CN110729525A - An air-cooled battery thermal management system cooling channel wind speed acquisition method - Google Patents

Abstract

A method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system relates to the field of heat dissipation of lithium ion batteries. The present invention aims to solve the problems that the traditional method of obtaining the wind speed distribution in the battery thermal management system is complicated and the efficiency of obtaining the wind speed distribution is low. The present application establishes a flow resistance network model of an air-cooled lithium-ion battery thermal management system to quickly calculate the cooling air flow rate in each flow channel. It is used to obtain the wind speed of the cooling channel.

Description

An air-cooled battery thermal management system cooling channel wind speed acquisition method

technical field

The invention relates to a method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system. It belongs to the field of heat dissipation of lithium ion batteries.

Background technique

At present, energy is scarce and the environment is deteriorating day by day. Li-ion batteries have the advantages of high average output voltage, high charge and discharge efficiency, and environmental friendliness, making them widely concerned in different applications.

The safety and life problems of lithium-ion batteries due to heat generation in practical applications are very prominent. On the one hand, in the process of charging and discharging, the internal heat of the battery keeps accumulating and the temperature keeps rising. If it is not controlled, it may cause the thermal runaway of the lithium battery, and even the danger of flatulence, leakage, and even explosion. On the other hand, the aging speed of lithium-ion batteries is affected by temperature. When the temperature of each battery cell inside the battery pack is uneven, the battery cells will gradually have performance differences. According to the short board principle, this will eventually lead to a shortened battery pack life. . Therefore, it is necessary to analyze and design the thermal management system of lithium-ion battery.

The forced air convection cooling method is simple in structure and low in cost, and is widely used in battery thermal management systems. When designing an air-cooled battery thermal management system (BTMS), the finite element simulation analysis method can effectively obtain the airflow distribution. Typically, structural parameter optimization of BTMS requires adjustments during the optimization process, and hundreds or thousands of finite element simulation calculations should be performed to explore the thermal performance of each structural parameter. The traditional finite element simulation analysis method is no longer applicable due to its low computational efficiency, and it is necessary to simplify the wind speed distribution calculation of BTMS.

SUMMARY OF THE INVENTION

The present invention is to solve the problems that the traditional way of obtaining the wind speed distribution in the battery thermal management system is complicated and the efficiency of obtaining the wind speed distribution is low. A method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system is provided.

A method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system, the method comprising the following steps:

Step 1. Set an air outlet deflector and an air inlet deflector on the top and bottom of the lithium-ion battery array in the Z-type air-cooled battery thermal management system, respectively, and the air outlet deflector and the Z-type air-cooled battery thermal The included angle between the top surface of the management system is θ ₂ , and the included angle between the air inlet deflector and the bottom surface of the Z-type air-cooled battery thermal management system is θ ₁ , so that the top of each row of lithium-ion batteries is guided to the air outlet. A confluence channel is formed between the flow plates, a shunt channel is formed between the bottom of each column of lithium-ion batteries and the air inlet guide plate, and two cooling channels are formed on both sides of each column of lithium-ion batteries;

Step 2. The summation of the gas pressures in the confluence channel at the top of each row of lithium-ion batteries, the shunt channel at the bottom and the cooling channels on both sides to obtain the pressure sum, and the flow resistance network model is obtained by using the air flow conservation equation. The air flow conservation equation Including the air flow conservation equation in the interconnected shunt channel and the cooling channel and the air flow conservation equation in the interconnected confluence channel and the cooling channel;

According to the total length and width of the lithium-ion battery array, θ ₂ , and the distance between two adjacent rows of lithium-ion batteries, the cross-sectional area of each shunt channel is obtained; according to the cross-sectional area, the diameter of each shunt channel is obtained and the flow ratio of two adjacent shunt channels;

According to the total length and width of the lithium-ion battery array, the distance between two adjacent rows of lithium-ion batteries and θ ₁ , the cross-sectional area of each bus channel is obtained; according to the cross-sectional area, the diameter of each bus channel is obtained and the flow ratio of two adjacent confluence channels;

According to the total length and width of the lithium-ion battery array, and the distance between two adjacent rows of lithium-ion batteries, the cross-sectional area of each cooling channel is obtained; according to the cross-sectional area, the diameter of each cooling channel is obtained;

According to the cross-sectional area of each cooling channel and the cross-sectional area of each shunt channel, the flow ratio of each cooling channel and each shunt channel is obtained;

According to the cross-sectional area of each cooling channel and the cross-sectional area of each collecting channel, the flow ratio of each cooling channel and each collecting channel is obtained;

Step 3: According to the flow resistance network model, the diameter of each shunt channel, the flow ratio of two adjacent shunt channels, the diameter of each confluence channel, the flow ratio of two adjacent confluence channels, the diameter of each cooling channel, The flow ratio of each cooling channel and each split channel, and the flow ratio of each cooling channel and each confluence channel, to obtain the wind speed of each cooling channel.

Beneficial effects of the present invention:

The present application establishes a flow resistance network model of an air-cooled lithium-ion battery thermal management system to achieve rapid calculation of the cooling air flow rate in each channel. When the shape of the air-cooled BTMS is fixed, the flow velocity of each part of the air can be obtained through the flow resistance network model. This application not only ensures high calculation accuracy, but also greatly improves the calculation speed of the channel wind speed, laying a foundation for the structural optimization design of the air-cooled BTMS.

