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Water-Mono Ethylene Glycol nanofluids as a car radiator coolant
Author’s Accepted Manuscript Experimental Investigation of Heat Transfer Potential of Al 2O3/Water-Mono Ethylene Glycol Nanofluids as a Car Radiator Coolant Dattatraya G. Subhedar, Bharat M. Ramani, Akhilesh Gupta www.elsevier.com/locate/csite
PII: DOI: Reference:
S2214-157X(16)30040-5 https://doi.org/10.1016/j.csite.2017.11.009 CSITE239
To appear in: Case Studies in Thermal Engineering Received date: 21 June 2016 Revised date: 17 November 2017 Accepted date: 28 November 2017 Cite this article as: Dattatraya G. Subhedar, Bharat M. Ramani and Akhilesh Gupta, Experimental Investigation of Heat Transfer Potential of Al 2O3/WaterMono Ethylene Glycol Nanofluids as a Car Radiator Coolant, Case Studies in Thermal Engineering, https://doi.org/10.1016/j.csite.2017.11.009 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 galley proof before it is published in its final citable 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.
Experimental Investigation of Heat Transfer Potential of Al2O3/Water-Mono Ethylene Glycol Nanofluids as a Car Radiator Coolant Dattatraya G. Subhedara, Bharat M. Ramanib, Akhilesh Guptac a
Chandubhai S Patel Institute of Technology, CHARUSAT Changa,388421, India Shri Labhubhai Trivedi Institute of Engineering & Technology, Rajkot, 360005, India c Indian Institute of Technology, Roorkee, 247667,India b
Abstract In this research, the heat transfer potential of Al2O3/Water-Mono Ethylene Glycol nanofluids is investigated experimentally as a coolant for car radiators. The base fluid was the mixture of water and mono ethylene glycol with 50:50 proportions by volume. The stable nanofluids obtained by ultra-sonication are used in all experiments. In this study nanoparticle volume fraction, coolant flow rate, inlet temperature used in the ranges of 0.2-0.8%, 4-9 l per minute and 65-850C. The results show that the heat transfer performance of radiator is enhanced by using nanofluids compared to conventional coolant. Nanofluid with lowest 0.2% volume fraction 30% rise in heat transfer is observed. Also the estimation of reduction in frontal area of radiator if base fluid is replaced by Nanofluid is done which will make lighter cooling system, produce less drag and save the fuel cost.
Keywords: Nanofluids; Car radiator; Nusselt number; Frontal area 1. Introduction Day today the people’s needs own automotive vehicle to make their work faster and simpler. So by seeing the increasing demand of vehicle, automotive industries continuously doing development for making high efficient and economical engines which consumes less fuel to attract the customers. There are various ways to increase the efficiency of engine like by using optimized design of engine which reduce the weight of automotive and efficient engine cooling system which will increase the performance of vehicle. Use of optimized designed fins and micro size tube is most conventional way to increase the performance of radiator is now reached to its limit. Another way of enhance the cooling effect is use of efficient coolant in the vehicle radiator. As conventional coolant is the mixture of water and ethylene glycol as anti-freeze agent to increase the boiling point and reduce the freezing point of water. By adding the anti-freeze in water make it possible to use water for wide range of temperature but for that we have to compromise the heat transfer performance of the radiator as the heat capacity of mixture is less that of water. Solid particles having size less than 100 nm has different thermal properties than the conventional solid particles. As nanometer size particles has large surface area as compare to micro size powder which enhance heat transfer rate. Choi [1] proposed the concept of adding the nanometer sized solid particles in conventional heat transfer fluid and by preparing stable fluid can enhance the heat transfer characteristics which he named as Nanofluids at Argonne National Laboratory of USA. Enhancement in thermal properties is depends on the method of preparation, particle size, type of particle etc. Now a days researchers also starts investigating the potential in hybrid Nanofluid to get more benefit in heat transfer rate. Nor Azwadi Che Sidik [2,3] has discussed the challenges to preparation of stable hybrid Nanofluid and enhancement in the thermal properties. Dattatraya Subhedar and Bharat Ramani [4] also observed that thermal conuctivity of Nanofluid is increases linearly as the volume concentration is increases, with 0.8 % volume fraction of Al2O3 nanoparticles of size 20 nm in water/MEG base fluid 8.5 % enhancement in thermal conductivity is observed. So to overcome the difficulty of heat transfer by using water with Ethylene Glycol it is necessary to add metallic or non-metallic oxides nanoparticles to enhance the thermal properties of the mixture. Enhancement in heat transfer by using nanofluids will make possible in reduction in frontal heat transfer area of the radiator. Improved thermal properties of nanofluids also allow circulating nanofluids with lower flow rate than the base fluid for the same heat transfer which in turn reduces the pumping power required than the base fluid. To understand the potential of nanofluids for car radiator the literature survey is carried out, few critical findings of them are discussed here. S. Zenali Heris et.al.[5] have experimentally investigated the performance of CuO/EG-water as a coolant in car radiator. In their study they used nanofluids with 0.05-0.8% volume fraction of CuO. For 0.8 % nanofluids the gain in the heat transfer coefficient they found 55% compared to the EG-water
mixture performance. M.Ali et.al[6] used Al2O3 water based nanofluid used in their experimental study as a coolant for automobile radiator. They study the effect of volume fraction of Al2O3 from 0.1% to 2% on heat transfer and pumping power. They found the heat transfer by nanofluid coolant increases upto 1% and beyond that it decreases as the concentration increases. S.M.Peyghambarzadeh et.al[7] has performed parametric study to investigate the potential of Al2O3/EG-Water nanofluid as a coolant for car radiator. In their study the used water EG mixture with 95:5, 90:10 and 80:20% by volume and 0.2-0.8% concentration of Al2O3 for preparing nanofluid. In the best conditions in their experiments 40% enhancement in heat transfer was observed over the performance of the base fluid. M.Naraki et.al[8] used CuO/water nanofluid in a vehicle radiator. Under laminar flow condition they investigated the performance of nanofluid with 0.15-0.4% concentration. The overall heat transfer coefficient with nanofluid was found 6-8% more than that of water. K.Y.Leong et.al.[9] studied the performance of ethylene glycol based copper nanofluid as a coolant in car radiator. They recorded that by adding 2% copper particles in EG 3.8% enhancement in heat transfer can be obtained than ethylene glycol under turbulent flow condition of coolant. M.Ebrahimi et.al.