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Experimental investigation on performance of lithium-ion battery thermal management system using flat plate loop heat pipe for electric vehicle application
Accepted Manuscript Title: Experimental investigation on performance of lithium-ion battery thermal management system using flat plate loop heat pipe for electric vehicle application Author: Putra Nandy, Bambang Ariantara, Rangga Aji Pamungkas PII: DOI: Reference:
S1359-4311(16)30073-4 http://dx.doi.org/doi: 10.1016/j.applthermaleng.2016.01.123 ATE 7683
To appear in:
Applied Thermal Engineering
Received date: Accepted date:
14-10-2015 29-1-2016
Please cite this article as: Putra Nandy, Bambang Ariantara, Rangga Aji Pamungkas, Experimental investigation on performance of lithium-ion battery thermal management system using flat plate loop heat pipe for electric vehicle application, Applied Thermal Engineering (2016), http://dx.doi.org/doi: 10.1016/j.applthermaleng.2016.01.123. 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.
Experimental Investigation on Performance of Lithium-Ion Battery Thermal Management System using Flat Plate Loop Heat Pipe for Electric Vehicle Application
Nandy Putra, Bambang Ariantara, Rangga Aji Pamungkas
Applied Heat Transfer Laboratory, Department of Mechanical Engineering Universitas Indonesia, 16424 Depok, Jawa Barat, Indonesia
This paper is an extended and revised article presented at the Asia-Pacific Conference on Engineering and Applied Science (APCEAS 2015), August 25-27, 2015, Osaka, Japan. Corresponding authors at: [email protected] .
Page 1 of 22
Highlights
Flat plate loop heat pipe (FPLHP) is studied in the thermal management system for electric vehicle.
Distilled water, alcohol, and acetone on thermal performances of FPLHP were tested
The FPLHP can start up at fairly low heat load
Temperature overshoot phenomena were observed during the start-up period.
Abstract The development of electric vehicle batteries has resulted in a very high energy density lithium-ion batteries. However, this growth is accompanied by the risk of thermal runaway, which can cause serious accidents. Heat pipes are heat exchangers that are suitable to be applied in electric vehicle battery thermal management for their lightweight, compact size and do not require external power supply. This study examined experimentally a flat plate loop heat pipe (FPLHP) performance as a heat exchanger in the thermal management system of the lithium-ion battery for electric vehicle application. The heat generation of the battery was simulated using a cartridge heater. Stainless steel screen mesh was used as the capillary wick. Distilled water, alcohol, and acetone were used as working fluids with a filling ratio of 60%. It was found that acetone gave the best performance that produces a thermal resistance of 0.22 W/°C with 50°C evaporator temperature at heat flux load of 1.61 W/cm2.
Page 2 of 22
Keywords: Electric vehicle; flat plate loop heat pipe; lithium-ion battery; thermal management system
Page 3 of 22
Nomenclatures A: Area, m2 k: Thermal conductivity, W/m. K q: Heat transfer rate, W R: Thermal resistance, °C/W Tb: Bottom surface temperature, °C Tt: Top surface temperature, °C Tc: Condenser temperature, °C Te: Evaporator temperature °C.
Page 4 of 22
1. Introduction The shares of electric vehicles in some European countries are assumed comprising 53% of the private passenger vehicle fleet in 2030 [1]. One of the important performance parameters of an electric vehicle is the range or cruising capability, which is mainly determined by the performance of the batteries. Batteries with high energy density are needed to deliver high cruising capabilities. Electric vehicles will rely on lithium-ion batteries according to their high energy density, high power density, long service life and environmental friendliness [2]. Advances in battery technology have resulted in very high energy density lithium-ion batteries. However, this progress is also accompanied by the risk of thermal runaway, which can lead to serious accidents such as experienced by the Boeing 787 Dreamliner of All Nippon Airways on January 16, 2013, in Japan [3].
Heat generated by a battery, either at the time of charging or discharging will increase its temperature. The battery performance and lifetime are strongly influenced by their working temperature. In general, the performance of electric vehicles is directly affected by the performance of their batteries [4]. At quite low or high temperatures, the battery performance can be destitute. At very high temperature, lithium-ion batteries can even explode [5]. The desired working temperature range for ordinary lithium-ion batteries in the range of 25°C to 50°C [6]. For the purpose of energy saving and reduction in the cost of electric vehicles, the batteries should be operated in a proper
Page 5 of 22
temperature range [7]. Therefore, an efficient thermal management system for the battery packs is essential. Heat pipes are heat exchangers that are suitable to be applied in thermal management of central processing unit (CPUs) and electric vehicle batteries for their lightweight, compact size and do not require external power supply. Studies on heat pipes for electronic cooling have been done by authors that can be found in many references [8, 9] and other researchers such as Wang [10], and Weng et al. [11]. Investigations on flat plate heat pipes in electronic cooling have been conducted by Chen et al. [12, 13] and Lu and Wei [14]. Rao et al. [7] have examined the use of straight heat pipes on thermal management system of a LiFePo4 battery. Their experimental results showed that the maximum temperature can be kept below 50°C if the rate of heat generation is below 50 W/cm2. Wang et al. [15] investigated the application of heat pipe for thermal management system of the electric vehicle battery. In their work, some Lshaped flattened heat pipes were used to transfer heat from the battery to the cooling water as shown in Fig. 1.
