A Three-Dimensional Numerical Simulation Method for the Entire Intercooler under a Local Non-Thermal Equilibrium State

Abstract

The present invention relates to the technical field of heat exchangers, and specifically relates to a method for overall three-dimensional numerical simulation of an intercooler under a local non-thermal equilibrium state. S1: Extract a periodic repeating micro-element structure of the intercooler as the object of simulation research. S2: Under the given inlet and outlet conditions, calculate the heat transfer quantity q of the micro-element structure r , the viscous resistance coefficient D of the hot-side fins h and the inertial resistance coefficient C h , the viscous resistance coefficient D of the cold-side fins c and the inertial resistance coefficient C c . S3: Establish a periodic micro-element model with the hot-side fins removed, and solve for the equivalent porosity ε of the hot-side channel e,h ; S4: Establish a periodic micro-element model with the cold-side fins removed, substitute it with the local thermal equilibrium model of porous media, and solve for the equivalent porosity ε of the cold-side channel e,c ; S5: Establish an overall three-dimensional simplified model, and solve for the pressure loss and heat transfer quantity of the entire heat exchanger under the specified inlet and outlet conditions. The simulation method proposed by the present invention can accurately simulate the performance of complex heat exchangers under a non-thermal equilibrium state.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchangers, and particularly to a method for overall three-dimensional numerical simulation of an intercooler under a local non-thermal equilibrium state. Background Technique

[0002] The traditional heat exchanger design method has a long design cycle and high cost. In recent years, with the rapid development of computational fluid dynamics (CFD) and the rapid improvement of computer performance, there have been more and more studies on numerical simulation of heat exchangers using CFD software. Currently, in countries with relatively developed vehicle fields, most of the intercoolers used are compact and efficient tube-fin intercoolers. In order to increase the heat dissipation area of the intercooler and enhance the disturbance of the fluid inside the tube, complex structures such as louvers are often added to the fins of the intercooler, which also greatly improves the difficulty of predicting the heat transfer and resistance performance of such intercoolers. The fins of the intercooler are closely distributed and generally have a thickness of no more than 0.1 mm. When directly meshing the entire intercooler, the number of mesh elements generally reaches billions, and the computational workload is still difficult to complete within a limited time for general computers. Therefore, on the basis of the existing computer capabilities, it is crucial to appropriately simplify the intercooler model to obtain an accurate overall simulation method for the intercooler.

[0003] Currently, the main methods for overall simulation of heat exchangers such as intercoolers are the distributed method and the porous medium method. Among them, the distributed method includes two types: the finite difference method based on discrete control volumes and the finite difference method based on the concept of thermal resistance. Although the distributed method has been proven to be able to effectively predict the heat transfer performance of the intercooler, the solution process needs to rely on experimental correlation formulas for estimation, which not only requires a large amount of preliminary work but also has a narrow application range. The porous medium method can utilize the effect of porous media equivalent fins on fluid flow and heat transfer, greatly reducing the number of required meshes, and thus has become the most common method for current research on heat exchangers such as intercoolers. And research shows that on the basis of the simple porous medium method, using a multi-scale coupling method, that is, first using fine meshes to study the simulation data of periodic repetitive local units in the heat exchanger and then applying it to the calculation of the entire model, higher solution accuracy can be obtained.

[0004] The heat transfer process in a porous medium can be divided into a Local Thermal Equilibrium (LTE) model or a Local Thermal Non-Equilibrium (LTNE) model according to whether the fluid temperature at the fluid-solid interface is equal to the solid temperature. For a model in thermal equilibrium, the heat transfer in the porous medium is treated as pure heat conduction, so only the porosity needs to be specified to accurately calculate the heat transfer amount. For a model in non-thermal equilibrium, the convective heat transfer due to the temperature difference at the fluid-solid interface also needs to be calculated, so the convective heat transfer coefficient at the fluid-solid interface needs to be additionally set. In most cases, non-thermal equilibrium models need to be used for heat exchangers such as intercoolers to accurately simulate their heat transfer processes. This also results in researchers spending a lot of time and effort extracting the convective heat transfer coefficient or heat flux density at the fluid-solid interface of the model when dealing with such problems, and the calculation accuracy is affected. Therefore, based on the thermal equilibrium state equation of the porous medium, an efficient processing method is proposed, which greatly simplifies the calculation of the heat transfer process of the intercooler, and the effectiveness of this method is verified by using the test report data.