Description of drawings

Figure 1 is a three-dimensional structural diagram of a plurality of lithium-ion battery cells placed in a Z-type air-cooled battery thermal management system;

Figure 2 is a two-dimensional structural diagram of a plurality of lithium-ion battery cells placed in a Z-type air-cooled battery thermal management system;

Figure 3 is a schematic diagram of the flow resistance network model;

Figure 4(a) is the curve comparison of the air velocity in the cooling channel obtained by using the flow resistance network model and the finite element simulation software when the air velocity at the air inlet is 3m/s, and Figure 4(b) is the air velocity at the air inlet of 5m/s When the flow resistance network model and finite element simulation software are used to obtain the curve comparison diagram of the wind speed in the cooling channel;

Figure 5(a) is the error curve of the air velocity in the cooling channel obtained by using the flow resistance network model and the finite element simulation software when the air velocity at the air inlet is 3m/s. Figure 5(b) is the air velocity at the air inlet of 5m/s s, the flow resistance network model and the finite element simulation software are used to obtain the error curve of the wind speed in the cooling channel respectively;

Figure 6(a) is a comparison diagram of the air velocity in the cooling channel obtained by using the flow resistance network model and experiment when the air velocity at the air inlet is 3m/s, and Figure 6(b) is when the air velocity at the air inlet is 5m/s, using The flow resistance network model and the experiment respectively obtain the curve comparison chart of the wind speed in the cooling channel;

Figure 7(a) is the error curve of the air velocity in the cooling channel obtained by using the flow resistance network model and experiment when the air velocity at the air inlet is 3m/s, and Figure 7(b) is when the air velocity at the air inlet is 5m/s , using the flow resistance network model and the experiment to obtain the error curve of the wind speed in the cooling channel, respectively.

Detailed ways

Embodiment 1: The present embodiment will be described in detail with reference to FIGS. 1 to 3. A method for obtaining the wind speed of the cooling channel of an air-cooled battery thermal management system described in the present embodiment includes the following steps:

Step 1. Set an air outlet deflector and an air inlet deflector on the top and bottom of the lithium-ion battery array in the Z-type air-cooled battery thermal management system, respectively, and the air outlet deflector and the Z-type air-cooled battery thermal The included angle between the top surface of the management system is θ ₂ , and the included angle between the air inlet deflector and the bottom surface of the Z-type air-cooled battery thermal management system is θ ₁ , so that the top of each row of lithium-ion batteries is guided to the air outlet. A confluence channel is formed between the flow plates, a shunt channel is formed between the bottom of each column of lithium-ion batteries and the air inlet guide plate, and two cooling channels are formed on both sides of each column of lithium-ion batteries;

Step 2. The summation of the gas pressures in the confluence channel at the top of each row of lithium-ion batteries, the shunt channel at the bottom and the cooling channels on both sides to obtain the pressure sum, and the flow resistance network model is obtained by using the air flow conservation equation. The air flow conservation equation Including the air flow conservation equation in the interconnected shunt channel and the cooling channel and the air flow conservation equation in the interconnected confluence channel and the cooling channel;

According to the total length and width of the lithium-ion battery array, θ ₂ , and the distance between two adjacent rows of lithium-ion batteries, the cross-sectional area of each shunt channel is obtained; according to the cross-sectional area, the diameter of each shunt channel is obtained and the flow ratio of two adjacent shunt channels;

According to the total length and width of the lithium-ion battery array, the distance between two adjacent rows of lithium-ion batteries and θ ₁ , the cross-sectional area of each bus channel is obtained; according to the cross-sectional area, the diameter of each bus channel is obtained and the flow ratio of two adjacent confluence channels;

According to the total length and width of the lithium-ion battery array, and the distance between two adjacent rows of lithium-ion batteries, the cross-sectional area of each cooling channel is obtained; according to the cross-sectional area, the diameter of each cooling channel is obtained;

According to the cross-sectional area of each cooling channel and the cross-sectional area of each shunt channel, the flow ratio of each cooling channel and each shunt channel is obtained;

According to the cross-sectional area of each cooling channel and the cross-sectional area of each collecting channel, the flow ratio of each cooling channel and each collecting channel is obtained;

Step 3: According to the flow resistance network model, the diameter of each shunt channel, the flow ratio of two adjacent shunt channels, the diameter of each confluence channel, the flow ratio of two adjacent confluence channels, the diameter of each cooling channel, The flow ratio of each cooling channel and each split channel, and the flow ratio of each cooling channel and each confluence channel, to obtain the wind speed of each cooling channel.

In this embodiment, the present application takes an N×M square aluminum shell power lithium-ion battery pack and its Z-slot battery thermal management system as an example, as shown in FIG. 1 . The lithium-ion battery pack is placed in the Z-type air-cooled battery thermal management system,

Air flows into the cooling system from the air inlet and enters the cooling channel through the Divergence Plenum (DP for short). The heat of the battery cells is taken away by the air in the cooling channel (CC for short), and then the air is collected in the converging chamber (CP) and flows out from the air outlet.

Considering that the thermal management system of the lithium-ion battery composed of Z-shaped grooves is under ideal conditions, the air velocity at the air inlet is uniform, the inner wall of the Z-shaped groove is uniform, and the poles of each battery cell in the battery pack can be ignored. The three-dimensional air-cooled BTMS can It is equivalent to a two-dimensional air-cooled BTMS, as shown in Figure 2.

