles takes place in the initial step and there after dispersed independently in liquid base as final step. On the other hand nano fluid manufacturing and dispersion in fluid takes place simultaneously in one stage technique. At present to set up the nano fluids, various number of two stage technique exits for example scanning lithography, electron beam lithography etc. and examples of one stage technique are sub-atomic affection, deposition of nuclear layer, DNA scaffolding etc. However, the formation of nanofluids mostly relies upon the properties of base liquid, particle measure, use of surfactant and concentration of nanofluid. Finally, properties on which the nanofluid stability relies upon are surface tension, pH values, viscosity etc.

5.2. Two stage technique For the preparation of nanofluids two stage technique is one of the most widely used technique. In this technique firstly the nanoparticles are produced in the form of dry powders with the help of some mechanical, chemical and physical methods. In the next step this nano powder is dispersed into the base fluid by the help of processes like ultrasonic vibrator stirring, high shear mixing, agitation by magnetic force and ball milling etc. For the large scale production two step methods is considered to be economical as the nano powders have already been manufactured in the industry. It can also be used for preparing nano fluids based on carbon nano tubes. Stability of nanofluids by using this method is a big issue as the accumulation of powder takes place due to strong Vander wall forces acting between the nanoparticles. But still this process is popular from economic point of view. With the use of surfactants stability can be enhanced. In outline, because of enhanced dispersion stability one stage technique has a higher number of points of interest than two stage technique. The disadvantages of one stage technique are reactants which are left over in nanofluids due to incomplete reaction and at high temperature the usage of stabilizers. Along these lines, as two stage techniques for nanofluid definition is basic and adaptable, two stage techniques for nanofluid plan has been generally utilized by researchers compared with one stage technique. Some mechanism for preparation of nanofluids by one stage technique and two stage technique are listed below in Tables 2 and 3 respectively. Much more attention has been aimed towards nanofluids preparation in the past decade. Applications in the vast area are the reason behind the research of nanofluids preparation. In the above section various method of preparation are discussed and in future some research should be carried out for the stability of nanofluids. 6. Effect on heat transfer coefficient and critical heat flux during boiling of nanofluids Utilization of heat transfer during boiling plays an important part in various mechanical areas, for example, aerating and cooling, refrigeration, power plant, atomic power plant, chemical engineering mixtures, flying aircraft machine and space craft thermal management, and high-control sections of refrigeration. Power of heat transfer is measured by coefficient of heat transfer regularly. Improvement of heat transfer coefficient during phenomena of boiling is necessary to make boiling system energy efficient. A very serious issue in boiling systems is critical heat flux enhancement to perform the operations safely in high heat fluxes. Depending upon situation the CHF is additionally called boiling crises, heat flux burn out, and dry out. During heating generally the thermal limit is shown by CHF. During the experiments of boiling,

5.1. One stage technique Advantages of the one stage technique over the two stage technique are stability growth and accumulation reduction. One stage technique uses simultaneous manufacturing along with nanoparticles dispersion in base liquid and the procedure avoid accumulate and drying. One stage strategy has a principle advantage that it works fairly well with the liquids which are at lower vapor pressure. There are two category of one stage technique: chemical and physical. The physical technique has high manufacturing cost and produces narrow range nanoparticles. Due to improved dispersion stability and higher thermal conductivity Table 2 One stage technique: mechanism for preparation of nanofluids. Nanofluid system

Concentration of Nanoparticle

Preparation mechanism

Water with Ag [85] Water with Au [86] Water with Al2O3 [87] Water with Au [88] Water with Al2O3 [89] Diethylene glycol with Ag [90] Water with Ag [91] Water with CuO [92] Water with Ag Water with Au [93]

5*10−1 by volume % 2.6 *10−1 by volume % 1 to 4.3 by volume % 1.8*10−2 by volume % 3 by weight % 1.1*10−1 to 4.38 by volume % 1 *10−2 by volume % 10 by volume % 1*10−3 by volume % 2.6*10−4 by volume %

Submerged arc nanoparticle synthesis system (SANSS) By the method of chemical reduction Inert gas condensation Pulsed laser ablation in liquids technique Plasma arc system Sputtering on running liquid technique Multi-pulse laser ablation technique Microwave irradiation Citrate reduction method

617

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Table 3 Two stage technique: mechanism for preparation of nanofluids. Nanofluid system

Concentration of Nanoparticle

Preparation mechanism

Ethylene-glycol with Fe3O4 and Ag [94]

0 to 1.2 by volume %

Water with Al2O3 [95] Water with Al2O3 [54] Water with graphene and Al2O3 [96]

5*10−1 to 6 by volume % 15 and 22 by volume % 10−1 by volume %

DI base fluid with CuO/HEG Ethylene glycol (Binary mixture) [97] Water with Al2O3 [98] Water with CuO [55] Distilled water with rGO and Fe3O4 [99] Water and ethylene glycol with Fe and CuO [100] DI base fluid with Al2Cu/Ag2Al and ethylene glycol [101] Water with TiO2 [102]

5*10−2 by volume %

Magnetic stirring was done for 2.5 h followed by ultrasonic processor with the power of 400 W and frequency of 24 kHz for 6 h For 90 min bath sonication was performed A vigorous stirring was done and the finally the surfactant were used for the better results In the base fluid to improve the uniformity and stability of the nanoparticles an ultrasonic homogenizer is used without adding any surfactant. Ultrasonication was performed for the optimized time period of 45 min to 1 h

1 to 4 by volume % 14 by volume % 5*10−1 by weight % 5 *10−2 to 1.5 by volume % 2*10−1 to 1.5 by volume % 2.7*10−1 to 1.39 by volume % 1*10−1 to 3*10−1 by weight % 1 to 6 by volume % 1*10−1 by volume %

De-ionized water with Hybrid TiO2 [103] Water with TiO2 [104] Sodium-lauryl sulphate with Al2O3 and Cu [105] Oil with SiC and TiO2 [106]

1*10−1 to 1 by volume %

For 24 h ultrasonic vibration were given for formation of stable nanofluid A vigorous stirring action was performed and surfactant were used for stability of nanofluid Homogenized by performing stirring action An ultrasonic processor was used for stable nanofluid formation. The specification of processor was power of 400 W and frequency of 24 kHz for 5–6 h At room temperature mechanical alloying using a planetary ball mill operating at 300 rpm and mechanism was performed for 10:1 ball to powder weight ratio Stirred bead milling and ultrasonication for 0–7 h nanofluid formation A magnetic stirrer was used and ultrasonic agitation was done using an ultrasonic cleaner for 30 min. A process of probe ultrasonication was carried out Nanofluids were kept under ultrasonic vibration for 6 h by using an ultrasonic vibrator generating ultrasonic pulses to get a uniform dispersion and stable suspension Magnetic stirring apparatus for 30 min continually stirring and finally using an ultra-sonication homogenizer Sonifier 250 for 2 h to obtain uniform nanofluids

6.1. For pool boiling

physical wear out of material of heated surface takes place, which is the most difficult issue which need to be specifically identified and needs to be resolve. For this, it is to make sure that the value of critical heat flux does not exceed in order to maintain system security. Current investigation concentrates on the nanofluid boiling in which the effect of nanoparticle on critical heat flux and heat transfer has been studied. After the inclusion of nanofluids in the boiling process of flow and pool boiling, the improvement in critical heat flux and heat transfer are the principal thing of research. On the basis of this research these two systems can be differentiated. In view of the research, important outcomes and logical contradiction are differentiated, and future research directions are proposed.

Enhancement and decreasing of critical heat flux and heat transfer coefficient in the process of pool boiling depends upon inclusion of nano particles in the base liquids. The related test outcomes are outlined in Tables 4 and 5, where C is the nanoparticle concentration.

• The explanation behind the CHF improvement is the change in

structure and features of the surface that are to be heated during boiling. The results may vary from deposition of nano particle on the surface and absence of nano particles on the surface. Stored nano particles enhances the heated surface characteristics e.g. roughness, wettability of surface and performance through capillary action which results in improvement of critical heat flux.