Flat plate loop heat pipes have the potential to be applied to the thermal management system of electric vehicle lithium-ion batteries since most of the electric vehicle lithium-ion battery pack has flat surfaces [16]. This paper aims to examine the performance of a flat plate loop heat pipe as a heat exchanger in the thermal management system of lithium-ion batteries for electric vehicle application experimentally.
Page 6 of 22
2. Methodology Battery simulator was made from aluminum alloy. As a heat source, a cylindrical cartridge heater with a power of 400 W was placed in the battery simulator. A conduction plate made of stainless steel with a size of 105 mm x 40 mm x 15 mm was placed above the battery simulator. Fig. 2 shows the arrangement of the flat loop heat pipe, conduction plate, battery simulator and insulating box used in the experiment in order to minimize heat lost.
The conduction plate was used to determine the conduction heat transfer from the heater to the evaporator by measuring the temperature difference across the plate. Instead of using electric power input, the conduction heat transfer through the conduction plate was used to determine the heat input to the evaporator. The heat input could be determined by the following equation: .
(1)
The thermal conductivity of the conduction plate which made of stainless steel was assumed to be 16 W/m K. The battery simulator and the conduction plate were placed inside an insulating box made of polyurethane. On top surfaces of the conduction plate and the battery simulator, grooves were made for the installation of thermocouples. At the condenser section, an annular heat exchanger was used for heat release to the cooling water. The thermal resistance of the FPLHP was calculated using: .
(2)
Page 7 of 22
The evaporator was made of copper with a size of 105 mm x 40 m x 15 mm. Each side has 5 mm thickness except the bottom side has 3 mm thickness. To assist the evaporation, 1 mm x 1mm x 60 mm grooves was made on the base surface of the evaporator as shown in Fig. 3.
A stainless steel screen mesh with a size of 300 mesh was placed above the grooves to serve as the capillary wick as shown in Fig. 4. The stainless steel screen meshes capillary wick were also placed on the liquid line to pump back the condensate from the condenser to the evaporator.
The k-type thermocouples with 0.2 mm diameter were used for temperature measurements. Fig. 5 shows the placement of the thermocouples. There were two thermocouples for the evaporator, two thermocouples for vapor line, three thermocouples for the condenser, and two thermocouples for liquid line.
The assembly of the FPLHP was then isolated using glass wool. Ceramic blanket, which has a higher working temperature, was used for the evaporator insulation. Finally, these insulation layers were covered by the aluminum foil as shown in Fig. 6.
The experimental setup is shown in Fig. 7. The heater power was controlled by adjusting the electric voltage through a voltage regulator. The thermocouple data were sent to an NI 9213 data acquisition module installed on an NI cDAQ 9174 chassis. A
Page 8 of 22
circulating thermostatic bath was used to simulate cooling condition at condenser side of the heat pipe. The circulating thermostatic bath was set to 28°C with water flow rate of 4 g/s. A DC power supply was used to activate a pressure sensor. An Autonics PSA-V01 digital pressure sensor with a range of 0 to -101.3 kPa was used to monitor the pressure inside the heat pipe, especially at the time of the evacuation process. The pressure sensor was placed at the vapor line using a tee connection.
Distilled water, alcohol 96%, and acetone 95% were used as working fluids with a filling ratio of 60%. The distilled water, alcohol, and acetone are compatible with copper as the heat pipe material. A filling ratio value from 60% to 80% is acceptable for the reliable start-up and steady-state operation of a loop heat pipe [17]. Alcohol and acetone were selected to investigate whether they can improve the performance of the FPLHP compared to distilled water. For all working fluids, the experiments used three different heat flux loads, i.e. 0.48 W/cm2, 0.96 W/cm2, and 1.61 W/cm2.
Page 9 of 22
3. Results and Discussion 3.1. Transient Temperature The transient temperature of the evaporator and the condenser for each working fluid at heat flux load of 0.48 W/cm2, 0.96 W/cm2, and 1.61 W/cm2 are presented in Fig. 8. These loads may be referred to low heat flux [18]. From the transient temperature curves for the evaporator, the start-up processes can be observed. Most of them demonstrate the temperature overshoot that followed by a rapid temperature drop. This overshoot pattern of evaporator temperatures corresponds to the boiling of working fluid in the initial state that is accompanied by some superheating [18].
In a particular condition where a free vapor-liquid interface exists in the evaporation zone, a smooth or stable start-up may proceed without being accompanied by a temperature overshoot [18, 19]. Fig. 8b shows that acetone, at a heat flux load of 0.96 W/cm2, demonstrates the smooth start-up process. This smooth start-up was probably caused by the higher temperature at the initial condition. The steady state temperatures are achieved at about 30 – 90 minutes depend on the heat flux load. The higher the heat flux load, the shorter the transient period. This quite long transient time can be caused by the high heat capacitance of the system according to the addition of mass such as conduction plate and insulating. When the capacitance of the system is substantially increased, the heat input will affect the transient period very significantly [20]. Also, it is seen that acetone and alcohol provide a shorter transient period for both the evaporator and condenser temperatures.