[0005] The existing Chinese patent document CN202210609536.8 discloses a heat transfer process analysis method for a finned tube sodium-air heat exchanger. The method includes: modeling the finned tube sodium-air heat exchanger to obtain a heat exchanger model; performing grid division on the heat exchanger model to generate a grid model; selecting a calculation model and an algorithm adapted to the calculation model; and using the algorithm to calculate the grid model to obtain the temperature field state and / or flow field state of the heat exchanger. Among them, modeling the finned tube sodium-air heat exchanger includes: modeling the finned heat exchange tubes of the finned tube sodium-air heat exchanger, and modeling the fins of each heat exchange tube of the finned heat exchange tubes as an equivalent porous medium model. However, the above invention only mentions using a porous medium model to replace the fins for simulation, and does not indicate that the existing porous medium simulation method has been improved, and cannot solve the problem of simulating whether the model is in a thermal equilibrium state.

[0006] The porous medium model is divided into two types: thermal equilibrium and non-thermal equilibrium models. Therefore, it is necessary to first judge the thermal equilibrium state at the fluid-solid interface of the model before use. In existing research, without special instructions, generally the thermal equilibrium model is used for calculation, even though the model is in a non-thermal equilibrium state, which will bring large errors to the calculation. The comparative document does not indicate which porous medium model is used for calculation, and probably also uses the thermal equilibrium porous medium model for calculation, although it is not certain whether the model is in a thermal equilibrium state.

[0007] When the model is in a thermal equilibrium state, a porous medium model in thermal equilibrium is selected for calculation. At this time, only the porosity of the porous medium region needs to be input. The porosity is equal to the solid volume / the total volume of the channels, and the solution process is simple.

[0008] When the model is in a non-thermal equilibrium state, a porous medium model in non-thermal equilibrium is selected for calculation. At this time, the porosity of the porous medium region and the convective heat transfer coefficient at the fluid-solid interface need to be input. Among them, the common method for the convective heat transfer coefficient is to solve it through empirical formulas, so the applicable range is narrow and the error is large. To avoid the error caused by using empirical formulas, currently, researchers have disclosed a method for calculating the heat flux density, using the heat flux density instead of the convective heat transfer coefficient, aiming to improve the calculation accuracy of the non-thermal equilibrium porous medium model. However, the calculation process is relatively complex and the calculation amount is large.

[0009] For heat exchangers, it is generally very difficult to be completely in a thermal equilibrium state. Therefore, a porous medium model in non-thermal equilibrium needs to be adopted. Aiming at the problems of complex solution process or large error in the non-thermal equilibrium model, the present invention is based on the thermal equilibrium state equation, and proposes an efficient and convenient simulation method for heat exchangers applicable to any thermal equilibrium state, and conducts error analysis and effectiveness verification. Summary of the Invention

[0010] The purpose of the present invention is to provide a method for overall three-dimensional numerical simulation of an intercooler in a locally non-thermal equilibrium state. Under 20 calculation conditions, the maximum difference in heat transfer amount between the simulation results and the test results is 4.33%, and the maximum difference in pressure drop is 4.68%, which proves that the present invention has high accuracy.

[0011] To achieve the above technical purposes and reach the above technical effects, the present invention is realized through the following technical solutions:

[0012] A method for overall three-dimensional numerical simulation of an intercooler in a locally non-thermal equilibrium state, including the following steps:

[0013] S1: Extract a periodic repeating micro-element structure of the intercooler as the simulation research object.

[0014] S2: Under the given inlet and outlet conditions, calculate the heat transfer amount q r of the micro-element structure, the viscous resistance coefficient D h of the hot-side fin, and the inertial resistance coefficient C h of the hot-side fin, the viscous resistance coefficient D c of the cold-side fin, and the inertial resistance coefficient C c of the cold-side fin.