Table 4 Results of experimental examinations of Heat Transfer Coefficient during nanofluid pool boiling. Nano-fluids Type

Concentration (C) of nanofluid

Size of Particle (nm)

Impact on Heat Transfer Coefficient

Ethylene glycol or Water with ZrO2 [107] Water with CuO [108]

2.5*10−2 to 10−1 by volume %

20 to 25

Increment in heat transfer coefficient was noticed

50 21

Increment and deterioration in heat transfer coefficient was noticed with and without surfactant respectively Deterioration in heat transfer coefficient was noticed

Less than 50

22% increment in heat transfer coefficient was noticed for volume concentration of 1.6

20 to 150

In case of smooth surface heat transfer coefficient was increased, but in case of rough surface no change was noticed. In case of copper surface deterioration in heat transfer coefficient was noticed. In case of stainless steel surface increment in heat transfer coefficient was noticed. Increment in heat transfer coefficient by 55% was noticed

Ethanol with TiO2 or R141 [109] Ethylene glycol with ZnO [110] Water with Al2O3 [111] Water with Al2O3 Water with copper [112] Ethylene glycol or Water with CuO [113] Water with Al2O3 [18]

10 10

−1

−2

to 4*10

−1

by weight %

−2

to 7.5*10

by volume %

5*10−1 to 0.375 *10−1 by volume % 10−3 to 10−1 by volume % −1

to 1 by weight % 10 10−2 to 1 by weight % 10−1 to 5*10−1 by weight %

5 to 250 7 to 257 40

5*10−1 to 2 by volume %

Less than 50

−1

Water with Al2O3 [114] Water with TiO2 [71]

8*10 to 1.4 by weight% 5*10−5 to 10−2 by volume %

20 to 30 21

Water with Al2O3 Water with SnO2 [115] Water with ZrO2 [27]

3*10−1 to 2 by weight % 5*10−1 to 3 by weight % 5*10−3 to 15*10−2 by volume %

20 to 30 55 20 to 25

In case of rough surface increment in heat transfer coefficient was noticed and in case of smooth surface deterioration in heat transfer coefficient up to 30% was noticed Increment in heat transfer coefficient by 25% was noticed In case of copper plate increment by 15% where as in case of aluminium plate deterioration in heat transfer coefficient was noticed Increment in heat transfer coefficient by 30% was noticed Increment in heat transfer coefficient by 20% was noticed At lower concentration increment where as at higher concentration deterioration in heat transfer coefficient was noticed

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Table 5 Results of experimental examinations of Critical Heat Flux during nanofluid pool boiling. Nano-fluids Type

Concentration (C) of nanofluid

Size of Particle (nm)

Impact on Critical Heat Flux

Water with Carbon Nano Tubes and Functional Carbon Nano Tubes [116] Water with TiO2 [117]

10−1 to 3*10−1 by weight % 2*10−3 by weight %

Diameter from 10 to 20 nm* length from 1.5 to 2 μm for both cases 25

R141b or SDBS with Copper [118] Water with Al2O3 Water with TiO2 [119] Water with SiC [120]

8*10−3 to 5*10−2 by volume % 10−3 to 10−1 by volume % for both case 10−4 to 10−2 by volume %

30 10 ± 5 5 to 30 Less than 100

Water with TiO2 [121] Water with ZnO [122]

10−5 to 10−1 by volume % 10−2 by volume %

27 to 85 38 to 68

Water with SiO2 [123]

10−1 to 2 by volume %

10

Increment in critical heat flux was noticed for both cases Increment in critical heat flux by 200% was noticed Deterioration in critical heat flux was noticed At lower concentration increment in critical heat flux was noticed Increment of critical heat flux by 105% was noticed Increment of critical heat flux was noticed Increment of critical heat flux by 160% was noticed Increment of critical heat flux by 270% was noticed Increment of critical heat flux by 130% was noticed Increment of critical heat flux by 240% was noticed Increment in critical heat flux by 91% was noticed Increment of critical heat flux by 100% was noticed

−2

to 5*10

−1

by volume %

10 to 100

Water with CuO [124]

10

Water with Fe3O4 [125]

10−4 to 10−2 by volume %

30

Water with TiO2 [126]

9.4*10−5 to 4.7*10−2 by volume % 0.0 to 10−2 by volume %

21

Water or ethylene glycol with Fe3O4 [5]

50

• Nanoparticles constantly stores on the heated surface during the

•

•

growing nucleate sites which generates dynamic cavities and deteriorates due to blocking of nucleation cavities.

pool bubbling procedure of nanofluids. An improvement can be seen in heat transfer coefficient at very less concentration because of fact that the effect of layer of nano particles is less dominant than effect of nanofluid thermal conductivity. In case when concentration is higher, lowering in quantity of nucleate sites and thermal resistance generation due to layer of stored nano particles turn out to be more superior when compared to nano fluid thermal conductivity, due to which heat transfer coefficient deteriorates. There is an ideal value for concentration of nano particle. At this value critical heat flux improvement achieve maximum and at the same time decrease in heat transfer coefficient does not occur. Enhancement of heat transfer coefficient and critical heat flux takes place as the nano particle concentration increases as the ideal value reaches and beyond the ideal value, with expanding concentration of nano particles, stability of critical heat flux continues while heat transfer coefficient decreases. Surface particle interaction plays an important role in the improvement or deterioration of pool boiling HTC. HTC is increased by

6.2. For flow boiling In the flow passage flow boiling has a greater number of utilizations in building thermal systems than pool boiling, and it can remarkably enhance the HT, CHF, and energy effectiveness of thermal systems. However, the printing of research papers of nanofluid flow boiling started to increase fundamentally than the pool boiling. Primary cause behind this that the nanofluid pool boiling is significantly less complex compared to flow boiling of nanofluid through channel. Heat transfer coefficient and critical heat flux are influenced by different elements for example, quality of vapor, mass flow rate, flow regime, size of channel and direction of flow, nanoparticle concentration and size, type of nanoparticle material used, its shape and orientation, roughness of surface, base liquid used, type of surfactant used and operating pressure during the process of flow boiling. The related test outcomes are outlined in Tables 6 and 7, where C is the nanoparticle concentration.

Table 6 Results of experimental examinations of Heat Transfer Coefficient during nanofluid flow boiling. Nano-fluids Type

Concentration (C) of nanofluid

Size of Particle (nm)

Impact on Heat Transfer coefficient

Water with CuO Water with Al2O3 [127] Water with Al2O3 [70] Water with Al2O3 [68] Ethanol with Al2O3 [128]

1*10−1 to 3*10−1 by weight %

45 to 50

10−3 by volume % 25*10−2 by volume % 10−2 to 10−1 by volume %

20 to 40 20 to 30 Less than 50

10−3 to 4*10−3 by weight % 10−1 to 4*10−1 by weight %

50 50

Increment and deterioration in heat transfer coefficient was noticed for CuO and Al2O3 respectively Increment in heat transfer coefficient was noticed Increment in heat transfer coefficient was noticed Increment by 400% in heat transfer coefficient was noticed at concentration of 5*10−2 by volume % Deterioration in heat transfer coefficient was noticed Deterioration in heat transfer coefficient was noticed

5*10−1 to 15*10−1 by volume %

50

Water with CuO2 [66] Ethylene glycol (EG) with CuO [129] Water with CuO [130] Water with ZnO [131]

−3

10

−1

−2

to 10

by volume % −1

Water with TiO2 [132]

10

Water with Ag [133] Water with Al2O3 [134] R113 with CuO [135]

2.37*10−4 to 4.75*10−4 by volume % 2*10−1 by weight % 0.0 to 5*10−1 by weight %

to 25*10

by volume %

Deterioration in heat transfer coefficient with increasing concentration was noticed Increment in heat transfer coefficient with increasing concentration was observed Increment in heat transfer coefficient with increasing concentration was noticed Increment by 132–162% in heat transfer coefficient was noticed Increment by 17% in heat transfer coefficient was noticed Increment by 29.7% in heat transfer coefficient was noticed

40 20 35 40 40

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Table 7 Results of experimental examinations of Critical Heat Flux during nanofluid flow boiling. Nano-fluids Type

Concentration (C) of nanofluid

Size of Particle (nm)

Impact on Critical Heat Flux

Water with Al2O3 [70] Water with Al2O3 [136] Water with Fe3O4 [137] Water with Fe3O4 Water with Al2O3 [138] Water with GO (grapheme oxide) [139] Water with Al2O3 and SiC 140]

10−3 10−1 10−2 10−2

20 to 40 26 15 to 20 43

10−2 by volume % 10−2 by volume %

– 50

Water with Al2O3 [141]

10−3 to 10−1 by volume %

25

Water with Al2O3 [142] Water with Al2O3 [143] Water with Al2O3 [144] Water with Al2O3 Water with ZnO [145] Water with Al2O3 [146]

