Heat Transfer Improvement of Prismatic Lithium-Ion Batteries via Mini-Channel Liquid Cooling Plate With Vortex Generators PDF

Heat Transfer Improvement of Huanwei Xu1 Downloaded from http:...

Heat Transfer Improvement of Huanwei Xu1 Downloaded from http://asmedigitalcollection.asme.org/electrochemical/article-pdf/21/3/031003/7047499/jeecs_21_3_031003.pdf by Universita Padova user on 06 March 2024 School of Mechanical and Electrical Engineering, University of Electronic Science Prismatic Lithium-Ion Batteries and Technology of China, Chengdu 611731, China e-mail: [email protected] via a Mini-Channel Liquid- Shizhe Xiong Cooling Plate With Vortex School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Generators Chengdu 611731, China Temperature is a critical factor affecting the performance and safety of battery packs of e-mail: [email protected] electric vehicles (EVs). The design of liquid cooling plates based on mini-channels has always been the research hotspots of battery thermal management systems (BTMS). This Wei Li paper investigates the effect of adding vortex generators (VGs) to the liquid cooling School of Mechanical Engineering, channel on the heat dissipation capacity and temperature uniformity of the battery. The Hefei University of Technology, shape of the vortex generators (triangle, trapezoid, and semicircle), placement position Hefei 230009, China (middle, inlet, and outlet of the channel), different flowrates, and different numbers of chan- e-mail: [email protected] nels on the heat dissipation of the battery are systematically analyzed. The research results indicate that (1) compared to the triangular and trapezoidal vortex generators, the semicir- Lingfeng Wu cular vortex generators have a lower cost in terms of pressure drop while maintaining the School of Mechanical and Electrical Engineering, same heat dissipation efficiency. The pressure drop of the semicircular vortex generators is University of Electronic Science 15.89% less than that of the trapezoidal vortex generators and 20.49% less than that of the and Technology of China, triangular vortex generators. (2) The effect of adding vortex generators is more obvious Chengdu 611731, China when the flowrate is small in the cooling channels. When the flow velocity is 0.025 m/s, e-mail: [email protected] the heat dissipation performance can be increased by 7.4%. (3) When the cross-sectional area of the inlet is fixed, the heat dissipation effect of more channels is better. The Zhonglai Wang average temperature of three and seven cooling channels decreases from 311.23 K to School of Mechanical and Electrical Engineering, 310.07 K, with a decrease of 8.87%. (4) The temperature difference can be effectively University of Electronic Science reduced when the vortex generators are concentrated near the outlet of the flow outlet. and Technology of China, Its temperature difference is 1.8 K lower than that when the vortex generators are placed Chengdu 611731, China near the inlet, with a decrease of 10.5%. [DOI: 10.1115/1.4063324] e-mail: [email protected] Keywords: electric vehicle, prismatic batteries, thermal management system, mini-channel cooling plate, vortex generator 1 Introduction The frequent use of EVs has also brought the performance require- ments of EVs in line with conventional fuel vehicles. Scenarios that In recent years, with growing concerns about the energy crisis may be encountered, such as driving at high speeds or frequent and climate issues in the international community, new energy vehi- deceleration and acceleration, are a severe test for the battery. cles have been promoted rapidly. Among all kinds of new energy LIBs have an obvious disadvantage; i.e., the requirements for tem- vehicles, electric vehicles (EVs) are undoubtedly the most impor- perature control are relatively high. Excessive temperature or exces- tant way. The crucial problems that have always plagued the field sive temperature difference will cause irreversible damage to the of EVs are the capacity and charge–discharge performance of the battery itself. This also makes the thermal management of LIBs a battery [1,2]. Lithium-ion batteries (LIBs) are widely used in EVs long-term issue worth studying [3–8]. due to their high energy density, high discharge power, low self- The battery thermal management system (BTMS) refers to mea- discharge rate, long life, and fast charging. With the popularity of sures that can control the battery temperature to a certain extent. EVs and charging piles, people’s demand for charging speed has Commonly used cooling methods include air cooling, liquid become