[10] did experimental study of heat transfer in car radiator with SiO2-water Nanaofluid. They found the Nusselt number increases as coolant inlet temperature, Reynolds number and volume fraction increases. Ravikanth S. Vajjha et. al. [11] used numerical approach to study heat transfer performance of CuO and Al2O3 nanofluid in the car radiator tube. They use water-EG mixture as a base fluid. They found 94% enhancement in average heat transfer coefficient in 10% volume fraction Al 2O3 nanofluid and 89% enhancement in 6% volume fraction CuO nanofluid under laminar condition. Beriache M'hamed et al.[12] has carried out an experimental investigation to study the suitability of MWCNT in car engine with base fluid EG-Water by 50:50 volume. They found as the concentration of MWCNT increases the heat transfer coefficient is also increased. In their study for 0.5 % volume fraction of MWCNT they found approximately 196 % rise in average heat transfer coefficient. Nor Azwadi Che Sidik et al. [13,14] has also concluded from their deep review on feasibility of Nanofluid as a automotive radiator coolant that there is approximately 50 % rise in heat transfer coefficient as compare to the base fluid coolant. Optimum performance is found by using less than 1 % concentration of nanoparticles. Nomenclature K
Thermal Conductivity, W/m-K
Cp
Specific heat J/kg-K
Q
Heat transfer by coolant, Watt
Re
Reynolds number
Nu
Nusselt number
m
Mass flow rate of coolant kg/s
T
Temperature, K
Dh
Hydraulic diameter, m
H
Convective heat transfer coefficient, W/m2K
As
Surface Area of coolant tube, m2
Pr
Prandtl number
L
Tube length, m
Pe
Peclet number
EG
Ethylene Glycol
MEG
Mono-Ethylene Glycol
Greek Letter µ
Viscosity, Pa-s
ρ
Density, kg/m3
ϕ
Volume fraction of nanoparticles
Subscripts bf
Base fluid
nf
Nanofluid
P
Nanoparticle
In this research Al2O3/Water-MEG based nanofluid is used as a coolant for a car radiator. Coolant side Nusselt number enhancement for nanofluid over base fluid is studied. To predict the coolant side Nusselt number under laminar flow condition Nusselt number correlation is developed from experimental data. To overcome the issue of increase in pumping power by using Nanofluid estimation of reduction in frontal area of radiator by using nanofluid is also done. Optimized parameter required to achieve maximum heat transfer at minimum consumption of pumping power is also find out. 2. Experimental setup To investigate the heat transfer potential of Nanofluids as Car radiator coolant the test rig is developed as shown in Fig.1. This test rig contains the coolant storage tank , coolant heating element, centrifugal pump, flow measuring instrument, piping network, ball valve to bypass the flow, needle valve to provide precision to flow stability, Pressure transducer to record the inlet and outlet pressure of coolant in radiator , resistance temperature detector to record inlet and outlet temperature of coolant in radiator, anemometer to record velocity of air, J-thermocouples to note down the surface temperature of radiator tube and flow lines. The Radiator was installed inside the air flow duct. The specifications of the radiator used for the research is mentioned in Table1. Coolant passes through the 36 vertical tubes of Radiator. Table: 1 Geometrical characteristics of the radiator Description Radiator Length (RL) Radiator Width (RW) Radiator Height(RH) Tube Width (TW) Tube Height (TH) Fin Width (FW) Fin Height (FH) Fin Thickness (FT) Distance between fins Number of tubes (TN)
Specification 36.0 cm 36.5 cm 1.60 cm 1.60 cm 0.18 cm 1.60 cm 0.9 cm 0.00254 cm 0.15875 cm 36
For cooling the coolant, 24” Axial flow fan is used which has capacity to produce flow with 6500 CFM. Dimmer is used to vary the air flow. Fan is installed at the beginning of the test section duct in such a way that the air and coolant flow have indirect cross flow contact and due to that the heat exchange takes place between hot coolant flowing in the vertical tubes and air passing over the tubes. The inlet air temperature was about 340C+-0.10C in the complete research. The centrifugal thermic pump is used which gives a constant flow rate of 0.9 m3/h, to vary the flow rate globe valve is used. In the test rig the coolant is stored in the storage tank of volume 33 liters (36.83cm X 31.75cm X 28.48cm) and heated with the electric heater (two immersion rod heater of capacity 3000 W each) fixed inside the reservoir. The controller is used to maintain the temperature between 40 0C to 900C. The coolant is filled 25-30% of the tank volume so the total volume of the circulating coolant is constant in the experiment. Two RTDs (Pt-100Ω) is used to record the inlet and outlet temperature of the coolant. Table: 2 Parameter range during experiments
Parameter
Nanoparticle volume fraction (%) Coolant flow rate (l/min) Air flow velocity (m/s) Coolant Inlet temperature (0C)
Al2O3/WaterMEG nanofluids 0-0.8 4-9 1-2.5 65-85
Fig.1. Radiator performance test rig
2.1 Uncertainty Analysis: Uncertainty analysis is carried out by calculating the error of the measurements. The uncertainty of Nusselt number comes from measurement error in coolant flow rate, all the temperatures, and hydraulic diameter. According to standard uncertainty analysis the measurement uncertainty in coolant flow rate is 5.709 % and for the Nusselt number is 18.8969%. 3. Synthesis and characterization of Nanofluid In this research spherical Al2O3 nanoparticles used are of about 20 nm size. Some other characteristics are given in Table3 Water and Mono Ethylene Glycol (50:50% by volume) is used as a base fluid. To prepare the nanofluids two step method is used. In this method the dry powder form of Al2O3 nanoparticles is dispersed into the base fluid under ultrasonic agitation to breakdown the aggregates of Nano powder. The samples having pH as 5.71, 6.46, 6.29, and 6.41 with different volume fractions 0.2%, 0.4%, 0.6% and 0.8 % respectively are found stable with less sedimentation after 6-7 days. As the particles dispersed uniformly in the base fluid, the thermo physical properties like density, specific heat, thermal conductivity and dynamic viscosity can be estimated. KD2 Pro thermal properties
analyzer was used to determine the thermal conductivity of prepared sample Eqn.1 and compare with theoretical value given by Hamilton and Crasser model at room temperature fig.2. In the present research to predict the thermal conductivity of Nanofluids Hamilton and Crasser model [15] is used as given in eqn.2
Thermal Conductivity Ratio (Knf/Kbf)
1.05
Present Study Hamilton and Crasser model
1.04
1.03
1.02
1.01
1.00 0.2
0.4
0.6
0.8
1.0
Volume fraction (%)
Fig.2.Effect of volume fraction of nanoparticles on the ratio of Thermal conductivity (Knf/Kbf) at room temperature 30 0C
K nf K bf
4..175 1.0052
K nf
(1)
K p ( 1) Kbf ( 1)( Kbf K p ) K p ( 1) Kbf ( Kbf K p )
Kbf
(2)
Ψ is the shape factor of Nanoparticles for spherical particles Ψ=3. Rehometer is used to determine the viscosity of nanofluids at different volume fraction and different temperatures. The viscosity model developed from the experiment (Eqn.3) is used to predict the viscosity of nanofluids.