10−4 to 10−3 by volume % 10−3 to 10−1 by volume % 10−2 by volume % Less than 10−1by volume %

25 50 47 Less than 100

Increment in critical heat flux was noticed Increment in critical heat flux was noticed Increment in critical heat flux was noticed Increment in critical heat flux was noticed when the combination of water with Fe3O4 was used Increment by 100% in critical heat flux was noticed Increment in critical heat flux was noticed by 41% for water with SiC and 15% for water with Al2O3 A very moderate increment in critical heat flux was noticed when the concentration was very less. Increment by 80% in critical heat flux was noticed Increment by 70.2% in critical heat flux was noticed Increment in the range of 24–51% was noticed in critical heat flux For both the cases increment by 53% in critical heat flux was noticed

10−2 to 10−1 by volume %

40 to 50

Increment by 30% in critical heat flux was noticed

by volume % and 3*10−1 by volume % and 10−1by volume % to 10−1 by volume %

• Nanofluids and nanoparticle covered surfaces may have same affect on the CHF enhancement. • For flow boiling of nanofluid the investigations of dynamics of bubbles and flow systems were rare, and come out to be doubtful. • Outcomes of heat transfer coefficient are both reliable and incon-

•

• •

•

were proposed to enhance the critical heat flux (CHF). CHF enhancement methods by the different surface modification mentioned in the previous literature is discussed in this section. 7.1. Pool boiling

sistent in flow boiling. Nano particle inclusion, even for a similar kind of nanofluids both heat transfer coefficient improvement and deterioration were described. But still, the nanofluid procedure is a favorable activity of heat transfer enhancement in flow boiling. In addition, when nanofluid flow and pool boiling are compared, flow shows better results for enhancement in heat transfer than that of pool. Nano particles get deposited on the surface which is to be heated; this was communicated by almost all the evaluated articles displaying surface investigation. As the operation time get increased corresponding concentration of nanofluid deposition also got increased. From a hypothetical statement that due to deposition of nano particles which changes the wettability of surface is principally responsible for unstable and opposing outcomes outlined in the previous literature. Most investigators for applications of nanofluid utilized low concentration of nanoparticles and felt that they are suitable for mini and micro channel flow boiling systems. The current clarifications about heat transfer in nanofluids are conflicting and opposing because the procedures of flow boiling of nanofluid heat transfer are indefinite. Flow boiling incorporate some principle aspects for the clarifications of the HTC improvement of nanofluid: the decrease of the boundary layer height because of nanoparticles influence and presence of sub-atomic layer of adsorption on the nanoparticle surface, secondly by fluid evaporation and separation pressure obstructs the growth of dry patch, thirdly due to nanoparticle inclusion which results in higher value of viscosity or thermal conductivity. Finally modification of surface by deposition of nanoparticles. Additionally the modification of surface was a perfect reason for deteriorating of heat transfer of nanofluid. Most of flow boiling in nanofluid research papers describes enhancement of critical heat flux. Yet understanding of the procedure is inadequate and deficient. The reason behind this is deposition of nano particle on the surface to be heated, due to which the contact angle of surface get reduced, thereby enhancing the wettability of surface. An additional part shows that suspended nano particles in the fluid played an important part.

Chang and You [22] in saturated FC-72 investigated the pool boiling by coating the surfaces with diamond particles of size ranging from 2 to 70 μm and reported that under high heat fluxes (> 2.5 W/cm2) the most significant heat transfer coefficients was observed and it was due to surface coated with 20 μm diamond stone particles. On wire heaters Kim et al. [147] revealed that when compared with an untreated surface, the diamond particle coating brought about two notable changes of smaller diameter of departing bubble and higher frequencies of bubble departure. It was additionally recommended that heat transfer of the coated surfaces can be improved by increasing convection and latent heat transfer at lower and higher heat fluxes respectively. Utilizing the dripping procedure Wu et al. [148] coated TiO2 nanoparticles of 10 nm particle measure. On the surface a moderate drop of ethanolTiO2 solution was stored and outspread. When the corresponding surface was heated to 200 °C, ethanol was dissipated and the thickness of TiO2 coating of 1 μm was left. With TiO2 coating it was observed that the significant boiling can be accomplished. 38.2% and 91.2% enhancements in CHF and heat transfer coefficients were observed when compared with plain surface of copper. El-Genk and Ali [149] with porous surfaces of various coating thicknesses in PF-5060 performed saturated pool boiling examinations. For all porous surfaces investigated whose surface superheats worked in the range of 2.16 K–12.89 K, CHF suddenly increased from 22.7 to 27.8 W/cm2. Most high CHF of 27.8 W/cm2 was noticed for least value of 2.16 K for the wall superheat for porous surface having coating thickness of 171.1 μm. Jones et al. [150] utilizing EDM provided specimens of various surface roughnesses. Utilizing different surface roughness parameters and having normal roughness (Ra) ranging from 1.08 μm to 10 μm the specimens were presented. With FC-77 and water analyses were carried out. The outcomes revealed that using FC-77 have more effect of Ra on heat transfer coefficients when water and FC-77 were compared. When compared with a smooth polished surface in FC77 the heat transfer coefficients of surface with roughness achieved higher value by 210%. Wen and Ho [151] investigated boiling phenomena heat transfer in two channels of V-shape, first channel whose wall was vertical (Channel 1) and second channel whose wall was horizontal (Channel 2). Angles of both the channel was different. When compared with the plainer surface HTC might have increase or decrease depending upon the geometrical angle and supplied heat flux. However, in the major part of the cases, the V-shaped channel positively affected

7. Effect of surface change on pool and flow boiling heat transfer During saturated flow and pool boiling various surface changes 620

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nucleation sites, low contact angles and swelling property given by the coating. Size of the tube was an inverse function of CHF, but CHF was solid function of mass flux. Morshed et al. [160] carried out an experiment with Cu–Al2O3 nano composite coatings on the base surface and heated from one side. Examination was done to determine the multiphase qualities of heat transfer for water streaming in a smaller channel having volumetric dimension of 0.360 × 5 × 26 mm3. Apart from increasing the CHF by mass flux, the CHF on the refined face was increased by 35–55%. In similar way, due to the change in surface morphology the enhancement was 100% for heat transfer coefficient because of coating. A multi walled carbon nano tubes (MWCNTs) having a height of 15–30 μm and diameter of 10–50 nm was used by Singh et al. [161] for carrying out experiments for subcooled flow boiling for water which was flowing through a full scale passage. The outcomes of plain surface were compared with MWCNT. Outcomes showed improvement in heat flux up to 180% when the surface was coated with MWCNT. With subcooling of fluid and rate of flow the increase in flow boiling flux with MWCNTs turned out to be less. Ho Seon Ahn et al. [162] used an oxidation reaction treated tube made of zirconium compound for investigating the critical heat flux for water in flow boiling. In changing CHF, an important part was not played by the inlet temperature. By restricting the mass flux to the value of 1500 kg/m2s and changing the surface structure; CHF had the biggest improvement of 60%. For subcooled flow boiling phenomena Hsieh and Lin [163] did an investigation on the walls and surfaces by giving them non uniform heating. Various fluids were taken during investigation in a heat apparatus made up of 75 smaller channels having parallel arrangements, moreover on the side walls of the apparatus there were cavities having various angles. Their outcomes revealed that for de-ionized water of 1 vol % of multi walled carbon nano tubes added substance solution (at G = 1600 kg/m2s, ΔTsub = 358 K) and surface heater made of Cu+2 μm diamond film, there was enhancement in CHF and heat transfer by 1.93 and 1.81, respectively.