[0015] S3: Establish a periodic micro-element model with the hot-side fin removed and replace it with a local thermal equilibrium model of the porous medium. By adjusting the porosity, make the heat transfer amount q e,h of this model equal to the actual heat transfer amount qr are equal, i.e., q e,h = q r , thereby determining the equivalent porosity ε of the hot-side channel e,h .

[0016] S4: Establish a periodic micro-element model by removing the cold-side fins and replace it with a local thermal equilibrium model of porous media. Keep the porosity of the hot-side channel at a fixed value ε e,h , adjust the porosity of the cold-side channel so that the heat transfer quantity q e,c of the model is equal to the actual heat transfer quantity q r , i.e., q e,c = q r , thereby obtaining the equivalent porosity ε of the cold-side channel e,c .

[0017] S5: Establish an overall three-dimensional simplified model, remove the heat dissipation fins of the hot and cold-side channels, and replace them with a local thermal equilibrium model of porous media; set the parameters of the porous media region by applying the viscous resistance coefficient D h 、inertial resistance coefficient C h 、viscous resistance coefficient D of the cold-side fins c 、inertial resistance coefficient C c 、porosity ε of the hot-side channel e,h and porosity ε of the cold-side channel e,c ; solve the pressure loss and heat transfer quantity of the overall heat exchanger under specified inlet and outlet conditions.

[0018] On the other hand, the present invention proposes an application of the above method in the design optimization of heat exchangers.

[0019] Advantages of the present invention:

[0020] Traditional full-scale model numerical simulation requires extremely large computing resources when calculating a high-precision network. On the one hand, due to the complex structure and dense distribution of the fins of the intercooler, the number of grid cells is huge during direct simulation. By extracting a periodically repeated micro-element structure and using a porous media model to approximate the actual fin structure, the present invention greatly reduces the required number of grid cells, thereby reducing the dependence on computing resources.

[0021] Traditional numerical simulation requires meshing the complex structure of the entire intercooler, resulting in a huge amount of calculation and long time consumption. The present invention uses an advanced local thermal equilibrium model of porous media to replace the actual fin structure of the intercooler. The present invention is convenient for setting parameters, such as porosity, viscous resistance coefficient and inertial resistance coefficient. By adjusting these parameters to match the actual heat transfer quantity and fluid resistance, the complexity of the model is greatly reduced, and the model is simplified, thereby accelerating the calculation speed.

[0022] In actual working conditions, heat exchangers often operate in a state of local non-thermal equilibrium. Directly applying a thermal equilibrium model will introduce significant errors. The present invention takes into account the non-thermal equilibrium state in actual heat exchangers, enabling more accurate simulation and prediction of the performance of heat exchangers under actual working conditions. This is because when conducting microstructural simulations, the heat transfer amount and resistance coefficient can be accurately calculated, and these data are used in the calculation of the overall model, ensuring the accuracy and reliability of the simulation results.

[0023] When designing and optimizing heat exchangers, it is costly and time-consuming to obtain performance data through actual tests. The present invention provides an efficient numerical simulation method. By establishing a micro-element periodic calculation model with full details, the heat transfer calculation result is used as the actual heat transfer amount q r , and based on this, the value of the equivalent thermal conductivity k eff,e is determined. Finally, the equivalent thermal conductivity k eff,e is assigned to the full-scale porous medium model to complete the heat transfer calculation of the full-scale model. This allows designers to conduct simulations on a computer and quickly obtain the performance of heat exchangers under different design schemes. In this way, designers can evaluate and select multiple design schemes without actually manufacturing and testing heat exchangers, significantly reducing the time and cost of design and testing. At the same time, by comparing with experimental data, the effectiveness of the present invention is verified, ensuring the accuracy of simulation.

[0024] In summary, the present invention accurately simulates the performance of complex heat exchangers in a non-thermal equilibrium state, while significantly improving the calculation efficiency and reducing the design cost. It has great practical value and market potential, providing a new efficient tool for the design and optimization of heat exchange equipment such as intercoolers.