Page 10 of 22
3.2 Steady-State Temperature Distribution The steady-state temperature distribution of the FPLHP wall is discussed below. It is seen that at heat flux load of 0.48 W/cm2 and 0.96 W/cm2, distilled water, and alcohol produce fairly close temperature distribution. However, at a heat flux load of 1.61 W/cm2, alcohol and acetone provide quite close temperature distribution. At all heat flux load, the evaporator temperature can be kept below 50°C, except for distilled water, which produced evaporator temperature of about 60°C at a heat flux load of 1.61 W/cm2. For the entire experiment using distilled water, alcohol and acetone as working fluids, acetone provides the lowest temperature difference between the evaporator and the condenser as presented in Fig. 9. It may be caused by the fact that acetone has the lowest saturation temperature compared to the distilled water and alcohol. The saturation temperatures at 1 atm are 100°C for water, 78.2°C for alcohol, and 56°C for acetone.
In Fig. 8 and 9, with the increase in heat flux, curve 2 (the evaporator temperature of alcohol) shows similar behavior with curve 1 (the evaporator temperature of distilled water) first, and then presents a similar performance with curve 3 (the evaporator temperature of acetone). It can be caused by the increase in the pressure that is different for each working fluid. At 0.48 W/cm2 and 0.96 W/cm2 the increase in pressure of the working fluids are such that the evaporation temperature of the water and alcohol are fairly close while acetone is quite far below. At the heat load of 1.61 W/cm2, the increase in the water pressure continues causing its evaporation temperature also continues to rise. The increase in the pressure of the alcohol is not as high as the water,
Page 11 of 22
so its evaporation temperature is not as high as the water. Meanwhile, the acetone pressure began to rise high enough so that its evaporation temperature approaching the alcohol. Accordingly, at some higher heat load the evaporation temperature of acetone can be predicted to approach that of the alcohol.
In Fig.9, the condenser temperature of acetone deviates a lot from alcohol and distilled water, especially at 1.61 W/cm2. It can be caused by superheating in the evaporator accompanied by infiltration of some vapor through the screen mesh capillary wick in the liquid lines thus increasing the temperature of the liquid line significantly. This increase in the liquid line temperature causes much heat transfer by conduction through the pipe wall from the liquid line to the condenser. It causes the temperature of the condenser of acetone is much higher than that of water and alcohol.
Fig. 10 shows the steady state temperature distribution along the heat pipe wall at various heat flux loads for acetone as working fluid. The lowest temperature difference between evaporator and condenser was achieved at the heat flux load of 0.48 W/cm2.
The performance of the FPLHP can be represented by thermal resistance, which was calculated by using (1). Fig. 11 shows the thermal resistance of the flat plate heat pipe for the entire experiments. The best performance was obtained at a heat flux load of 1.61 W/cm2 with acetone as working fluid. The thermal resistance achieved is 0.22
Page 12 of 22
W/°C. The maximum evaporator temperature for alcohol and acetone are about 50°C, which is within the working temperature range of common lithium-ion batteries.
Figure 11 shows that for heat load increasing above 1.61 W/cm2 alcohol and acetone are converging to similar values of thermal resistance. At some higher heat loads, the vapor pressure of acetone tends to approach that of the alcohol so that their evaporation temperature will become quite close. Meanwhile, the condensing temperature of both fluids are practically the same, so the temperature difference between the evaporator and the condenser become fairly close resulting in the same thermal resistance values. Therefore, at heat loads above 1.61 W/cm2 the performance of the flat plate loop heat pipes with alcohol can be predicted to approximate those with acetone.
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4. Conclusions This experiment leads to the practical potential of flat plate loop heat pipe usage in the thermal management system of lithium-ion battery. The flat plate loop heat pipe could start-up at heat flux load as low as 0.48 W/cm2. Temperature overshoot phenomena were observed during the start-up period. The best performance of the flat plate loop heat pipe was obtained with acetone used as working fluid with a heat flux loads of 1.61 W/cm2. The thermal resistance achieved was 0.22 W/°C. The maximum evaporator temperature with alcohol and acetone was about 50°C, which is within the operating temperature range of common lithium-ion batteries. At heat loads above 1.61 W/cm2 the performance of the flat plate loop heat pipes with alcohol is predicted to approximate those with acetone.
Acknowledgment We would like to thank the LPDP - Ministry of the Finance Republic of Indonesia for funding this research through the RISPRO 2014 scheme.
