- Email: [email protected]
Enhancement of pool boiling heat transfer using innovative non-ionic surfactant on a wire heater
Accepted Manuscript Enhancement of pool boiling heat transfer using innovative non-ionic surfactant on a wire heater Abdul Najim, Vasudha More, Aarti Thorat, Sahil Patil, Sanket Savale PII: DOI: Reference:
S0894-1777(16)30355-7 http://dx.doi.org/10.1016/j.expthermflusci.2016.11.039 ETF 8961
To appear in:
Experimental Thermal and Fluid Science
Received Date: Revised Date: Accepted Date:
3 July 2016 29 November 2016 29 November 2016
Please cite this article as: A. Najim, V. More, A. Thorat, S. Patil, S. Savale, Enhancement of pool boiling heat transfer using innovative non-ionic surfactant on a wire heater, Experimental Thermal and Fluid Science (2016), doi: http://dx.doi.org/10.1016/j.expthermflusci.2016.11.039
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Enhancement of pool boiling heat transfer using innovative non-ionic surfactant on a wire heater Abdul Najim1*, Vasudha More2, Aarti Thorat3, Sahil Patil4, Sanket Savale5 1*
Department of Mechanical Engineering, KIT’s College of Engineering, Kolhapur, Maharashtra, India, 416234 2,3,4,5
Department of Mechanical Engineering, A.D.C.E.T., Ashta, Sangli, Maharashtra, India, 416301
Abstract Saturated pool boiling of aqueous Nicotine (an innovative non-ionic surfactant) solutions, on a Nichrome wire heater was studied experimentally. Pool boiling experiments were started by boiling pure (distilled) water. After that, pure water was replaced by the aqueous surfactant solutions by 100, 500, 1000, 1500, 2000, 2500, 3000, 3500 and 4000 ppm on weight basis. The drop volume method was used to measure surface tension of aqueous solutions. The experiments of aqueous surfactant solutions were conducted under the same conditions of baseline (water) experiment. The boiling behaviour was studied by using high speed video technique. Pool boiling curves for various concentrations were obtained, and compared. Pool boiling performance was found to be enhanced significantly by the addition of Nicotine relative to pure water. An optimum level of enhancement was observed in solutions at 2500 ppm, which was critical micelle concentration (cmc) of the surfactant. No enhancement was observed in higher concentration solutions. It was observed that addition of Nicotine into pure water reduces its surface tension considerably which in turn enhances heat transfer. Keywords: pool boiling heat transfer; surfactant; enhancement; nicotine
1.Introduction Boiling has been found in a wide range of applications of heating, cooling and electric power generation. It is one of the major research topics because it involves transfer of large amount heat *
Corresponding Author. Tel.:+91-231-2638143; fax: +91-231-2638141. Email address: [email protected] (Abdul Najim)
Page 1
Nomenclature A d
heater surface area, (m2) diameter of Nichrome wire heater, (mm)
Greek Symbols
g
gravitational acceleration, m/s2
σ
h m
heat transfer coefficient, (W/m2 K) mass of a single drop, (kg)
r
outer radius of capillary tube, (m)
q Tw Ts (Tw – Ts )
wall heat flux, (W/m2) temperature of heater wire, (K) saturation temperature of liquid, (K) wall superheat, (K)
surface tension of liquid, (N/m)
with a minimum temperature difference. Over the past decades, a great amount of research on had carried out enhancement of pool boiling heat transfer and it is still going on. Accordingly, various techniques for enhancement of boiling heat transfer had proposed and studied. Among different enhancement techniques investigated, the use of surfactant additives in water has been found to be very effective. Cheng et al. [1] presented a state of the art review on boiling phenomenon with surfactant and polymeric additives. It was reported that surfactant at low concentration could increase boiling heat transfer considerably. Also, they suggested that experimental work needed to be done to explore this research area. Researchers [2-13] have reported considerable enhancement of heat transfer during saturated pool boiling of surfactant solution. The comparison of their work has shown in the Table 1. Wu et al. [14] conducted experimental investigation with seven different surfactants to study enhancement of nucleate boiling heat transfer. They related augmentation of boiling heat transfer with depression of surface tension of aqueous solution. The addition of low concentration surfactant in pure water decreases the surface tension of aqueous solution considerably, and, critical micelle concentration (cmc) decides the limit of reduction in surface tension with increasing additive concentration. The critical micelle concentration (cmc) indicates effectiveness of a surfactant to reduce surface tension of the solution. After critical micelle concentration (cmc), the surface tension doesn’t reduce. Tzan and Yang [15] measured heat transfer coefficient during pool boiling of aqueous Sodium Lauryl Sulphate (an anionic surfactant) using stainless steel as heating surface. They concluded that addition of an anionic surfactant into water affect both convection component and latent Page 2
heat component of the heat flux. Inoue et al. [16] also measured boiling heat transfer coefficient for platinum wire as heating surface and proposed that boiling on the heated wire is same as that on an infinite surface. Hetsroni et al. [17] investigated subcooled pool boiling phenomenon using Habon G surfactant on horizontal stainless steel tube. They observed boiling hysteresis for aqueous surfactant solutions.
Table 1 Literature comparison of researchers [2-13] for different conditions such as different surfactants and different heating surfaces Sr. No.