Figure 3 is a schematic diagram of the flow resistance network model, in which each box area represents the pressure difference of this part due to air flow, which is called flow resistance. This phenomenon is mainly due to the energy conversion of the air between its kinetic energy and static pressure when the airflow velocity changes, and due to energy losses, including irreversible losses due to friction between the air and rough channel walls and at some special locations Local energy loss due to air distribution and convergence. According to the relevant fluid mechanics theory, the wind speed is much lower than the sound speed in the actual working process of the lithium-ion battery, so air is considered as an incompressible Newtonian fluid. For the continuous flow process, according to the Bernoulli equation, Equation 1 and Equation 2 are obtained.

The lithium-ion battery array includes a plurality of cells arranged in a rectangular array. The spacing between two adjacent columns of cells may or may not be equal.

Embodiment 2: This embodiment further describes the method for calculating the wind speed of the cooling channel of an air-cooled battery thermal management system described in Embodiment 1. In this embodiment, in step 2, the specific process of obtaining the sum of pressures for:

According to Bernoulli's equation, the pressure P _DP,i of the ith branch channel and the pressure P _CP,i of the ith confluence channel are obtained as:

In the formula, P _DP,1 is the pressure of the first shunt channel, ρ _air is the air density, v _DP,i is the wind speed of the ith shunt channel, i=1 to n, n is the number of columns of lithium-ion batteries, ΔP _loss,DP,k is the total pressure difference of the k-th shunt channel, P _CP,1 P _CP,i is the pressure of the first confluence channel, v _CP,i is the wind speed of the i-th confluence channel, v _{CP, 1} is the wind speed of the first confluence channel, ΔP _{loss, CP,k} is the total pressure difference of the k-th confluence channel;

The wind flows from the i-1th split channel to the i-th cooling channel and the i-th confluence channel in turn. The pressure relationship between the i-1th split channel, the i-th cooling channel and the i-th confluence channel is:

In the formula, ΔP _loss,CC,i is the total pressure difference of the ith cooling channel, _vDP,i-1 is the wind speed of the ith-1th shunt channel, and _vDP,0 is the thermal management of the Z-type air-cooled battery The wind speed of the air inlet of the system;

According to Equation 1 to Equation 3, the sum of the pressures formed by the gas pressures in the top bus channel, bottom shunt channel and cooling channels on both sides of each column of lithium-ion batteries is obtained:

ΔP _loss,DP,i +ΔP _loss,CC,i+1 -ΔP _loss,CP,i -ΔP _loss,CC,i =0 Equation 4,

In the formula, ΔP _loss,DP,i is the total pressure difference of the ith shunt channel, ΔP _loss,CC,i+1 is the total pressure difference of the ith+1 cooling channel, ΔP _loss,CP,i is the ith The total pressure difference of the bus channels.

In this embodiment, Equation 4 is the main governing equation for forming the flow resistance network model, which is similar to Kirchhoff's voltage law in the circuit. As can be seen from Equation 4, the sum of the static differential pressures for each closed loop in Figure 3 is zero.

Embodiment 3: This embodiment further describes the method for calculating the wind speed of a cooling channel of an air-cooled battery thermal management system described in Embodiment 2. In this embodiment, the total pressure difference ΔP of the i-th shunt channel _loss,DP,i , the total pressure difference ΔP _loss,CC,i of the ith cooling channel and the total pressure difference ΔP _loss,CP,i of the ith confluence channel are determined by the local pressure difference ΔP _local and along the path of the corresponding channel. The pressure difference ΔP _friction is composed, and the formula is expressed as:

ΔP _loss = ΔP _local + ΔP _friction Formula 5,

In the formula,

λ _DP,i is the dimensionless friction constant of the ith shunt channel, λ _CP,i is the dimensionless friction constant of the ith confluence channel, λ _CC,i is the dimensionless friction constant of the ith cooling channel, l _{DP ,i} is the length of the i-th shunt channel, l _CP,i is the length of the ith-th confluence channel, l _CC,i is the length of the ith-th cooling channel, D _DP,i is the cross-sectional area of the ith-th shunt channel, etc. Efficiency is the diameter of the circular shunt channel after the area of the circular shunt channel, D _CP,i is the diameter of the circular shunt channel after the cross-sectional area of the i-th shunt channel is equivalent to the area of the circular shunt channel, D _CC,i is the diameter of the circular cooling channel after the cross-sectional area of the ith cooling channel is equivalent to the area of the circular cooling channel, ζ _DP,i is the local pressure difference coefficient between the ith branch channel and the i-1th branch channel, ζ _CP,i is the local pressure difference coefficient between the ith bus channel and the i-1th bus channel, ζ _DP,0→CC,1 is the air inlet of the Z-type air-cooled battery thermal management system and the first cooling channel The local pressure difference _{coefficient between} the The coefficient of local pressure difference between the cooling channel and the i-th confluence channel, v _DP,i-1 is the wind speed of the i-1th branch channel, v _DP,0 is the wind speed of the air inlet of the Z-type air-cooled battery thermal management system , v _CP,i is the wind speed of the ith confluence channel, v _DP,i is the wind speed of the ith shunt channel, and v _CC,i is the wind speed of the ith cooling channel.