nf bf
0.8899e 99.699
(3)
The following correlations have been used to predict the density and specific heat of the nanofluids developed by B.C. Pak, Y.I. Cho [16]
nf p (1 ) bf
(4)
( Cp) nf ( Cp) p (1 )( Cp) bf
(5)
Table: 3 Characteristics of Al2O3 nanoparticles Physical Properties of Al2O3 nanoparticles
Shape of nanoparticle
Spherical
Average Nanoparticle Size
20 nm
Purity
> 99.8 %
Bulk Density of nanoparticles
3890 kg/ m3
X- Ray analysis
γ - Al2O3
Thermal properties of Al2O3 nanoparticles Thermal Conductivity @ 20 C
28 -35W/m-K
Thermal Expansivity 20 -1000 C
8.0 x10-6 m/m-K
4. Estimation of Nusselt Number Coolant side heat transfer rate can be estimated as follows:
Q m Cp(Tin Tout )
(6)
According to Newton’s law of cooling
Q hAs (Tb Tw )
(7)
Equating Equation 6 and 7 m Cp(T T ) D hD in out Nu (8) K As (T T ) K b w where m is nanofluids mass flow rate, Cp is specific heat of the coolant, K is thermal conductivity of nanofluids, As is a surface area of oval tubes of radiator, Tin and Tout are the inlet and outlet coolant temperatures and Tb is the bulk temperature which is average of inlet and outlet temperature of the coolant. Tw is the tube surface temperature which is the mean of the three surface temperature. Nu is the coolant side Nusselt number for the radiator. The physical properties of coolant were estimated at the bulk temperature.
5. Results and discussion Before the experimentation with the nanofluids the validation of the measurements is done by operating the test rig with distilled water as a coolant and compares the coolant side Nusselt number calculated from experimental data with prediction various correlations like: (a) Sider-Tate correlation for laminar flow [17] 1/ 3
Re Pr Nu 1.86 L / Dh
s
0.14
(b) Dehghandokht et.al correlation for compact heat exchanger[18]
(09)
Nu 0.951 Re0.173 Pr(1/ 3)
(10)
(c) Shah and London correlation[19]
Re Pr Dh Nu 4.364 0.0722 * L
7.0
(11)
Experimental Data Sider-Tate Correlation Shah & London Dehghandokht et al
6.5 6.0
Nu
5.5 5.0 4.5 4.0 3.5
Air Velocity=1.05m/s 3.0 2
3
4
5
6
7
8
9
10
Water Flow Rate (LPM) Figure 3 Comparison between predicted and measured Nusselt number for pure water (Tin=80 0C)
Fig.3. shows that present study results had good agreement with the Sider and Tate correlation and Shah & London correlation with 11.12% and 6.03% absolute average error. The correlation given by Dehghandokht et. al. is not agree with the present study results for this the absolute average is found 32.83%. 5.1 Effect of nanofluids volume fraction on the coolant side Nusselt number: Nanofluids with volume fraction 0.2%, 0.4%, 0.6% and 0.8% were synthesized by sonication and its performance in radiator is experimentally studied. To study the effect of coolant inlet temperature on the heat transfer performance the experiment is conducted for inlet temperature 65 0C, 700C, 750C, 800C, and 850C. The coolant flow rate was used from 4LPM- 9LPM. Also the air flow effect is also studied for air flow velocity 1.05m/s, 1.38m/s, 1.77m/s, 2.39m/s. As we observed that the thermal conductivity and the density of nanofluids increases, Sp. Heat decreases slightly but its viscosity enhancement as compare to base fluid is very large. Ding and Wen[20 suggested that the thermal boundary layer thickness reduces in nanofluids because of random motion of nanoparticles within the carrier fluid which create slip velocity between the solid particles and the fluid medium. They found that the concentration of nanoparticles tends to near the tube wall side, which causes the rise in the heat transfer coefficient around the wall in the thermal boundary layer. Fig.4 shows
the enhancement in Nusselt number by using nanofluids as compare to base fluid. As we increases the volume fraction the heat transfer rate is increases. It was found due to addition of Al2O3 nanoparticles only by volume fraction 0.2% in the water/MEG base fluid (50:50 by volume) the thermal conductivity enhancement was 0.63%-, Viscosity increase by 24.52% which causes heat transfer enhancement approximately 30% for 8.82LPM coolant flow rate. S.M. Peyghambarzadeh et. al [7] also found the 40% enhancement in EG based Al2O3 nanofluids with approximately 4% variation in Thermal conductivity. For less than 15% enhancement in conductivity water based Al2O3 nanofluids Heris et.al.[5] also found 40% enhancement in heat transfer.