Researcher
Year
Boiling Type, Heating surface
1
Yang and Maa [2]
2001
Pool, Tube
2
Wasekar and Manglik [3]
2002
Pool, Cylinder
3 4 5 6 7 8 9 10 11 12
Hetsroni et al. [4] Zhang and Manglik [5] Ding et al. [6] Inoue and Monde [7] Gajghate et al. [8] Najim et al. [9] Cho et al. [10] Najim and Pise [11] Wang et al. [12] Wang et al. [13]
2004 2005 2011 2012 2013 2014 2015 2016 2016 2016
Pool, Tube Pool, Cylinder Pool, Plate Pool, Wire Pool, Wire Pool, Needle Pool, Plane Pool, Needle Pool, Wire Pool, Wire
Surfactant SDS; Tergitol; Triton SP-175; Triton SP-190; Aerosol-22; Tween 20; Tween 40; Triton X-100 SDS; SLES; Triton X-100; Triton X-305 Alkyl Poly-glycoside HEC-QP300 SDS; CTAB; Span-80 Perfluoroalkyl Compound Ammonium Chloride Ammonium Chloride NaBr, MEGA-10, S10S, SDS, DTAB 2-Ethyl-1-Hexanol CTAC Alkyl Poly-glycoside, CTAB, SDBS
The enhancement of boiling heat transfer using non-ionic surfactant is important for engineering applications because anionic and non–ionic surfactants fulfils most of the industrial surfactant requirements. But, most of the surfactants are not suited for industrial purpose because they are more or less toxic to aquatic organisms and non-biodegradable. So, it is necessary to search new surfactants with insignificant environmental impact. The objective of the present investigation is to verify whether the addition of Nicotine (a non-ionic surfactant) into water enhances boiling heat transfer or not. The addition of Nicotine into pure water reduces its surface tension significantly till critical micelle concentration. Nicotine is new and innovative surfactant. It produces from plant and it is biodegradable too. The molecular weight of Nicotine is 162.23 g/mol, and it is soluble in water. In lesser doses, Nicotine acts as a stimulant in mammals. Page 3
2. Experimental 2.1 Measurement of surface tension and dynamic viscosity The surface tension of all solutions was measured by KOCOUR™ Stalagmometer (2.5 ml, suitable for low viscosity liquids) at atmospheric pressures, which is based on Drop Volume Method, used by Yuan and Herold [18]. This method is based on force balance on drops as they separate from a capillary tube feeding the liquid. Figure 1 shows the schematic of Stalagmometer, and force balance on drops.
Fig. 1 Schematic of Stalagmometer, and force balance for a drop [18]
The weight of drop is assumed to be balanced by the surface tension force as
mg = 2πr σ
(1)
The dynamic viscosity of all solutions was determined in the temperature range 200C - 800C with Ostwald’s viscometer. The standard deviation was 5%.
Page 4
2.2 Apparatus The schematic of the apparatus used to study pool boiling is shown in Figure 2. This apparatus was designed to study the pool boiling phenomenon up to critical heat flux point. The apparatus consists of a glass container of 2 litres capacity housing a test heater and auxiliary heater. A Nichrome wire (diameter d=0.3mm, length l=100mm) was used as test heater (heating surface). The glass container was covered with clay lid having holes. The clay lid allows vapours to flow through the holes during boiling process, which maintain pressure of liquid pool at atmospheric level. The temperature of the liquid pool was maintained at saturation temperature using auxiliary heater and it was directly connected to the mains. Test heater was connected to mains via a dimmer. An ammeter and a voltmeter were used to read the current and voltage, respectively. There was provision of illuminating the test heater wire with the help of a lamp projecting light from behind the container and the heater wire could be viewed through lens. The pool temperature was measured by three K-type thermocouple located uniformly in liquid pool. The temperature of wire heater was measured using calibrated four-wire resistance measurement system [12]. The four-wire resistance measurement system eliminates effect of mild steel bar resistance and contact resistance. To measure voltage, conducting wires were welded at two ends of wire heater.
Fig. 2 Schematic of the pool boiling apparatus
Page 5
2.3 Experimental Procedure Initially, glass container was filled with 1500ml of pure water to bring the surface to a level 80-90 mm above heater. The effect of dissolved gases vanishes as the surface temperature of wire reaches saturation temperature of liquid [17]. Precaution was taken to avoid effect of dissolved gases on bubble formation by conducting experiments after 20 minutes when saturated pool boiling began. Water was heated to saturation temperature at atmospheric pressure using auxiliary heater. Nichrome wire heater was switched ON as soon as pure water reaches saturation temperature. The electric power supply to the Nichrome wire was controlled by using dimmer. The temperature of water, and test heater were recorded at each step. Temperature of test heater was recorded 15 minutes after supply of electric power to test heater which seemed to be a steady state condition. The steady state condition was defined as a state at which no change in temperature of test heater was observed. The experiments were stopped at Critical Heat Flux (CHF). CHF is defined as the heat flux at which heater wire burnt out. The boiling behaviour was recorded on high speed camera for additional analysis. The procedure was repeated. Glass container was emptied, cleaned, and replaced with aqueous surfactant solutions of concentrations 100, 500, 1000, 1500, 2000, 2500, 3000, 3500 and 4000 ppm on weight basis. New Nichrome wire heater was used for each run.
2.4 Uncertainty Analysis Uncertainty analysis was done as per method stated by Holman [19]. The heat flux was calculated as
. A linear relationship was found between temperature of heated wire (Tw) and resistance
of heated wire (R) as Tw=
, where a and b are constants, which were determined by temperature
calibration. The average heat transfer coefficient was calculated as
where Ts = 373.15K.
The uncertainty of wall heat flux, temperature of heated wire and average heat transfer coefficient was obtained using following equations (Eqs. (2)-(4)). The uncertainties in the experimental measurements have given in Table 2.
Page 6
V I D L q q V I D L 2
Tw b
V I
2
V I V I 2
2
2
2
(2)
2
q (Tw Ts ) h h q (Tw Ts
(3)
2
(4)
Table 2 Uncertainties in experimental measurements Parameter
Uncertainty
Voltage (V)
1V
Current (I)
0.1A
Diameter of wire
0.015 mm
Length of wire
1mm
Wall heat flux
4.63%
Temperature of wire (Tw)
1.5K
Temperature of liquid pool (T s)
1K
Heat transfer coefficient (h)
5.28%
Nicotine concentration
5ppm
Surface tension
0.1mN/m
Dynamic Viscosity
0.1Ns/m2
3. Results and Discussion 3.1 Effect of surfactant concentration and temperature on surface tension The experiments of measurement of surface of aqueous Nicotine solutions at different concentrations were performed 7 times to obtain reliable estimates of average values. The average values were plotted to study surface tension. The variation with concentration and temperature of the measured Page 7
surface tension of aqueous Nicotine solutions was plotted in Figure 3. It was observed that, addition of Nicotine into pure water reduces surface tension of aqueous solution by
50% at a concentration of
2500 ppm which is critical micelle concentration of the aqueous solution. No significant reduction was observed after 2500ppm concentration. The critical micelle concentration (cmc) indicates effectiveness of a surfactant to reduce surface tension of the solution. After critical micelle concentration (cmc), the surface tension will not reduce. So, one can conclude that, addition of Nicotine into water reduces the surface tension of aqueous solution. Similar results have been obtained by Wasekar and Manglik [3] using SDS, SLES, Triton X-100, and Triton X-305, Hetsroni et al. [4] using Alkyl Poly-glycosides, and Gajghate et al. [8] using Ammonium Chloride as surfactants.
