Method for calculating heat exchange performance of oil cooler of automobile electric drive system

Abstract

The invention discloses a method for calculating the heat exchange performance of an oil cooler of an automobile electric drive system. The method comprises the following steps: creating a three-dimensional model of the oil cooler; obtaining 1D model parameters; creating a local heat exchange unit three-dimensional model; simplifying the CFD simulation model; determining a physical model and a turbulence model; calculating the heat exchange amount of the local heat exchange unit; fitting a Nu calculation formula; establishing an oil cooler 1D model; and calculating the total heat exchange amount of the oil cooler. The method has the following positive effects that through establishment of the local heat exchange unit CFD simulation model and the oil cooler 1D model, rapid iteration and optimization of oil cooler design are achieved, repeated sample piece trial-manufacturing and testing are avoided, and the development period is shortened; through the combination of the three-dimensional model and the 1D model parameters and the detailed physical and turbulent flow models, the calculation accuracy of the heat exchange performance of the oil cooler is improved. And self-definition of physical property parameters of various working media is supported, so that the model is suitable for different types of cooling liquid and oil products.

Description

Technical Field

[0001] The present invention relates to the technical field of automotive electric drive system components, and particularly to a method for calculating the heat transfer performance of an oil cooler in an automotive electric drive system. Background Art

[0002] During the operation of the drive motor and its controller in new energy vehicles, significant heat is generated, which not only affects the working efficiency of the motor but also may threaten the safety and lifespan of the system. To solve this problem, an oil cooler is introduced as a key component for heat exchange between the motor cooling circuit and the battery cooling circuit to ensure the effective cooling of the electric drive system. The oil cooler not only helps dissipate heat in high-temperature environments but also transfers excess heat to parts that need heating, such as the vehicle interior or the battery pack, in low-temperature environments, thereby optimizing the vehicle's thermal management system.

[0003] Currently, the design of oil coolers is mostly based on experience and repeated verification, and a 1D model is established by combining the basic principles of fluid dynamics and heat transfer. However, this method is difficult to ensure the optimization of the design. In existing technical literature, the parameters required for the 1D model are usually obtained by conducting heat transfer amount tests on oil coolers multiple times. This not only requires a large number of heat transfer amount test results of different oil coolers but also increases the difficulty and cost of design optimization.

[0004] Computational Fluid Dynamics (CFD) analysis provides precise fluid flow and heat transfer simulation means for oil cooler design, especially showing significant advantages when dealing with complex geometric structures. However, simplified modeling methods are commonly used in the prior art due to computational resource limitations. In a method for designing a wide-channel plate heat exchanger and a particle swarm optimization structure of the heat exchanger (CN110160380A), 25 groups of single-layer heat exchange plate structure parameters are generated by the orthogonal test method, numerical simulation is carried out on the single-layer channel based on the Fluent software, and a correlation model between the Nusselt number and the pressure drop is established. Although this typical method improves the design efficiency of the single-layer structure through parameter optimization, its essence still belongs to the hierarchical independent simulation technology.

[0005] There is a significant defect in the prior art: the simulation of the single-layer channel cannot reflect the thermal-fluid coupling effect between the flow channels in the actual multi-layer structure, resulting in a large prediction error in the overall heat transfer amount. This is the core technical problem that the present invention needs to solve: how to construct a CFD simulation model that takes into account both the multi-layer coupling effect and the computational efficiency under limited computational resources to achieve accurate prediction of the overall heat transfer performance of the oil cooler. Summary of the Invention

[0006] The present invention establishes a three-dimensional model based on the geometric parameters of the oil cooler, and calculates 1D model parameters such as the heat transfer area, fluid volume, and flow cross-sectional area of the oil cooler. Considering the temperature characteristics of the coolant and engine oil in the oil cooler, a CFD simulation model of the local heat transfer unit with general boundary conditions is established. By calculating the heat transfer amount of the local heat transfer unit under different boundary conditions, the calculation formula of the Nusselt number (Nu) is fitted. Using the 1D model parameters and the Nu calculation formula, a 1D model of the oil cooler is established using 1D simulation software, which can calculate the heat transfer performance of the oil cooler under different working conditions and provide a reference basis for the structural optimization of the oil cooler.