[0025] Of course, it is not necessary for any product implementing the present invention to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 is a schematic diagram of the overall multi-scale coupling calculation process of the present invention;

[0028] Figure 2 is a schematic diagram of the intercooler structure model of the present invention; (a) external structure; (b) flat tube cross-sectional structure view; (c) top view of the external louver fins of the flat tube;

[0029] Figure 3Schematic diagram of the small-scale periodic repetitive micro-element structure of the present invention;

[0030] Figure 4 Schematic diagram of the full-scale simulation model of the present invention;

[0031] Figure 5 Schematic diagram of the micro-element structure calculation model of the present invention;

[0032] Figure 6 Schematic diagram of the overall calculation model of the intercooler in the present invention. Specific embodiments

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0034] Embodiment 1

[0035] An overall three-dimensional numerical simulation method for an intercooler in a local non-thermal equilibrium state described in this embodiment includes the following steps:

[0036] S1: Extract a periodic repetitive micro-element structure of the intercooler as the simulation research object.

[0037] S2: Under the given inlet and outlet conditions, calculate the heat transfer amount q r of the micro-element structure, the viscous resistance coefficient D h of the hot-side fins, and the inertial resistance coefficient C h , the viscous resistance coefficient D c of the cold-side fins, and the inertial resistance coefficient C c .

[0038] S3: Establish a periodic micro-element model with the hot-side fins removed and replace it with a local thermal equilibrium model of porous media. By adjusting the porosity, make the heat transfer amount q e,h of this model equal to the actual heat transfer amount q r , that is: q e,h =q r , so as to determine the equivalent porosity ε e,h of the hot-side channel.

[0039] S4: Establish a periodic micro-element model with the cold-side fins removed and replace it with a local thermal equilibrium model of porous media. Keep the porosity of the hot-side channel as a fixed value ε e,h , adjust the porosity of the cold-side channel, so that the heat transfer amount q e,c of the model is equal to the actual heat transfer amount q r , that is: qe,c = q r , thereby obtaining the equivalent porosity ε of the cold-side channel e,c .

[0040] S5: Establish an overall three-dimensional simplified model, remove the heat dissipation fins of the hot and cold-side channels, and replace them with a local thermal equilibrium model of porous media; the parameter settings of the porous media region apply the viscous resistance coefficient D of the micro-element structure h , the inertial resistance coefficient C h , the viscous resistance coefficient D of the cold-side fins c , the inertial resistance coefficient C c , the porosity ε of the hot-side channel e,h and the porosity ε of the cold-side channel e,c ; Solve the pressure loss and heat transfer amount of the overall heat exchanger under specified inlet and outlet conditions.

[0041] On the other hand, the present invention proposes the application of the above method in the design optimization of heat exchangers.

[0042] Example 2

[0043] Porous media model

[0044] Flow process

[0045] Porous media generally refers to solid materials containing numerous pores inside. Most of the pores in the solid are interconnected, and fluids can penetrate from one end of the porous media to the other end through the interconnected pores. The continuity equation of porous media is the same as the standard continuity equation and can be expressed as:

[0046]

[0047] For fluids flowing in porous media, due to the existence of flow resistance, the simulation calculation of the flow in the porous region is realized by adding a resistance source term in the flow momentum equation. Initially, Darcy obtained Darcy's law through experiments, but Darcy's law is only applicable to laminar flows with a small Reynolds number. At this time, the internal flow resistance of porous media mainly comes from the viscous force of the fluid itself, while the inertial force is ignored because of its relatively small proportion. Later, many scholars modified Darcy's law, taking into account the combined effects of fluid viscous dissipation and flow inertia. Among them, the commonly used one is the Brinkman-Forchheimer correction. The modified momentum equation can still be expressed as adding a momentum source term based on the standard momentum equation, that is:

[0048]

[0049] The first term on the right side of the source term equation is the viscous resistance loss part, and the second term is the inertial resistance loss part. μ is the dynamic viscosity of the fluid, α is the permeability, and C is the inertial resistance coefficient. Let:

[0050] Let D be the viscous drag coefficient, then we have:

[0051]

[0052] When the fluid flows through the resistance region with length l, the relationship between the pressure drop generated and the resistance source term is:

[0053] ΔP = S i l (5)

[0054] Combining equation (4) and equation (5), we can obtain the relationship between the pressure drop and the flow velocity:

[0055]

[0056] By calculating the pressure drop caused by the fluid flowing through the resistance region at different flow velocities and fitting the calculated results into the form of equation (6) using the least squares method, the viscous drag coefficient D and the inertial drag coefficient C of the corresponding resistance region can be obtained.

[0057] For a hollow pipe model, by setting the inside of the pipe as a porous medium region and setting the viscous drag coefficient and inertial drag coefficient of the region, the equivalent physical resistance characteristics can be obtained. This method can be used to replace the fin structure of heat exchangers such as intercoolers to achieve the effect of reducing the number of grids.

[0058] Energy control equation

[0059] For the heat transfer process in porous media, its energy equation can be analyzed using the Local Thermal Equilibrium (LTE) model or the Local Thermal Non-Equilibrium (LTNE) model. Among them, the local thermal equilibrium model is widely used to analyze the convective heat transfer process in porous media. This model assumes that the temperature of the porous solid skeleton is locally equal to the fluid temperature (T s = T f ), that is, the average temperature of the two phases in the representative elementary volume is equal. The thermal equilibrium model is applicable to the occasions where the local temperature difference between the porous solid skeleton and the fluid is not large. Its control equation is as follows:

[0060]

[0061] In the formula, ρ is the density, c p is the specific heat capacity at constant pressure, T is the temperature, is the gradient operator, k eff is the effective thermal conductivity of the porous medium, and the subscripts f and s represent the fluid and the solid respectively.

[0062] When the heat exchanger is in a local thermal equilibrium state, k effThe relationship with the porosity ε is as follows:

[0063] k eff = εk f + (1 - ε)k s (8)

[0064] Therefore, only by setting the porosity ε can the energy control equation be solved.

[0065] When the internal heat transfer of the porous medium is insufficient, the temperature difference between the two phases in the porous medium cannot be ignored, and the local thermal equilibrium assumption is no longer applicable. At this time, the heat transfer process must be described using the local non-thermal equilibrium model. For the local non-thermal equilibrium model, considering the convective heat transfer between the porous solid skeleton and the fluid, its control equations include the fluid energy equation and the porous solid skeleton energy equation. The common forms are as follows:

[0066]

[0067] Compared with the local thermal equilibrium model, the local non-thermal equilibrium model additionally introduces the internal convective heat transfer coefficient h sf between the porous medium solid skeleton and the fluid and the concept of the volume surface ratio a. For heat exchangers, the porosity ε and the volume surface ratio a are not difficult to obtain. Therefore, obtaining the convective heat transfer coefficient h sf at the internal two-phase interface is the key to solving the equation. At present, although many scholars have measured and studied h sf and obtained many correlation formulas, most of these correlation formulas are related to their Re and Pr numbers. Therefore, using the correlation formula to solve the convective heat transfer coefficient will introduce additional errors, and indirectly solving the convective heat transfer coefficient using the heat flux density requires a large amount of computational work and the process is relatively complex.

[0068] Necessity of an efficient simulation method

[0069] It can be analyzed from the energy control equation that the local non-thermal equilibrium model is more complex than the local thermal equilibrium model, and using the empirical correlation formula to solve the internal convective heat transfer coefficient also makes its calculation error larger than that of the local thermal equilibrium model. Therefore, when the error caused by the local thermal equilibrium model is not large, people are more willing to choose the local thermal equilibrium model to simplify the research difficulty. However, only when the heat transfer at the internal interface is good enough and the local temperature difference between the two phases can be ignored, using the local thermal equilibrium model will not cause result deviation. For heat exchangers, the hot and cold fluids attached to both sides of the solid phase generally have a large temperature difference. Especially when the fluid is gaseous, there is also a large thermal conductivity difference between the gas-solid two phases, resulting in it being difficult to fully achieve the local thermal equilibrium state. Therefore, directly applying the thermal equilibrium model to calculate the internal heat transfer process of an air-cooled heat exchanger will produce a large error. In this context, it is necessary to explore a simulation method that is both applicable to solving the non-thermal equilibrium state model and has the solution efficiency and accuracy of the thermal equilibrium model.