Fig. 3 Surface tension variation of aqueous Nicotine solution
3.2 Effect of surfactant concentration and temperature on dynamic viscosity Figure 4 shows measured dynamic viscosities of pure water and aqueous surfactant solution of 2500ppm concentration at different temperatures. There was no considerable difference among dynamic viscosities for the two fluids at the same temperature. This shows that surfactant solutions reveal Newtonian fluid behaviour as that of water. Similar behaviour was observed by Cheng et al. [1] with aqueous SDS solution, aqueous Triton X-100 solution and water. Page 8
Fig. 4 Variation of measured dynamic viscosity with temperature 3.3 Boiling Behaviour Figure 5 shows different photographs of boiling behaviour with increasing heat flux (q = 100 and 200 kW/m2) for aqueous solutions of surfactant at 100 ppm concentration and for pure water. Video recording was done to study boiling behaviour for each run. The boiling behaviour was observed to be different for aqueous Nicotine solution from that in pure water. The addition of surfactant into pure water decreases surface tension of aqueous solution at liquid–vapour interface. Surfactant addition makes water impure and promotes activation of nucleation sites. The boiling pool became significantly cloudier with increasing surfactant concentration. It was more vigorous, and characterised by smaller diameter bubbles. The bubbles appear in a cluster mode. There is an early evolution of bubbles with the faster covering of heating surface, and higher bubble departure frequency which is essentially the outcome of reduced surface tension at the liquid vapour interface. As concentration increases, boiling pool became considerably cloudier; bubbles tends to coalesce forming slugs and columns. So, it was very difficult to get clear photograph at higher concentrations and at higher heat fluxes. Hence photographs of higher concentration solutions and higher heat fluxes have not included.
Page 9
Fig. 5 Boiling behaviour of pure water, and aqueous Nicotine solutions of different concentration at different heat fluxes 3.4 Pool boiling curves Pool boiling data as a function of heat flux versus wall superheat was plotted for pure water, and different aqueous solutions of Nicotine in Figure 6. For each concentration and heat flux, seven trials were performed and average values obtained from these measurements were plotted. Remarkable behaviour was observed in boiling curves. The heat transfer rate was found to be continuously enhanced as boiling curve shifted leftward relative to pure water till 2500ppm concentration. After 2500 ppm no enhancement was observed. The reason for such behaviour was related to diffusion controlled mechanism proposed by Hetsroni et al. [17]. They stated that diffusion of surfactant molecules and their adsorption rates controls the number of active nucleation sites. Bubble explosion and bubble jet phenomenon were occurred in aqueous surfactant solutions, revealing enhanced heat transfer effect [12-13]. The wall superheat was observed to be decreased with increasing surfactant concentration. The last data point on pool boiling curves indicates Critical Heat Flux (CHF) condition. CHF data for pool boiling of aqueous Nicotine solution at different concentrations was given in Table 3. CHF was found to be enhanced by
at
2500 ppm Nicotine concentration. No enhancement was found after 2500 ppm Nicotine concentration.
Page 10
Fig. 6 Pool boiling curves of aqueous Nicotine solutions and pure water Table 3 CHF data pool boiling of aqueous Nicotine solution at different concentrations Nicotine concentrations (ppm)
0 (pure water)
100
500
1000
1500
2000
2500
3000
3500
4000
CHF (MW/m2)
1
1.09
1.15
1.23
1.34
1.41
1.45
1.44
1.44
1.44
3.5 h-q plot Figure 7 shows plot of heat transfer coefficient versus heat flux to clarify the effect of heat flux, and surfactant additive concentration on the boiling heat transfer coefficient of aqueous Nicotine solutions. As heat flux and concentrations increases, heat transfer coefficients increases, except the concentration are higher than 2500 ppm. The slope of the lines in h-q plot increases with the addition of surfactant. This is due to the fact that number of nucleation sites increases and bubbles were generated more easily in presence of surfactant, because of reduced surface tension. Thus, both increase in the slope of h-q plot and advancement of the onset of boiling enhances boiling heat transfer. The results obtained in
Page 11
present study are consistent with Wasekar and Manglik [3] with SDS, SLES, Triton X-100, and Triton X-305, Hetsroni et al. [4] with Alkyl Poly-glycosides, and Inoue and Monde [7] with Surflon S-451 as surfactants.
Fig. 7 Heat transfer coefficient versus heat flux for different aqueous Nicotine solution concentrations and pure water 5. Conclusion Pool boiling phenomenon was studied in saturated aqueous nicotine (novel non-ionic surfactant) solution of different concentrations, and pure water on a Nichrome wire heater experimentally. High speed video technique was used to study pool boiling phenomenon. More chaotic bubble action was observed for aqueous surfactant solution compared to water. Bubbles formed in Nicotine solution were smaller than those in water; coalesce quickly, and heater surface became covered with them faster. The surface tension of aqueous surfactant solution at 2500 ppm was almost 50% less than that in water. The reduced surface tension results in a decrease of energy required to create a bubble, and thus in more bubbles, and smaller ones. The boiling curves of surfactant were different from the boiling curve of pure water. Pool boiling heat transfer was observed to be enhanced significantly by the addition of Nicotine relative to pure water. An optimum level of enhancement was observed in solutions up to 2500 ppm, which was critical micelle concentration of the surfactant. CHF was found to be enhanced by
at 2500 ppm Nicotine Page 12
concentration. Nicotine produces from plant and it is biodegradable with negligible environmental impact. The surfactant additive Nicotine can successfully be used to enhance nucleate boiling heat transfer.
Acknowledgements This work was supported by KIT’s College of Engineering, Kolhapur, India.
