Method for simulating and controlling liquid inlet flow of whole-stack three-dimensional flow of flow battery through thermal coupling

Abstract

A method for simulating and controlling liquid inlet flow of a whole pile of three-dimensional flow of a flow battery through thermal coupling belongs to the technical field of energy storage of the flow battery, and comprises the following steps: S1, calculating the calorific value of each section according to the actual operation inspection voltage; s2, carrying out three-dimensional simulation calculation on heat flow coupling of the whole electric pile; s3, determining whether high and low temperature distribution in the electric pile meets requirements or not; and S4, applying the simulation flow to an electric pile operation strategy. According to the method, a flow-heat coupling mode is adopted to perform simulation calculation, a simplified heat transfer calculation method is provided, and compared with theoretical calculation of firstly solving a flow field and then performing heat transfer, the calculation mode considers real-time dynamic interaction of electrolyte flow and stack heat production, and is higher in precision and simpler and more convenient; according to the method disclosed by the invention, different flows can be set according to different electrolyte temperatures and different charge states so as to ensure that the battery is always in a safe and efficient charge-discharge temperature environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of liquid flow battery energy storage, and particularly relates to a method for controlling liquid inflow of three-dimensional flow-heat coupling simulation of a whole liquid flow battery stack. BACKGROUND

[0002] 1. CN 106920985 A "A liquid flow battery stack and a method for uniformly distributing electrolyte in each battery to improve battery performance"

[0003] 2. CN 116125285 A "Liquid flow battery performance prediction method based on uneven flow between single bodies"

[0004] 1. The first patent-approaching technology is that both use whole-stack fluid simulation methods.

[0005] 2. The second patent-approaching technology is that both guide the safe operation of the stack through the temperature field model.

[0006] 1. The above-mentioned technologies mostly use two-dimensional simplified models for temperature simulation, ignoring the specific details of the flow field and the differences between each section of the flow field, resulting in large flow field temperature prediction errors.

[0007] 2. The above-mentioned existing technology decouples flow and heat transfer for calculation, ignoring the energy bidirectional transfer generated thereby, resulting in possible low precision.

[0008] 3. The above-mentioned existing liquid flow battery system flow control strategy mostly uses fixed numerical values, lacking real-time flow adjustment strategies for different environments or stack operating conditions. SUMMARY

[0009] To solve the above-mentioned problems, the application proposes a method for controlling liquid inflow of three-dimensional flow-heat coupling simulation of a whole liquid flow battery stack, comprising the following steps:

[0010] S1. Calculate the heat generation of each section according to the actual operating patrol voltage.

[0011] S2. Perform three-dimensional simulation calculation of the whole stack heat flow coupling.

[0012] S3. Determine whether the high and low temperature distribution inside the stack meets the requirements.

[0013] S4. Apply the simulation flow to the stack operation strategy.

[0014] Further, in step S1, first, collect the patrol voltage of each section of the actual stack at different state of charge (SOC) and the corresponding open circuit voltage (OCV) of the whole stack, and calculate the heat generation of each section by formula (1):

[0015] P heat,cell =I·|V oc,cell-V cell | (1)

[0016] P heat,cell : single cell heat power;

[0017] I: single cell current;

[0018] V oc,cell : single cell open circuit voltage;

[0019] V cell : single cell inspection voltage.

[0020] Further, the step S2 comprises the following steps:

[0021] S21, establishing a whole stack fluid domain geometric model;

[0022] S22, defining vanadium electrolyte material properties;

[0023] S23, defining electrode heat source terms;

[0024] S24, defining boundary conditions;

[0025] S25, solving method;

[0026] S26, result viewing.

[0027] Further, the step S21 comprises the following steps:

[0028] Further, the step S22 comprises the following steps:

[0029] Further, the step S23 comprises the following steps:

[0030]

[0031] wherein, d f : electrode porous medium fiber diameter;

[0032] ε: electrode porosity;

[0033] K ck : Kozeny-Carman constant.

[0034] Further, in the step S24, the boundary conditions are defined: the inlet electrolyte flow rate and temperature setting are consistent with the actual situation; the outlet is set as a pressure outlet, which is standard atmospheric pressure; the stack performs radiation and convection heat transfer to the outside, and the external heat transfer amount is converted into a wall heat flux form, and the external heat transfer power is determined by measuring the difference between the actual heating power and the heat absorbed by the electrolyte, as shown in formulas (3-5), and the calculated external heat transfer power is set as the second type of wall heat transfer boundary condition of the stack wall, i.e. wall heat flux:

[0035] P loss = P heat -P electrolyte (3)

[0036] P heat = |V oc -V|·I (4)

[0037] P electrolyte = q m ·c p ·(T out -T in ) (5)

[0038] wherein P loss : total heat transfer power of the stack to the outside (radiation + convection);

[0039] P heat : actual heating power of the stack;

[0040] P electrolyte : heat absorbed by the electrolyte;

[0041] V oc : open-circuit voltage of the stack;

[0042] V: actual working voltage of the stack;

[0043] q m : mass flow rate of the electrolyte;

[0044] c p : specific heat capacity of the electrolyte;

[0045] T in : inlet temperature of the electrolyte;

[0046] T out : outlet temperature of the electrolyte.