heat transfer of pool boiling. Effects of geometric parameters on CHF was efficiently investigated by Li and Peterson [152] for example, volumetric porosity and thickness of coating. The outcomes showed that with increase of coating thickness the CHF increases. To look at the impact of aluminum porous covered layer on copper plate having thickness of 150 μm and heat transfer of boiling methanol confined in control space Liu and Yang [153] carried out a test examination. When the values of heat fluxes are moderately low, HTC improvement ratio of smaller scale porous surfaces to plainer surfaces expanded with limited space. In any case, this upgrade weakens for high heat fluxes. Moreover it was discovered that specifically boiling heat transfer was affected for moderately low heat fluxes and smaller scale porous covering. CHF increase of 56% was noticed for restricted spaces greater than 2 mm and the existence of smaller scale porous covering. But in case when Bond number (Bo) was under one and space restriction was 1 mm, CHF increment decreases down to 32%. Seo et al. [154] using DC sputtering created a layer of FeCrAl on metal surface. Characteristics of FeCrAl layer was affected by time of sputtering and temperature. In the temperature range of 150 °C – 600 °C considerable increment in surface roughness was observed. After that pool boiling experiments were conducted to determine the effect of FeCrAl layer on CHF. Considerable enhancement was observed in CHF with FeCrAl layer. The best CHF enhancement (60%) was achieved for 1 h sputtering time and 150 °C temperature. Thermal safety was also increased by this process of sputtering. 7.2. Flow boiling Variation of hydraulic diameters in the range of 0.49–1.26 mm Sun et al. [155] coated the horizontal mini channels with the particles of copper having dimension of 20, 50 and 120 μm. On the base surface of the channel with the sintering process; spherical particles of copper were coated. When compared with an uncoated surface heat transfer coefficients in the range of 7 and 10 times were achieved. The suppression effect was additionally observed in examinations. Due to lowering of fluid mass flux and size of channel strengthens confinement effect, bringing about the decrease in CHF values. Guo et al. [156] carried out subcooled flow boiling on the chip made of silicon with fins having micro size. FC-72 was impinged on the chip. They showed that by increasing the aggregate impinged jet velocity and surface area the boiling heat transfer can be improved. It was seen that cause for more turbulence and lower convection was large jet impingement velocity, due to which the occurrence of CHF was delayed and at high heat flux the heat transfer was enhanced. . Ammerman and You [157] utilized FC-87 on porous coated surfaces to accomplish flow boiling. It was seen that the existence of coating brings about beginning of boiling at lower value of wall superheats, delayed value of CHF and increased heat transfer coefficients. The acknowledgement of enhancement goes to bubble departure repetition and increased nucleation sites. The coated surfaces could increase CHF in the range of 14% and 36%, when compared with a plain surface. To consider flow boiling of anhydrous ethanol Bai et al. [158] constructed a parallel short channels by the process of sintering with porous coated surfaces comprising of powders of copper having diameter of 30, 55 and 90 mm. Their investigated outcomes showed that the channels which were coated has more value of HTC compared with uncoated channels when vapor quality was under 0.15 for a value of 182.8 kg/m2s for mass flux in saturated flow boiling. For sub cooled flow boiling Kaya et al. [159] performed the investigatory studies, the experiments were carried out with (pHEMA) poly hydroxy-ethyl meth acrylate for large mass fluxes working in the range of 10000–13000 kgm−2s−1. The thickness of pHEMA coatings was 30 nm. The coating was done on the inward face of various micro tubes having internal diameters starting from 249 to 998 μm. The coated surfaces had the capacity of raising CHF up to 24% and enhancing heat transfer up to 109% which was clarified with more

8. Conclusions Viscosity and thermal conductivity of nanofluids are fundamentally affected by size of particle, temperature and concentration. Surface tension reduces with rise in temperature and concentrations of nanoparticle. Nanomaterials selected for nanofluid production must be of lower density, as less material will be consumed for specific concentration. Specific heat and thermal conductivity of nanomaterials must be high. Viscosity and thermal conductivity of nanofluids were more influenced by nanoparticles of hydrodynamic size rather than primary size. Enlarged nanostructures with length give higher thermal conductivity improvement as compared with spherical nanoparticles. However, nanoparticles with high aspect ratio bring about major increase in viscosity. For flow boiling heat transfer; model based on flow pattern should be produced which performs sensibly well. Various models of computational fluid dynamics simulations and multiphase schemes of boiling were utilized during the numerical simulation, alongside the computational methods utilized for comparisons with experimental data. For heat transfer coefficients better performance; development and improvement of models and techniques are further needed. For flow boiling phenomena many correlation ships for calculation of the Nusselt number were created for straight and helically coiled tubes. The nanofluids preparation, nanofluids thermal transport properties and nanoparticles size may be the explanation behind disorganized outcomes in CHF. Uses of smaller size nanoparticles were ideal during experiments. For the researchers the stable nanofluids formulation was the greatest difficulties in applications. To avoid accumulation and sedimentation different methodologies were utilized like pH control, surfactants and surface functionalization, yet they are at research level. In this way, for large volume production of nanofluids the researchers 621

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some recommendations are given below for the future work:

should put additional attempt to assure long term physical and chemical steadiness of nanofluids and make it possible to utilize nanofluids for improving the CHF in numerous modern applications. By the utilization of nanofluids the thermo-hydrodynamic performances of pipes were enhanced when compared with conventional fluids. The heat transfer coefficients and pressure drop of nanofluids were observed to be larger. In analyses of nanofluid boiling TiO2, CuO and Al2O3 were the most regularly utilized nanoparticles and investigative examinations revealed more occasion of enhancement than deteriorating for the CHF and HTC of boiling nanofluids. The deterioration and improvement of CHF and HT utilizing nanofluids in pool and flow boiling relies upon the below mentioned components like material, size, concentration of nanofluids, material, shape, orientation and roughness of the heated surface, surfactant, base liquid, operating pressure and finally the heat flux. If the appropriate combination of the above mentioned factors is considered in any application it would bring about enhancement in flow and pool boiling CHF and HT utilizing nanofluids. To enhance flow boiling HT utilization of nanofluids was a feasible approach. Dependent on many elements and their mutual interactions, both improvement and deterioration were accounted for HT. By giving an appropriate combination of the variables, for example, mass flux, vapor quality, flow regime, flow direction and subcooling brings about improvement of HT. CHF and HTC of the nanofluids boiling have a significant influence by nanoparticles concentration. Up to a specific point with increase in concentration of nanoparticle CHF and HTC increases, past which additional increase reduces the boiling HTC and influence on CHF, is not noticed. So for the production of CHF enhancement at maximum level without embarrassing the boiling HT there exists an optimum nanoparticle concentration. The knowledge is quite insufficient and lower for the better understanding of CHF enhancement of nanofluid flow boiling. One of the main reasons for the CHF enhancement is nanoparticle deposition on the heated surface, and this need to be studied properly for the better understanding of the system. In case of nanofluid flow boiling there has been no CHF deterioration reported, which should be credited to the essential flow conditions played in the CHF enhancement of nanofluid flow boiling. Subsequently, investigation of the nanofluid flow boiling CHF should look for combined effect of deposition of nanoparticle on the surfaces and suspension of nanoparticle in the nanofluids. The heated surface characteristics were modified with the deposition of nanoparticle. Further the size of cavities was modified by a moderate porous layer of deposited nanoparticles on the heated surface. Both of the above mentioned variables bring about the improvement of HTC. The nanoparticle deposition is the explanation for the decrease of HTC which lower down the number nucleation sites. A thick layer of nano particles formed on the surface due to which thermal resistance of surface is increased which brings about the fouling formation of nanoparticles on the surface which decreases the capillary action on the heated surface. Surface microstructure and topography was changed by the deposition of nanoparticles and because of which the surface characteristics, for example, surface wettability, roughness, and capillary action performance were improved. Every characteristic causes the enhancement of CHF. In the recent couple of decades a significant progress has been achieved in enhancing boiling heat transfer by using various techniques of surface modification. The evaluation of heat transfer performances of these modification techniques and surface enhancement were carried out. Extended surface area results in CHF enhancement. Suggestions on few CHF enhancement models were given but the validity of the models should be confirmed for various changed surfaces and liquids.