increasingly prominent, and fast charging is bound to cooling, and phase change material (PCM) cooling. Air cooling cause a large amount of heat release in a short period of time. has the advantages of simple installation, low cost, and small size, but because of the limited cooling efficiency, it is usually 1 Corresponding author. only used in the case of small heat generation. Some related Manuscript received January 11, 2023; final manuscript received July 31, 2023; studies on improving heat dissipation capacity by optimizing air published online October 5, 2023. Assoc. Editor: Ankur Jain. ducts and adding fins have been studied [11,12]. Phase change Journal of Electrochemical Energy Conversion and Storage AUGUST 2024, Vol. 21 / 031003-1 Copyright © 2023 by ASME material cooling uses the endothermic phenomenon of materials to consumption, weight and temperature standard deviation than tradi- control the temperature during the phase change process, so the tional uniform fin designs, respectively. The maximum temperature battery temperature can be very stable within a certain range. was also reduced by 1.04 K. Liu et al. designed a double-layer Research in recent years also tends to be combined with liquid staggered cavity mini-channel radiator structure and compared it cooling. It is to let the PCM flow improve its continuous heat with a straight-channel mini-channel radiator. The staggered cavi- exchange capacity, but the pressure change in the pipeline puts ties can enhance the mixing, interruption, and redevelopment of forward higher requirements on sealing and other aspects, which the thermal boundary layer of the fluid, thereby improving the will undoubtedly greatly increase the cost [13,14]. heat transfer capacity. Liquid cooling is a method that takes out the heat from the battery Although many studies on mini-channel liquid cooling pack with a liquid medium that has a larger specific heat capacity BTMS have been investigated, few studies have applied mini- such as water. Liquid-cooled BTMS usually requires components channels with VGs to BTMS. In fact, with the further exploration such as pumps and radiators. The structure is more complicated of battery performance and the further improvement of battery than that of air cooling but simple than phase-change cooling. heat generation, the heat dissipation of the battery has increasing Downloaded from http://asmedigitalcollection.asme.org/electrochemical/article-pdf/21/3/031003/7047499/jeecs_21_3_031003.pdf by Universita Padova user on 06 March 2024 Therefore, when air cooling is difficult to meet heat dissipation similarities with the heat dissipation of chips and chemical indus- requirements, the application of liquid cooling is becoming increas- tries. The practice of arranging VGs in the cooling channel is a ingly widespread. For reasons of safety and flow controllability, common way to enhance heat transfer. The longitudinal vortex gen- liquid cooling usually uses indirect cooling, i.e., using a metal erated after the fluid flows through the VG can reduce the local cold plate with cooling channels in contact with the battery thermal resistance. To a certain extent, adjust the thermal resistance instead of directly immersing the battery in the liquid [15–17]. of different positions of the cooling channel to achieve the purpose Jarrett and Kim carried out multi-objective optimization of of improving temperature uniformity. the parametric model of the single-flow serpentine channel This work mainly studies the further improvement of the cooling cooling plate in terms of pressure drop, average temperature, and capacity and temperature uniformity of the liquid cooling by adding temperature difference, and found that the optimization directions VGs to the cooling channel of the liquid cooling BTMS. The com- of pressure drop and average temperature were basically consistent. parative analysis was carried out from the following four aspects: Huo et al. studied the influence of the number of channels, flow (1) By comparing the temperature rise and pressure drop perfor- direction, flowrate, and ambient temperature on the temperature rise mance of the triangular, trapezoidal, and semicircular VGs, a rela- and distribution of the multi-channel mini-channel cold plate, and tively better shape of the VGs was obtained. (2) The performance found that more channels and faster flowrate can improve heat dis- of VGs on thermal dissipation improvement at different flowrates sipation capacity of the cold plate. Fan et al. designed a double- was observed by comparing the temperature rise with and without layer tree-like