Nusselt Number ratio (Nunf/ Nubf)
2.0
4.06 LPM 5.25 LPM 6.44 LPM 7.63 LPM 8.82 LPM
1.8
1.6
1.4
1.2 0
Tin=75 C Velocity of air = 1.05 m/s
1.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Alumina Volume Fraction (%) Figure 4 Effect of volume fraction of nanoparticles on the ratio of Nusselt Number (Nu nf/Nubf) 5.2 Effect of Nanofluids Inlet Temperature on the coolant side Nusselt number: Fig.5 shows the comparison of the results for nanofluids flow rate 4.06 LPM, air velocity 1.05 m/s and at different inlet temperatures to study effect on coolant side Nusselt. It is clearly seen from Fig.6 that under all experiment condition as the inlet coolant temperature is increased, the heat transfer enhancement is very less. The results show that maximum variation in Nusselt number of 26% for the change in inlet temperature from 700C to 850C due to variation in the physical properties with respect to temperature of the coolant.
20
0.2% 0.4% 0.6% 0.8%
Nusselt Number (Nunf)
18
16
14
Coolant flow rate= 4.06LPM Air velocity =1.05 m/s 12 65
70
75
80
85
90
0
Coolant Inlet Temperature ( C) Figure 5 Effect of coolant inlet temperature on the coolant side Nusselt number (Nu n) 5.3 Effect of Nanofluids flow rate on the coolant side Nusselt number: Fig.6 shows the enhancement in Nusselt number with nanofluids as a function of the coolant flow rate. It is seen that Nusselt number significantly increases with increasing coolant flow rate. It is seen that for nanofluids coolant with 0.2% volume fraction at 800C inlet temperature the Nusselt number with nanofluids are 24.39 and 27.34 at coolant flow rate 7.63 and 8.82 LPM respectively. From the experimental data of the present study, the correlation is developed for the prediction of Nusselt number in forced convection heat transfer of nanofluids under laminar flow condition. For that regression analysis was carried out in Minitab. The correlation developed is given in Eqn.12.
Nu 0.70091(110.4576 0.9 Pe 0.353548 ) Re 0.495596 Pr 0.061752
(12)
The Nusselt number of Al2O3/Water-MEG nanofluid obtained from Experimental observations at Laminar flow condition is compared with the predicted Nusselt number value from above correlation is shown in fig. This shows very good agreement. The absolute average error in prediction of Nusselt number is found 25% as shown in Fig.7. From the experiment with water/MEG as coolant at inlet coolant temperature 80 0C, Air flow velocity 1.05 m/s and coolant flow rate as 8.818 LPM we found the heat transfer coefficient found as 49.078 W/m2K.. Fig.8 shows that at the same inlet condition with same overall heat transfer coefficient as base fluid it is found that only 0.2% volume fraction Nano fluid can gives 41.157 % reduction in surface area of radiator. Also it is observed in this research work that to maintain the same pumping power observed in water/MEG coolant at inlet coolant temperature 80 0C with 8.818 LPM the reduction in frontal area observed with respect to the volume fraction of Al 2O3. By using 0,2 % concentration Nanofluid approximately 21% reduction is possible. Minitab software is used to optimize the operating parameter to attain maximum heat transfer and minimum pumping power. The Prediction and Optimization Report shows for obtaining maximum overall heat transfer coefficient and minimizing pumping power. The optimal setting for the Nanofluid is volume fraction 0.7030 %, Coolant inlet temperature 65 0C and Coolant flow rate 8.820 LPM. For these
sets, the models predict overall heat transfer coefficient as 199.7068 W/m2-K Watt and pumping power as 0.4245 watts. So the Nanofluid coolant not only improves the heat transfer performance of heavy-duty automobile but also it can be helpful in reducing the size of the cooling system which makes system lighter with less drag so it will also save the fuel. Table 4. Effect of volume fraction of nanoparticles on overall heat transfer coefficient for same Pumping power as base fluid Volume fraction in %
45
Total Surface Area (A) in m2 3.118
0.2
0.285
2.468
0.4
0.230
1.992
0.6
0.185
1.602
0.8
0.150
1.299
0.2% 0.4% 0.6% 0.8%
40
Nusselt Number (Nunf)
0.0
Length of Radiator tube in m 0.360
35
30
25
20
0
Tin=80 C Velocity of air =1.05 m/s
15 3
4
5
6
7
8
9
Coolant Flow Rate (LPM) Figure 6 Effect of coolant inlet temperature on the coolant side Nusselt number (Nun)
10
50
Nusselt Number Predicted 45
Nusselt Number Predicted
40 35
+25%
30 25
-25%
20 15 10 5 0 0
5
10
15
20
25
30
35
40
45
Nusselt Number Measured Figure7 Comparison of Experimental Nusselt number with predicted from correlation
80
Frontal Area Reduction
Frontal Area Reduction (%)
70
60
50
40
30 0.0
0.2
0.4
0.6
0.8
1.0
Volume Fraction (%)
Figure 8 Effect of volume fraction of the reduction in radiator frontal area
50
6. Conclusion: In this research paper, performance of Al2O3/water-MEG based nanofluids as a car radiator coolant has been experimentally investigated at different coolant inlet temperatures, nanofluids flow rates, air flow rates and various volume fractions of nanoparticles. From this study following outcome can be drawn: Heat transfer rate by nanofluid coolant is significantly increases with the increase in concentration of nanoparticles. For lowest coolant flow rate 4.06LPM as the volume fraction increases form 0.2-0.8% the enhancement in Nusselt number changes from 3.89% to 28.47%. Major contribution in heat transfer enhancement is flow rate for nanofluid and volume fraction of nanoparticles. The enhancement in heat transfer due to inlet temperature of coolant is very less. This experimental investigation proves that Nanofluid has great potential as heat transfer fluid. Also use of nanofluid make possible to design compact size radiator which also reduces weight of the system, reduction in drag and so saving in fuel cost.
Acknowledgements This work has been supported by GUJCOST grant number GUJCOST/MRP/2015-16/2630 sanctioned under Minor Research Scheme (MRP). We are thankful to President and Provost of CHARUSAT for supporting this research work. We are thankful to Dr. R.V. Upadhyay, Head, Dr. K. C. Patel Research and Development Centre (KRADLE) affiliated to Charotar University of Science and Technology (CHARUSAT), India, for granting permission to use various equipment available in their characterization laboratory.