[0007] The present invention is implemented by at least one of the following technical solutions.

[0008] A method for calculating the heat transfer performance of an oil cooler for an automotive electric drive system, characterized by comprising the following steps:

[0009] (1) Construct a three-dimensional model of the oil cooler using modeling software according to the actual geometric dimensions and structural characteristics of the oil cooler;

[0010] (2) Measure and extract the key 1D model parameters of the oil cooler from the three-dimensional model of the oil cooler;

[0011] (3) Based on the spacing and pitch of the fins on the oil side and liquid side of the oil cooler, establish a three-dimensional model of the local heat transfer unit, and the three-dimensional model of the local heat transfer unit includes a single-layer oil-side liquid, a single-layer liquid-side liquid, and a partition fin model;

[0012] (4) Simplify the three-dimensional model of the local heat transfer unit to obtain a model suitable for computational fluid dynamics simulation;

[0013] (5) Adopt a constant physical property model for the partition and fins, introduce a polynomial function to describe the relationship between the physical properties and temperature for the engine oil and coolant, and calculate the flow in the fluid domain as well as the changes in the physical properties and temperature distribution in the fluid domain;

[0014] (6) According to the working flow rate and flow cross-sectional area during the actual operation of the oil cooler, calculate the mass flux at the inlets on both sides of the local heat transfer unit, and calculate the heat transfer amount through numerical simulation;

[0015] (7) Based on the calculated Reynolds number, Prandtl number, Nusselt number, and j factor, obtain the coefficients in the Nusselt number calculation formula through data fitting;

[0016] (8) Use the non-phase change heat exchanger component in the 1D analysis software, and input relevant parameters into the 1D analysis software to construct a 1D model of the oil cooler;

[0017] (9) Iteratively optimize the design of the oil cooler. If the total heat transfer amount of the oil cooler calculated by the 1D model does not meet the expectation, adjust the geometric parameters of the oil cooler until the design goal is satisfied.

[0018] Furthermore, in step (1), the actual geometric dimensions of the oil cooler include the length, width, inlet and outlet positions and number of layers of the oil-side and liquid-side flow channels, and the spacing, pitch, height, thickness and inclination of the fins.

[0019] Furthermore, in step (2), the key 1D model parameters of the oil cooler include the characteristic heat exchange length of the oil side and the liquid side, the convection heat transfer area, the fluid volume, the flow cross-sectional area, and the total mass of the partition and the fin, among which the characteristic heat exchange length is used to calculate the hydraulic diameter, and the flow cross-sectional area selects the minimum cross-section close to the center of the flow channel.

[0020] Furthermore, in step (3), based on the spacing and pitch of the fins on the oil side and liquid side of the oil cooler, a common multiple of the fin spacing is selected as the length standard of the local heat exchange unit, and a common multiple of the fin pitch is selected as the width standard of the local heat exchange unit. Based on this standard, a baffle fin model containing a single layer of oil-side liquid and a single layer of liquid-side liquid is established. The flow area including the baffle fin is extracted from the baffle fin model, and the flow areas upstream and downstream of the inlet and outlet are considered at the same time to construct a complete flow area model. Finally, by stretching the inlet and outlet planes of the flow area model, it is ensured that the model can accurately reflect the actual situation of the fluid in and out. Furthermore, in step (4), symmetric boundary conditions are used to describe the flow field distribution on both sides of the oil side and liquid side channels, and periodic boundary conditions are used to simulate the periodic changes in fluid temperature.

[0021] Furthermore, in step (4), the core area of the fluid domain uses polyhedral grid units, the boundary layer area uses prismatic layer grid units; and the solid domain uses cutter grid units.