channel cooling plate and optimized its structural VGs at different flowrates. (3) Divide the cooling channels into dif- parameters, which reduced the maximum temperature and standard ferent numbers while fixing the cross-sectional area, and the optimal deviation of the surface temperature of the optimized cold plate by solution for the number of cooling channels was obtained. (4) Place 1.79% and 69.25%, respectively. The pressure drop was reduced by the VGs in the middle, the inlet, and the outlet of the cooling 79.13%. Li et al. designed a mini-channel cooling plate struc- channel, respectively, and compare their effects on the temperature ture with a side cover to reduce the temperature difference of the uniformity. battery and also found that increasing the depth while fixing the The rest of this work is arranged as follows. Section 2 describes cross-sectional area of the channel can reduce the temperature dif- the problems studied. Section 3 states the numerical simulation. ference. Kalkan et al. designed a leaf-vein-like mini-channel Section 4 contains the analysis and discussion of different situa- serpentine channel cold plate and optimized its parameters using tions. Section 5 summarizes this study. the design of experiments (DoE) method, obtained a series of optimal parameters at maximum temperature (MBT), maximum temperature difference (MTD), pressure drop (ΔP), respectively. Wu et al. studied the heat dissipation performance of three 2 Problem Statement types of parallel mini-channel cold plates and concluded that the 2.1 Physical Model of Mini-Channel BTMS With Vortex segmented centralized mini-channels have better heat dissipation Generators. A power LIB pack of EVs contains thousands of capacity and heat uniformity. Guo and Li studied the effect LIB cells, which will generate a lot of heat when charging or dis- of four different serpentine channel cold plates on the performance charging. If the heat cannot be dissipated in time, the temperature of BTMS and, after experimental analysis and optimization, con- of the battery pack will rise continuously. This will not only cluded that the comprehensive performance of the parallel spiral reduce battery life but even cause explosion in severe cases [31,32]. channel cold plate was better, and further optimized its specific Liquid-cooled BTMS is a common way to dissipate heat for parameters. Jaffal et al. studied the effect of different rib battery packs, and its cold plate structures usually have three cate- shapes and angles in the ribbed serpentine channel cold plate gories: that is, the serpentine cold plate for cylindrical battery, the (SCCP), and came to the conclusion that the thermal-hydraulic per- integral cold plate for rectangular battery, and the single cold formance was the best when the triangular rib was at an angle of plate with higher cooling efficiency. In the research of this work, 45 deg. Jin et al. directly faced the heat transfer problem of the cell level heat dissipation mode of the rectangular battery is mini-channels in the vertical direction of flow and designed a explored, i.e., the cold plate and the cell are arranged alternately. cooling plate that weakened the fluid boundary layer through an The heat generated by the battery is transferred to the cold plate oblique bifurcation channel, which significantly improved the through the contact surface with the cold plate and then carried cooling efficiency at low flowrates. Al-Asadi et al. studied out through the liquid in the microchannel. the effect of setting different gaps along the direction of the VG For the cooling and heat dissipation problem of this type of in the mini-channel and found that setting a gap between the VG battery, Fig. 1 is a cold plate structure designed in this work. This and the sidewall of the channel can effectively improve the heat dis- structure uses the alternating overlap of cold plate and battery. In sipation efficiency and reduce the pressure drop. Raihan et al. order to simplify the calculation, this paper selects three lithium studied the relationship between the increased heat transfer capacity battery clips sandwiched between two cold plates for simulation cal- and pressure drop after VGs were added in the mini-channel, and culation. The specific parameters of the cold plate are shown in found that the increase in heat transfer capacity must be accompa- Table 1. nied by an increase in pressure drop. Zhao et al. designed a The length and width of the cold plate shall be consistent with mini-channel cooling plate structure with non-uniform fins and per- that of the battery, and the