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PII: DOI: Reference:
S2214-157X(16)30040-5 https://doi.org/10.1016/j.csite.2017.11.009 CSITE239
To appear in: Case Studies in Thermal Engineering Received date: 21 June 2016 Revised date: 17 November 2017 Accepted date: 28 November 2017 Cite this article as: Dattatraya G. Subhedar, Bharat M. Ramani and Akhilesh Gupta, Experimental Investigation of Heat Transfer Potential of Al 2O3/WaterMono Ethylene Glycol Nanofluids as a Car Radiator Coolant, Case Studies in Thermal Engineering, https://doi.org/10.1016/j.csite.2017.11.009 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 galley proof before it is published in its final citable 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.
Experimental Investigation of Heat Transfer Potential of Al2O3/Water-Mono Ethylene Glycol Nanofluids as a Car Radiator Coolant Dattatraya G. Subhedara, Bharat M. Ramanib, Akhilesh Guptac a
Chandubhai S Patel Institute of Technology, CHARUSAT Changa,388421, India Shri Labhubhai Trivedi Institute of Engineering & Technology, Rajkot, 360005, India c Indian Institute of Technology, Roorkee, 247667,India b
Abstract In this research, the heat transfer potential of Al2O3/Water-Mono Ethylene Glycol nanofluids is investigated experimentally as a coolant for car radiators. The base fluid was the mixture of water and mono ethylene glycol with 50:50 proportions by volume. The stable nanofluids obtained by ultra-sonication are used in all experiments. In this study nanoparticle volume fraction, coolant flow rate, inlet temperature used in the ranges of 0.2-0.8%, 4-9 l per minute and 65-850C. The results show that the heat transfer performance of radiator is enhanced by using nanofluids compared to conventional coolant. Nanofluid with lowest 0.2% volume fraction 30% rise in heat transfer is observed. Also the estimation of reduction in frontal area of radiator if base fluid is replaced by Nanofluid is done which will make lighter cooling system, produce less drag and save the fuel cost.
Keywords: Nanofluids; Car radiator; Nusselt number; Frontal area 1. Introduction Day today the people’s needs own automotive vehicle to make their work faster and simpler. So by seeing the increasing demand of vehicle, automotive industries continuously doing development for making high efficient and economical engines which consumes less fuel to attract the customers. There are various ways to increase the efficiency of engine like by using optimized design of engine which reduce the weight of automotive and efficient engine cooling system which will increase the performance of vehicle. Use of optimized designed fins and micro size tube is most conventional way to increase the performance of radiator is now reached to its limit. Another way of enhance the cooling effect is use of efficient coolant in the vehicle radiator. As conventional coolant is the mixture of water and ethylene glycol as anti-freeze agent to increase the boiling point and reduce the freezing point of water. By adding the anti-freeze in water make it possible to use water for wide range of temperature but for that we have to compromise the heat transfer performance of the radiator as the heat capacity of mixture is less that of water. Solid particles having size less than 100 nm has different thermal properties than the conventional solid particles. As nanometer size particles has large surface area as compare to micro size powder which enhance heat transfer rate. Choi [1] proposed the concept of adding the nanometer sized solid particles in conventional heat transfer fluid and by preparing stable fluid can enhance the heat transfer characteristics which he named as Nanofluids at Argonne National Laboratory of USA. Enhancement in thermal properties is depends on the method of preparation, particle size, type of particle etc. Now a days researchers also starts investigating the potential in hybrid Nanofluid to get more benefit in heat transfer rate. Nor Azwadi Che Sidik [2,3] has discussed the challenges to preparation of stable hybrid Nanofluid and enhancement in the thermal properties. Dattatraya Subhedar and Bharat Ramani [4] also observed that thermal conuctivity of Nanofluid is increases linearly as the volume concentration is increases, with 0.8 % volume fraction of Al2O3 nanoparticles of size 20 nm in water/MEG base fluid 8.5 % enhancement in thermal conductivity is observed. So to overcome the difficulty of heat transfer by using water with Ethylene Glycol it is necessary to add metallic or non-metallic oxides nanoparticles to enhance the thermal properties of the mixture. Enhancement in heat transfer by using nanofluids will make possible in reduction in frontal heat transfer area of the radiator. Improved thermal properties of nanofluids also allow circulating nanofluids with lower flow rate than the base fluid for the same heat transfer which in turn reduces the pumping power required than the base fluid. To understand the potential of nanofluids for car radiator the literature survey is carried out, few critical findings of them are discussed here. S. Zenali Heris et.al.[5] have experimentally investigated the performance of CuO/EG-water as a coolant in car radiator. In their study they used nanofluids with 0.05-0.8% volume fraction of CuO. For 0.8 % nanofluids the gain in the heat transfer coefficient they found 55% compared to the EG-water
mixture performance. M.Ali et.al[6] used Al2O3 water based nanofluid used in their experimental study as a coolant for automobile radiator. They study the effect of volume fraction of Al2O3 from 0.1% to 2% on heat transfer and pumping power. They found the heat transfer by nanofluid coolant increases upto 1% and beyond that it decreases as the concentration increases. S.M.Peyghambarzadeh et.al[7] has performed parametric study to investigate the potential of Al2O3/EG-Water nanofluid as a coolant for car radiator. In their study the used water EG mixture with 95:5, 90:10 and 80:20% by volume and 0.2-0.8% concentration of Al2O3 for preparing nanofluid. In the best conditions in their experiments 40% enhancement in heat transfer was observed over the performance of the base fluid. M.Naraki et.al[8] used CuO/water nanofluid in a vehicle radiator. Under laminar flow condition they investigated the performance of nanofluid with 0.15-0.4% concentration. The overall heat transfer coefficient with nanofluid was found 6-8% more than that of water. K.Y.Leong et.al.[9] studied the performance of ethylene glycol based copper nanofluid as a coolant in car radiator. They recorded that by adding 2% copper particles in EG 3.8% enhancement in heat transfer can be obtained than ethylene glycol under turbulent flow condition of coolant. M.Ebrahimi et.al.