References [1] L. Cheng, D. Mewes, A. Luke, Boiling Phenomenon with Surfactants and Polymeric Additives: A state
of
the
art
review,
Int.
J.
Heat
Mass
Transfer,
50(2006),
2744-2771.
DOI:10.1016/j.ijheatmasstransfer.2006.11.016 [2] Y. M. Yang, J. R. Maa, On the criteria of Nucleate Pool Boiling Enhancement by Surfactant Addition to Water”, Institution of Chemical Engineers, Trans I, ChemE- Part A, 79(2001), 409-416. [3] V. M. Wasekar, R. M. Manglik, Influence of Additive Molecular Weight and Ionic Nature on the Pool Boiling Performance of Aqueous Surfactant Solutions,
Int. J. Heat Mass Transfer, 45(2002),
483-493. [4] G. Hetsroni, M. Gurevich, A. Mosyak, R. Rozenblit, Z. Segal, Boiling Enhancement with Environmentally
Acceptable
Surfactants,
25(2004),
841-848.
DOI:10.1016/j.ijheatfluidflow.2004.05.005 [5] J. Zhang, R. Manglik, Nucleate Pool Boiling of Aqueous Polymer Solutions on a Cylindrical Heater, J. Non-Newtonian Fluid Mechanics, 125 (2005), 185-196. DOI: 10.1016/j.jnnfm.2004.12.001 [6] G. Ding, H. Peng, H. Hu, Effect of Surfactant Additives on Nucleate Pool Boiling Heat Transfer of Refrigerant
Based
Nanofluid,
Expt.
Thermal
Fluid
Science,
35(2011),
960-970.
DOI:10.1016/j.expthermflusci.2011.01.016 [7] T. Inoue, M. Monde, Enhancement of Nucleate Pool Boiling Heat Transfer in Ammonia-water mixtures with a surface active agent, Int. J. Heat Mass Transf., 55, (2012), 3395-3399. Page 13
DOI:10.1016/j.ijheatmasstransfer.2012.03.004 [8] S. S. Gajghate, A. R. Acharya, A. T. Pise, Experimental Study of Aqueous Ammonium Chloride in Pool Boiling Heat Transfer, Expt. Heat Transfer: J. Thermal Energy Generation, Transport, Storage, and Conversion, 27(2)(2013), 113-123. DOI: 10.1080/08916152.2012.757673 [9] A. Najim, A. R. Acharya, A. T. Pise, S. S. Gajghate, Experimental Study of Bubble Dynamics in Pool Boiling Heat Transfer using Saturated Water and Surfactant Solution, Proc. IEEE-ICAET, EGS Pillay College of Engg. and Tech., Nagapattinum, May 2-3, 2014, Nagapattinum, Tamilnadu. DOI: 10.1109/ICAET. 2014.7105293 [10] H. Cho, J. Mizerak, E. Wang, Turning Bubbles On and Off during boiling using charged surfaces, Nature Comms., 6:8599(2015), 01-03. DOI: 10.1038/ncomms9599 [11] A. Najim, S. Pise, Boiling Heat Transfer Enhancement with Surfactant on the Tip of a Submerged Hypodermic
Needle
as
Nucleation
Site,
App.
Thermal
Engg.,
103(2016),
989-995.
DOI: 10.1016/j.applthermaleng.2016.05.001 [12] J. Wang, F. Li, X. Li, Bubble Explosion in Pool Boiling Around A heated Wire in Surfactant Solution,
Int.
J.
Heat
Mass
Transf.,
99(2016),
569-575.
DOI: 10.1016/j.ijheatmasstransfer.2016.03.111 [13] J. Wang, F. Li, X. Li, On the Mechanism of Boiling Heat Transfer Enhancement by Surfactant Addition, Int. J. Heat Mass Transf., 101(2016), 800-806. DOI:10.1016/j.ijheatmasstransfer.2016.05.121 [14] W. Wu, Y. Yang, J. Maa, Enhancement of Nucleate Boiling Heat Transfer and Depression of Surface Tension by Surfactant Additives, Trans. ASME, 117 (1995), 526–529. [15] Y. Tzan, Y. Yang, Experimental Study of Surfactant Effects on Pool Boiling Heat Transfer, J. Heat Transf., 112(1990), 207-212. [16] T. Inoue, Y. Teruya, M. Monde, Enhancement of Pool Boiling Heat Transfer in Water and Ethanol / Water Mixture with Surface Active Agent, Int. J. Heat Mass Transfer, 47(2004), 5555-5563. DOI:10.1016/j.ijheatmasstransfer.2004.05.037 Page 14
[17] G. Hetsroni, M. Gurevich, A. Mosyak, R. Rozenblit, L. Yarin, Subcooled Boiling of Surfactant Solutions, Int. J. Multiphase Flow, 28(2002), 347-361. [18] Z. Yuan, K. E. Herold, Surface Tension of Pure Water and Aqueous Lithium Bromide with 2- EthylHexanol, App. Thermal Engg., 21(2001), 881-897. [19] J. P. Holman, Experimental Methods for Engineers, 7th edition, Tata McGraw Hill, India, 2007, p. 51. ISBN: 978-0-07-064776-3.
Page 15
Table Captions List Table No.
Caption Literature comparison of researchers [2-13] for different
1
conditions such as different surfactants and different heating surfaces
2
Uncertainties in experimental measurements CHF data pool boiling of aqueous Nicotine solution at different
3 concentrations
Page 16
Figure Captions List Figure No.
Caption
1
Schematic of Stalagmometer, and force balance for a drop [18]
2
Schematic of the pool boiling apparatus
3
Surface tension variation of aqueous Nicotine solution
4
Variation of measured dynamic viscosity with temperature
5
Boiling behaviour of pure water, and aqueous Nicotine solutions of different concentration at different heat fluxes
6
Pool boiling curves of aqueous Nicotine solutions and pure water
7
Heat transfer coefficient versus heat flux for different aqueous Nicotine solution concentrations and pure water
Page 17
Highlights 1. Effect of addition of Nicotine into pure water on boiling was studied. 2. Optimum concentration of Nicotine for maximum heat transfer coefficient was found. 3. Addition of Nicotine into pure water reduces its surface tension by almost 50%. 4. Boiling heat transfer found to be enhanced in aqueous Nicotine solution. 5. Nicotine produces from plant and it is biodegradable.