thickness is d1. The channel is symme- formed multi-objective optimization via a multi-island genetic algo- trical along the middle surface of the cold plate, and the section rithm. The result was 29.84%, 29.00%, and 17.43% lower power height and width are d2 and d3, respectively. Semicircular VGs 031003-2 / Vol. 21, AUGUST 2024 Transactions of the ASME  Downloaded from http://asmedigitalcollection.asme.org/electrochemical/article-pdf/21/3/031003/7047499/jeecs_21_3_031003.pdf by Universita Padova user on 06 March 2024 Fig. 1 Structural diagram of cold plate along the length direction are arranged in the cooling channel, and ∂EO the gap width between the two sides of the VGs and the inner wall q = I 2 R + IT (1) ∂T of the cooling channel is d4. There are five pairs of VGs in each cooling channel, with a symmetrical distribution interval of d5 q along the centerline. There are three cooling channels symmetri- Qb = (2) cally distributed in the cold plate, with an interval of d6. The Vb radius of the semicircular VG is d7. where q is the total heat generation of the battery. I is the charging and discharging current of the battery. R is the ohmic internal resis- tance. EO is the open circuit voltage of the battery. T is the battery 2.2 Thermophysical Parameters. The LIB studied in this temperature. ∂Eo/∂T is the entropy heat coefficient. I 2R represents work is a rectangular battery. The size of a single battery is the joule heat generated during battery charging and discharging. 27 mm × 180 mm × 97 mm. The rated voltage of each single IT (∂Eo/∂T ) represents the reversible heat of the battery, which is battery is 3.7 V, and the capacity is 40 Ah. The cooling medium generated with the reversible isothermal operation of the battery. is water, and the cooling plate material through which it flows is alu- Qb is the heat generation rate of the battery, and Vb is the volume minum. Table 2 shows the thermal physical parameters of the of the battery. However, this heat generation model ignores the components of the cooling system of the LIB pack. These thermo- side reaction heat and polarization heat of the battery. Through physical parameters are considered constant values, regardless of experiments, Sato’s research shows that the heat released by the their effects on temperature or time [33,34]. battery is mainly divided into four parts: reaction heat, polarization heat, joule heat, and side reaction heat. 2.3 Heat Dissipation Model. The internal chemical reaction The main ways of heat transfer are heat conduction, heat convec- process of LIB is very complex, which leads to the complexity of tion, and heat radiation. When the lithium battery is charged and discharged, the electrolyte itself does not flow, so the heat convec- its internal heat generation. However, the heat generation of the battery is relatively uniform as a whole. Therefore, it is now a tion is not obvious. At the same time, considering that the normal operating temperature of a lithium battery is between −20°C and common practice to use Bernardi’s heat generation model to calcu- late battery heat generation. This model assumes that the heat 60°C , the thermal radiation is not significant and can be generation of the battery is stable and uniform ignored. Therefore, the main heat transfer mode of LIB is heat conduction. According to Eq. (1) and ohmic internal resistance measured by Table 1 Dimension of cold plate model lithium battery experiment, the heat generation rate of lithium battery at different charge–discharge rates can be obtained as d1 d2 d3 d4 d5 d6 d7 given in Table 3. The heat generation rate of the battery is input into the computa- Unit: mm 4 5.2 2.6 0.4 30 30 2 tional fluid dynamics (CFD) calculation model through a user- defined parameter. In this study, the discharge rate is set to 5C, Journal of Electrochemical Energy Conversion and Storage AUGUST 2024, Vol. 21 / 031003-3  Table 2 Thermophysical parameters of lithium battery pack cooling system materials Material Density (kg/m3) Specific heat capacity (J/(kgK)) Thermal conductivity (W/(mK)) Viscosity (kg/(ms)) Aluminum 2719 891 202.4 N/A Water 998.2 4128 0.6 1.003 × 10−3 Battery 2018 1282 2.7 N/A