[10] did experimental study of heat transfer in car radiator with SiO2-water Nanaofluid. They found the Nusselt number increases as coolant inlet temperature, Reynolds number and volume fraction increases. Ravikanth S. Vajjha et. al. [11] used numerical approach to study heat transfer performance of CuO and Al2O3 nanofluid in the car radiator tube. They use water-EG mixture as a base fluid. They found 94% enhancement in average heat transfer coefficient in 10% volume fraction Al 2O3 nanofluid and 89% enhancement in 6% volume fraction CuO nanofluid under laminar condition. Beriache M'hamed et al.[12] has carried out an experimental investigation to study the suitability of MWCNT in car engine with base fluid EG-Water by 50:50 volume. They found as the concentration of MWCNT increases the heat transfer coefficient is also increased. In their study for 0.5 % volume fraction of MWCNT they found approximately 196 % rise in average heat transfer coefficient. Nor Azwadi Che Sidik et al. [13,14] has also concluded from their deep review on feasibility of Nanofluid as a automotive radiator coolant that there is approximately 50 % rise in heat transfer coefficient as compare to the base fluid coolant. Optimum performance is found by using less than 1 % concentration of nanoparticles. Nomenclature K
Thermal Conductivity, W/m-K
Cp
Specific heat J/kg-K
Q
Heat transfer by coolant, Watt
Re
Reynolds number
Nu
Nusselt number
m
Mass flow rate of coolant kg/s
T
Temperature, K
Dh
Hydraulic diameter, m
H
Convective heat transfer coefficient, W/m2K
As
Surface Area of coolant tube, m2
Pr
Prandtl number
L
Tube length, m
Pe
Peclet number
EG
Ethylene Glycol
MEG
Mono-Ethylene Glycol
Greek Letter µ
Viscosity, Pa-s
ρ
Density, kg/m3
ϕ
Volume fraction of nanoparticles
Subscripts bf
Base fluid
nf
Nanofluid
P
Nanoparticle
In this research Al2O3/Water-MEG based nanofluid is used as a coolant for a car radiator. Coolant side Nusselt number enhancement for nanofluid over base fluid is studied. To predict the coolant side Nusselt number under laminar flow condition Nusselt number correlation is developed from experimental data. To overcome the issue of increase in pumping power by using Nanofluid estimation of reduction in frontal area of radiator by using nanofluid is also done. Optimized parameter required to achieve maximum heat transfer at minimum consumption of pumping power is also find out. 2. Experimental setup To investigate the heat transfer potential of Nanofluids as Car radiator coolant the test rig is developed as shown in Fig.1. This test rig contains the coolant storage tank , coolant heating element, centrifugal pump, flow measuring instrument, piping network, ball valve to bypass the flow, needle valve to provide precision to flow stability, Pressure transducer to record the inlet and outlet pressure of coolant in radiator , resistance temperature detector to record inlet and outlet temperature of coolant in radiator, anemometer to record velocity of air, J-thermocouples to note down the surface temperature of radiator tube and flow lines. The Radiator was installed inside the air flow duct. The specifications of the radiator used for the research is mentioned in Table1. Coolant passes through the 36 vertical tubes of Radiator. Table: 1 Geometrical characteristics of the radiator Description Radiator Length (RL) Radiator Width (RW) Radiator Height(RH) Tube Width (TW) Tube Height (TH) Fin Width (FW) Fin Height (FH) Fin Thickness (FT) Distance between fins Number of tubes (TN)
Specification 36.0 cm 36.5 cm 1.60 cm 1.60 cm 0.18 cm 1.60 cm 0.9 cm 0.00254 cm 0.15875 cm 36
For cooling the coolant, 24” Axial flow fan is used which has capacity to produce flow with 6500 CFM. Dimmer is used to vary the air flow. Fan is installed at the beginning of the test section duct in such a way that the air and coolant flow have indirect cross flow contact and due to that the heat exchange takes place between hot coolant flowing in the vertical tubes and air passing over the tubes. The inlet air temperature was about 340C+-0.10C in the complete research. The centrifugal thermic pump is used which gives a constant flow rate of 0.9 m3/h, to vary the flow rate globe valve is used. In the test rig the coolant is stored in the storage tank of volume 33 liters (36.83cm X 31.75cm X 28.48cm) and heated with the electric heater (two immersion rod heater of capacity 3000 W each) fixed inside the reservoir. The controller is used to maintain the temperature between 40 0C to 900C. The coolant is filled 25-30% of the tank volume so the total volume of the circulating coolant is constant in the experiment. Two RTDs (Pt-100Ω) is used to record the inlet and outlet temperature of the coolant. Table: 2 Parameter range during experiments
Parameter
Nanoparticle volume fraction (%) Coolant flow rate (l/min) Air flow velocity (m/s) Coolant Inlet temperature (0C)
Al2O3/WaterMEG nanofluids 0-0.8 4-9 1-2.5 65-85
Fig.1. Radiator performance test rig
2.1 Uncertainty Analysis: Uncertainty analysis is carried out by calculating the error of the measurements. The uncertainty of Nusselt number comes from measurement error in coolant flow rate, all the temperatures, and hydraulic diameter. According to standard uncertainty analysis the measurement uncertainty in coolant flow rate is 5.709 % and for the Nusselt number is 18.8969%. 3. Synthesis and characterization of Nanofluid In this research spherical Al2O3 nanoparticles used are of about 20 nm size. Some other characteristics are given in Table3 Water and Mono Ethylene Glycol (50:50% by volume) is used as a base fluid. To prepare the nanofluids two step method is used. In this method the dry powder form of Al2O3 nanoparticles is dispersed into the base fluid under ultrasonic agitation to breakdown the aggregates of Nano powder. The samples having pH as 5.71, 6.46, 6.29, and 6.41 with different volume fractions 0.2%, 0.4%, 0.6% and 0.8 % respectively are found stable with less sedimentation after 6-7 days. As the particles dispersed uniformly in the base fluid, the thermo physical properties like density, specific heat, thermal conductivity and dynamic viscosity can be estimated. KD2 Pro thermal properties
analyzer was used to determine the thermal conductivity of prepared sample Eqn.1 and compare with theoretical value given by Hamilton and Crasser model at room temperature fig.2. In the present research to predict the thermal conductivity of Nanofluids Hamilton and Crasser model [15] is used as given in eqn.2
Thermal Conductivity Ratio (Knf/Kbf)
1.05
Present Study Hamilton and Crasser model
1.04
1.03
1.02
1.01
1.00 0.2
0.4
0.6
0.8
1.0
Volume fraction (%)
Fig.2.Effect of volume fraction of nanoparticles on the ratio of Thermal conductivity (Knf/Kbf) at room temperature 30 0C
K nf K bf
4..175 1.0052
K nf
(1)
K p ( 1) Kbf ( 1)( Kbf K p ) K p ( 1) Kbf ( Kbf K p )
Kbf
(2)
Ψ is the shape factor of Nanoparticles for spherical particles Ψ=3. Rehometer is used to determine the viscosity of nanofluids at different volume fraction and different temperatures. The viscosity model developed from the experiment (Eqn.3) is used to predict the viscosity of nanofluids.