[0070] Internal mechanism: For a porous medium model in a non-thermal equilibrium state, if the thermal equilibrium model is used, that is, assuming that the temperatures at the two-phase interfaces are equal, this will make the temperature gradients in the fluid and solid domains greater than the actual situation, that is greater than the actual value. Therefore, when using equation (7) to calculate the heat transfer process of a non-thermal equilibrium state model, the calculated heat transfer quantity q e will be greater than the actual heat transfer quantity q r . Observing the right side of equation (7), it can be seen that in this case, if an accurate heat transfer quantity is still to be obtained, it can be achieved by adjusting the effective thermal conductivity k eff , that is, there exists an equivalent thermal conductivity k eff,e that can make q e = q r . Therefore, it is necessary to first obtain an actual heat transfer quantity q r . By establishing a micro-element periodic calculation model including all details and using its heat transfer calculation result as the actual heat transfer quantity q r , the value of the equivalent thermal conductivity k eff,e is determined. Finally, this equivalent thermal conductivity k eff,e is assigned to the full-size porous medium model to complete the heat transfer calculation of the full-size model.

[0071] Example 3

[0072] As can be analyzed from Example 2, if the local thermal equilibrium model is to be used to solve the heat transfer process of a non-local thermal equilibrium model, it is necessary to first obtain an equivalent thermal conductivity k r based on a known actual heat transfer quantity q eff，e in order to accurately solve the heat transfer process of the model. Therefore, based on the multi-scale coupled porous medium model method, the present invention proposes a three-dimensional efficient numerical simulation method applicable to heat exchangers such as intercoolers with periodic repeating structures, and the calculation process is as Figure 1 shown.

[0073] Taking the A260110J-DFT00(8110025100) intercooler as the research object, its external structure is as Figure 2 (a) shown, and it mainly consists of an intake chamber, an outlet chamber and a heat dissipation core. When the intercooler works, the fluid flow inside and outside the tubes belongs to the cross-flow mode where they do not mix with each other. The hot fluid flows into the intake chamber from the intake port and then is split by 8 aluminum flat tubes distributed longitudinally in parallel. The hot fluid flows along the flat tubes to the outlet chamber and then flows out of the intercooler from the outlet. In order to increase the heat transfer area of the hot fluid inside the tubes, equally spaced parallel fins are arranged inside the flat tube channels, and each flat tube channel is divided into 31 small channels. The cross-sectional structure view of the flat tube is as Figure 2(as shown in (b)). Outside the flat heat dissipation tubes, cold air blows through the channels between the flat tubes in a direction perpendicular to the flat tubes. Since cold fluids often have low velocity, low density, and low thermal conductivity, in order to increase the heat transfer performance on this side, interruptions and offsets (louver fins) are provided on the basis of the straight fins to induce turbulent mixing and improve the heat transfer rate by breaking the growth of the thermal boundary layer. The top view of the louver fins outside the flat tubes is as shown in Figure 2 (c). All the geometric parameters of the intercooler are shown in Table 1.

[0074] Table 1 Structural parameters of the intercooler

[0075]

[0076] The inside of the intercooler contains numerous thin heat dissipation fins. Due to the limitations of the calculation conditions, it is difficult to simulate a complete model. Therefore, the method of a multi-scale coupled porous medium model is adopted to explore the overall pressure drop and heat transfer performance of the intercooler. According to the structural characteristics of the intercooler, a micro-element structure with periodic repeatability marked in purple as shown in Figure 3 is selected as the small-scale simulation model. The length of the heat dissipation flat tube of this micro-element structure in the direction of the hot fluid flow is 3.3 mm. Louver fins are connected to the upper and lower surfaces outside the flat tube. The intercepted height of the louver fins is half of its total height, that is, 3.6 mm. The full-scale intercooler simulation uses the porous medium model, and the fins of the intercooler are removed, as shown in Figure 4 .