Embodiment 4: This embodiment further describes the method for calculating the wind speed of a cooling channel of an air-cooled battery thermal management system described in Embodiment 3. In this embodiment, the i-th shunt channel and the i-1th The local differential pressure coefficient ζ _DP,i of each shunt channel is expressed as:

In the formula, p _DP,i is the flow ratio of the i-th shunt channel to the i-1 th shunt channel;

The local pressure difference coefficient ζ _{DP,i-1→CC,i} between the i-1th shunt channel and the i-th cooling channel is expressed as:

In the formula, p _{DP,i-1→CC,i} is the ratio of the flow rate of the i-1th cooling channel to the i-th split channel, ψ _{DP,i-1→CC,i} is the i-1th split channel and The ratio of the cross-sectional area of the i-th cooling channel, p _DP,0→CC,1 is the ratio of the air inlet of the Z-type air-cooled battery thermal management system to the flow rate of the first shunt channel, ψ _DP,0→CC,1 is The ratio of the air inlet of the Z-type air-cooled battery thermal management system to the cross-sectional area of the first cooling channel;

The local pressure difference coefficient ζ _CP,i of the ith confluence channel and the i-1 th confluence channel is expressed as:

ζ _CP,i =1-p ² _CP,i Formula 8,

In the formula, p _CP,i is the flow ratio between the ith confluence channel and the i-1 th confluence channel;

The local pressure difference coefficient ζ _CC,i→CP,i between the ith cooling channel and the ith confluence channel is expressed as:

ζ _CC,i→CP,i =p ² _CC,i→CP,i ψ ² _CC,i→CP,i −2p ² _CC,i→CP,i −1 Equation 9,

In the formula, p ² _CC,i→CP,i is the ratio of the flow of the ith cooling channel to the ith confluence channel, ψ _CC,i→CP,i is the cross section of the ith confluence channel and the ith cooling channel area ratio.

Embodiment 5: This embodiment further describes a method for calculating the wind speed of a cooling channel of an air-cooled battery thermal management system described in Embodiment 3. In this embodiment, the dimensionless friction constant of the i-th shunt channel is λ _DP,i , the dimensionless friction constant λ _CP,i of the ith confluence channel and the dimensionless friction constant λ _CC,i of the ith cooling channel are all expressed as:

where _Re is the local Reynolds number, _Re = ρDU/μ, D is the diameter of each channel, μ is the dynamic viscosity of air, and F is the shape correction factor.

Embodiment 6: This embodiment further describes the method for calculating the wind speed of a cooling channel in an air-cooled battery thermal management system described in Embodiment 3. In this embodiment, according to formula 11, the shunt channels that communicate with each other are obtained. The conservation equation with the air flow in the cooling channel is:

v _DP,i A _DP,i =v _DP,i+1 A _DP,i+1 +v _CC,i+1 A _CC,i+1 Equation 11,

In the formula, Q ₀ =v _DP,1 A _DP,1 , Q ₀ is the air flow at the air inlet, A _DP,i is the cross-sectional area of the i-th shunt channel, A _DP,i+1 is the i+1-th channel The cross-sectional area of the split channel, v _CC,i+1 is the wind speed of the i+1th cooling channel, v _DP,i+1 is the wind speed of the i+1th split channel,

According to Equation 12, the air flow conservation equation in the interconnected confluence channel and cooling channel is obtained as:

v _CP,i A _CP,i =v _CP ,i _-1 A _CP ,i _-1 +v _CC,i A _CC,i Equation 12,

In the formula, A _CP,i is the cross-sectional area of the ith confluence channel, A _CP,i-1 is the cross-sectional area of the i-1 th confluence channel, A _CC,i is the cross-sectional area of the ith cooling channel, A _CP,i-1 is the cross-sectional area of the i-1th cooling channel, v _CP,0 =0, A _CP,0 =0.

In this embodiment, considering that the cooled air is incompressible, the air flow rate is conserved at each air split point and collection point. Therefore, Equation 11 and Equation 12 can be obtained.

Equations 4-12 provide 3*(N+1) independent equations. Therefore, when the shape of the parallel air-cooled BTMS is fixed, the flow velocity of each part of the air can be obtained through the flow resistance network model. The magnitude of the local differential pressure coefficient ξ depends on the local geometry and flow state.

Embodiment 7: This embodiment further describes the method for calculating the wind speed of the cooling channel of the air-cooled battery thermal management system described in Embodiment 1. In this embodiment, in step 3, the total amount of the lithium-ion battery array is The length W _x is expressed as:

In the formula, N is the number of columns of lithium-ion batteries, lx is the length of each lithium-ion battery cell in each column of lithium-ion batteries, and d _{i is} the distance between two adjacent columns of lithium-ion batteries;

The total width W _y of the total length of the lithium-ion battery array is expressed as:

W _y =M× _ly +(M+1)× _dy Equation 14,

In the formula, M is the number of lithium-ion battery cells in each column of lithium-ion batteries, _ly is the width of each lithium-ion battery cell, and _dy is the distance between two adjacent columns of lithium-ion batteries.