1. Based on huge variety of nanofluid thermo physical properties, numerical and experimental investigations of boiling of nanofluids; reasonable expected correlation ships must be proposed for pressure drop, CHF and HTC of nanofluids boiling [62–64,67,69,77]. 2. For nanofluids preparation for long time period use, there is an urgent need to build up a widespread basic technique which does not influence its thermal transport properties. Directly at research level there are various techniques for nanofluids preparation. So research should be done as such that these techniques must be made perfect for the general mechanical applications. In addition the generation cost and stability of nanofluids that should be taken care of appropriately [87–89,91,92,97,106]. 3. The establishment of effects on mechanisms of heat transfer and dynamics of bubbles related with enhanced surface features is still not up to the mark. To understand the bubble behavior and the mechanisms involved with the procedure, parametric investigations of enhanced surfaces like extended fin, porous cavities surfaces with changing diameters, heights and pitches utilizing high speed resolution camera for the visualization are to be done for further research work [147,148,150,152,155,157,161]. 4. For building the effective database a careful examination of basic nanofluids properties like, density, viscosity, specific heat, surface tension and thermal conductivity, must be done for simulation, modeling and analysis [31,34,39,40,54,60]. 5. The most important issue in heat transfer applications is size of nanoparticles. Smaller size nanoparticles are the most preferred to use for boiling phenomena. So, for the preparation of nanoparticles of smaller size it is important to developed financially effective techniques [89,104,110,111,113]. 6. In the above review it was seen that nanofluid boiling researches based on experimental investigations represented over 90%, and numerical simulations based on commercial and open source software were extremely less. The numerical simulations techniques deserves more consideration as it assumes an important part in building CHF models and saves time and money [74,78,81–83]. References [1] Nukiyama S. The maximum and minimum values of the heat Q transmitted from metal to boiling water under atmospheric pressure. Int J Heat Mass Transf 1966;9(12):1419–33. [2] Ciloglu D, Bolukbasi A. A comprehensive review on pool boiling of nanofluids. Appl Therm Eng 2015;84:45–63. [3] Fang X, Wang R, Chen W, Zhang H, Ma C. A review of flow boiling heat transfer of nanofluids. Appl Therm Eng 2015;91:1003–17. [4] Seon Ahn H, Hwan Kim M. A review on critical heat flux enhancement with nanofluids and surface modification. J Heat Transf 2011;134(2):024001. [5] Bahiraei M, Hangi M. Flow and heat transfer characteristics of magnetic nanofluids: a review. J Magn Magn Mater 2015;374:125–38. [6] Kutateladze SS. “Boiling heat transfer,” in heat transfer conference. June 5-10 Minsk, USSR; 1961. p. 1–39. [7] Choi S, Estman J. Enhancing thermal conductivity of fluids with nanoparticles. In Proceedings of the ASME international mechanical engineering congress and exposition. New York: ASME; 1995. p. 99–106. [8] Dhir VK, Warrier GR, Aktinol E. Numerical simulation of pool boiling: a review. J Heat Transf 2013;135(6):061502. 1-17. [9] Kandlikar SG. A general correlation for saturated two-phase flow boiling heat transfer inside horizontal and vertical tubes. J Heat Transf 2008;112(1):219–28. [10] Kamatchi R, Venkatachalapathy S. “Parametric study of pool boiling heat transfer with nano fluids for the enhancement of critical heat flux : a review. Int J Therm Sci 2015;87:228–40. [11] Gorenflo D, Baumhögger E, Herres G, Kotthoff S. Prediction methods for pool boiling heat transfer: a state-of-the-art review. Int J Refrig 2014;43:203–26. [12] Wongwises S, Mahian O, Aktas M, Celen A, Çebi A, Dalkilic AS. A review of nanorefrigerants: flow characteristics and applications. Int J Refrig 2014;44:125–40. [13] You SM, Kim JH, Kim KH. Effect of nanoparticles on critical heat flux of water in pool boiling heat transfer. Appl Phys Lett 2003;83(16):3374–6. [14] Milanova D, Kumar R. Role of ions in pool boiling heat transfer of pure and silica nanofluids. Appl Phys Lett 2005;87(1–3):233107. [15] Kathiravan R, Kumar R, Gupta A, Chandra R. Preparation and pool boiling characteristics of copper nanofluids over a flat plate heater. Int J Heat Mass Transf

9. Future studies Every point of the future studies is written after studying the work done in the cited paper after every point. Based on the above review 622

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viscosity. Fluid Phase Equilib 2011;300(1–2):188–96. [51] V Timofeeva E, Smith DS, Yu W, France DM, Singh D, Routbort JL. Particle size and interfacial effects on thermo-physical and heat transfer characteristics of water-based α-SiC nanofluids. Nanotechnology 2010;21:1–10. [52] Yoo J, Kwark SM, You SM, Moreno G, Kumar R. Pool boiling characteristics of low concentration nanofluids. Int J Heat Mass Transf 2009;53(5–6):972–81. [53] Das SK, Putra N, Roetzel W. Pool boiling characteristics of nano-fluids. Int J Heat Mass Transf 2003;46(5):851–62. [54] Kulkarni DP, Das DK, Chukwu GA. Temperature dependent rheological property of copper oxide nanoparticles suspension (nanofluid). J Nanosci Nanotechnol 2006;6(4):1150–4. [55] Nguyen CT, et al. Temperature and particle-size dependent viscosity data for water-based nanofluids-Hysteresis phenomenon. Int J Heat Fluid Flow 2007;28:1492–506. [56] Sundar LS, Ramana EV, Singh MK, Sousa ACM. “Thermal conductivity and viscosity of stabilized ethylene glycol and water mixture Al2O3 nano fluids for heat transfer applications : an experimental study. Int Commun Heat Mass Transf 2014;56:86–95. [57] Vafaei S, Purkayastha A, Jain A, Ramanath G, Borca-Tasciuc T. “The effect of nanoparticles on the liquid–gas surface tension of Bi2Te3 nanofluids. Nanotechnology 2009;20:1–6. [58] Jeong YH, Chang WJ, Chang SH. Wettability of heated surfaces under pool boiling using surfactant solutions and nano-fluids. Int J Heat Mass Transf 2008;51(11–12):3025–31. [59] Kumar R, Milanova D. Effect of surface tension on nanotube nanofluids. Appl Phys Lett 2009;94(1–3):073107. –. [60] Chinnam J, Das DK, Vajjha RS, Satti JR. Measurements of the surface tension of nanofluids and development of a new correlation. Int J Therm Sci 2015;98:68–80. [61] Bhuiyan MHU, Saidur R, Amalina MA, Mostafizur RM, Islam A. Effect of nanoparticles concentration and their sizes on surface tension of nanofluids. Procedia Eng. 2014;105:431–7. Icte. 2015. [62] Suresh S, Chandrasekar M, Sekhar SC. Experimental studies on heat transfer and friction factor characteristics of CuO/water nanofluid under turbulent flow in a helically dimpled tube. Exp Therm Fluid Sci 2011;35:542–9. [63] Kahani M, Zeinali Heris S, Mousavi SM. Comparative study between metal oxide nanopowders on thermal characteristics of nanofluid flow through helical coils. Powder Technol 2013;246:82–92. [64] hua Liu Z, guo Xiong J, Bao R. Boiling heat transfer characteristics of nanofluids in a flat heat pipe evaporator with micro-grooved heating surface. Int J Multiph Flow 2007;33(12):1284–95. [65] Sheikhbahai M, Nasr Esfahany M, Etesami N. Experimental investigation of pool boiling of Fe3O4/ethylene glycol-water nanofluid in electric field. Int J Therm Sci 2012;62:149–53. [66] Nikkhah V. Application of spherical copper oxide (II) water nano-fluid as a potential coolant in a boiling annular heat exchanger. Chem Biochem Eng Q 2016;29(3):405–15. [67] Hashemi SM, Akhavan-Behabadi MA. “An empirical study on heat transfer and pressure drop characteristics of CuO–base oil nano fluid flow in a horizontal helically coiled tube under constant heat flux. Int Commun Heat Mass Transf 2012;39:144–51. [68] Setoodeh H, Keshavarz A, Ghasemian A, Nasouhi A. Subcooled flow boiling of alumina/water nanofluid in a channel with a hot spot: an experimental study. Appl Therm Eng 2015;90:384–94. [69] Wu Z, Wang L, Sundén B. Pressure drop and convective heat transfer of water and nanofluids in a double-pipe helical heat exchanger. Appl Therm Eng 2013;60(1–2):266–74. [70] Edel Z, Mukherjee A. Flow boiling dynamics of water and nanofluids in a single microchannel at different heat fluxes. J Heat Transf 2014;137(1):011501. 1-8. [71] Suriyawong A, Wongwises S. Nucleate pool boiling heat transfer characteristics of TiO2-water nanofluids at very low concentrations. Exp Therm Fluid Sci 2010;34(8):992–9. [72] Mehendale S. A new heat transfer coefficient correlation for pure refrigerants and near-azeotropic refrigerant mixtures flow boiling within horizontal microfin tubes. Int J Refrig 2018;86:292–311. [73] Anwar Z, Palm B, Khodabandeh R. Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf: experimental results and predictions. Exp Therm Fluid Sci 2015;66:137–49. [74] Li K, Li XD, Tu JY, Wang HG. A mathematic model considering the effect of Brownian motion for subcooled nucleate pool boiling of dilute nanofluids. Int J Heat Mass Transf 2015;84:46–53. [75] Akbaridoust F, Rakhsha M, Abbassi A, Saffar-Avval M. Experimental and numerical investigation of nanofluid heat transfer in helically coiled tubes at constant wall temperature using dispersion model. Int J Heat Mass Transf 2013;58(1–2):480–91. [76] Wang Y, Wu JM. Numerical simulation on single bubble behavior during Al2O3/ H2O nano fluids flow boiling using Moving Particle Simi-implicit method. Prog Nucl Energy 2015;85:130–9. [77] Zachár A. Analysis of coiled-tube heat exchangers to improve heat transfer rate with spirally corrugated wall. Int J Heat Mass Transf 2010;53(19–20):3928–39. [78] Di Piazza I, Ciofalo M. Numerical prediction of turbulent flow and heat transfer in helically coiled pipes. Int J Therm Sci 2010;49:653–63. [79] Conté I, Peng XF. Numerical investigations of laminar flow in coiled pipes. Appl Therm Eng 2008;28(5–6):423–32. [80] Sasmito AP, Kurnia JC, Mujumdar AS. Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes. Nanoscale Res. Lett. 2011;6:1–14.