[0047] Further, in the step S25, the solving method is: adopting SIMPLEC algorithm to perform iterative calculation on the continuity equation, momentum equation and energy equation, adopting second-order upwind discrete mode for the pressure term and energy term, setting the outlet average temperature as the convergence detection value, regarding the convergence when the residual curve and the outlet average temperature are stable, and the iteration step number is generally between 1000-5000.

[0048] Further, in the step S26, the result checking is: after the simulation solving is finished, checking the whole stack temperature distribution, determining the numerical values of each section and the whole stack maximum temperature, minimum temperature, average temperature, each section temperature average absolute deviation and the like for the next step judgment.

[0049] Further, in the step S3, based on the simulation results, it is determined whether the high and low temperature regions in the stack meet the operation requirements, if it is found that the temperature of part of the unit cells exceeds the specified range, the flow needs to be adjusted to perform a new round of simulation, and when the extreme value and average standard deviation of the stack temperature field meet the actual requirements, the simulation is stopped.

[0050] The beneficial effects of the present application are:

[0051] 1. The present application draws a three-dimensional stack model based on polyhedral or hexahedral grid, has accurate flow channel details, sets the electrode region as porous medium region and heating unit, and can accurately simulate the temperature field of each section in the stack compared with two-dimensional calculation, and the temperature field simulation error is ≤1℃ through actual measurement;

[0052] 2. The present application adopts flow-heat coupling mode for simulation calculation, proposes a simplified heat transfer calculation method, and compared with the method of first solving flow field and then performing heat transfer theoretical calculation, the real-time dynamic interaction of electrolyte flow and stack heat generation is considered, the precision is higher and the method is more simple;

[0053] 3. In actual operation, the stack working condition is complex and changeable, and the static flow strategy cannot guarantee the operation safety and charging and discharging efficiency of the stack, through the method of the present application, different flow can be set according to different electrolyte temperatures and different state of charge, so that the battery can always be in a safe and efficient charging and discharging temperature environment. In actual operation, the variable flow strategy can improve the overall energy efficiency of the stack by 1.3% compared with the constant flow strategy, and the comprehensive pump consumption is reduced by 8%. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 It is a flow chart of the flow control method of the flow battery stack based on flow-heat coupling simulation;

[0055] Figure 2 It is an initial stack temperature field cloud picture;

[0056] Figure 3 It is a stack temperature field cloud picture after adjusting the flow;

[0057] Figure 4 The average temperature broken line chart of each section of the battery stack;

[0058] Figure 5 The absolute deviation bar chart of the temperature of each section of the battery stack. DETAILED DESCRIPTION

[0059] In order to make the technical means adopted by the present application and the purpose easy to understand, the present application is further described below in combination with specific embodiments, a liquid flow battery whole stack three-dimensional flow-heat coupling simulation control liquid inflow method, as shown in the figure, comprising the following steps: Figure 1

[0060] S1, calculating the heat generation of each section according to the actual operation patrol voltage;

[0061] S2, whole battery heat flow coupling three-dimensional simulation calculation;

[0062] S3, determining whether the high and low temperature distribution inside the battery stack meets the requirements;

[0063] S4, applying the simulation flow to the battery stack operation strategy.

[0064] S1, calculating the heat generation of each section according to the actual operation patrol voltage:

[0065] (1) First, collect the patrol voltage of each section of the actual battery stack at different SOC (state of charge), especially at the end of charging and discharging (because the charging and discharging efficiency is low and the heat generation is large at this stage, generally select the interval: SOC≤20%; SOC≥80%), and the corresponding OCV (open circuit voltage) of the whole battery, calculate the heat generation of each section by formula (1):

[0066] P heat,cell =I·|V oc,cell -V cell | (1)

[0067] Where, P heat,cell : single battery heat generation power;

[0068] I: unit cell current;

[0069] V oc,cell : single open circuit voltage;

[0070] V cell : single patrol voltage.

[0071] S2, whole battery heat flow coupling three-dimensional simulation calculation:

[0072] S21, establish the whole stack fluid domain geometric model:

[0073] ​Based on the internal flow field of the stack to establish a three-dimensional model, ignore some small features that do not affect the calculation to reduce the difficulty of simulation, such as the positive and negative electrodes are the same structure, which can be regarded as the same model. Generally, polyhedral mesh or hexahedral mesh division method is used to reduce the number of meshes, and the total number of meshes is between 300W~1000W;

[0074] S22, define the material properties of vanadium electrolyte:

[0075] Including density, specific heat capacity, thermal conductivity, dynamic viscosity, etc. The above parameter values change with electrolyte concentration and temperature, and the temperature-dependent linear approximation constant needs to be determined by experimental test. If higher accuracy is required, a temperature-dependent polynomial fitting curve is used to represent it.