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References [1] K. Hedegaard, H. Ravn, N. Juul, P. Meibom, Effects of electric vehicles on power systems in Northern Europe, Energy, 48 (2012) 356-368. [2] L. Lu, X. Han, J. Li, J. Hua, M. Ouyang, A review on the key issues for lithium-ion battery management in electric vehicles, Journal of power sources, 226 (2013) 272-288. [3] P.E. Ross, Boeing's battery blues [News], Spectrum, IEEE, 50 (2013) 11-12. [4] X. Duan, G.F. Naterer, Heat transfer in phase change materials for thermal management of electric vehicle battery modules, International Journal of Heat and Mass Transfer, 53 (2010) 5176-5182. [5] J.X. Weinert, A.F. Burke, X. Wei, Lead-acid and lithium-ion batteries for the Chinese electric bike market and implications on future technology advancement, Journal of power sources, 172 (2007) 938945. [6] T.-H. Tran, S. Harmand, B. Desmet, S. Filangi, Experimental investigation on the feasibility of heat pipe cooling for HEV/EV lithium-ion battery, Applied Thermal Engineering, 63 (2014) 551-558. [7] Z. Rao, S. Wang, M. Wu, Z. Lin, F. Li, Experimental investigation on thermal management of electric vehicle battery with heat pipe, Energy Conversion and Management, 65 (2013) 92-97. [8] N. Putra, W.N. Septiadi, R. Sahmura, C.T. Anggara, Application of Al2O3 Nanofluid on Sintered Copper-Powder Vapor Chamber for Electronic Cooling, Advanced Materials Research, 789 (2013) 423428. [9] N. Putra, F.N. Iskandar, Application of nanofluids to a heat pipe liquid-block and the thermoelectric cooling of electronic equipment, Experimental Thermal and Fluid Science, 35 (2011) 1274-1281. [10] J.-C. Wang, L-type heat pipes application in electronic cooling system, International Journal of Thermal Sciences, 50 (2011) 97-105. [11] Y.-C. Weng, H.-P. Cho, C.-C. Chang, S.-L. Chen, Heat pipe with PCM for electronic cooling, Applied Energy, 88 (2011) 1825-1833. [12] B.B. Chen, W. Liu, Z.C. Liu, H. Li, J.G. Yang, Experimental investigation of loop heat pipe with flat evaporator using biporous wick, Applied Thermal Engineering, 42 (2012) 34-40. [13] B.B. Chen, Z.C. Liu, W. Liu, J.G. Yang, H. Li, D.D. Wang, Operational characteristics of two biporous wicks used in loop heat pipe with flat evaporator, International Journal of Heat and Mass Transfer, 55 (2012) 2204-2207. [14] X. Lu, J.-J. Wei, Experimental study on a novel loop heat pipe with both flat evaporator and boiling pool, International Journal of Heat and Mass Transfer, 79 (2014) 54-63. [15] Q. Wang, B. Jiang, Q. Xue, H. Sun, B. Li, H. Zou, Y. Yan, Experimental investigation on EV battery cooling and heating by heat pipes, Applied Thermal Engineering, (2014). [16] M.M. Thackeray, J.O. Thomas, M.S. Whittingham, Science and applications of mixed conductors for lithium batteries, MRS bulletin, 25 (2000) 39-46. [17] G.P. Celata, M. Cumo, M. Furrer, Experimental tests of a stainless steel loop heat pipe with flat evaporator, Experimental Thermal and Fluid Science, 34 (2010) 866-878. [18] Y. Maydanik, S. Vershinin, M. Chernysheva, S. Yushakova, Investigation of a compact copper–water loop heap pipe with a flat evaporator, Applied Thermal Engineering, 31 (2011) 3533-3541. [19] D. Wang, Z. Liu, J. Shen, C. Jiang, B. Chen, J. Yang, Z. Tu, W. Liu, Experimental study of the loop heat pipe with a flat disk-shaped evaporator, Experimental Thermal and Fluid Science, 57 (2014) 157-164. [20] Y. Wang, K. Vafai, Transient characterization of flat plate heat pipes during startup and shutdown operations, International Journal of Heat and Mass Transfer, 43 (2000) 2641-2655.
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Figures
Fig. 1 Thermal management system of electric vehicle battery [15]
Fig. 2. Flat plate loop heat pipe with battery simulator
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Fig. 3. The Evaporator Design
Fig. 4 Stainless steel screen mesh capillary wick
Page 17 of 22
Fig. 5. Thermocouples placement
Fig. 6. Flat plate loop heat pipe assembly.
Page 18 of 22
Fig. 7. Experimental setup
Page 19 of 22
o
Temperature ( C)
60
(a). 0.48 W.cm
2
1. Evaporator: Distilled Water 2. Evaporator: Alcohol 3. Evaporator: Acetone 4. Condenser: Distilled Water 5. Condenser: Alcohol 6. Condenser: Acetone
50
2
1
40 3
30
20
6
0
1800
3600
5
4
5400
7200
Time (s)
(a)
o
Temperature ( C)
60
(b). 0.96 W/cm
2
1. Evaporator: Distilled Water 2. Evaporator: Alcohol 3. Evaporator: Acetone 4. Condenser: Distilled Water 5. Condenser: Alcohol 6. Condenser: Acetone
50 1 2
40
3
30 5
0
1800
6
4
3600
Time (s)
(b) 90 (c). 1.61 W/cm
2
1. Evaporator: Distilled Water 2. Evaporator: Alcohol 3. Evaporator: Acetone 4. Condenser: Distilled Water 5. Condenser: Alcohol 6. Condenser: Acetone
70
o
Temperature ( C)
80
60
1 2
50
3
40 6
30
5 4
0
1800
3600
Time (s)
(c) Fig. 8. Transient temperature
Page 20 of 22
60 (a). 0.48 Watt/cm
2
Distilled Water Alcohol Acetone
o
Temperature C
50
40
30
0
10
20
30
40
50
60
Position (cm)
(a)
Temperature (oC)
60
(b). 0.96 Watt/cm
2
Distilled Water Alcohol Acetone
50
40
30 0
10
20
30
40
50
60
Position (cm)
(b)
o
Temperature ( C)
60
(c). 1.61 Watt/cm
2
Distilled Water Alcohol Acetone
50
40
30 0
10
20
30
40
50
60
Position (cm)
(c) Fig. 9 Steady state temperature distribution
Page 21 of 22
Acetone
2
0.48 W/cm ) 2 0.96 W/cm ) 2 1.61 W/cm )
Temperature (°C)
50
40
30
0
10
20
30
40
50
60
Position (cm)
Distilled Water Alcohol Acetone
0.8
o
Thermal Resistance ( C/W)
Fig. 10. Steady state temperature distribution for acetone as the working fluid
0.6
0.4
0.2 0.0
0.5
1.0
1.5
2.0
2
Heat Flux (W/cm )
Fig. 11 Thermal resistances
Page 22 of 22
S1359-4311(16)30073-4 http://dx.doi.org/doi: 10.1016/j.applthermaleng.2016.01.123 ATE 7683
To appear in:
Applied Thermal Engineering
Received date: Accepted date:
14-10-2015 29-1-2016
Please cite this article as: Putra Nandy, Bambang Ariantara, Rangga Aji Pamungkas, Experimental investigation on performance of lithium-ion battery thermal management system using flat plate loop heat pipe for electric vehicle application, Applied Thermal Engineering (2016), http://dx.doi.org/doi: 10.1016/j.applthermaleng.2016.01.123. 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.