   and the discharge time is 1200 s. It is assumed that the heat gener- ∂ρε μt ation of the battery is uniform. The heat transfer of the liquid + ∇ · (ρVε) = ∇ · μ + ∇ε ∂t σε cooling BTMS only considers heat conduction and heat convection. Because the thermal radiation is negligible at the operating temper- ε ε2 + C1ε (Gk + C3ε Gb ) − C2ε ρ + Sε Downloaded from http://asmedigitalcollection.asme.org/electrochemical/article-pdf/21/3/031003/7047499/jeecs_21_3_031003.pdf by Universita Padova user on 06 March 2024 (7) ature of the battery. k k where σk and σs are turbulent Prandtl number of k and ɛ, respec- tively; C1ɛ C2ɛ, C3ɛ are the model constants, Gk is the turbulent kinetic energy caused by mean velocity gradient, Gb is the turbulent 3 Numerical Model kinetic energy caused by buoyancy, Ym is the contribution of undu- 3.1 Computational Fluid Dynamics Model. During the lating expansion in compressible turbulence to overall dispersion working process, the heat generated by the battery pack is trans- velocity, and Sk and Sɛ are user-defined resource item. The turbu- ferred to the cooling plate through direct contact, and this part of lence viscosity (μt) depending on k, ɛ, and the coefficient Cμ, the heat is absorbed by the coolant in the cooling plate. Heat is which is defined as a constant value, is calculated by the following transferred between the battery pack and the cooling plate equation: through heat conduction. Due to the existence of a vortex gener- ator, the flow of fluid in the channel is usually turbulent, so the k2 μt = Cμ ρ (8) standard k–e turbulence model is used in this study. The ε standard k–e turbulence model with enhanced wall treatment is where C and μ are constant. a strong turbulence model, and the analytical solution of The ANSYS FLUENT was used in this study because of its flexibility turbulence is very complex and difficult. Therefore, continuity and availability. Starting from an initial condition, the solution and Navier–Stokes are used for numerical analysis of the flow strides toward a steady-state. Convergence was judged against the model. normalized continuity, momentum, and energy residuals and is Computational fluid dynamics model is solved by using the fol- considered converged when these residuals have been reduced to lowing RANS (Reynolds average Navier–Stokes) equation and 1 × 10−6. Reynolds average energy equation ∇·V=0 (3) 3.2 Boundary Conditions. Because the heat generated by the battery during discharge is variable, the solution of the model is transient. The battery is assumed to be fully discharged under the

∂V constant current mode with a discharge rate of 5 C, and the total ρ
= −∇P + (μ∇2 V + (V · ∇V)
− λ) (4) discharge time is 720 s. The inlet coolant temperature is set at ∂t 298.15 K. The heat exchange between battery and cold plate, and between cold plate and coolant is completed by temperature cou-
   ∂ρT
μ μ pling surface. There is no heat transfer at the battery boundary + ρV∇T = ∇ + t ∇T
(5) and the heat generated in the battery is directly transferred to the ∂t Pr Prt coolant. Gravity is not considered. The mass flow inlet and pressure outlet boundaries are used for the inlet and outlet of the coolant flow where V is the coolant velocity (m/s), ρ is the coolant density
is the average coolant velocity (m3/s), t is the time (s), in the mini-channels, respectively. The boundary condition at the (kg/m3), V inlet of the flow channel is set as the flow velocity of 0.1 m/s, P is the pressure (Pa), λ is the Reynolds stress gradient, T is the tem- and the outlet condition is a pressure outlet with a gauge pressure perature (K ), T
is the average temperature (K), μ is the viscosity of 0 Pa. For all the simulations, the initial temperature of the com- (Pa · s), μt is the turbulent viscosity (Pa · s), Pr is the Prandtl putational domains and the ambient temperature are assumed to be number, and Prt is the turbulent Prandtl number. 298.15 K. The transfer equation used in the ANSYS FLUENT analysis of the standard k–e model is defined as 3.3 Grid Independence Test. The thermal analysis of the
   ∂ρk μ entire model was done in ANSYS. The 3D modeling of the liquid + ∇ · (ρVk) = ∇ · μ + t ∇k + Gk + Gb − ρε + Ym + Sk cooling BTMS was done using the SPACECLAIM and the mesh ∂t σk module was used to divide the grids. Fluent is used to calculate (6) the 3D heat flow coupling model. The calculation setup used a stan- dard turbulence model for CFD analysis because of the complex shape of the channel. The semi-implicit method of pressure connec- Table 3 Battery heat generation rate under different charge and tion equation is used for velocity pressure coupling. discharge rates In order to ensure the simulation accuracy and save computing resources as much as possible, the grid independence test was Charge and discharge rates Heat generation rate (W/m3) carried out on the computational model. Grid independence test is 1C 5318 a common method to verify whether the model is reliable. When 2C 19,452 the dependent variables of the model (such as the maximum