[0076] S23, define the electrode heat source term:

[0077] Set the reaction electrode area of each unit cell to be a porous area and a heat source area, input the electrode permeability, porosity and single cell heat power, and the heat power of each electrode can be approximated as half of the total heat power. The permeability is calculated as shown in formula (2):

[0078]

[0079] Where, d f : Electrode porous medium fiber diameter;

[0080] ε: Electrode porosity;

[0081] K ck : Kozeny-Carman constant.

[0082] S24, define the boundary conditions:

[0083] The inlet electrolyte flow rate and temperature are set to be consistent with the actual situation; the outlet is set to be a pressure outlet (generally standard atmospheric pressure); the stack exchanges heat with the outside by radiation and convection. To simplify the calculation, the external heat exchange amount is converted to a wall heat flux form. The external heat exchange power can be determined by measuring the difference between the actual heat power and the heat absorbed by the electrolyte, as shown in formulas (3-5). The calculated external heat exchange power is set as the second type of heat exchange boundary condition of the stack wall, that is, the wall heat flux.

[0084] P loss =P heat -P electrolyte (3)

[0085] P heat =|V oc -V|·I (4)

[0086] P electrolyte =qm ·c p ·(T out -T in ) (5)

[0087] wherein, P loss : total heat exchange power of the stack (radiation + convection) to the outside;

[0088] P heat : actual heat generation power of the stack;

[0089] P electrolyte : heat absorbed by the electrolyte;

[0090] V oc : open circuit voltage of the stack;

[0091] V: actual working voltage of the stack;

[0092] q m : mass flow rate of the electrolyte;

[0093] c p : specific heat capacity of the electrolyte;

[0094] T in : inlet temperature of the electrolyte;

[0095] T out : outlet temperature of the electrolyte;

[0096] S25, solving method

[0097] The SIMPLEC algorithm is used to iteratively calculate the continuity equation, momentum equation and energy equation, the second-order upwind discrete method is used for the pressure term and energy term, the outlet average temperature is set as the convergence detection value, and when the residual curve and the outlet average temperature are stable, it is considered to be converged, and the iteration step number is generally between 1000 and 5000.

[0098] S26, result viewing

[0099] After the simulation solving is completed, the temperature distribution of the whole stack is viewed, and the numerical values such as the highest temperature, the lowest temperature, the average temperature, the average absolute deviation of the temperature of each section and the whole stack are determined to be used for the next step of judgment.

[0100] S3, determining whether the high and low temperature distribution in the stack meets the requirements

[0101] The temperature of the electrolyte inside the stack is generally recommended to be between 10°C and 40°C. When the temperature of some of the cells is too low, the concentration polarization increases, and the reaction efficiency decreases. When the temperature of some of the cells is too high, the voltage difference between the cells increases, the side reactions increase, and the risk of thermal runaway increases. Based on the simulation results, it is determined whether the high and low temperature regions inside the stack meet the operation requirements. If it is found that the temperature of some of the cells exceeds the specified range, the flow rate needs to be adjusted to perform a new round of simulation. For example, when the temperature of a cell is too low, the flow rate needs to be appropriately reduced to increase the temperature of the cell. When the temperature of a cell is too high, the flow rate needs to be increased to reduce the temperature of the cell. When the extreme value and average standard deviation of the temperature field of the stack meet the actual requirements, the simulation is stopped.

[0102] S4, applying the simulated flow rate to the stack operation strategy

[0103] After the above cycle debugging, the most suitable flow rate under the working condition is determined, and the flow rate value is updated in the stack operation strategy, so that the stack can ensure that each cell is within a reasonable temperature range when operating to a certain state of charge, thereby improving the safety and energy efficiency of the system.

[0104] Figure 2 、 3 respectively, the stack temperature field cloud map before and after adjusting the flow rate according to the temperature, after adjusting the flow rate in the increasing flow rate mode, the high and low temperature intervals of the stack are shortened by about 50%, and the high temperature region is significantly reduced; Figure 4 To control the temperature of each cell of the stack before and after adjusting the flow rate, the temperature of each cell of the stack is reduced after adjusting the flow rate, and the temperature fluctuation is reduced; Figure 5 is the average absolute deviation of the temperature of each cell of the stack. It can be seen that the temperature inside the stack is more uniform after adjusting the flow rate, which is beneficial to the stable operation of the stack.

[0105] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can make equivalent replacements or changes to the technical solution and concept of the present application within the scope of the disclosed technology, which should be covered within the protection scope of the present application.