[0077] For the simulation models of the two scales, their calculation domains are set as shown in Figure 5 and Figure 6 respectively, and fluid-structure interaction solutions are carried out. In the micro-element structure calculation model, the four cold-side channel boundaries marked in red are set as periodic boundaries, and the four hot-side channel boundaries marked in gray are set as wall boundaries. The hot-side inlet is set as a mass flow inlet, with a flow rate of 1 / 8 of the intercooler inlet flow rate, a temperature of 423 K, and a pressure of 200 kPa; since an ideal gas is used as the fluid medium in this study, setting a velocity inlet boundary may lead to non-physical solutions, so the cold-side inlet is set as a flow inlet, and the flow rate is adjusted so that this inlet has a corresponding velocity value, with the velocity value range being 2 - 6 m / s, a temperature of 298 K, and a pressure of 101.325 kPa; the cold and hot-side outlets of the model are both set as pressure outlets.

[0078] In the full-scale calculation model of the intercooler, the fins of the core are removed and replaced by the porous medium model, as shown in the orange and blue-gray marked areas in the figure. In order to be consistent with the experimental test process conditions, extended sections are set at the cold-side fluid inlet and outlet, and they are set as non-slip wall boundaries. The hot-side inlet flow rate of the intercooler varies in the range of 0.05 - 0.125 kg / s, and the other boundaries are the same as those of the small-scale calculation model.

[0079] Small-scale model simulation results

[0080] Calculate the heat transfer rate q of the micro-element structure under each test condition r And the pressure drop ΔP are shown in Table 4. According to the calculation method in the above flow process, the relationship between the hot-side flow velocity and its pressure drop per unit distance is fitted into the format of Equation (6) using the least squares method, and we get

[0081] ΔP h = 284.18u + 8.369u 2 (11)

[0082] Thus, the viscous resistance coefficient D of the hot-side fin is obtained h = 1.189*10 7 , and the inertial resistance coefficient C h = 9.966

[0083] Similarly, the relationship between the cold-side flow velocity and its pressure drop per unit distance is fitted into the format of Equation (6) using the least squares method, and we get

[0084] ΔP c = 405.71u + 40.915u 2 (12)

[0085] Thus, the viscous resistance coefficient D of the cold-side fin is obtained c = 2.181*107, and the inertial resistance coefficient C c = 70.5

[0086] Remove the hot-side channel fins of the micro-element structure and replace them with a porous medium model. The viscous resistance coefficient D and inertial resistance coefficient C of the porous medium region refer to the above D h and C h Calculation results. By adjusting the porosity, make the heat transfer rate q e,h of the porous medium model equal to the heat transfer rate q r of the micro-element structure model, and thus obtain the equivalent porosity ε e,h of the hot-side channel under each test inlet condition as shown in Table 5

[0087] Furthermore, replace the cold-side channel fins of the micro-element structure model with a porous medium model. The viscous resistance coefficient D and inertial resistance coefficient C of this porous medium region refer to the above D c and C c Calculation results. At this time, both the hot and cold-side channels of the small-scale model are replaced by the porous medium model. The porosity of the hot-side channel adopts the calculation results in Table 5, and adjust the porosity of the cold-side channel to make the heat transfer rate q e of the porous medium model equal to the heat transfer rate q r of the micro-element structure model, and thus the equivalent porosity ε of the cold-side channel under various test inlet conditions is obtained e,c As shown in Table 6.

[0088] Table 4 Calculation results of micro-element structure

[0089]

[0090] Table 5 Equivalent porosity ε of the hot-side channel e,h

[0091]

[0092] Table 6 Equivalent porosity ε of the hot-side channel e,c

[0093]

[0094]

[0095] In the porous medium model, the porosity is defined as the ratio of the fluid region to the total volume. According to the actual fin structure selected in the present invention, the porosity ε of the hot-side channel is calculated r,h = 0.9411, and the porosity ε of the cold-side channel r,c = 0.9294.