2010;53(9–10):1673–81. [16] Kim SJ, Bang IC, Buongiorno J, Hu LW. Surface wettability change during pool boiling of nanofluids and its effect on critical heat flux. Int J Heat Mass Transf 2007;50(19–20):4105–16. [17] Stutz B, Morceli CHS, da Silva M de F, Cioulachtjian S, Bonjour J. Influence of nanoparticle surface coating on pool boiling. Exp Therm Fluid Sci 2011;35(7):1239–49. [18] Harish G, Emlin V, Sajith V. Effect of surface particle interactions during pool boiling of nanofluids. Int J Therm Sci 2011;50(12):2318–27. [19] Kim H, Kim J, Kim M. Experimental study on CHF characteristics of water-TiO2 nano-fluids. Nucl. Eng. Technol. 2005;38(1):61–8. [20] Seon H, Min J, Hwan M. Experimental study of the effect of a reduced graphene oxide coating on critical heat flux enhancement. Int J Heat Mass Transf 2013;60:763–71. [21] Barber J, Brutin D, Tadrist L. A review on boiling heat transfer enhancement with nanofluids. Nanoscale Res. Lett. 2011;6(1):1–16. [22] Chang JY, You SM. Boiling heat transfer phenomena from micro-porous and porous surfaces in saturated FC-72. Int J Heat Mass Transf 1997;40(18):4437–47. [23] Thome JR, Cheng L, Ribatski G, Vales LF. Flow boiling of ammonia and hydrocarbons: a state-of-the-art review. Int J Refrig 2008;31(4):603–20. [24] Vassallo P, Kumar R, Amico SD. “Pool boiling heat transfer experiments in silica–water nano-fluids. Int J Heat Mass Transf 2004;47:407–11. [25] Bang IC, Heung Chang S. Boiling heat transfer performance and phenomena of Al2O3-water nano-fluids from a plain surface in a pool. Int J Heat Mass Transf 2005;48(12):2407–19. [26] Coursey JS, Kim J. Nanofluid boiling: the effect of surface wettability. Int J Heat Fluid Flow 2008;29(6):1577–85. [27] Chopkar M, Das AK, Manna I, Das PK. Pool boiling heat transfer characteristics of ZrO2-water nanofluids from a flat surface in a pool. Heat Mass Transf. und Stoffuebertragung 2008;44(8):999–1004. [28] David D, David T. Producing a systematic review. Sage Handb. Organ. Res. Methods 2009:671–89. [29] Philip J, Shima PD. Thermal properties of nanofluids. Adv Colloid Interface Sci 2012;183(184):30–45. [30] Altan CL, Bucak S. The effect of Fe3O4 nanoparticles on the thermal conductivities of various base fluids. Nanotechnology 2011;22(28):1–5. [31] Rizvi IH, Jain A, Ghosh SK, Mukherjee PS. Mathematical modelling of thermal conductivity for nanofluid considering interfacial nano-layer. Heat Mass Transf. und Stoffuebertragung 2013;49(4):595–600. [32] Patel HE, Sundararajan T, Das SK. An experimental investigation into the thermal conductivity enhancement in oxide and metallic nanofluids. J Nanoparticle Res 2010;12(3):1015–31. [33] Sun H, et al. Effects of particle surface charge, species, concentration, and dispersion method on the thermal conductivity of nanofluids. Adv Mech Eng 2010:1–10. 2010. [34] Zhu H, Zhang C, Liu S, Tang Y, Yin Y. Effects of nanoparticle clustering and alignment on thermal conductivities of Fe3O4 aqueous nanofluids. Appl Phys Lett 2006;89(1–3):023123. [35] Ahmed O, Hamed MS. Experimental investigation of the effect of particle deposition on pool boiling of nanofluids. Int J Heat Mass Transf 2012;55:3423–36. [36] Ahn HS, Kim JM, Kaviany M, Kim MH. “Pool boiling experiments in reduced graphene oxide colloids part II – behavior after the CHF, and boiling hysteresis. Int J Heat Mass Transf 2014;78:224–31. [37] Yang XF, Liu ZH. Pool boiling heat transfer of functionalized nanofluid under subatmospheric pressures. Int J Therm Sci 2011;50(12):2402–12. [38] Gavili A, Zabihi F, Isfahani TD, Sabbaghzadeh J. The thermal conductivity of water base ferrofluids under magnetic field. Exp Therm Fluid Sci 2012;41:94–8. [39] Pantzali MN, Mouza AA, Paras SV. Investigating the efficacy of nanofluids as coolants in plate heat exchangers (PHE). Chem Eng Sci 2009;64(14):3290–300. [40] Kedzierski MA. Viscosity and density of CuO nanolubricant. Int J Refrig 2012;35:1997–2002. [41] Sekhar YR, V Sharma K. Study of viscosity and specific heat capacity characteristics of water-based Al2O3 nanofluids at low particle concentrations. J Exp Nanosci 2015;10(2):86–102. [42] Vajjha RS, Das DK. Specific heat measurement of three nanofluids and development of new correlations. J Heat Transf 2009;131(7):071601. [43] Teng T, Hung Y. Estimation and experimental study of the density and specific heat for alumina nanofluid. J Exp Nanosci 2014;9(7):707–18. [44] Mahian O, Kianifar A, Wongwises S. Dispersion of ZnO nanoparticles in a mixture of ethylene glycol-water, exploration of temperature-dependent density, and sensitivity analysis. J Clust Sci 2013;24(4):1103–14. [45] Mariano A, Pastoriza-gallego MJ, Lugo L, Camacho A, Canzonieri S, Pi MM. Thermal conductivity , rheological behaviour and density of non-Newtonian ethylene glycol-based SnO2 nanofluids. Fluid Phase Equilib 2013;337:119–24. [46] Wang B, Zhou L, Peng X. Surface and size effects on the specific heat capacity of nanoparticles. Int J Thermophys 2006;27(1):139–51. [47] Kedzierski MA. Viscosity and density of aluminum oxide nanolubricant. Int J Refrig 2013;36(4):1333–40. [48] Ho CJ, Gao JY. Preparation and thermophysical properties of nanoparticle-inparaffin emulsion as phase change material. Int Commun Heat Mass Transf 2009;36(5):467–70. [49] He Q, Wang S, Tong M, Liu Y. Experimental study on thermophysical properties of nanofluids as phase-change material (PCM) in low temperature cool storage. Energy Convers Manag 2012;64:199–205. [50] Pastoriza-Gallego MJ, Casanova C, Legido JL, Piñeiro MM. CuO in water nanofluid: influence of particle size and polydispersity on volumetric behaviour and