Experimental Investigation on Performance of Lithium-Ion Battery Thermal Management System using Flat Plate Loop Heat Pipe for Electric Vehicle Application
Nandy Putra, Bambang Ariantara, Rangga Aji Pamungkas
Applied Heat Transfer Laboratory, Department of Mechanical Engineering Universitas Indonesia, 16424 Depok, Jawa Barat, Indonesia
This paper is an extended and revised article presented at the Asia-Pacific Conference on Engineering and Applied Science (APCEAS 2015), August 25-27, 2015, Osaka, Japan. Corresponding authors at: [email protected] .
Page 1 of 22
Highlights
Flat plate loop heat pipe (FPLHP) is studied in the thermal management system for electric vehicle.
Distilled water, alcohol, and acetone on thermal performances of FPLHP were tested
The FPLHP can start up at fairly low heat load
Temperature overshoot phenomena were observed during the start-up period.
Abstract The development of electric vehicle batteries has resulted in a very high energy density lithium-ion batteries. However, this growth is accompanied by the risk of thermal runaway, which can cause serious accidents. Heat pipes are heat exchangers that are suitable to be applied in electric vehicle battery thermal management for their lightweight, compact size and do not require external power supply. This study examined experimentally a flat plate loop heat pipe (FPLHP) performance as a heat exchanger in the thermal management system of the lithium-ion battery for electric vehicle application. The heat generation of the battery was simulated using a cartridge heater. Stainless steel screen mesh was used as the capillary wick. Distilled water, alcohol, and acetone were used as working fluids with a filling ratio of 60%. It was found that acetone gave the best performance that produces a thermal resistance of 0.22 W/°C with 50°C evaporator temperature at heat flux load of 1.61 W/cm2.
Page 2 of 22
Keywords: Electric vehicle; flat plate loop heat pipe; lithium-ion battery; thermal management system
Page 3 of 22
Nomenclatures A: Area, m2 k: Thermal conductivity, W/m. K q: Heat transfer rate, W R: Thermal resistance, °C/W Tb: Bottom surface temperature, °C Tt: Top surface temperature, °C Tc: Condenser temperature, °C Te: Evaporator temperature °C.
Page 4 of 22
1. Introduction The shares of electric vehicles in some European countries are assumed comprising 53% of the private passenger vehicle fleet in 2030 [1]. One of the important performance parameters of an electric vehicle is the range or cruising capability, which is mainly determined by the performance of the batteries. Batteries with high energy density are needed to deliver high cruising capabilities. Electric vehicles will rely on lithium-ion batteries according to their high energy density, high power density, long service life and environmental friendliness [2]. Advances in battery technology have resulted in very high energy density lithium-ion batteries. However, this progress is also accompanied by the risk of thermal runaway, which can lead to serious accidents such as experienced by the Boeing 787 Dreamliner of All Nippon Airways on January 16, 2013, in Japan [3].
Heat generated by a battery, either at the time of charging or discharging will increase its temperature. The battery performance and lifetime are strongly influenced by their working temperature. In general, the performance of electric vehicles is directly affected by the performance of their batteries [4]. At quite low or high temperatures, the battery performance can be destitute. At very high temperature, lithium-ion batteries can even explode [5]. The desired working temperature range for ordinary lithium-ion batteries in the range of 25°C to 50°C [6]. For the purpose of energy saving and reduction in the cost of electric vehicles, the batteries should be operated in a proper
Page 5 of 22
temperature range [7]. Therefore, an efficient thermal management system for the battery packs is essential. Heat pipes are heat exchangers that are suitable to be applied in thermal management of central processing unit (CPUs) and electric vehicle batteries for their lightweight, compact size and do not require external power supply. Studies on heat pipes for electronic cooling have been done by authors that can be found in many references [8, 9] and other researchers such as Wang [10], and Weng et al. [11]. Investigations on flat plate heat pipes in electronic cooling have been conducted by Chen et al. [12, 13] and Lu and Wei [14]. Rao et al. [7] have examined the use of straight heat pipes on thermal management system of a LiFePo4 battery. Their experimental results showed that the maximum temperature can be kept below 50°C if the rate of heat generation is below 50 W/cm2. Wang et al. [15] investigated the application of heat pipe for thermal management system of the electric vehicle battery. In their work, some Lshaped flattened heat pipes were used to transfer heat from the battery to the cooling water as shown in Fig. 1.