[0022] Furthermore, in step (5), a constant physical property model is used to calculate the temperature distribution of the solid domain, a shear stress transport (SST) k-ω turbulence model is used to calculate the flow of the fluid domain, and a temperature polynomial function is used to accurately describe the physical property changes and temperature distribution of the fluid domain.

[0023] Furthermore, in step (6), the mass flux at the inlets on both sides of the local heat exchange unit is calculated by dividing the mass flow rate of the single-layer flow channel of the oil cooler by the cross-sectional area of the flow channel, and the inlet temperature is set according to the specific regional position represented by the local heat exchange unit.

[0024] Furthermore, in step (7), the calculation formula of the Reynolds number Re under different working conditions is obtained based on the fitted j factor j=aRe b-1 , and obtain the coefficients a and b of the Nusselt number calculation formula.

[0025] Furthermore, in step (8), if the physical property parameters of the required liquid are not preset in the 1D analysis software, the required liquid is defined by importing a text file containing the physical property parameters at different temperatures, including the following steps:

[0026] Step 1: Prepare the physical property parameter file: Create a text parameter file that lists the key physical property parameters of the liquid at different temperatures, such as density, specific heat capacity, dynamic viscosity, and thermal conductivity;

[0027] Step 2: Import the physical property parameter file: In the 1D analysis software, find the corresponding option or function and import the parameter file from step 1 into the software to ensure that the software can recognize and use these parameters;

[0028] Step 3: Set liquid parameters: In the phase-change heat exchanger assembly, correctly set the parameters of the liquid on both sides, including selecting the correct liquid type, i.e. the imported liquid, and specifying the corresponding inlet flow rate and temperature.

[0029] Compared with the existing technology, the beneficial effects of the present invention are:

[0030] (1) By establishing a CFD simulation model of the local heat exchange unit and a 1D model of the oil cooler, rapid iteration and optimization of the oil cooler design were achieved, avoiding repeated prototype production and testing, and shortening the development cycle.

[0031] (2) The accuracy of the oil cooler heat transfer performance calculation is improved by combining 3D and 1D model parameters, as well as detailed physical and turbulence models. The model supports customization of physical parameters for multiple working fluids, making it suitable for different types of coolants and oils. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart for calculating the heat exchange performance of an oil cooler according to an embodiment of the present invention;

[0033] Figure 2 Schematic diagram of fin structure parameters in an embodiment of the present invention;

[0034] Figure 3 2. It is a schematic diagram of a local heat exchange unit model in an embodiment of the present invention;

[0035] Figure 4 is a schematic diagram of a CFD model grid in an embodiment of the present invention;

[0036] Figure 5a : is a fitted curve diagram of the oil j factor versus Re in an embodiment of the present invention;

[0037] Figure 5b 3 is a fitted coolant j factor versus Re curve in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions and advantages of the present invention clearer and more definite, the following further describes the present invention in detail with reference to the accompanying drawings and by way of examples.

[0039] As Figure 1 shown, a method for calculating the heat exchange performance of an oil cooler for an automotive electric drive system provided in this embodiment includes the following implementation steps:

[0040] Step 1, create a 3D model of the oil cooler: First, based on the actual geometric dimensions and structural characteristics of the oil cooler, use professional modeling software to construct its 3D model.

[0041] In this embodiment, based on the actual geometric dimensions and structural characteristics of the oil cooler, the Siemens NX modeling software is used to construct the 3D model of the oil cooler. During this process, it is necessary to determine the length and width of the internal flow channels of the oil cooler, and design the positions of the inlets and outlets accordingly to ensure the accuracy and practicability of the model. Then, separately establish the 3D digital models of a layer of partition plates and a layer of fins, and then use the array replication function of the software to replicate the required number of partition plates and fins according to actual needs. Finally, assemble these components together to form a complete 3D model of the oil cooler.