Page 18
S0894-1777(16)30355-7 http://dx.doi.org/10.1016/j.expthermflusci.2016.11.039 ETF 8961
To appear in:
Experimental Thermal and Fluid Science
Received Date: Revised Date: Accepted Date:
3 July 2016 29 November 2016 29 November 2016
Please cite this article as: A. Najim, V. More, A. Thorat, S. Patil, S. Savale, Enhancement of pool boiling heat transfer using innovative non-ionic surfactant on a wire heater, Experimental Thermal and Fluid Science (2016), doi: http://dx.doi.org/10.1016/j.expthermflusci.2016.11.039
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Enhancement of pool boiling heat transfer using innovative non-ionic surfactant on a wire heater Abdul Najim1*, Vasudha More2, Aarti Thorat3, Sahil Patil4, Sanket Savale5 1*
Department of Mechanical Engineering, KIT’s College of Engineering, Kolhapur, Maharashtra, India, 416234 2,3,4,5
Department of Mechanical Engineering, A.D.C.E.T., Ashta, Sangli, Maharashtra, India, 416301
Abstract Saturated pool boiling of aqueous Nicotine (an innovative non-ionic surfactant) solutions, on a Nichrome wire heater was studied experimentally. Pool boiling experiments were started by boiling pure (distilled) water. After that, pure water was replaced by the aqueous surfactant solutions by 100, 500, 1000, 1500, 2000, 2500, 3000, 3500 and 4000 ppm on weight basis. The drop volume method was used to measure surface tension of aqueous solutions. The experiments of aqueous surfactant solutions were conducted under the same conditions of baseline (water) experiment. The boiling behaviour was studied by using high speed video technique. Pool boiling curves for various concentrations were obtained, and compared. Pool boiling performance was found to be enhanced significantly by the addition of Nicotine relative to pure water. An optimum level of enhancement was observed in solutions at 2500 ppm, which was critical micelle concentration (cmc) of the surfactant. No enhancement was observed in higher concentration solutions. It was observed that addition of Nicotine into pure water reduces its surface tension considerably which in turn enhances heat transfer. Keywords: pool boiling heat transfer; surfactant; enhancement; nicotine
1.Introduction Boiling has been found in a wide range of applications of heating, cooling and electric power generation. It is one of the major research topics because it involves transfer of large amount heat *
Corresponding Author. Tel.:+91-231-2638143; fax: +91-231-2638141. Email address: [email protected] (Abdul Najim)
Page 1
Nomenclature A d
heater surface area, (m2) diameter of Nichrome wire heater, (mm)
Greek Symbols
g
gravitational acceleration, m/s2
σ
h m
heat transfer coefficient, (W/m2 K) mass of a single drop, (kg)
r
outer radius of capillary tube, (m)
q Tw Ts (Tw – Ts )
wall heat flux, (W/m2) temperature of heater wire, (K) saturation temperature of liquid, (K) wall superheat, (K)
surface tension of liquid, (N/m)
with a minimum temperature difference. Over the past decades, a great amount of research on had carried out enhancement of pool boiling heat transfer and it is still going on. Accordingly, various techniques for enhancement of boiling heat transfer had proposed and studied. Among different enhancement techniques investigated, the use of surfactant additives in water has been found to be very effective. Cheng et al. [1] presented a state of the art review on boiling phenomenon with surfactant and polymeric additives. It was reported that surfactant at low concentration could increase boiling heat transfer considerably. Also, they suggested that experimental work needed to be done to explore this research area. Researchers [2-13] have reported considerable enhancement of heat transfer during saturated pool boiling of surfactant solution. The comparison of their work has shown in the Table 1. Wu et al. [14] conducted experimental investigation with seven different surfactants to study enhancement of nucleate boiling heat transfer. They related augmentation of boiling heat transfer with depression of surface tension of aqueous solution. The addition of low concentration surfactant in pure water decreases the surface tension of aqueous solution considerably, and, critical micelle concentration (cmc) decides the limit of reduction in surface tension with increasing additive concentration. The critical micelle concentration (cmc) indicates effectiveness of a surfactant to reduce surface tension of the solution. After critical micelle concentration (cmc), the surface tension doesn’t reduce. Tzan and Yang [15] measured heat transfer coefficient during pool boiling of aqueous Sodium Lauryl Sulphate (an anionic surfactant) using stainless steel as heating surface. They concluded that addition of an anionic surfactant into water affect both convection component and latent Page 2
heat component of the heat flux. Inoue et al. [16] also measured boiling heat transfer coefficient for platinum wire as heating surface and proposed that boiling on the heated wire is same as that on an infinite surface. Hetsroni et al. [17] investigated subcooled pool boiling phenomenon using Habon G surfactant on horizontal stainless steel tube. They observed boiling hysteresis for aqueous surfactant solutions.
Table 1 Literature comparison of researchers [2-13] for different conditions such as different surfactants and different heating surfaces Sr. No.