temper- 3C 42,400 ature or temperature change) remain stable, it indicates that 4C 74,163 the mesh number of the model is appropriate. The heat output set in this test is constant 100,000 W/m3, and the inlet flowrate is 031003-4 / Vol. 21, AUGUST 2024 Transactions of the ASME 0.1 m/s. The three channels of the cold plate flow in the same direc- tion. The number of grids from 1.43 × 106 to 2.59 × 106, the temper- ature, and the pressure drop changes are shown in Fig. 2. In each flow channel, 5 VGs with a radius of 2 mm are set at 30-mm intervals. As can be seen from Fig. 2(a), the number of grids reaches 2.06 × 106; after that the change in temperature and pressure drop is no longer obvious. The structured mesh is shown in Fig. 2(b). The grid in the battery domain are hexahedral grids, the cold plate and the channel domain are tetrahedral grids, and the channel domain is locally refined to promote the simulation accuracy. 4 Heat Dissipation Analysis of BTMS With Downloaded from http://asmedigitalcollection.asme.org/electrochemical/article-pdf/21/3/031003/7047499/jeecs_21_3_031003.pdf by Universita Padova user on 06 March 2024 Vortex Generators The following research is conducted under the condition that the Fig. 3 The shapes of semicircular_VG, triangular_VG, and heat generation rate of the battery is 5 C; that is, the discharge Trapezoidal_VG current is 100 A. The inlet water temperature is set at 298.15 K, and the flowrate is 0.1 m/s The initial temperature of the battery Table 4 Effect of different VG shape and cold plate is set to 298.15 K. All battery parameters and heat generation equations are as described before. Max temperature Average temperature Pressure VG shape (K) (K) (Pa) 4.1 Effect of Different Vortex Generator Shape. The Non 317.97 311.96 83.50 research of Wu and Tao showed that adding VGs in the flow Triangular 317.52 311.49 235.99 channel can effectively improve heat transfer efficiency. Trapezoidal 317.30 311.27 281.90 Semicircular 317.26 311.23 243.25 In this part, the influence of whether to add VGs and what kind of VGs is studied. On the premise of ensuring that the length, width, and height of the VG remain unchanged (Fig. 3), change the shape of the VG and set it as triangle, trapezoid, and semicircle, respectively. To explore the influence of different shapes of VGs on heat dissipation and pressure drop. Table 4 and Fig. 4 clearly show the difference in maximum temperature, average temperature, and pressure drop between non-VGs, triangular VGs, trapezoidal VGs, and semicircular VGs. Figure 5 shows the max temperature Fig. 4 Effect of different VG shapes variation of lithium batteries over time in different VG-type schemes. The following observations can be drawn from the data in Table 4. Obviously, no matter what kind of VGs is added, the heat dissipation efficiency will be improved, but the pressure drop will also be increased. A better vortex generator should have both lower temperature and lower pressure drop, so it is obvious that semicircular vortex generators are superior to trapezoidal vortex generators. However, compared to the triangular vortex generator, it is not sure which one is better. Considering that the triangular vortex generator may have a higher temperature due to a smaller contact area with the water flow, the length of the bottom edge of the triangle is revised from 4 mm to 6.28 mm (Fig. 6). The new simulation results shown in Table 5 indicate that the maximum temperature of the modified- triangular vortex generator reduces from 317.52 K to 317.29 K, and the pressure drop increases from 235.99 Pa to 293.1 Pa. Obvi- ously, the semicircular vortex generator is superior to the modified- Fig. 2 (a) Grid independence test and (b) structured grid and the triangular vortex generator. This means that to achieve the same local enlarged mesh heat dissipation efficiency, the triangular vortex generator requires Journal of Electrochemical Energy Conversion and Storage AUGUST 2024, Vol. 21 / 031003-5  Fig. 6 Triangular vortex generators with different bottom edges Downloaded from http://asmedigitalcollection.asme.org/electrochemical/article-pdf/21/3/031003/7047499/jeecs_21_3_031003.pdf by Universita Padova user on 06 March 2024 Table 5 Comparison between semicircular and modified-triangular VGs Max temperature Average Pressure VG shape (K) temperature (K) (PA) Fig. 5 Max temperature variations with different shapes of VGs Semicircular 317.26 311.23 243.25 Modified-triangular 317.29 311.29 293.10 a greater pressure drop. The final results indicate that different types of vortex generators can improve the heat dissipation