Flat plate loop heat pipes have the potential to be applied to the thermal management system of electric vehicle lithium-ion batteries since most of the electric vehicle lithium-ion battery pack has flat surfaces [16]. This paper aims to examine the performance of a flat plate loop heat pipe as a heat exchanger in the thermal management system of lithium-ion batteries for electric vehicle application experimentally.
Page 6 of 22
2. Methodology Battery simulator was made from aluminum alloy. As a heat source, a cylindrical cartridge heater with a power of 400 W was placed in the battery simulator. A conduction plate made of stainless steel with a size of 105 mm x 40 mm x 15 mm was placed above the battery simulator. Fig. 2 shows the arrangement of the flat loop heat pipe, conduction plate, battery simulator and insulating box used in the experiment in order to minimize heat lost.
The conduction plate was used to determine the conduction heat transfer from the heater to the evaporator by measuring the temperature difference across the plate. Instead of using electric power input, the conduction heat transfer through the conduction plate was used to determine the heat input to the evaporator. The heat input could be determined by the following equation: .
(1)
The thermal conductivity of the conduction plate which made of stainless steel was assumed to be 16 W/m K. The battery simulator and the conduction plate were placed inside an insulating box made of polyurethane. On top surfaces of the conduction plate and the battery simulator, grooves were made for the installation of thermocouples. At the condenser section, an annular heat exchanger was used for heat release to the cooling water. The thermal resistance of the FPLHP was calculated using: .
(2)
Page 7 of 22
The evaporator was made of copper with a size of 105 mm x 40 m x 15 mm. Each side has 5 mm thickness except the bottom side has 3 mm thickness. To assist the evaporation, 1 mm x 1mm x 60 mm grooves was made on the base surface of the evaporator as shown in Fig. 3.
A stainless steel screen mesh with a size of 300 mesh was placed above the grooves to serve as the capillary wick as shown in Fig. 4. The stainless steel screen meshes capillary wick were also placed on the liquid line to pump back the condensate from the condenser to the evaporator.
The k-type thermocouples with 0.2 mm diameter were used for temperature measurements. Fig. 5 shows the placement of the thermocouples. There were two thermocouples for the evaporator, two thermocouples for vapor line, three thermocouples for the condenser, and two thermocouples for liquid line.
The assembly of the FPLHP was then isolated using glass wool. Ceramic blanket, which has a higher working temperature, was used for the evaporator insulation. Finally, these insulation layers were covered by the aluminum foil as shown in Fig. 6.
The experimental setup is shown in Fig. 7. The heater power was controlled by adjusting the electric voltage through a voltage regulator. The thermocouple data were sent to an NI 9213 data acquisition module installed on an NI cDAQ 9174 chassis. A
Page 8 of 22
circulating thermostatic bath was used to simulate cooling condition at condenser side of the heat pipe. The circulating thermostatic bath was set to 28°C with water flow rate of 4 g/s. A DC power supply was used to activate a pressure sensor. An Autonics PSA-V01 digital pressure sensor with a range of 0 to -101.3 kPa was used to monitor the pressure inside the heat pipe, especially at the time of the evacuation process. The pressure sensor was placed at the vapor line using a tee connection.
Distilled water, alcohol 96%, and acetone 95% were used as working fluids with a filling ratio of 60%. The distilled water, alcohol, and acetone are compatible with copper as the heat pipe material. A filling ratio value from 60% to 80% is acceptable for the reliable start-up and steady-state operation of a loop heat pipe [17]. Alcohol and acetone were selected to investigate whether they can improve the performance of the FPLHP compared to distilled water. For all working fluids, the experiments used three different heat flux loads, i.e. 0.48 W/cm2, 0.96 W/cm2, and 1.61 W/cm2.
Page 9 of 22
3. Results and Discussion 3.1. Transient Temperature The transient temperature of the evaporator and the condenser for each working fluid at heat flux load of 0.48 W/cm2, 0.96 W/cm2, and 1.61 W/cm2 are presented in Fig. 8. These loads may be referred to low heat flux [18]. From the transient temperature curves for the evaporator, the start-up processes can be observed. Most of them demonstrate the temperature overshoot that followed by a rapid temperature drop. This overshoot pattern of evaporator temperatures corresponds to the boiling of working fluid in the initial state that is accompanied by some superheating [18].
In a particular condition where a free vapor-liquid interface exists in the evaporation zone, a smooth or stable start-up may proceed without being accompanied by a temperature overshoot [18, 19]. Fig. 8b shows that acetone, at a heat flux load of 0.96 W/cm2, demonstrates the smooth start-up process. This smooth start-up was probably caused by the higher temperature at the initial condition. The steady state temperatures are achieved at about 30 – 90 minutes depend on the heat flux load. The higher the heat flux load, the shorter the transient period. This quite long transient time can be caused by the high heat capacitance of the system according to the addition of mass such as conduction plate and insulating. When the capacitance of the system is substantially increased, the heat input will affect the transient period very significantly [20]. Also, it is seen that acetone and alcohol provide a shorter transient period for both the evaporator and condenser temperatures.