Researcher
Year
Boiling Type, Heating surface
1
Yang and Maa [2]
2001
Pool, Tube
2
Wasekar and Manglik [3]
2002
Pool, Cylinder
3 4 5 6 7 8 9 10 11 12
Hetsroni et al. [4] Zhang and Manglik [5] Ding et al. [6] Inoue and Monde [7] Gajghate et al. [8] Najim et al. [9] Cho et al. [10] Najim and Pise [11] Wang et al. [12] Wang et al. [13]
2004 2005 2011 2012 2013 2014 2015 2016 2016 2016
Pool, Tube Pool, Cylinder Pool, Plate Pool, Wire Pool, Wire Pool, Needle Pool, Plane Pool, Needle Pool, Wire Pool, Wire
Surfactant SDS; Tergitol; Triton SP-175; Triton SP-190; Aerosol-22; Tween 20; Tween 40; Triton X-100 SDS; SLES; Triton X-100; Triton X-305 Alkyl Poly-glycoside HEC-QP300 SDS; CTAB; Span-80 Perfluoroalkyl Compound Ammonium Chloride Ammonium Chloride NaBr, MEGA-10, S10S, SDS, DTAB 2-Ethyl-1-Hexanol CTAC Alkyl Poly-glycoside, CTAB, SDBS
The enhancement of boiling heat transfer using non-ionic surfactant is important for engineering applications because anionic and non–ionic surfactants fulfils most of the industrial surfactant requirements. But, most of the surfactants are not suited for industrial purpose because they are more or less toxic to aquatic organisms and non-biodegradable. So, it is necessary to search new surfactants with insignificant environmental impact. The objective of the present investigation is to verify whether the addition of Nicotine (a non-ionic surfactant) into water enhances boiling heat transfer or not. The addition of Nicotine into pure water reduces its surface tension significantly till critical micelle concentration. Nicotine is new and innovative surfactant. It produces from plant and it is biodegradable too. The molecular weight of Nicotine is 162.23 g/mol, and it is soluble in water. In lesser doses, Nicotine acts as a stimulant in mammals. Page 3
2. Experimental 2.1 Measurement of surface tension and dynamic viscosity The surface tension of all solutions was measured by KOCOUR™ Stalagmometer (2.5 ml, suitable for low viscosity liquids) at atmospheric pressures, which is based on Drop Volume Method, used by Yuan and Herold [18]. This method is based on force balance on drops as they separate from a capillary tube feeding the liquid. Figure 1 shows the schematic of Stalagmometer, and force balance on drops.
Fig. 1 Schematic of Stalagmometer, and force balance for a drop [18]
The weight of drop is assumed to be balanced by the surface tension force as
mg = 2πr σ
(1)
The dynamic viscosity of all solutions was determined in the temperature range 200C - 800C with Ostwald’s viscometer. The standard deviation was 5%.
Page 4
2.2 Apparatus The schematic of the apparatus used to study pool boiling is shown in Figure 2. This apparatus was designed to study the pool boiling phenomenon up to critical heat flux point. The apparatus consists of a glass container of 2 litres capacity housing a test heater and auxiliary heater. A Nichrome wire (diameter d=0.3mm, length l=100mm) was used as test heater (heating surface). The glass container was covered with clay lid having holes. The clay lid allows vapours to flow through the holes during boiling process, which maintain pressure of liquid pool at atmospheric level. The temperature of the liquid pool was maintained at saturation temperature using auxiliary heater and it was directly connected to the mains. Test heater was connected to mains via a dimmer. An ammeter and a voltmeter were used to read the current and voltage, respectively. There was provision of illuminating the test heater wire with the help of a lamp projecting light from behind the container and the heater wire could be viewed through lens. The pool temperature was measured by three K-type thermocouple located uniformly in liquid pool. The temperature of wire heater was measured using calibrated four-wire resistance measurement system [12]. The four-wire resistance measurement system eliminates effect of mild steel bar resistance and contact resistance. To measure voltage, conducting wires were welded at two ends of wire heater.
Fig. 2 Schematic of the pool boiling apparatus
Page 5
2.3 Experimental Procedure Initially, glass container was filled with 1500ml of pure water to bring the surface to a level 80-90 mm above heater. The effect of dissolved gases vanishes as the surface temperature of wire reaches saturation temperature of liquid [17]. Precaution was taken to avoid effect of dissolved gases on bubble formation by conducting experiments after 20 minutes when saturated pool boiling began. Water was heated to saturation temperature at atmospheric pressure using auxiliary heater. Nichrome wire heater was switched ON as soon as pure water reaches saturation temperature. The electric power supply to the Nichrome wire was controlled by using dimmer. The temperature of water, and test heater were recorded at each step. Temperature of test heater was recorded 15 minutes after supply of electric power to test heater which seemed to be a steady state condition. The steady state condition was defined as a state at which no change in temperature of test heater was observed. The experiments were stopped at Critical Heat Flux (CHF). CHF is defined as the heat flux at which heater wire burnt out. The boiling behaviour was recorded on high speed camera for additional analysis. The procedure was repeated. Glass container was emptied, cleaned, and replaced with aqueous surfactant solutions of concentrations 100, 500, 1000, 1500, 2000, 2500, 3000, 3500 and 4000 ppm on weight basis. New Nichrome wire heater was used for each run.
2.4 Uncertainty Analysis Uncertainty analysis was done as per method stated by Holman [19]. The heat flux was calculated as
. A linear relationship was found between temperature of heated wire (Tw) and resistance
of heated wire (R) as Tw=
, where a and b are constants, which were determined by temperature
calibration. The average heat transfer coefficient was calculated as
where Ts = 373.15K.
The uncertainty of wall heat flux, temperature of heated wire and average heat transfer coefficient was obtained using following equations (Eqs. (2)-(4)). The uncertainties in the experimental measurements have given in Table 2.
Page 6
V I D L q q V I D L 2
Tw b
V I
2
V I V I 2
2
2
2
(2)
2
q (Tw Ts ) h h q (Tw Ts
(3)
2
(4)
Table 2 Uncertainties in experimental measurements Parameter
Uncertainty
Voltage (V)
1V
Current (I)
0.1A
Diameter of wire
0.015 mm
Length of wire
1mm
Wall heat flux
4.63%
Temperature of wire (Tw)
1.5K
Temperature of liquid pool (T s)
1K
Heat transfer coefficient (h)
5.28%
Nicotine concentration
5ppm
Surface tension
0.1mN/m
Dynamic Viscosity
0.1Ns/m2
3. Results and Discussion 3.1 Effect of surfactant concentration and temperature on surface tension The experiments of measurement of surface of aqueous Nicotine solutions at different concentrations were performed 7 times to obtain reliable estimates of average values. The average values were plotted to study surface tension. The variation with concentration and temperature of the measured Page 7
surface tension of aqueous Nicotine solutions was plotted in Figure 3. It was observed that, addition of Nicotine into pure water reduces surface tension of aqueous solution by
50% at a concentration of
2500 ppm which is critical micelle concentration of the aqueous solution. No significant reduction was observed after 2500ppm concentration. The critical micelle concentration (cmc) indicates effectiveness of a surfactant to reduce surface tension of the solution. After critical micelle concentration (cmc), the surface tension will not reduce. So, one can conclude that, addition of Nicotine into water reduces the surface tension of aqueous solution. Similar results have been obtained by Wasekar and Manglik [3] using SDS, SLES, Triton X-100, and Triton X-305, Hetsroni et al. [4] using Alkyl Poly-glycosides, and Gajghate et al. [8] using Ammonium Chloride as surfactants.