[0042] The actual geometric dimensions of the oil cooler mainly include the following aspects: the length, width, inlet and outlet positions and numbers of the oil side and liquid side flow channels; the spacing S, pitch L, height H, thickness t p and inclination angle θ of the fins, as Figure 2 shown. When actually arranging the oil side and liquid side interfaces, a certain margin is usually reserved around the interfaces to ensure the convenience and sealing of installation. Therefore, the outer shape length of the oil cooler not only depends on the length of the flow channels, but also needs to add the part of the interface margin.

[0043] Step 2, obtain the 1D model parameters: From the constructed 3D model, accurately measure and extract the key 1D model parameters of the oil cooler, including but not limited to the characteristic heat transfer lengths (L c ) of the oil side and liquid side, convective heat transfer area (A), fluid volume (V), flow cross-sectional area (A c) and the total mass (M) of the partition and fins. Among them, the characteristic heat transfer length is obtained by measuring the distance between the upper and lower planes inside the fins. The characteristic heat transfer length is mainly used to calculate the hydraulic diameter, which is very important for determining the flow characteristics of the fluid in the flow channel; the convective heat transfer area is composed of the surface area of the fins perpendicular to the partition plus the areas of the upper and lower partitions; the fluid volume refers to the total volume of the extracted flow channel area; the flow cross-sectional area is the smallest cross-sectional dimension in the flow channel area model. When measuring the flow cross-sectional area, the smallest cross-section near the center of the flow channel is selected because the flow characteristics at the center position can better represent the average condition in the entire flow channel, thereby improving the accuracy of the calculation; while the total mass of the partition fins is obtained by calculating the sum of the volumes of all fins and partitions and multiplying by the density of the aluminum material. In some embodiments of the present invention, the parameter measurement results are shown in Table 1. The accurate measurement of this series of parameters is crucial for the subsequent heat transfer performance analysis and can effectively improve the accuracy of the calculation results.

[0044] Table 1 Measurement Results of Oil Cooler 1D Model Parameters

[0045]

[0046] (3) Create a three-dimensional model of the local heat transfer unit: Based on the specific spacing and pitch of the fins on the oil side and liquid side of the oil cooler, select the least common multiple of the two as the length and width standards of the local heat transfer unit. In some embodiments of the present invention, the fin spacing on the oil side and liquid side is 4 mm and 9 mm, and the fin pitch is 1.4 mm and 2 mm. Therefore, the length and width of the local heat transfer unit are 36 mm and 7 mm. Establish a partition fin model containing a single layer of oil-side liquid and a single layer of liquid-side liquid according to this standard. Further, extract the flow region including the partition fins from this model, and at the same time consider the flow regions of a certain length upstream and downstream of the inlet and outlet to construct a complete flow region model. Finally, by stretching the inlet and outlet planes of the flow region model, ensure that the model can accurately reflect the real situation of fluid inlet and outlet, as Figure 3 shown.

[0047] In step (3), the design of the local heat transfer unit aims to represent the general situation of heat transfer between two layers of liquid in different regions of the oil cooler. When stretching the inlet and outlet planes of the flow region model, the stretching length is set to more than 10 times the hydraulic diameter. Such a design can ensure that the flow at the inlet and outlet has fully developed, avoiding the influence of inlet and outlet effects on the internal heat transfer performance, so that the simulation results of the local heat transfer unit are closer to the actual situation. In this way, the heat transfer process inside the oil cooler can be effectively simulated, providing a reliable basis for subsequent performance optimization.