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3.2 Steady-State Temperature Distribution The steady-state temperature distribution of the FPLHP wall is discussed below. It is seen that at heat flux load of 0.48 W/cm2 and 0.96 W/cm2, distilled water, and alcohol produce fairly close temperature distribution. However, at a heat flux load of 1.61 W/cm2, alcohol and acetone provide quite close temperature distribution. At all heat flux load, the evaporator temperature can be kept below 50°C, except for distilled water, which produced evaporator temperature of about 60°C at a heat flux load of 1.61 W/cm2. For the entire experiment using distilled water, alcohol and acetone as working fluids, acetone provides the lowest temperature difference between the evaporator and the condenser as presented in Fig. 9. It may be caused by the fact that acetone has the lowest saturation temperature compared to the distilled water and alcohol. The saturation temperatures at 1 atm are 100°C for water, 78.2°C for alcohol, and 56°C for acetone.
In Fig. 8 and 9, with the increase in heat flux, curve 2 (the evaporator temperature of alcohol) shows similar behavior with curve 1 (the evaporator temperature of distilled water) first, and then presents a similar performance with curve 3 (the evaporator temperature of acetone). It can be caused by the increase in the pressure that is different for each working fluid. At 0.48 W/cm2 and 0.96 W/cm2 the increase in pressure of the working fluids are such that the evaporation temperature of the water and alcohol are fairly close while acetone is quite far below. At the heat load of 1.61 W/cm2, the increase in the water pressure continues causing its evaporation temperature also continues to rise. The increase in the pressure of the alcohol is not as high as the water,
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so its evaporation temperature is not as high as the water. Meanwhile, the acetone pressure began to rise high enough so that its evaporation temperature approaching the alcohol. Accordingly, at some higher heat load the evaporation temperature of acetone can be predicted to approach that of the alcohol.
In Fig.9, the condenser temperature of acetone deviates a lot from alcohol and distilled water, especially at 1.61 W/cm2. It can be caused by superheating in the evaporator accompanied by infiltration of some vapor through the screen mesh capillary wick in the liquid lines thus increasing the temperature of the liquid line significantly. This increase in the liquid line temperature causes much heat transfer by conduction through the pipe wall from the liquid line to the condenser. It causes the temperature of the condenser of acetone is much higher than that of water and alcohol.
Fig. 10 shows the steady state temperature distribution along the heat pipe wall at various heat flux loads for acetone as working fluid. The lowest temperature difference between evaporator and condenser was achieved at the heat flux load of 0.48 W/cm2.
The performance of the FPLHP can be represented by thermal resistance, which was calculated by using (1). Fig. 11 shows the thermal resistance of the flat plate heat pipe for the entire experiments. The best performance was obtained at a heat flux load of 1.61 W/cm2 with acetone as working fluid. The thermal resistance achieved is 0.22
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W/°C. The maximum evaporator temperature for alcohol and acetone are about 50°C, which is within the working temperature range of common lithium-ion batteries.
Figure 11 shows that for heat load increasing above 1.61 W/cm2 alcohol and acetone are converging to similar values of thermal resistance. At some higher heat loads, the vapor pressure of acetone tends to approach that of the alcohol so that their evaporation temperature will become quite close. Meanwhile, the condensing temperature of both fluids are practically the same, so the temperature difference between the evaporator and the condenser become fairly close resulting in the same thermal resistance values. Therefore, at heat loads above 1.61 W/cm2 the performance of the flat plate loop heat pipes with alcohol can be predicted to approximate those with acetone.
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4. Conclusions This experiment leads to the practical potential of flat plate loop heat pipe usage in the thermal management system of lithium-ion battery. The flat plate loop heat pipe could start-up at heat flux load as low as 0.48 W/cm2. Temperature overshoot phenomena were observed during the start-up period. The best performance of the flat plate loop heat pipe was obtained with acetone used as working fluid with a heat flux loads of 1.61 W/cm2. The thermal resistance achieved was 0.22 W/°C. The maximum evaporator temperature with alcohol and acetone was about 50°C, which is within the operating temperature range of common lithium-ion batteries. At heat loads above 1.61 W/cm2 the performance of the flat plate loop heat pipes with alcohol is predicted to approximate those with acetone.
Acknowledgment We would like to thank the LPDP - Ministry of the Finance Republic of Indonesia for funding this research through the RISPRO 2014 scheme.