Fig. 3 Surface tension variation of aqueous Nicotine solution
3.2 Effect of surfactant concentration and temperature on dynamic viscosity Figure 4 shows measured dynamic viscosities of pure water and aqueous surfactant solution of 2500ppm concentration at different temperatures. There was no considerable difference among dynamic viscosities for the two fluids at the same temperature. This shows that surfactant solutions reveal Newtonian fluid behaviour as that of water. Similar behaviour was observed by Cheng et al. [1] with aqueous SDS solution, aqueous Triton X-100 solution and water. Page 8
Fig. 4 Variation of measured dynamic viscosity with temperature 3.3 Boiling Behaviour Figure 5 shows different photographs of boiling behaviour with increasing heat flux (q = 100 and 200 kW/m2) for aqueous solutions of surfactant at 100 ppm concentration and for pure water. Video recording was done to study boiling behaviour for each run. The boiling behaviour was observed to be different for aqueous Nicotine solution from that in pure water. The addition of surfactant into pure water decreases surface tension of aqueous solution at liquid–vapour interface. Surfactant addition makes water impure and promotes activation of nucleation sites. The boiling pool became significantly cloudier with increasing surfactant concentration. It was more vigorous, and characterised by smaller diameter bubbles. The bubbles appear in a cluster mode. There is an early evolution of bubbles with the faster covering of heating surface, and higher bubble departure frequency which is essentially the outcome of reduced surface tension at the liquid vapour interface. As concentration increases, boiling pool became considerably cloudier; bubbles tends to coalesce forming slugs and columns. So, it was very difficult to get clear photograph at higher concentrations and at higher heat fluxes. Hence photographs of higher concentration solutions and higher heat fluxes have not included.
Page 9
Fig. 5 Boiling behaviour of pure water, and aqueous Nicotine solutions of different concentration at different heat fluxes 3.4 Pool boiling curves Pool boiling data as a function of heat flux versus wall superheat was plotted for pure water, and different aqueous solutions of Nicotine in Figure 6. For each concentration and heat flux, seven trials were performed and average values obtained from these measurements were plotted. Remarkable behaviour was observed in boiling curves. The heat transfer rate was found to be continuously enhanced as boiling curve shifted leftward relative to pure water till 2500ppm concentration. After 2500 ppm no enhancement was observed. The reason for such behaviour was related to diffusion controlled mechanism proposed by Hetsroni et al. [17]. They stated that diffusion of surfactant molecules and their adsorption rates controls the number of active nucleation sites. Bubble explosion and bubble jet phenomenon were occurred in aqueous surfactant solutions, revealing enhanced heat transfer effect [12-13]. The wall superheat was observed to be decreased with increasing surfactant concentration. The last data point on pool boiling curves indicates Critical Heat Flux (CHF) condition. CHF data for pool boiling of aqueous Nicotine solution at different concentrations was given in Table 3. CHF was found to be enhanced by
at
2500 ppm Nicotine concentration. No enhancement was found after 2500 ppm Nicotine concentration.
Page 10
Fig. 6 Pool boiling curves of aqueous Nicotine solutions and pure water Table 3 CHF data pool boiling of aqueous Nicotine solution at different concentrations Nicotine concentrations (ppm)
0 (pure water)
100
500
1000
1500
2000
2500
3000
3500
4000
CHF (MW/m2)
1
1.09
1.15
1.23
1.34
1.41
1.45
1.44
1.44
1.44
3.5 h-q plot Figure 7 shows plot of heat transfer coefficient versus heat flux to clarify the effect of heat flux, and surfactant additive concentration on the boiling heat transfer coefficient of aqueous Nicotine solutions. As heat flux and concentrations increases, heat transfer coefficients increases, except the concentration are higher than 2500 ppm. The slope of the lines in h-q plot increases with the addition of surfactant. This is due to the fact that number of nucleation sites increases and bubbles were generated more easily in presence of surfactant, because of reduced surface tension. Thus, both increase in the slope of h-q plot and advancement of the onset of boiling enhances boiling heat transfer. The results obtained in
Page 11
present study are consistent with Wasekar and Manglik [3] with SDS, SLES, Triton X-100, and Triton X-305, Hetsroni et al. [4] with Alkyl Poly-glycosides, and Inoue and Monde [7] with Surflon S-451 as surfactants.
Fig. 7 Heat transfer coefficient versus heat flux for different aqueous Nicotine solution concentrations and pure water 5. Conclusion Pool boiling phenomenon was studied in saturated aqueous nicotine (novel non-ionic surfactant) solution of different concentrations, and pure water on a Nichrome wire heater experimentally. High speed video technique was used to study pool boiling phenomenon. More chaotic bubble action was observed for aqueous surfactant solution compared to water. Bubbles formed in Nicotine solution were smaller than those in water; coalesce quickly, and heater surface became covered with them faster. The surface tension of aqueous surfactant solution at 2500 ppm was almost 50% less than that in water. The reduced surface tension results in a decrease of energy required to create a bubble, and thus in more bubbles, and smaller ones. The boiling curves of surfactant were different from the boiling curve of pure water. Pool boiling heat transfer was observed to be enhanced significantly by the addition of Nicotine relative to pure water. An optimum level of enhancement was observed in solutions up to 2500 ppm, which was critical micelle concentration of the surfactant. CHF was found to be enhanced by
at 2500 ppm Nicotine Page 12
concentration. Nicotine produces from plant and it is biodegradable with negligible environmental impact. The surfactant additive Nicotine can successfully be used to enhance nucleate boiling heat transfer.
Acknowledgements This work was supported by KIT’s College of Engineering, Kolhapur, India.
References [1] L. Cheng, D. Mewes, A. Luke, Boiling Phenomenon with Surfactants and Polymeric Additives: A state
of
the
art
review,
Int.
J.