efficiency of the cold plate, and compared to triangular and trapezoidal vortex 4.2 Effect of Inlet Mass Flowrate. In order to further studying generators, semicircular vortex generators pay a lower price in the effect of this scheme in the case of different inlet flowrates, the terms of pressure drop. flowrate is changed while other conditions remain unchanged. Here, Fig. 7 (a) Tm, (b) Ta, and (c) Pa variation with different flowrates 031003-6 / Vol. 21, AUGUST 2024 Transactions of the ASME  Table 6 Corresponding dimensions of runner number Runner number Height d2 Width d3 Gap width d4 VG radius d7 3 5.2 2.6 0.4 2 5 4 2 0.3 1.5 7 3.4 1.7 0.26 1.3 Table 7 Ta and Pa for different channel numbers Runner number Average temperature (K) Pressure (Pa) Fig. 9 Temperature distribution when (a) d6 = 30 mm and (b) d6 = 10 mm Downloaded from http://asmedigitalcollection.asme.org/electrochemical/article-pdf/21/3/031003/7047499/jeecs_21_3_031003.pdf by Universita Padova user on 06 March 2024 3 311.23 243.25 5 310.5 299.93 7 310.07 347.86 Table 8 Average temperature (Ta), max temperature (Tm), and temperature difference (TD) for different VGs positions only the conditions without VGs and semicircular VGs are com- Original plan VGs at middle VGs at inlet VGs at outlet pared. The maximum temperature, average temperature, and pres- Ta (K) 311.23 311.41 311.44 311.5 sure drop of the two are shown in Fig. 7. Tm (K) 317.26 317.45 317.87 316.9 When the flowrate in the figure is 0.2 m/s, the average tempera- TD (K) 16 16.2 17.2 15.4 ture of the non-VGs group is 309.7 K, the semicircular VGs group is 309.1 K, and the difference is 0.6 K. The temperature rising rel- ative to the initial temperature of 298.15 K is 11.25 K, and the per- centage of the difference relative to the temperature rise is 5.3. respectively, and the radius of VGs is 1.5 mm. When there are When the maximum flowrate is 0.025 m/s, the average temperature seven channels, the height and width of the flow channel are of the non-VG group is 326.2 K, the semicircular VG group is 3.4 mm and 1.7 mm, and the radius of VGs is 1.3 mm. 324.2 K, and the difference is 2 K. The temperature rising relative Table 7 shows the average temperature and pressure drop corre- to the initial temperature of 298.15 K is 27 K, and the percentage sponding to different number of channels, respectively. It can be of the difference relative to the temperature rise is 7.4. It can seen that the temperature decreases with the increase in the be seen that the scheme of adding VG has a better effect when number of channels, while the pressure drop increases. The the inlet velocity is low. average temperature of 7 channels is 310.07 K, which is 1.16 K lower than 311.23 K of 3 channels. At the same time, the pressure drop also increased from 243.25 Pa to 347.86 Pa. Figure 8 shows 4.3 Effect of Cooling Channel Number. In this study, the the temperature distribution under different numbers of flow total sectional area of the flow channel remains unchanged, and channels. the number of flow channels is changed from 3 to 5 and 7; i.e., the sizes of the flow channel and VG are reduced in proportion, and other conditions remain unchanged. The size parameters corre- 4.4 Effect of Vortex Generator Distribution. The previous sponding to different channel numbers are shown in Table 6. The research is based on the situation that the VGs are evenly distributed height and width of the five channels are 4 mm and 2 mm, in the flow channel; i.e., the VGs are symmetrically separated by Fig. 8 Temperature distributions of different number of channels: (a) 3 channels, (b) 5 chan- nels, and (c) 7 channels Journal of Electrochemical Energy Conversion and Storage AUGUST 2024, Vol. 21 / 031003-7  Obviously, concentrating the VGs near the outlet of the flow channel can effectively reduce the temperature differ- ence of the battery. This is of great significance to the study of battery temperature uniformity. 