nf bf
0.8899e 99.699
(3)
The following correlations have been used to predict the density and specific heat of the nanofluids developed by B.C. Pak, Y.I. Cho [16]
nf p (1 ) bf
(4)
( Cp) nf ( Cp) p (1 )( Cp) bf
(5)
Table: 3 Characteristics of Al2O3 nanoparticles Physical Properties of Al2O3 nanoparticles
Shape of nanoparticle
Spherical
Average Nanoparticle Size
20 nm
Purity
> 99.8 %
Bulk Density of nanoparticles
3890 kg/ m3
X- Ray analysis
γ - Al2O3
Thermal properties of Al2O3 nanoparticles Thermal Conductivity @ 20 C
28 -35W/m-K
Thermal Expansivity 20 -1000 C
8.0 x10-6 m/m-K
4. Estimation of Nusselt Number Coolant side heat transfer rate can be estimated as follows:
Q m Cp(Tin Tout )
(6)
According to Newton’s law of cooling
Q hAs (Tb Tw )
(7)
Equating Equation 6 and 7 m Cp(T T ) D hD in out Nu (8) K As (T T ) K b w where m is nanofluids mass flow rate, Cp is specific heat of the coolant, K is thermal conductivity of nanofluids, As is a surface area of oval tubes of radiator, Tin and Tout are the inlet and outlet coolant temperatures and Tb is the bulk temperature which is average of inlet and outlet temperature of the coolant. Tw is the tube surface temperature which is the mean of the three surface temperature. Nu is the coolant side Nusselt number for the radiator. The physical properties of coolant were estimated at the bulk temperature.
5. Results and discussion Before the experimentation with the nanofluids the validation of the measurements is done by operating the test rig with distilled water as a coolant and compares the coolant side Nusselt number calculated from experimental data with prediction various correlations like: (a) Sider-Tate correlation for laminar flow [17] 1/ 3
Re Pr Nu 1.86 L / Dh
s
0.14
(b) Dehghandokht et.al correlation for compact heat exchanger[18]
(09)
Nu 0.951 Re0.173 Pr(1/ 3)
(10)
(c) Shah and London correlation[19]
Re Pr Dh Nu 4.364 0.0722 * L
7.0
(11)
Experimental Data Sider-Tate Correlation Shah & London Dehghandokht et al
6.5 6.0
Nu
5.5 5.0 4.5 4.0 3.5
Air Velocity=1.05m/s 3.0 2
3
4
5
6
7
8
9
10
Water Flow Rate (LPM) Figure 3 Comparison between predicted and measured Nusselt number for pure water (Tin=80 0C)
Fig.3. shows that present study results had good agreement with the Sider and Tate correlation and Shah & London correlation with 11.12% and 6.03% absolute average error. The correlation given by Dehghandokht et. al. is not agree with the present study results for this the absolute average is found 32.83%. 5.1 Effect of nanofluids volume fraction on the coolant side Nusselt number: Nanofluids with volume fraction 0.2%, 0.4%, 0.6% and 0.8% were synthesized by sonication and its performance in radiator is experimentally studied. To study the effect of coolant inlet temperature on the heat transfer performance the experiment is conducted for inlet temperature 65 0C, 700C, 750C, 800C, and 850C. The coolant flow rate was used from 4LPM- 9LPM. Also the air flow effect is also studied for air flow velocity 1.05m/s, 1.38m/s, 1.77m/s, 2.39m/s. As we observed that the thermal conductivity and the density of nanofluids increases, Sp. Heat decreases slightly but its viscosity enhancement as compare to base fluid is very large. Ding and Wen[20 suggested that the thermal boundary layer thickness reduces in nanofluids because of random motion of nanoparticles within the carrier fluid which create slip velocity between the solid particles and the fluid medium. They found that the concentration of nanoparticles tends to near the tube wall side, which causes the rise in the heat transfer coefficient around the wall in the thermal boundary layer. Fig.4 shows
the enhancement in Nusselt number by using nanofluids as compare to base fluid. As we increases the volume fraction the heat transfer rate is increases. It was found due to addition of Al2O3 nanoparticles only by volume fraction 0.2% in the water/MEG base fluid (50:50 by volume) the thermal conductivity enhancement was 0.63%-, Viscosity increase by 24.52% which causes heat transfer enhancement approximately 30% for 8.82LPM coolant flow rate. S.M. Peyghambarzadeh et. al [7] also found the 40% enhancement in EG based Al2O3 nanofluids with approximately 4% variation in Thermal conductivity. For less than 15% enhancement in conductivity water based Al2O3 nanofluids Heris et.al.[5] also found 40% enhancement in heat transfer.