In this embodiment, the length, width, and height of the lithium-ion battery cells are set as lx, _ly , and _lz , respectively, the number of the horizontal arrangement of the batteries _is N, the number of the vertical arrangement of the batteries is M, and the horizontal arrangement of the battery pack is The spacings are d ₁ , d ₂ , ..., d _i , ..., d _N , d _N+1 , and the longitudinal spacing of the battery pack is _dy , then the expressions of the total length W _x and the total width W _y of the lithium ion battery pack as shown in Equations 13 and 14, respectively.

Embodiment 8: This embodiment further describes the method for calculating the wind speed of a cooling channel of an air-cooled battery thermal management system described in Embodiment 7. In this embodiment, in step 2, the transverse direction of each shunt channel is The process of obtaining the cross-sectional area is:

The angle _θ1 between the air inlet deflector and the bottom surface of the Z-type air-cooled battery thermal management system is expressed as:

In the formula, w ₁ is the angle adjustment parameter of the air inlet deflector;

Bringing Equation 15 into Equation 16, the cross-sectional area A _DP,i of the shunt channel is obtained as:

The process of obtaining the cross-sectional area of each bus channel is:

The angle θ2 between the air outlet baffle and the top surface of the Z-type air _- cooled battery thermal management system is expressed as:

In the formula, w ₂ is the adjustment parameter of the angle of the confluence channel;

The cross-sectional area A _CP,i of the bus channel is expressed as:

The cross-sectional area A _CC,i of the cooling channel is expressed as:

A _{CC,i =} W _y ·di Equation 19.

In this embodiment, both the air inlet and the air outlet are provided with a deflector, the angles of the air inlet and the air outlet deflector are θ ₁ and θ ₂ respectively, and the angle adjustment parameters of the air inlet and the air outlet deflector are respectively w ₁ and w ₂ .

Embodiment 9: This embodiment further describes the method for calculating the wind speed of a cooling channel of an air-cooled battery thermal management system described in Embodiment 8. In this embodiment, the cross-sectional area A of the i-th shunt channel is _DP,i is equivalent to the area of the circular shunt channel, and the diameter D _DP,i of the equivalent circular shunt channel is expressed as:

The cross-sectional area A _CP,i of the ith confluence channel is equivalent to the area of the circular shunt channel, and the diameter D _CP,i of the equivalent circular shunt channel is expressed as:

The cross-sectional area A _CC,i of the i-th cooling channel is equivalent to the area of the circular shunt channel, and the diameter D _CC,i of the equivalent circular shunt channel is expressed as:

Embodiment 10: This embodiment further describes the method for calculating the wind speed of a cooling channel of an air-cooled battery thermal management system described in Embodiment 9. In this embodiment, according to the cross-sectional area of each cooling channel and the The cross-sectional area of each shunt channel yields the flow ratio p _{DP,i-1→CC,i} of each cooling channel and each shunt channel:

The ratio of the flow rate of the i-th cooling channel to the i-1-th split channel flow is expressed as:

In the formula, p _{DP,i-1→CC,i} is the ratio of the flow rate of the i-th cooling channel to the i-1th split channel;

According to the cross-sectional area of each cooling channel and the cross-sectional area of each collecting channel, the flow ratio p _CC,i→CP,i of each cooling channel and each collecting channel is obtained:

In the formula, p _CC,i→CP,i is the ratio of the flow rate of the ith cooling channel to the ith confluence channel;

The flow ratio p _DP,i of the ith branch channel and the i-1th branch channel is expressed as:

In the formula, when i=1, A _DP,0 represents the cross-sectional area of the air inlet.

The flow ratio p _CP,i of the ith confluence channel and the i-1 th confluence channel is expressed as:

Experimental verification:

This application verifies the validity and reliability of using the flow resistance network model to calculate the cooling channel wind speed of the air-cooled lithium-ion battery thermal management system from the perspectives of finite element simulation and experiment.

This application adopts an air-cooled BTMS structure device composed of a battery pack composed of 8 × 3 square aluminum shell power lithium-ion battery cells, and the specific parameters are shown in Table 1.

Table 1 Parameters of air-cooled BTMS structure device

The relevant parameters of the square aluminum shell ternary (materials are nickel, cobalt, manganese) lithium-ion battery cells are shown in Table 3-2.

Table 2 Basic battery parameters

The material properties of the air in the flow domain of the air-cooled battery thermal management system are shown in Table 3.

Table 3 Air material properties

Use simulation software to verify the accuracy of the flow resistance network model:

In this section, a simulation model of an air-cooled lithium-ion battery thermal management system is established in the COMSOL Multiphysics simulation software to verify the accuracy and reliability of the established flow resistance network model.

The geometric model of the battery pack established by the COMSOL Multiphysics simulation software ignores the influence of the battery cell pole and welding seat on the finite element simulation results.

Considering that the fluid part of the air-cooled lithium-ion battery thermal management system established in this application is relatively complex, a structured mesh division method is adopted, a free tetrahedral mesh element is used, and a refined mesh element size is selected. The battery cell part adopts the combination of free triangular mesh and sweep, and selects the conventional mesh unit size. Mesh the Li-Ion battery pack and the fluid section.

The comparison is made under the condition that the air-cooled BTMS device has a deflector, and the angle adjustment parameters w ₁ and w ₂ of the air inlet and air outlet deflector are both 10mm, and the arrangement spacing of each lithium-ion battery cell is 20mm. Figure 4 shows the comparison between the flow resistance network model and the finite element simulation software for the air velocity v _in of the tuyere, which are 3m/s and 5m/s respectively.