[0048] (4) Simplify the CFD simulation model: Based on the above three-dimensional model of the local heat exchange unit, a model suitable for computational fluid dynamics (CFD) simulation is further simplified, as shown in Figure 4 . The computational domain of this model not only includes the solid sub-domain (i.e., the partition fin model), but also covers the fluid sub-domain (i.e., the flow region model of engine oil and coolant). To more realistically simulate the flow field distribution in the local heat exchange unit and the heat transfer of the plate fins, symmetric boundary conditions are used in the CFD simulation software Star-CCM+ to describe the flow field distribution on both sides of the channel. In addition, by setting periodic boundary conditions, the periodic variation of the fluid temperature between different layers can be effectively simulated, as well as the process of how heat is transferred along the plate fins from the high-temperature region to the low-temperature region. In the local heat exchange unit, polyhedral mesh elements are used in the core region of the fluid domain to ensure the calculation accuracy, while prism layer mesh elements are used in the boundary layer region to enhance the analytical ability of the boundary layer; the solid domain is mainly composed of cut cell mesh elements to adapt to the complex geometry and ensure the high accuracy and reliability of the entire model. In some embodiments of the present invention, the average mesh size of the core flow region is 0.2 mm, and the number of prism layers is set to 10 layers with a thickness of 0.2 mm.

[0049] (5) Determine the physical model and turbulence model: Aluminum is selected as the material for both the partition and the fins. Given that the physical properties of aluminum are relatively stable within the experimental temperature range, a constant density and thermal conductivity model is used in Star-CCM+ to calculate the temperature distribution of the partition and the fins. In some embodiments of the present invention, the density of aluminum is 2.73 g / cm 3 , and the thermal conductivity is 237 W / (m-K). However, for engine oil and coolant, their physical properties (such as viscosity, density, etc.) change significantly with temperature. According to the viscosity, density, etc. values at different temperatures, temperature polynomial functions of the physical property parameters of the coolant and engine oil can be fitted. Using polynomial functions to accurately describe the relationship between these physical properties and temperature can improve the calculation accuracy. In some embodiments of the present invention, 50% ethylene glycol aqueous solution is used as the coolant, and 0W-30 engine oil is used as the engine oil. Their key physical property parameters are shown in Tables 2 and 3. Given that the cooling oil and coolant exhibit turbulent characteristics at low Reynolds numbers when flowing through the oil cooler, a turbulence model suitable for low Reynolds number conditions is specifically selected. Specifically, the shear stress transport (SST) k-ω turbulence model is selected in Star-CCM+. This model can better handle the turbulent effects in the near-wall region. Especially when dealing with the case of low y+ values (i.e., the fluid layer close to the wall), the SST k-ω model can provide more accurate wall treatment and turbulence prediction, thus ensuring the reliability and accuracy of the simulation results. In this way, not only can the flow state of the fluid inside the oil cooler be accurately simulated, but also the heat transfer efficiency of the oil cooler can be accurately evaluated.

[0050] Table 2 Physical Property Parameters of 50% Ethylene Glycol Aqueous Solution

[0051]

[0052] Table 3 Physical Property Parameters of 0W-30 Engine Oil

[0053]

[0054]

[0055] (6) Calculate the heat transfer amount of the local heat exchange unit: First, according to the working flow rate during the actual operation of the oil cooler and the previously determined flow cross-sectional area, calculate the mass flux at the inlets on both sides of the local heat exchange unit. The calculation method of the mass flux is to divide the mass flow rate of the single-layer flow channel of the oil cooler by the cross-sectional area of this layer of flow channel. This means that for each layer of flow channel, its mass flux is specific and calculable. When setting the inlet temperature, the specific regional position represented by the local heat exchange unit should be considered. The closer to the inlet and outlet of the oil cooler, the inlet temperature should be set closer to the actual inlet and outlet temperatures. Doing so can more accurately simulate the heat exchange situation at different positions inside the oil cooler and improve the credibility of the calculation results. Subsequently, between the lower temperature range of the coolant inlet and the higher temperature range of the cooling oil inlet, reasonably select the temperatures at the inlets on both sides of the local heat exchange unit. In some embodiments of the present invention, when the actual working liquid side and oil side inlet temperatures of the oil cooler are 0°C and 30°C respectively, then the liquid side and oil side inlet temperatures of the local heat exchange unit can be set as: 6°C and 30°C, 3°C and 22°C, 1°C and 16°C, and 0°C and 12°C. Next, through numerical simulation or experimental testing methods, calculate the outlet temperature and heat transfer amount of the local heat exchange unit under different inlet mass flux and temperature conditions. This step is crucial for understanding the performance of the oil cooler under different operating conditions and helps to optimize its design and operating conditions.