623

Renewable and Sustainable Energy Reviews 112 (2019) 607–625

M. Dadhich and O.S. Prajapati [81] Jayakumar JS, Mandal JC, Iyer KN, Vijayan PK, Mahajani SM. “Thermal hydraulic characteristics of air–water two-phase flows in helical pipes. Chem Eng Res Des 2009;88(4):501–12. [82] Lin WC, Ferng YM, Chieng CC. Numerical computations on flow and heat transfer characteristics of a helically coiled heat exchanger using different turbulence models. Nucl Eng Des 2013;263:77–86. [83] Akbarinia A, Behzadmehr A. Numerical study of laminar mixed convection of a nanofluid in horizontal curved tubes. Appl Therm Eng 2007;27(8–9):1327–37. [84] Akbarinia A, Laur R. Investigating the diameter of solid particles effects on a laminar nanofluid flow in a curved tube using a two phase approach. Int J Heat Fluid Flow 2009;30(4):706–14. [85] Lo CH, Tsung TT, Lin HM. Preparation of silver nanofluid by the submerged arc nanoparticle synthesis system (SANSS). J Alloy Comp 2007;434(435):659–62. SPEC. ISS. [86] Paul G, Pal T, Manna I. Thermo-physical property measurement of nano-gold dispersed water based nanofluids prepared by chemical precipitation technique. J Colloid Interface Sci 2010;349(1):434–7. [87] Lee S, Choi SU-S, Li S, Eastman JA. Measuring thermal conductivity of fluids containing oxide nanoparticles. J Heat Transf 2008;121(2):280–9. [88] Kim HJ, Bang IC, Onoe J. Characteristic stability of bare Au-water nanofluids fabricated by pulsed laser ablation in liquids. Optic Laser Eng 2009;47(5):532–8. [89] Chang H, Chang Y. Fabrication of Al2O3 nanofluid by a plasma arc nanoparticles synthesis system. J Mater Process Technol 2008;207:193–9. [90] Tamjid E, Guenther BH. Rheology and colloidal structure of silver nanoparticles dispersed in diethylene glycol. Powder Technol 2010;197(1–2):49–53. [91] Phuoc TX, Soong Y, Chyu MK. Synthesis of Ag-deionized water nanofluids using multi-beam laser ablation in liquids. Optic Laser Eng 2007;45:1099–106. [92] Zhu HT, Zhang CY, Tang YM, Wang JX. Novel synthesis and thermal conductivity of CuO nanofluid. J Phys Chem 2007;111:1646–50. [93] Patel HE, Das SK, Nair TSS, George B, Pradeep T. “Thermal conductivities of naked and monolayer protected metal nanoparticle based nanofluids : manifestation of anomalous enhancement and chemical effects. Appl Phys Lett 2003;83(14):2931–3. [94] Afrand M, Toghraie D, Ruhani B. Effects of temperature and nanoparticles concentration on rheological behavior of Fe3O4-Ag/EG hybrid nanofluid: an experimental study. Exp Therm Fluid Sci 2016;77:38–44. [95] Li CH, Peterson GP. The effect of particle size on the effective thermal conductivity of Al2O3-water nanofluids. J Appl Phys 2007;101(4):1–5. [96] Ahammed N, Godson L, Wongwises S. “Entropy generation analysis of graphene–alumina hybrid nanofluid in multiport minichannel heat exchanger coupled with thermoelectric cooler. Int J Heat Mass Transf 2016;103:1084–97. [97] Baby TT, Sundara R. Synthesis and transport properties of metal oxide decorated graphene dispersed nanofluids. J Phys Chem C 2011;115(17):8527–33. [98] Das SK, Putra N, Thiesen P, Roetzel W. Temperature dependence of thermal conductivity enhancement for nanofluids. J Heat Transf 2003;125:567–74. [99] Mehrali M, et al. Heat transfer and entropy generation analysis of hybrid graphene/Fe3O4 ferro-nanofluid flow under the influence of a magnetic field. Powder Technol 2017;308:149–57. [100] Bahrami M, Akbari M, Karimipour A, Afrand M. “An experimental study on rheological behavior of hybrid nanofluids made of iron and copper oxide in a binary mixture of water and ethylene glycol : non-Newtonian behavior. Exp Therm Fluid Sci 2016;79:231–7. [101] Chopkar M, Kumar S, Bhandari DR, Das PK, Manna I. Development and characterization of Al2Cu and Ag2Al nanoparticle dispersed water and ethylene glycol based nanofluid. Mater. Sci. Eng. B Solid-State Mater. Adv. Technol. 2007;139(2–3):141–8. [102] Silambarasan M, Manikandan S, Rajan KS. Viscosity and thermal conductivity of dispersions of sub-micron TiO2 particles in water prepared by stirred bead milling and ultrasonication. Int J Heat Mass Transf 2012;55(25–26):7991–8002. [103] Shao X, et al. Solidification behavior of hybrid TiO2 nanofluids containing nanotubes and nanoplatelets for cold thermal energy storage. Appl Therm Eng 2017;117:427–36. [104] Longo GA, Zilio C. Experimental measurement of thermophysical properties of oxide-water nano-fluids down to ice-point. Exp Therm Fluid Sci 2011;35(7):1313–24. [105] Suresh S, Venkitaraj KP, Selvakumar P, Chandrasekar M. “Effect of Al2O3–Cu/ water hybrid nanofluid in heat transfer. Exp Therm Fluid Sci 2012;38:54–60. [106] Wei B, Zou C, Yuan X, Li X. Thermo-physical property evaluation of diathermic oil based hybrid nanofluids for heat transfer applications. Int J Heat Mass Transf 2017;107:281–7. [107] Sarafraz MM, Kiani T, Hormozi F. Critical heat flux and pool boiling heat transfer analysis of synthesized zirconia aqueous nano-fluids. Int Commun Heat Mass Transf 2016;70:75–83. [108] Diao Y, Liu Y, Wang R, Zhao Y, Guo L. Experimental investigation of the Cu/R141b nanofluids on the evaporation/boiling heat transfer characteristics for surface with capillary micro-channels. Heat Mass Transf. und Stoffuebertragung 2014;50(9):1261–74. [109] Naphon P, Thongjing C. Pool boiling heat transfer characteristics of refrigerantnanoparticle mixtures. Int Commun Heat Mass Transf 2014;52:84–9. [110] Kole M, Dey TK. Thermophysical and pool boiling characteristics of ZnO-ethylene glycol nano fluids. Int J Therm Sci 2012;62:61–70. [111] Wen D. Influence of nanoparticles on boiling heat transfer. Appl Therm Eng 2012;41:2–9. [112] Cieslinski JT, Kaczmarczyk TZ. Pool boiling of water-Al2O3 and water-Cu nanofluids on horizontal smooth tubes. Nanoscale Res. Lett. 2011;6(1):1–9. [113] Heris SZ. “Experimental investigation of pool boiling characteristics of low-

[114] [115]

[116]

[117] [118]

[119]

[120] [121] [122]

[123] [124] [125] [126] [127]

[128]

[129]

[130]

[131] [132]

[133]

[134] [135]

[136]

[137]

[138]

[139] [140]

[141]

[142]

[143]

[144]

[145]