The error curves of the COMSOL Multiphysics simulation and the flow resistance network model are shown in Figure 5.

It can be seen from the figure that within the allowable error range, the flow resistance network model is relatively accurate in calculating the wind speed in the cooling channel.

Verify the accuracy of the flow resistance network model with an experimental setup:

Finally, the accuracy of the flow resistance network model is verified from the experimental point of view. The accuracy of the flow resistance network model is verified by an experimental device consisting of a Z-type air-cooled battery thermal management system, an air inlet device, an air speed tester, a single-phase fan speed regulator and a cooling channel air speed test hole.

The air-cooled BTMS has a Z-shaped slot, and the battery packs are arranged in an 8×3 arrangement with 8 strings and 3 parallels. The wiring should be as close to the wall as possible to reduce its influence on the air velocity distribution of the air-cooled BTMS cooling channel. The cooling air at the air inlet is provided by a fan, and the speed of the fan is controlled by a single-phase anemometer, and the air speed of the cooling channel is obtained by a thermal anemometer.

When the air-cooled BTMS device has a baffle, and the angle adjustment parameters w ₁ and w ₂ of the air inlet and outlet baffles are both 10 mm, and the arrangement spacing of each lithium-ion battery cell is 20 mm, the air velocity at the air inlet is The results obtained from the experiment and the flow resistance network model with v _in being 3m/s and 5m/s respectively for the wind speed in the cooling channel are shown in Figure 6 for comparison.

The error curve of the second set of experimental verification and the flow resistance network model is shown in Figure 7. It can be seen from the figure that the flow resistance network model is more accurate in calculating the wind speed in the cooling channel.

This application realizes the rapid calculation of the wind speed in the cooling channel of the air-cooled battery thermal management system by establishing a flow resistance network model. According to the device structure of the air-cooled BTMS, the finite element simulation fluid model of the air-cooled BTMS was established and the simulation analysis was carried out. The calculation time of the single finite element simulation software is more than 3h, while the calculation time of the single flow resistance network model is less than 1s. Compared with the traditional finite element simulation analysis method, under the premise of ensuring the calculation accuracy, the flow resistance network model can quickly calculate the wind speed in the air-cooled BTMS cooling channel. Finally, an experimental device platform was built to verify the feasibility and accuracy of the air-cooled BTMS cooling channel wind speed calculation method based on the flow resistance network model.

Claims (10)

1. A method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system, wherein the method comprises the following steps: Step 1. Set an air outlet deflector and an air inlet deflector on the top and bottom of the lithium-ion battery array in the Z-type air-cooled battery thermal management system, respectively, and the air outlet deflector and the Z-type air-cooled battery thermal The included angle between the top surface of the management system is θ ₂ , and the included angle between the air inlet deflector and the bottom surface of the Z-type air-cooled battery thermal management system is θ ₁ , so that the top of each row of lithium-ion batteries is guided to the air outlet. A confluence channel is formed between the flow plates, a shunt channel is formed between the bottom of each column of lithium-ion batteries and the air inlet guide plate, and two cooling channels are formed on both sides of each column of lithium-ion batteries; Step 2. The summation of the gas pressures in the confluence channel at the top of each row of lithium-ion batteries, the shunt channel at the bottom and the cooling channels on both sides to obtain the pressure sum, and the flow resistance network model is obtained by using the air flow conservation equation. The air flow conservation equation Including the air flow conservation equation in the interconnected shunt channel and the cooling channel and the air flow conservation equation in the interconnected confluence channel and the cooling channel; According to the total length and width of the lithium-ion battery array, θ ₂ , and the distance between two adjacent rows of lithium-ion batteries, the cross-sectional area of each shunt channel is obtained; according to the cross-sectional area, the diameter of each shunt channel is obtained and the flow ratio of two adjacent shunt channels; According to the total length and width of the lithium-ion battery array, the distance between two adjacent rows of lithium-ion batteries and θ ₁ , the cross-sectional area of each bus channel is obtained; according to the cross-sectional area, the diameter of each bus channel is obtained and the flow ratio of two adjacent confluence channels; According to the total length and width of the lithium-ion battery array and the distance between two adjacent rows of lithium-ion batteries, the cross-sectional area of each cooling channel is obtained; according to the cross-sectional area, the diameter of each cooling channel is obtained; According to the cross-sectional area of each cooling channel and the cross-sectional area of each shunt channel, the flow ratio of each cooling channel and each shunt channel is obtained; According to the cross-sectional area of each cooling channel and the cross-sectional area of each collecting channel, the flow ratio of each cooling channel and each collecting channel is obtained; Step 3: According to the flow resistance network model, the diameter of each shunt channel, the flow ratio of two adjacent shunt channels, the diameter of each confluence channel, the flow ratio of two adjacent confluence channels, the diameter of each cooling channel, The flow ratio of each cooling channel and each split channel, and the flow ratio of each cooling channel and each confluence channel, to obtain the wind speed of each cooling channel. 2. A method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system according to claim 1, wherein in step 2, the specific process for obtaining the sum of pressures is: According to Bernoulli's equation, the pressure P _DP,i of the ith branch channel and the pressure P _CP,i of the ith confluence channel are obtained as:

In the formula, P _DP,1 is the pressure of the first shunt channel, ρ _air is the air density, v _DP,i is the wind speed of the ith shunt channel, i=1 to n, n is the number of columns of lithium-ion batteries, ΔP _loss,DP,k is the total pressure difference of the k-th shunt channel, P _CP,1 P _CP,i is the pressure of the first confluence channel, v _CP,i is the wind speed of the i-th confluence channel, v _{CP, 1} is the wind speed of the first confluence channel, ΔP _{loss, CP,k} is the total pressure difference of the k-th confluence channel; The wind flows from the i-1th split channel to the i-th cooling channel and the i-th confluence channel in turn. The pressure relationship between the i-1th split channel, the i-th cooling channel and the i-th confluence channel is:

In the formula, ΔP _loss,CC,i is the total pressure difference of the ith cooling channel, _vDP,i-1 is the wind speed of the ith-1th shunt channel, and _vDP,0 is the thermal management of the Z-type air-cooled battery The wind speed at the air inlet of the system; According to Equation 1 to Equation 3, the sum of the pressures formed by the gas pressures in the top bus channel, bottom shunt channel and cooling channels on both sides of each column of lithium-ion batteries is obtained: ΔP _loss,DP,i +ΔP _loss,CC,i+1 -ΔP _loss,CP,i -ΔP _loss,CC,i =0 Equation 4, In the formula, ΔP _loss,DP,i is the total pressure difference of the ith shunt channel, ΔP _l oss,CC _,i+1 is the total pressure difference of the i+1th cooling channel, ΔP _loss,CP,i is the ith The total pressure difference of the i bus channels. 3. The method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system according to claim 2, wherein the total pressure difference ΔP _loss,DP,i of the i-th shunt channel and the total pressure of the i-th cooling channel The pressure difference ΔP _loss,CC,i and the total pressure difference ΔP _loss,CP,i of the ith confluence channel are both composed of the local pressure difference ΔP _local and the pressure difference ΔP _friction along the path of the corresponding channel, and the formula is expressed as: ΔP _loss = ΔP _local + ΔP _friction Formula 5, In the formula,

λ _DP,i is the dimensionless friction constant of the ith shunt channel, λ _CP,i is the dimensionless friction constant of the ith confluence channel, λ _CC,i is the dimensionless friction constant of the ith cooling channel, l _{DP ,i} is the length of the i-th shunt channel, l _CP,i is the length of the ith-th confluence channel, l _CC,i is the length of the ith-th cooling channel, D _DP,i is the cross-sectional area of the ith-th shunt channel, etc. Efficiency is the diameter of the circular shunt channel after the area of the circular shunt channel, D _CP,i is the diameter of the circular shunt channel after the cross-sectional area of the i-th shunt channel is equivalent to the area of the circular shunt channel, D _CC,i is the diameter of the circular cooling channel after the cross-sectional area of the ith cooling channel is equivalent to the area of the circular cooling channel, ζ _DP,i is the local pressure difference coefficient between the ith branch channel and the i-1th branch channel, ζ _CP,i is the local pressure difference coefficient between the ith bus channel and the i-1th bus channel, ζ _DP,0→CC,1 is the air inlet of the Z-type air-cooled battery thermal management system and the first cooling channel The local pressure difference coefficient between , ζ _{DP,i-1→CC,i} is the local pressure difference coefficient between the i-1th branch channel and the ith cooling channel, ζ _CC,i→CP,i is the ith The coefficient of local pressure difference between the cooling channel and the i-th confluence channel, v _DP,i-1 is the wind speed of the i-1th branch channel, v _DP,0 is the wind speed of the air inlet of the Z-type air-cooled battery thermal management system , v _CP,i is the wind speed of the i-th confluence channel, v _DP,i is the wind speed of the i-th split channel, and v _CC,i is the wind speed of the i-th cooling channel. 4. The method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system according to claim 3, wherein the local pressure difference coefficient ζ _{DP of} the i-th split channel and the i-1th split channel is represented by for: In the formula, p _DP,i is the flow ratio of the i-th shunt channel to the i-1 th shunt channel; The local pressure difference coefficient ζ _{DP,i-1→CC,i} between the i-1th shunt channel and the i-th cooling channel is expressed as:

In the formula, p _{DP,i-1→CC,i} is the ratio of the flow rate of the i-1th cooling channel to the i-th split channel, ψ _{DP,i-1→CC,i} is the i-1th split channel and The ratio of the cross-sectional area of the i-th cooling channel, p _DP,0→CC,1 is the ratio of the air inlet of the Z-type air-cooled battery thermal management system to the flow rate of the first shunt channel, ψ _DP,0→CC,1 is The ratio of the air inlet of the Z-type air-cooled battery thermal management system to the cross-sectional area of the first cooling channel; The local pressure difference coefficient ζ _CP,i of the ith confluence channel and the i-1 th confluence channel is expressed as: ζ _CP,i =1-p ² _CP,i Formula 8, In the formula, p _CP,i is the flow ratio between the ith confluence channel and the i-1 th confluence channel; The local pressure difference coefficient ζ _CC,i→CP,i between the ith cooling channel and the ith confluence channel is expressed as: ζ _CC,i→CP,i =p ² _CC,i→CP,i ψ ² _CC,i→CP,i −2p ² _CC,i→CP,i −1 Equation 9, In the formula, p ² _CC,i→CP,i is the ratio of the flow of the ith cooling channel to the ith confluence channel, ψ _CC,i→CP,i is the cross section of the ith confluence channel and the ith cooling channel area ratio. 5. The method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system according to claim 3, wherein the dimensionless friction constant λ _DP,i of the i-th shunt channel and the dimensionless of the i-th confluence channel The friction constant λ _CP,i and the dimensionless friction constant λ _CC,i of the ith cooling channel are both expressed as:

where _Re is the local Reynolds number, _Re = ρDU/μ, D is the diameter of each channel, μ is the dynamic viscosity of air, and F is the shape correction factor. 6. The method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system according to claim 3, wherein, according to formula 11, the air flow conservation equation in the interconnected shunt channel and the cooling channel is obtained as: v _DP,i A _DP,i =v _DP,i+1 A _DP,i+1 +v _CC,i+1 A _CC,i+1 Equation 11, In the formula, Q ₀ =v _DP,1 A _DP,1 , Q ₀ is the air flow at the air inlet, A _DP,i is the cross-sectional area of the i-th shunt channel, A _DP,i+1 is the i+1-th channel The cross-sectional area of the split channel, v _CC,i+1 is the wind speed of the i+1th cooling channel, v _DP,i+1 is the wind speed of the i+1th split channel, According to Equation 12, the air flow conservation equation in the interconnected confluence channel and cooling channel is obtained as: v _CP,i A _CP,i =v _CP,i-1 A _CP,i-1 +v _CC,i A _CC,i Equation 12, In the formula, A _CP,i is the cross-sectional area of the ith confluence channel, A _CP,i-1 is the cross-sectional area of the i-1 th confluence channel, A _CC,i is the cross-sectional area of the ith cooling channel, A _CP,i-1 is the cross-sectional area of the i-1th cooling channel, v _CP,0 =0, A _CP,0 =0. 7. The method for obtaining the wind speed of the cooling channel of an air-cooled battery thermal management system according to claim 1, wherein in step 3, the total length W _x of the lithium-ion battery array is expressed as:

In the formula, N is the number of columns of lithium-ion batteries, lx is the length of each lithium-ion battery cell in each column of lithium-ion batteries, and d _{i is} the distance between two adjacent columns of lithium-ion batteries; The total width W _y of the total length of the lithium-ion battery array is expressed as: W _y =M× _ly +(M+1)× _dy Equation 14, In the formula, M is the number of lithium-ion battery cells in each column of lithium-ion batteries, _ly is the width of each lithium-ion battery cell, and _dy is the distance between two adjacent columns of lithium-ion batteries. 8. The method for obtaining the wind speed of the cooling channel of an air-cooled battery thermal management system according to claim 7, wherein in step 2, the process of obtaining the cross-sectional area of each shunt channel is: The angle _θ1 between the air inlet deflector and the bottom surface of the Z-type air-cooled battery thermal management system is expressed as: In the formula, w ₁ is the angle adjustment parameter of the air inlet deflector; Bringing Equation 15 into Equation 16, the cross-sectional area A _DP,i of the shunt channel is obtained as:

The process of obtaining the cross-sectional area of each bus channel is: The angle θ2 between the air outlet baffle and the top surface of the Z-type air _- cooled battery thermal management system is expressed as:

In the formula, w ₂ is the adjustment parameter of the angle of the confluence channel; The cross-sectional area A _CP,i of the bus channel is expressed as:

The cross-sectional area A _CC,i of the cooling channel is expressed as: A _CC,i =W _y ·d _i Formula 19. 9. The method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system according to claim 8, wherein the cross-sectional area A _DP,i of the i-th shunt channel is equivalent to the area of a circular shunt channel, The diameter D _DP,i of the equivalent circular shunt channel is expressed as:

The cross-sectional area A _CP,i of the ith confluence channel is equivalent to the area of the circular shunt channel, and the diameter D _CP,i of the equivalent circular shunt channel is expressed as:

The cross-sectional area A _CC,i of the i-th cooling channel is equivalent to the area of the circular shunt channel, and the diameter D _CC,i of the equivalent circular shunt channel is expressed as: 10 . The method for obtaining the wind speed of a cooling channel of an air-cooled battery thermal management system according to claim 9 , wherein each cooling channel is obtained according to the cross-sectional area of each cooling channel and the cross-sectional area of each branch channel. 11 . With the flow ratio p _{DP,i-1→CC,i} of each branch channel: The ratio of the flow rate of the i-th cooling channel to the i-1-th split channel flow is expressed as:

In the formula, p _{DP,i-1→CC,i} is the ratio of the flow rate of the i-th cooling channel to the i-1th split channel; According to the cross-sectional area of each cooling channel and the cross-sectional area of each collecting channel, the flow ratio p _CC,i→CP,i of each cooling channel and each collecting channel is obtained:

In the formula, p _CC,i→CP,i is the ratio of the flow rate of the ith cooling channel to the ith confluence channel; The flow ratio p _DP,i of the ith branch channel and the i-1th branch channel is expressed as:

In the formula, when i=1, A _DP,0 represents the cross-sectional area of the air inlet. The flow ratio p _CP,i of the ith confluence channel and the i-1 th confluence channel is expressed as:

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