[0056] (7) Fit the calculation formula of the Nusselt number Nu: Based on the data obtained in step (6), first determine the physical property parameters of the fluid such as density ρ, dynamic viscosity μ, specific heat capacity c p , thermal conductivity λ, etc. according to the average temperature at the inlet and outlet of the local heat exchange unit. Then, use the following formulas to calculate the Reynolds number (Re), Prandtl number (Pr), Nusselt number (Nu), and j factor under different working conditions:

[0057] Reynolds number: re = G·D h / μ;

[0058] Prandtl number: Pr = μ·c p / λ;

[0059] Nusselt number:

[0060] j factor: j = Nu / (Re·Pr c );

[0061] Here, G represents mass flux; D h represents hydraulic diameter; Q represents heat transfer capacity; is the average value of the heat transfer area on both sides of the local heat exchange unit; ΔT is the logarithmic mean temperature difference. Through the above calculations, we can obtain the values of Re, Pr, Nu and j factor under a series of different working conditions. Finally, through data fitting, we can obtain the Nusselt number calculation formula Nu=aRe b Pr c The coefficients a, b and c in . In some embodiments of the present invention, the coefficient c is 1 / 3. The determination of these coefficients is of great significance for predicting the heat transfer performance of the oil cooler under different operating conditions.

[0062] Based on the data obtained in step (6), Re, Pr and j factor under different working conditions are calculated, and the calculation formula of j factor with respect to Re is fitted:

[0063] j=aRe b-1

[0064] Thus, the coefficients a and b of the Nu calculation formula are obtained, and the coefficient c takes an empirical value.

[0065] (8) Establishing a 1D model of the oil cooler to calculate heat transfer performance: Using the phase-shift heat exchanger component in the 1D analysis software Amesim, the previously determined characteristic heat exchange length, convection heat transfer area, fluid volume, flow cross-sectional area, baffle fin mass, and the Nusselt number (Nu) calculation formula obtained through fitting were input into the software to construct a 1D model of the oil cooler. The inlet flow rate and temperature conditions of the oil cooler were set in the 1D model, and the model was run to calculate the overall heat transfer capacity of the oil cooler.

[0066] When using the phase-change heat exchanger component in Amesim, you need to set the parameters of the liquids on both sides in detail, and support the customization of the physical properties of multiple working fluids. If the physical properties of the required liquid are not preset in Amesim, you can define the required liquid by importing a text file containing physical properties such as liquid density and specific heat capacity at different temperatures. The specific steps are as follows:

[0067] Step 1: Prepare the physical property parameter file: Create a text file that lists the key physical property parameters of the liquid at different temperatures, such as density, specific heat capacity, dynamic viscosity, and thermal conductivity.

[0068] Step 2: Import the physical property parameter file: In Amesim, find the corresponding option or function, import the physical property parameter file prepared above into the software, and ensure that the software can recognize and use these parameters.

[0069] Step 3: Set liquid parameters: In the phase-change heat exchanger assembly, correctly set the parameters of the liquid on both sides, including selecting the correct liquid type (i.e. the introduced liquid) and specifying the corresponding inlet flow rate and temperature.

[0070] Through these steps, it can be ensured that the 1D model can accurately reflect the heat exchange performance of the oil cooler under actual operating conditions, thereby providing strong support for the design and optimization of the oil cooler.