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References [1] K. Hedegaard, H. Ravn, N. Juul, P. Meibom, Effects of electric vehicles on power systems in Northern Europe, Energy, 48 (2012) 356-368. [2] L. Lu, X. Han, J. Li, J. Hua, M. Ouyang, A review on the key issues for lithium-ion battery management in electric vehicles, Journal of power sources, 226 (2013) 272-288. [3] P.E. Ross, Boeing's battery blues [News], Spectrum, IEEE, 50 (2013) 11-12. [4] X. Duan, G.F. Naterer, Heat transfer in phase change materials for thermal management of electric vehicle battery modules, International Journal of Heat and Mass Transfer, 53 (2010) 5176-5182. [5] J.X. Weinert, A.F. Burke, X. Wei, Lead-acid and lithium-ion batteries for the Chinese electric bike market and implications on future technology advancement, Journal of power sources, 172 (2007) 938945. [6] T.-H. Tran, S. Harmand, B. Desmet, S. Filangi, Experimental investigation on the feasibility of heat pipe cooling for HEV/EV lithium-ion battery, Applied Thermal Engineering, 63 (2014) 551-558. [7] Z. Rao, S. Wang, M. Wu, Z. Lin, F. Li, Experimental investigation on thermal management of electric vehicle battery with heat pipe, Energy Conversion and Management, 65 (2013) 92-97. [8] N. Putra, W.N. Septiadi, R. Sahmura, C.T. Anggara, Application of Al2O3 Nanofluid on Sintered Copper-Powder Vapor Chamber for Electronic Cooling, Advanced Materials Research, 789 (2013) 423428. [9] N. Putra, F.N. Iskandar, Application of nanofluids to a heat pipe liquid-block and the thermoelectric cooling of electronic equipment, Experimental Thermal and Fluid Science, 35 (2011) 1274-1281. [10] J.-C. Wang, L-type heat pipes application in electronic cooling system, International Journal of Thermal Sciences, 50 (2011) 97-105. [11] Y.-C. Weng, H.-P. Cho, C.-C. Chang, S.-L. Chen, Heat pipe with PCM for electronic cooling, Applied Energy, 88 (2011) 1825-1833. [12] B.B. Chen, W. Liu, Z.C. Liu, H. Li, J.G. Yang, Experimental investigation of loop heat pipe with flat evaporator using biporous wick, Applied Thermal Engineering, 42 (2012) 34-40. [13] B.B. Chen, Z.C. Liu, W. Liu, J.G. Yang, H. Li, D.D. Wang, Operational characteristics of two biporous wicks used in loop heat pipe with flat evaporator, International Journal of Heat and Mass Transfer, 55 (2012) 2204-2207. [14] X. Lu, J.-J. Wei, Experimental study on a novel loop heat pipe with both flat evaporator and boiling pool, International Journal of Heat and Mass Transfer, 79 (2014) 54-63. [15] Q. Wang, B. Jiang, Q. Xue, H. Sun, B. Li, H. Zou, Y. Yan, Experimental investigation on EV battery cooling and heating by heat pipes, Applied Thermal Engineering, (2014). [16] M.M. Thackeray, J.O. Thomas, M.S. Whittingham, Science and applications of mixed conductors for lithium batteries, MRS bulletin, 25 (2000) 39-46. [17] G.P. Celata, M. Cumo, M. Furrer, Experimental tests of a stainless steel loop heat pipe with flat evaporator, Experimental Thermal and Fluid Science, 34 (2010) 866-878. [18] Y. Maydanik, S. Vershinin, M. Chernysheva, S. Yushakova, Investigation of a compact copper–water loop heap pipe with a flat evaporator, Applied Thermal Engineering, 31 (2011) 3533-3541. [19] D. Wang, Z. Liu, J. Shen, C. Jiang, B. Chen, J. Yang, Z. Tu, W. Liu, Experimental study of the loop heat pipe with a flat disk-shaped evaporator, Experimental Thermal and Fluid Science, 57 (2014) 157-164. [20] Y. Wang, K. Vafai, Transient characterization of flat plate heat pipes during startup and shutdown operations, International Journal of Heat and Mass Transfer, 43 (2000) 2641-2655.
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Figures
Fig. 1 Thermal management system of electric vehicle battery [15]
Fig. 2. Flat plate loop heat pipe with battery simulator
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Fig. 3. The Evaporator Design
Fig. 4 Stainless steel screen mesh capillary wick
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Fig. 5. Thermocouples placement
Fig. 6. Flat plate loop heat pipe assembly.
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Fig. 7. Experimental setup
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o
Temperature ( C)
60
(a). 0.48 W.cm
2
1. Evaporator: Distilled Water 2. Evaporator: Alcohol 3. Evaporator: Acetone 4. Condenser: Distilled Water 5. Condenser: Alcohol 6. Condenser: Acetone
50
2
1
40 3
30
20
6
0
1800
3600
5
4
5400
7200
Time (s)
(a)
o
Temperature ( C)
60
(b). 0.96 W/cm
2
1. Evaporator: Distilled Water 2. Evaporator: Alcohol 3. Evaporator: Acetone 4. Condenser: Distilled Water 5. Condenser: Alcohol 6. Condenser: Acetone
50 1 2
40
3
30 5
0
1800
6
4
3600
Time (s)
(b) 90 (c). 1.61 W/cm
2
1. Evaporator: Distilled Water 2. Evaporator: Alcohol 3. Evaporator: Acetone 4. Condenser: Distilled Water 5. Condenser: Alcohol 6. Condenser: Acetone
70
o
Temperature ( C)
80
60
1 2
50
3
40 6
30
5 4
0
1800
3600
Time (s)
(c) Fig. 8. Transient temperature
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60 (a). 0.48 Watt/cm
2
Distilled Water Alcohol Acetone
o
Temperature C
50
40
30
0
10
20
30
40
50
60
Position (cm)
(a)
Temperature (oC)
60
(b). 0.96 Watt/cm
2
Distilled Water Alcohol Acetone
50
40
30 0
10
20
30
40
50
60
Position (cm)
(b)
o
Temperature ( C)
60
(c). 1.61 Watt/cm
2
Distilled Water Alcohol Acetone
50
40
30 0
10
20
30
40
50
60
Position (cm)
(c) Fig. 9 Steady state temperature distribution
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Acetone
2
0.48 W/cm ) 2 0.96 W/cm ) 2 1.61 W/cm )
Temperature (°C)
50
40
30
0
10
20
30
40
50
60
Position (cm)
Distilled Water Alcohol Acetone
0.8
o
Thermal Resistance ( C/W)
Fig. 10. Steady state temperature distribution for acetone as the working fluid
0.6
0.4
0.2 0.0
0.5
1.0
1.5
2.0
2
Heat Flux (W/cm )
Fig. 11 Thermal resistances
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