Heat
Mass
Transfer,
50(2006),
2744-2771.
DOI:10.1016/j.ijheatmasstransfer.2006.11.016 [2] Y. M. Yang, J. R. Maa, On the criteria of Nucleate Pool Boiling Enhancement by Surfactant Addition to Water”, Institution of Chemical Engineers, Trans I, ChemE- Part A, 79(2001), 409-416. [3] V. M. Wasekar, R. M. Manglik, Influence of Additive Molecular Weight and Ionic Nature on the Pool Boiling Performance of Aqueous Surfactant Solutions,
Int. J. Heat Mass Transfer, 45(2002),
483-493. [4] G. Hetsroni, M. Gurevich, A. Mosyak, R. Rozenblit, Z. Segal, Boiling Enhancement with Environmentally
Acceptable
Surfactants,
25(2004),
841-848.
DOI:10.1016/j.ijheatfluidflow.2004.05.005 [5] J. Zhang, R. Manglik, Nucleate Pool Boiling of Aqueous Polymer Solutions on a Cylindrical Heater, J. Non-Newtonian Fluid Mechanics, 125 (2005), 185-196. DOI: 10.1016/j.jnnfm.2004.12.001 [6] G. Ding, H. Peng, H. Hu, Effect of Surfactant Additives on Nucleate Pool Boiling Heat Transfer of Refrigerant
Based
Nanofluid,
Expt.
Thermal
Fluid
Science,
35(2011),
960-970.
DOI:10.1016/j.expthermflusci.2011.01.016 [7] T. Inoue, M. Monde, Enhancement of Nucleate Pool Boiling Heat Transfer in Ammonia-water mixtures with a surface active agent, Int. J. Heat Mass Transf., 55, (2012), 3395-3399. Page 13
DOI:10.1016/j.ijheatmasstransfer.2012.03.004 [8] S. S. Gajghate, A. R. Acharya, A. T. Pise, Experimental Study of Aqueous Ammonium Chloride in Pool Boiling Heat Transfer, Expt. Heat Transfer: J. Thermal Energy Generation, Transport, Storage, and Conversion, 27(2)(2013), 113-123. DOI: 10.1080/08916152.2012.757673 [9] A. Najim, A. R. Acharya, A. T. Pise, S. S. Gajghate, Experimental Study of Bubble Dynamics in Pool Boiling Heat Transfer using Saturated Water and Surfactant Solution, Proc. IEEE-ICAET, EGS Pillay College of Engg. and Tech., Nagapattinum, May 2-3, 2014, Nagapattinum, Tamilnadu. DOI: 10.1109/ICAET. 2014.7105293 [10] H. Cho, J. Mizerak, E. Wang, Turning Bubbles On and Off during boiling using charged surfaces, Nature Comms., 6:8599(2015), 01-03. DOI: 10.1038/ncomms9599 [11] A. Najim, S. Pise, Boiling Heat Transfer Enhancement with Surfactant on the Tip of a Submerged Hypodermic
Needle
as
Nucleation
Site,
App.
Thermal
Engg.,
103(2016),
989-995.
DOI: 10.1016/j.applthermaleng.2016.05.001 [12] J. Wang, F. Li, X. Li, Bubble Explosion in Pool Boiling Around A heated Wire in Surfactant Solution,
Int.
J.
Heat
Mass
Transf.,
99(2016),
569-575.
DOI: 10.1016/j.ijheatmasstransfer.2016.03.111 [13] J. Wang, F. Li, X. Li, On the Mechanism of Boiling Heat Transfer Enhancement by Surfactant Addition, Int. J. Heat Mass Transf., 101(2016), 800-806. DOI:10.1016/j.ijheatmasstransfer.2016.05.121 [14] W. Wu, Y. Yang, J. Maa, Enhancement of Nucleate Boiling Heat Transfer and Depression of Surface Tension by Surfactant Additives, Trans. ASME, 117 (1995), 526–529. [15] Y. Tzan, Y. Yang, Experimental Study of Surfactant Effects on Pool Boiling Heat Transfer, J. Heat Transf., 112(1990), 207-212. [16] T. Inoue, Y. Teruya, M. Monde, Enhancement of Pool Boiling Heat Transfer in Water and Ethanol / Water Mixture with Surface Active Agent, Int. J. Heat Mass Transfer, 47(2004), 5555-5563. DOI:10.1016/j.ijheatmasstransfer.2004.05.037 Page 14
[17] G. Hetsroni, M. Gurevich, A. Mosyak, R. Rozenblit, L. Yarin, Subcooled Boiling of Surfactant Solutions, Int. J. Multiphase Flow, 28(2002), 347-361. [18] Z. Yuan, K. E. Herold, Surface Tension of Pure Water and Aqueous Lithium Bromide with 2- EthylHexanol, App. Thermal Engg., 21(2001), 881-897. [19] J. P. Holman, Experimental Methods for Engineers, 7th edition, Tata McGraw Hill, India, 2007, p. 51. ISBN: 978-0-07-064776-3.
Page 15
Table Captions List Table No.
Caption Literature comparison of researchers [2-13] for different
1
conditions such as different surfactants and different heating surfaces
2
Uncertainties in experimental measurements CHF data pool boiling of aqueous Nicotine solution at different
3 concentrations
Page 16
Figure Captions List Figure No.
Caption
1
Schematic of Stalagmometer, and force balance for a drop [18]
2
Schematic of the pool boiling apparatus
3
Surface tension variation of aqueous Nicotine solution
4
Variation of measured dynamic viscosity with temperature
5
Boiling behaviour of pure water, and aqueous Nicotine solutions of different concentration at different heat fluxes
6
Pool boiling curves of aqueous Nicotine solutions and pure water
7
Heat transfer coefficient versus heat flux for different aqueous Nicotine solution concentrations and pure water
Page 17
Highlights 1. Effect of addition of Nicotine into pure water on boiling was studied. 2. Optimum concentration of Nicotine for maximum heat transfer coefficient was found. 3. Addition of Nicotine into pure water reduces its surface tension by almost 50%. 4. Boiling heat transfer found to be enhanced in aqueous Nicotine solution. 5. Nicotine produces from plant and it is biodegradable.
Page 18