[0071] In some embodiments of the present invention, the fitting curves of the j factor on the oil side and the coolant side as a function of Re are shown as follows: Figure 5a and Figure 5b As shown. The Nu calculation formulas for the oil side and liquid side are:

[0072] Oil side: Nu = 0.431 Re 0.383 ·Pr 1 / 3 ;

[0073] Liquid side: Nu = 0.216·Re 0.566 ·Pr 1 / 3 ;

[0074] The heat transfer of the oil cooler 1D model under different inlet flow rates and temperature conditions is shown in Table 4. The use of the 1D model can greatly reduce the computational time and resource consumption while providing sufficient accuracy to evaluate the overall heat transfer performance of the oil cooler.

[0075] Table 4 Heat transfer of oil cooler 1D model

[0076]

[0077]

[0078] (9) Iteratively optimize the oil cooler design: If the total heat transfer capacity of the oil cooler calculated by the 1D model fails to meet the preset target heat transfer capacity, it is necessary to re-examine the geometric design of the oil cooler. At this time, the heat transfer effect can be optimized by adjusting the geometric parameters of the oil cooler (for example, changing the fin pitch, increasing or decreasing the number of baffle plates, etc.). After completing the adjustment of the geometric parameters, the process from step (1) to (8) needs to be repeated, that is, recreate the 3D model, obtain the 1D model parameters, create the 3D model of the local heat transfer unit, simplify the CFD simulation model, determine the physical model and turbulence model, calculate the heat transfer capacity of the local heat transfer unit, and fit the Nu calculation formula until the total heat transfer capacity of the oil cooler reaches or exceeds the predetermined target. This iterative process is the key link in the design optimization of the oil cooler, which can ensure that the final product has efficient heat transfer performance in practical applications. The method of the present invention realizes the rapid iteration and optimization of the oil cooler design, shortens the development cycle, improves the accuracy of the heat transfer performance calculation of the oil cooler, and is applicable to different types of coolants and oils.

[0079] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, according to the content of this specification, many modifications and changes can be made. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the relevant technical fields can well understand and utilize the present invention.

Claims

1. A calculation method for the heat exchange performance of an oil cooler in an automotive electric drive system, characterized in that, It includes the following steps: (1) According to the actual geometric dimensions and structural characteristics of the oil cooler, use modeling software to construct a three-dimensional model of the oil cooler; (2) Measure and extract the key 1D model parameters of the oil cooler from the three-dimensional model of the oil cooler; (3) Based on the spacing and pitch of the fins on the oil side and liquid side of the oil cooler, establish a three-dimensional model of the local heat transfer unit, which includes a single-layer oil-side liquid, a single-layer liquid-side liquid, and a partition fin model; (4) Simplify the three-dimensional model of the local heat transfer unit to obtain a model suitable for computational fluid dynamics simulation; (5) Adopt a constant physical property model for the partition and fins, and introduce a polynomial function to describe the relationship between the physical properties and temperature of the engine oil and coolant, and calculate the flow in the fluid domain, as well as the changes in the physical properties and temperature distribution in the fluid domain; (6) According to the working flow rate and flow cross-sectional area during the actual operation of the oil cooler, calculate the mass flux at the inlets on both sides of the local heat transfer unit, and calculate the heat transfer amount through numerical simulation; (7) Based on the calculated Reynolds number, Prandtl number, Nusselt number, and j factor, obtain the coefficient in the Nusselt number calculation formula through data fitting; (8) Use the non-phase change heat exchanger component in the 1D analysis software, and input the relevant parameters into the 1D analysis software to construct a 1D model of the oil cooler; (9) Iteratively optimize the design of the oil cooler. If the overall heat transfer amount of the oil cooler calculated by the 1D model does not meet the expectation, adjust the geometric parameters of the oil cooler until the design goal is met.

2. The heat exchange performance calculation method of an oil cooler for an automotive electric drive system according to claim 1, wherein In step (1), the actual geometric dimensions of the oil cooler include the length, width, positions and number of layers of the inlets and outlets on the oil side and liquid side, the spacing, pitch, height, thickness, and inclination angle of the fins.