Claims

1. A method for controlling the liquid inlet flow rate of a flow battery stack using three-dimensional flow-thermal coupling simulation, characterized in that: The steps include: S1. Calculate the heat generation of each section based on the actual operating inspection voltage; S2. 3D simulation calculation of thermal-fluid coupling of the entire stack; S3. Determine whether the high and low temperature distribution inside the fuel cell stack meets the requirements; S4. Apply the simulated traffic to the stack operation strategy.

2. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 1, characterized in that: In step S1, the patrol voltage of each cell and the corresponding open circuit voltage (OCV) of the entire stack at different states of charge (SOC) of the actual stack are first collected, and the calorific value of each cell is calculated using formula (1): P heat,cell =I·|V oc,cell -V cell | (1) Among them, P heat,cell : Single battery heating power; I: current flowing through the unit cell; V oc,cell : Single-cell open circuit voltage; V cell : Single-section inspection voltage.

3. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 2, characterized in that: The step S2 includes the following steps: S21. Establishing a geometric model of the fluid domain of the entire stack; S22. Define the material properties of the vanadium electrolyte; S23. Define the electrode heating source term; S24. Define boundary conditions; S25, solution method; S26. Check the results.

4. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 3, characterized in that: In step S21, a geometric model of the fluid domain of the entire stack is established: a three-dimensional model is established based on the internal flow field of the stack, and some small geometric features that do not affect the calculation are ignored to reduce the difficulty of simulation. The positive and negative electrodes with the same structure are regarded as the same model; the meshing method is used for polyhedral meshing or hexahedral meshing to reduce the number of meshes, and the overall number of meshes is between 300W and 1000W.

5. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 4, characterized in that: In step S22, the material properties of the vanadium electrolyte are defined, including density, heat capacity at constant pressure, thermal conductivity, and dynamic viscosity. The values ​​of the above parameters vary with the electrolyte concentration and temperature. Temperature-dependent linear approximate constants need to be determined through experimental testing. If higher accuracy is required, a temperature-dependent polynomial fitting curve is used for characterization.

6. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 5, characterized in that: In step S23, the electrode heat source term is defined: the reaction electrode area of ​​each unit cell is set as a porous area and a heat source term area, and the electrode permeability, porosity and single cell heat power are input. The heat power of each electrode is approximately half the overall heat power. The permeability is calculated as shown in formula (2): Among them, d f : diameter of electrode porous medium fiber; ε: electrode porosity; K ck : Kozeny-Carman constant.

7. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 6, characterized in that: In step S24, boundary conditions are defined: the flow rate and temperature of the inlet electrolyte are set to be consistent with the actual situation; The outlet is set as a pressure outlet with standard atmospheric pressure. The stack performs radiation heat exchange and convection heat exchange to the outside, converting the external heat exchange amount into the form of wall heat flux. The external heat exchange power is determined by measuring the difference between the actual heat generation power and the heat absorbed by the electrolyte, as shown in formulas (3-5). The calculated external heat exchange power is set as the second type of heat exchange boundary condition of the stack wall, that is, the wall heat flux: P loss =P heat -P electrolyte (3) P heat =|V oc -V|·I (4) P electrolyte =q m ·c p ·(T out -T in ) (5) Among them, P loss : Total external heat transfer power of the stack (radiation + convection); P heat : actual heating power of the stack; P electrolyte : The electrolyte absorbs heat; V oc : stack open circuit voltage; V: actual working voltage of the stack; q m : electrolyte mass flow rate; c p : Heat capacity of electrolyte at constant pressure; T in : electrolyte inlet temperature; T out : Electrolyte outlet temperature.

8. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 7, characterized in that: In step S25, the solution method is as follows: the continuity equation, momentum equation, and energy equation are iteratively calculated using the SIMPLEC algorithm, the pressure term and the energy term are discretized using a second-order upwind method, the outlet average temperature is set as the convergence detection value, and convergence is considered when the residual curve and the outlet average temperature are stable. The number of iteration steps is generally between 1000 and 5000.

9. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 8, characterized in that: In step S26, the results are checked: after the simulation solution is completed, the temperature distribution of the entire stack is checked to determine the maximum temperature, minimum temperature, average temperature, average absolute deviation of the temperature of each section and the entire stack, etc., for the next step of judgment.

10. The method for controlling liquid inlet flow rate by three-dimensional flow-thermal coupling simulation of a whole flow battery stack according to claim 9, characterized in that: In step S3, based on the above simulation results, it is determined whether the high and low temperature areas inside the fuel cell stack meet the operating requirements. If it is found that the temperature of some unit cells exceeds the specified range, the flow rate needs to be adjusted and a new round of simulation is carried out. The simulation is stopped when the extreme value and average standard deviation of the fuel cell temperature field meet the actual requirements.

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