Nusselt Number ratio (Nunf/ Nubf)
2.0
4.06 LPM 5.25 LPM 6.44 LPM 7.63 LPM 8.82 LPM
1.8
1.6
1.4
1.2 0
Tin=75 C Velocity of air = 1.05 m/s
1.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Alumina Volume Fraction (%) Figure 4 Effect of volume fraction of nanoparticles on the ratio of Nusselt Number (Nu nf/Nubf) 5.2 Effect of Nanofluids Inlet Temperature on the coolant side Nusselt number: Fig.5 shows the comparison of the results for nanofluids flow rate 4.06 LPM, air velocity 1.05 m/s and at different inlet temperatures to study effect on coolant side Nusselt. It is clearly seen from Fig.6 that under all experiment condition as the inlet coolant temperature is increased, the heat transfer enhancement is very less. The results show that maximum variation in Nusselt number of 26% for the change in inlet temperature from 700C to 850C due to variation in the physical properties with respect to temperature of the coolant.
20
0.2% 0.4% 0.6% 0.8%
Nusselt Number (Nunf)
18
16
14
Coolant flow rate= 4.06LPM Air velocity =1.05 m/s 12 65
70
75
80
85
90
0
Coolant Inlet Temperature ( C) Figure 5 Effect of coolant inlet temperature on the coolant side Nusselt number (Nu n) 5.3 Effect of Nanofluids flow rate on the coolant side Nusselt number: Fig.6 shows the enhancement in Nusselt number with nanofluids as a function of the coolant flow rate. It is seen that Nusselt number significantly increases with increasing coolant flow rate. It is seen that for nanofluids coolant with 0.2% volume fraction at 800C inlet temperature the Nusselt number with nanofluids are 24.39 and 27.34 at coolant flow rate 7.63 and 8.82 LPM respectively. From the experimental data of the present study, the correlation is developed for the prediction of Nusselt number in forced convection heat transfer of nanofluids under laminar flow condition. For that regression analysis was carried out in Minitab. The correlation developed is given in Eqn.12.
Nu 0.70091(110.4576 0.9 Pe 0.353548 ) Re 0.495596 Pr 0.061752
(12)
The Nusselt number of Al2O3/Water-MEG nanofluid obtained from Experimental observations at Laminar flow condition is compared with the predicted Nusselt number value from above correlation is shown in fig. This shows very good agreement. The absolute average error in prediction of Nusselt number is found 25% as shown in Fig.7. From the experiment with water/MEG as coolant at inlet coolant temperature 80 0C, Air flow velocity 1.05 m/s and coolant flow rate as 8.818 LPM we found the heat transfer coefficient found as 49.078 W/m2K.. Fig.8 shows that at the same inlet condition with same overall heat transfer coefficient as base fluid it is found that only 0.2% volume fraction Nano fluid can gives 41.157 % reduction in surface area of radiator. Also it is observed in this research work that to maintain the same pumping power observed in water/MEG coolant at inlet coolant temperature 80 0C with 8.818 LPM the reduction in frontal area observed with respect to the volume fraction of Al 2O3. By using 0,2 % concentration Nanofluid approximately 21% reduction is possible. Minitab software is used to optimize the operating parameter to attain maximum heat transfer and minimum pumping power. The Prediction and Optimization Report shows for obtaining maximum overall heat transfer coefficient and minimizing pumping power. The optimal setting for the Nanofluid is volume fraction 0.7030 %, Coolant inlet temperature 65 0C and Coolant flow rate 8.820 LPM. For these
sets, the models predict overall heat transfer coefficient as 199.7068 W/m2-K Watt and pumping power as 0.4245 watts. So the Nanofluid coolant not only improves the heat transfer performance of heavy-duty automobile but also it can be helpful in reducing the size of the cooling system which makes system lighter with less drag so it will also save the fuel. Table 4. Effect of volume fraction of nanoparticles on overall heat transfer coefficient for same Pumping power as base fluid Volume fraction in %
45
Total Surface Area (A) in m2 3.118
0.2
0.285
2.468
0.4
0.230
1.992
0.6
0.185
1.602
0.8
0.150
1.299
0.2% 0.4% 0.6% 0.8%
40
Nusselt Number (Nunf)
0.0
Length of Radiator tube in m 0.360
35
30
25
20
0
Tin=80 C Velocity of air =1.05 m/s
15 3
4
5
6
7
8
9
Coolant Flow Rate (LPM) Figure 6 Effect of coolant inlet temperature on the coolant side Nusselt number (Nun)
10
50
Nusselt Number Predicted 45
Nusselt Number Predicted
40 35
+25%
30 25
-25%
20 15 10 5 0 0
5
10
15
20
25
30
35
40
45
Nusselt Number Measured Figure7 Comparison of Experimental Nusselt number with predicted from correlation
80
Frontal Area Reduction
Frontal Area Reduction (%)
70
60
50
40
30 0.0
0.2
0.4
0.6
0.8
1.0
Volume Fraction (%)
Figure 8 Effect of volume fraction of the reduction in radiator frontal area
50
6. Conclusion: In this research paper, performance of Al2O3/water-MEG based nanofluids as a car radiator coolant has been experimentally investigated at different coolant inlet temperatures, nanofluids flow rates, air flow rates and various volume fractions of nanoparticles. From this study following outcome can be drawn: Heat transfer rate by nanofluid coolant is significantly increases with the increase in concentration of nanoparticles. For lowest coolant flow rate 4.06LPM as the volume fraction increases form 0.2-0.8% the enhancement in Nusselt number changes from 3.89% to 28.47%. Major contribution in heat transfer enhancement is flow rate for nanofluid and volume fraction of nanoparticles. The enhancement in heat transfer due to inlet temperature of coolant is very less. This experimental investigation proves that Nanofluid has great potential as heat transfer fluid. Also use of nanofluid make possible to design compact size radiator which also reduces weight of the system, reduction in drag and so saving in fuel cost.
Acknowledgements This work has been supported by GUJCOST grant number GUJCOST/MRP/2015-16/2630 sanctioned under Minor Research Scheme (MRP). We are thankful to President and Provost of CHARUSAT for supporting this research work. We are thankful to Dr. R.V. Upadhyay, Head, Dr. K. C. Patel Research and Development Centre (KRADLE) affiliated to Charotar University of Science and Technology (CHARUSAT), India, for granting permission to use various equipment available in their characterization laboratory.
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