624

concentrated CuO ethylene glycol–water nano fluids. Int Commun Heat Mass Transf 2011;38:1470–3. Soltani S, Etemad SG, Thibault J. Pool boiling heat transfer of non-Newtonian nanofluids. Int Commun Heat Mass Transf 2010;37(1):29–33. Soltani S, Etemad SG, Thibault J. Pool boiling heat transfer performance of Newtonian nanofluids. Heat Mass Transf. und Stoffuebertragung 2009;45(12):1555–60. Sarafraz MM, Hormozi F, Silakhori M, Peyghambarzadeh SM. On the fouling formation of functionalized and non-functionalized carbon nanotube nano-fluids under pool boiling condition. Appl Therm Eng 2016;95:433–44. Sakashita H. Pressure effect on CHF enhancement in pool boiling of nanofluids. J Nucl Sci Technol 2016;53(6):797–802. Diao YH, Li CZ, Zhao YH, Liu Y, Wang S. Experimental investigation on the pool boiling characteristics and critical heat flux of Cu-R141b nanorefrigerant under atmospheric pressure. Int J Heat Mass Transf 2015;89:110–5. Ulcay MS. CHF enhancement of Al2O3, TiO2and Ag nanofluids and effect of nucleate pool boiling time. Thermomechanical Phenom. Electron. Syst. -Proceedings Intersoc. Conf. 2014:756–64. Song SL, Lee JH, Chang SH. CHF enhancement of SiC nanofluid in pool boiling experiment. Exp Therm Fluid Sci 2014;52:12–8. Hyungdae JJ, Moo K, Kim H. Effect of ionic additive on pool boiling critical heat flux of titania/water nanofluids. Heat Mass Transf 2013;49:1–10. Sharma VI, Buongiorno J, McKrell TJ, Hu LW. Experimental investigation of transient critical heat flux of water-based zinc-oxide nanofluids. Int J Heat Mass Transf 2013;61(1):425–31. Vazquez DM, Kumar R. Surface effects of ribbon heaters on critical heat flux in nano fluid pool boiling. Int Commun Heat Mass Transf 2013;41:1–9. Hegde RN, Rao SS, Reddy RP. Experimental studies on CHF enhancement in pool boiling with CuO-water nanofluid. Heat Mass Transf 2012;48:1031–41. Hyuk J, Lee T, Hoon Y. Experimental study on the pool boiling CHF enhancement using magnetite-water nanofluids. Int J Heat Mass Transf 2012;55:2656–63. Okawa T, Takamura M, Kamiya T. Boiling time effect on CHF enhancement in pool boiling of nanofluids. Int J Heat Mass Transf 2012;55(9–10):2719–25. Sarafraz MM, Hormozi F. Comparatively experimental study on the boiling thermal performance of metal oxide and multi-walled carbon nanotube nanofluids. Powder Technol 2016;287:412–30. Wang Y, Harmand S, Sefiane K, Dehaene A, Duursma G. Flow and heat transfer of single-and two-phase boiling of nanofluids in microchannels. Heat Transf Eng 2014;36(14–15):1252–65. Sarafraz MM, Hormozi F. Convective boiling and particulate fouling of stabilized CuO-ethylene glycol nanofluids inside the annular heat exchanger. Int Commun Heat Mass Transf 2014;53:116–23. Sarafraz MM, Hormozi F. Scale formation and subcooled flow boiling heat transfer of CuO-water nanofluid inside the vertical annulus. Exp Therm Fluid Sci 2014;52:205–14. Rana KB, Rajvanshi AK, Agrawal GD. A visualization study of flow boiling heat transfer with nanofluids. J Vis 2013;16(2):133–43. Abedini E, Behzadmehr A, Rajabnia H, Sarvari SMH, Mansouri SH. “Experimental investigation and comparison of subcooled flow boiling of TiO2 nanofluid in a vertical and horizontal tube,” in Proceedings of the Institution of Mechanical Engineers, Part C. J Mech Eng Sci 2013;227(8):1742–53. Chehade AA, Gualous HL, Le Masson S, Fardoun F, Besq A. Boiling local heat transfer enhancement in minichannels using nanofluids. Nanoscale Res. Lett. 2013;8(1):1–20. Xu L, Xu J. Nanofluid stabilizes and enhances convective boiling heat transfer in a single microchannel. Int J Heat Mass Transf 2012;55(21–22):5673–86. Peng H, Ding G, Jiang W, Hu H, Gao Y. Heat transfer characteristics of refrigerantbased nanofluid flow boiling inside a horizontal smooth tube. Int J Refrig 2009;32:1259–70. Paul G, Das PK, Manna I. Assessment of the process of boiling heat transfer during rewetting of a vertical tube bottom flooded by alumina nanofluid. Int J Heat Mass Transf 2016;94:390–402. Aminfar H, Mohammadpourfard M, Maroofiazar R. Experimental study on the effect of magnetic field on critical heat flux of ferrofluid flow boiling in a vertical annulus. Exp Therm Fluid Sci 2014;58:156–69. Lee T, Lee JH, Jeong YH. Flow boiling critical heat flux characteristics of magnetic nanofluid at atmospheric pressure and low mass flux conditions. Int J Heat Mass Transf 2013;56:101–6. Lee SW, Kim KM, Bang IC. Study on flow boiling critical heat flux enhancement of graphene oxide/water nanofluid. Int J Heat Mass Transf 2013;65:348–56. Lee SW, et al. Critical heat flux enhancement in flow boiling of Al2O3 and SiC nanofluids under low pressure and low flow conditions. Nucl. Eng. Technol. 2012;44(4):429–36. Vafaei S, Wen D. Flow boiling heat transfer of alumina nanofluids in single microchannels and the roles of nanoparticles. J Nanoparticle Res 2011;13(3):1063–73. Il Kim T, Chang WJ, Chang SH. Flow boiling CHF enhancement using Al2O3 nanofluid and an Al2O3 nanoparticle deposited tube. Int J Heat Mass Transf 2011;54(9–10):2021–5. Il Kim T, Jeong YH, Chang SH. An experimental study on CHF enhancement in flow boiling using Al2O3 nano-fluid. Int J Heat Mass Transf 2010;53(5–6):1015–22. Ahn HS, Kim H, Jo HJ, Kang SH, Chang WP, Kim MH. Experimental study of critical heat flux enhancement during forced convective flow boiling of nanofluid on a short heated surface. Int J Multiph Flow 2010;36(5):375–84. Kim SJ, McKrell T, Buongiorno J, Hu L-W. Experimental study of flow critical heat

Renewable and Sustainable Energy Reviews 112 (2019) 607–625

M. Dadhich and O.S. Prajapati

[146]

[147]

[148]

[149] [150] [151]

[152] [153] [154]

flux in alumina-water, zinc-oxide-water, and diamond-water nanofluids. J Heat Transf 2009;131(4):043204. 1-7. Kim SJ, McKrell T, Buongiorno J, Hu L-W. Alumina nanoparticles enhance the flow boiling critical heat flux of water at low pressure. J Heat Transf 2008;130(4):044501. 1-3. Kim JH, Rainey KN, You SM, Pak JY. Mechanism of nucleate boiling heat transfer enhancement from microporous surfaces in saturated FC-72. J Heat Transf 2002;124(3):500–6. Wu W, Bostanci H, Chow LC, Hong Y, Su M, Kizito JP. Nucleate boiling heat transfer enhancement for water and FC-72 on titanium oxide and silicon oxide surfaces. Int J Heat Mass Transf 2010;53(9–10):1773–7. El-genk MS, Ali AF. Enhanced nucleate boiling on copper micro-porous surfaces. Int J Multiph Flow 2010;36:780–92. Jones BJ, Mchale JP, V Garimella S. The influence of surface roughness on nucleate pool boiling heat transfer. J Heat Transf 2009;131(December):1–14. 2009. Wen MY, Ho CY. Pool boiling heat transfer of deionized and degassed water in vertical/horizontal V-shaped geometries. Heat Mass Transf. und Stoffuebertragung 2003;39(8–9):729–36. Li C, Peterson GP. Geometric effects on critical heat flux on horizontal microporous coatings. J Thermophys Heat Transf 2010;24(3):449–55. Liu CF, Yang CY. Effect of space distance for boiling heat transfer on micro porous coated surface in confined space. Exp Therm Fluid Sci 2013;50:163–71. Seo GH, Jeun G, Kim SJ. Enhanced pool boiling critical heat flux with a FeCrAl layer fabricated by DC sputtering. Int J Heat Mass Transf 2016;102:1293–307.

[155] Sun Y, Zhang L, Xu H, Zhong X. Flow boiling enhancement of FC-72 from microporous surfaces in minichannels. Exp Therm Fluid Sci 2011;35:1418–26. [156] Guo D, Wei JJ, Zhang YH. Enhanced flow boiling heat transfer with jet impingement on micro-pin-finned surfaces. Appl Therm Eng 2011;31(11–12):2042–51. [157] Ammerman CN, You SM. Enhancing small-channel convective boiling performance using a microporous surface coating. J Heat Transf 2002;123(5):976. [158] Bai P, Tang T, Tang B. Enhanced flow boiling in parallel microchannels with metallic porous coating. Appl Therm Eng 2013;58(1–2):291–7. [159] Kaya A, Demiryurek R, Armagan E, Ozaydin-Ince G, Sezen M, Kosar A. Boiling heat transfer enhancement in mini/microtubes via polyhydroxyethylmethacrylate (pHEMA) coatings on inner microtube walls at high. J Micromech Microeng 2013;23:1–11. [160] Morshed AKMM, Paul TC, Khan J. Effect of Cu-Al2O3 nanocomposite coating on flow boiling performance of a microchannel. Appl Therm Eng 2013;51(1–2):1135–43. [161] Singh N, Sathyamurthy V, Peterson W, Arendt J, Banerjee D. Flow boiling enhancement on a horizontal heater using carbon nanotube coatings. Int J Heat Fluid Flow 2010;31(2):201–7. [162] Kang SH, Kim J, Kim MH, Ahn HS, Lee C. The effect of liquid spreading due to micro-structures of flow boiling critical heat flux. Int J Multiph Flow 2012;43:1–12. [163] Hsieh SS, Lin CY. Subcooled convective boiling in structured surface microchannels. J Micromech Microeng 2010;20(1):1–13.

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