5 Conclusion Many studies on mini-channel liquid cooling BTMS have been investigated. However, few studies have applied mini-channels with VGs to BTMS. This work studies the heat transfer improve- ment of lithium-ion battery packs via a mini-channel liquid cooling plate with vortex generators. Through the comparison of the shape of VGs, inlet flowrate, number of channels, and the dis- Downloaded from http://asmedigitalcollection.asme.org/electrochemical/article-pdf/21/3/031003/7047499/jeecs_21_3_031003.pdf by Universita Padova user on 06 March 2024 tribution of VGs, the advantages of VG in improving the heat dis- sipation efficiency and temperature uniformity of liquid cooling Fig. 10 Temperature distributions for cold plate at different VGs locations: (a) VGs at inlet, (b) VGs at middle, and (c) VGs at outlet BTMS are demonstrated. (1) Adding VGs of different shapes in the mini-channels of liquid cooling BTMS can improve the heat dissipation effi- 30 mm in the flow channel. When we reduce this interval to 10 mm, ciency of the cold plate, among which the shape of semicir- the average temperature of the battery rises from 311.21 K to cular VGs is the best. When the temperature decreases by the 311.41 K, which means that the overall heat dissipation effect same magnitude, the pressure drop of the semicircular VGs is becomes worse. But the maximum temperature changes little. 15.89% lower than that of the trapezoidal VGs and 20.49% Figure 9 shows the temperature distribution of the battery. It can lower than that of the triangular VGs. be seen that the temperature distribution of the battery has (2) When the inlet flowrate is small, setting the VGs will greatly changed slightly, which may be beneficial to reduce the temperature improve the heat dissipation performance. Specifically, when difference of the battery. the inlet flowrate is 0.2 m/s and 0.025 m/s, the average tem- Based on this finding, the VGs with a spacing of 10 mm were perature will drop 0.6 K and 2 K, respectively. moved to the inlet and outlet of the flow channel as a whole, and (3) When the sectional area of the inlet is fixed, the heat dissipa- the results obtained after simulation are shown in Table 8 and tion effect is better when the inlet is divided into more chan- Fig. 10. Looking at the average temperature, the two schemes are nels. When the inlet is divided into three channels and seven 311.44 K and 311.5 K, respectively, which is no better than channels, the average temperature decreases by 1.16 K. 311.41 K in the middle distribution. However, it is worth noting (4) The temperature uniformity can be affected by changing the that from the distribution of the highest temperature, the outlet distribution position of the VGs. When the VGs are set near scheme of 316.9 K is nearly 1 K lower than the inlet scheme of the outlet of the flow channel, the temperature difference is 317.87 K. This means that the temperature difference of the 1.8 K less than that near the inlet. battery can be effectively reduced by placing the VGs near the outlet of the flow channel. The life safety and endurance of In the future, the main research direction is to find the optimal the pool group play a better role in ensuring the safety of EVs. solution for the size and distribution of the VGs, and the surrogate model method will also be used to find the optimal parameters of BTMS. 4.5 Discussion. In this study, a mini channel liquid cooling system is designed to improve the heat transfer and thermal unifor- mity for the LIB pack. Through simulation analysis and discussion, Acknowledgment the main conclusions of this work are as follows: This research is supported by the National Natural Science Foun- (1) Adding VGs in the mini channel can improve the heat dissi- dation of China under Contract No. 51975106, and Sichuan Science pation efficiency of the cold plate. Compared with the control and Technology Program under Contract No. 2020JDJQ0036. group without VGs, the average temperature of the ex- perimental group with triangle, trapezoid, and semicircle VGs decreased by 0.7 K, 0.69 K, and 0.73 K, respectively, Conflict of Interest while the pressure drop reached 293.1 Pa, 281.9 Pa, and 243.25 Pa. In general, the semicircular VGs have the best There are no conflicts of interest. performance. (2) The scheme of adding VGs designed can improve the heat dissipation effect by 5.3% when the inlet flowrate is Data Availability Statement 0.2 m/s, and by 7.4% when the inlet flowrate is 0.025 m/s, The datasets generated and supporting the findings of this article which is more obvious when the inlet flowrate is low. are obtainable from the corresponding author upon reasonable (3) On the premise that the total sectional area of the flow request. channel remains unchanged, the original three flow channels are scaled down to seven, the average temperature is reduced from 311.23 K to 310.07 K, but the corresponding pressure drop is also increased from 243.25 Pa to 347.86 Pa. At the References expense of a large amount of pressure drop, the heat dissipa- Li, Y. S., Garg, A., Shevya, S., Li, W., Gao, L., and Lam, J. S. L., 2022, “A Hybrid Convolutional Neural Network-Long Short Term Memory for tion effect is improved accordingly. 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