3. A method for calculating the heat exchange performance of an oil cooler of an automotive electric drive system according to claim 1, characterized in that, In step (2), the key 1D model parameters of the oil cooler include the characteristic heat transfer lengths on the oil side and liquid side, the convective heat transfer area, the fluid volume, the flow cross-sectional area, and the total mass of the partition and fins. The characteristic heat transfer length is used to calculate the hydraulic diameter, and the flow cross-sectional area is selected as the minimum cross-section near the center of the flow channel.

4. The heat transfer performance calculation method of an oil cooler for an automotive electric drive system according to claim 1, characterized in that, In step (3), based on the spacing and pitch of the fins on the oil side and liquid side of the oil cooler, select the least common multiple of the fin spacing as the length standard of the local heat transfer unit, and select the least common multiple of the fin pitch as the width standard of the local heat transfer unit. Establish a partition fin model containing a single-layer oil-side liquid and a single-layer liquid-side liquid according to this standard, extract the flow region including the partition fins from the partition fin model, and at the same time consider the flow regions upstream and downstream of the inlets and outlets to construct a complete flow region model. Finally, by stretching the inlet and outlet planes of the flow region model, ensure that the model can accurately reflect the real situation of fluid inlet and outlet.

5. A calculation method for the heat exchange performance of an oil cooler of an automotive electric drive system according to claim 1, characterized in that, In step (4), use symmetric boundary conditions to describe the flow field distribution on both sides of the oil side and liquid side channels, and simulate the periodic change of fluid temperature through periodic boundary conditions.

6. The heat exchange performance calculation method of an oil cooler for an automotive electric drive system according to claim 1, wherein, In step (4), polyhedral grid elements are used in the core region of the fluid domain, and prism layer grid elements are used in the boundary layer region; cut body grid elements are used in the solid domain.

7. A method for calculating the heat exchange performance of an oil cooler of an automotive electric drive system according to claim 1, characterized in that, In step (5), a constant physical property model is used to calculate the temperature distribution of the solid domain, a shear stress transport k-ω turbulence model is used to calculate the flow of the fluid domain, and a temperature polynomial function is used to accurately describe the physical property changes and temperature distribution of the fluid domain.

8. A calculation method for the heat exchange performance of an oil cooler of an automotive electric drive system according to claim 1, characterized in that, In step (6), the mass flux at the inlets on both sides of the local heat exchange unit is calculated by dividing the mass flow rate of the single-layer flow channel of the oil cooler by the cross-sectional area of the flow channel, and the inlet temperature is set according to the specific area position represented by the local heat exchange unit.

9. The heat exchange performance calculation method of an oil cooler for an automotive electric drive system according to claim 1, characterized in that In step (7), based on the fitted calculation formula of the j factor with respect to the Reynolds number Re under different working conditions, j = aRe b-1 , the coefficients a and b of the calculation formula of the Nusselt number Nu are obtained.

10. The heat exchange performance calculation method of an oil cooler for an automotive electric drive system according to claim 1, characterized in that, In step (8), if the physical property parameters of the required liquid are not preset in the 1D analysis software, the required liquid is defined by importing a text file containing the physical property parameters at different temperatures, including the following steps: Step 1: Prepare the physical property parameter file: Create a text parameter file that lists the key physical property parameters of the liquid at different temperatures, such as density, specific heat capacity, dynamic viscosity, and thermal conductivity; Step 2: Import the physical property parameter file: In the 1D analysis software, find the corresponding option or function and import the parameter file from step 1 into the software to ensure that the software can recognize and use these parameters; Step 3: Set liquid parameters: In the phase-change heat exchanger assembly, correctly set the parameters of the liquid on both sides, including selecting the correct liquid type, i.e. the imported liquid, and specifying the corresponding inlet flow rate and temperature.

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