[0096] From the calculation results in Table 5 and Table 6, it can be seen that under all working conditions, the equivalent porosities ε e,h 、ε r,h of the hot-side channel and the cold-side channel are not equal to the actual porosities ε r,h 、ε r,c respectively, indicating that both channels on both sides of the model are in a non-local thermal equilibrium state. It is known from the analysis of the equivalent treatment method under the non-thermal equilibrium state that the greater the difference between the equivalent porosity and the actual porosity, the more significant the non-local thermal equilibrium characteristics. Observing Table 5, it can be found that when the hot-side flow rate increases, the difference between ε e,h and ε r,h increases, that is, the non-thermal equilibrium characteristics are enhanced, indicating that when the hot-side flow rate increases, the temperature difference at the two-phase interface will increase. Observing Table 6, it can be found that when the cold-side velocity increases, the difference between ε e,c and ε r,c decreases, that is, the non-thermal equilibrium characteristics are weakened, indicating that when the cold-side velocity increases, the convective heat transfer at the two-phase interface on the cold side will be enhanced and the temperature difference will decrease.

[0097] Large-scale model simulation results

[0098] According to the fin resistance characteristics of the model calculated in the small-scale model simulation results and the equivalent porosity results in Table 5 and Table 6, the porous medium model is used to simulate and calculate the working process of the intercooler.

[0099] Under 20 sets of working conditions, the calculated heat transfer amount and the flow pressure drops on the hot and cold sides of the intercooler are shown in Table 7. Comparing the calculated values with the experimental values, the results are shown in Table 8, where a positive value indicates that the calculated value is greater than the experimental value, and a negative value indicates that the calculated value is less than the experimental value. It can be seen from Table 8 that the heat transfer amount of the intercooler obtained by simulation calculation is greater than the experimental value. Under 20 sets of working conditions, the maximum value of δ Q,e is 4.33%, and the maximum value of δ P,e is -4.68%, both of which are less than 5%, indicating that this simulation method has high accuracy.

[0100] Table 7 Numerical simulation results of the intercooler

[0101]

[0102] Table 8 Error percentage between numerical simulation results and experimental values

[0103]

[0104] The heat transfer process of a heat exchanger in a locally thermal equilibrium state can be quickly solved by the porous medium thermal equilibrium model by setting the porosity. However, for a heat exchanger in a locally non-thermal equilibrium state, when using the porous medium non-thermal equilibrium model to solve, the convective heat transfer coefficient at the two-phase interface of the heat exchanger needs to be input, resulting in a more complex solution process. For a heat exchanger in a locally non-thermal equilibrium state, if the thermal equilibrium model is directly used for processing, that is, assuming that the heat transfer performance at the two-phase interface is better than the actual situation, that is, raising the temperature of the low-temperature phase surface to be equal to that of the high-temperature phase surface, this will lead to a temperature gradient in the low-temperature phase greater than the actual situation, making the calculated heat transfer amount greater than the actual value. Therefore, based on the porous medium thermal equilibrium state equation and the definition of the effective thermal conductivity, a calculation method for efficiently solving the heat transfer process of a heat exchanger in a non-thermal equilibrium state is proposed.

[0105] Using the simulation method proposed in the present invention to conduct an overall three-dimensional numerical simulation on the working process of a certain type of intercooler, under 20 calculation working conditions, the maximum difference in heat transfer amount between the simulation results and the test results is 4.33%, and the maximum difference in pressure drop is 4.68%, proving that the present invention has high accuracy.

[0106] 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 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 art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A three-dimensional numerical simulation method for an intercooler under local non-thermal equilibrium state, characterized in that: The following steps are involved: S1: Extract a periodic repetitive micro-element structure of the intercooler as the simulation research object; S2: Under given inlet and outlet conditions, calculate the heat transfer q of the micro-element structure r , Viscous drag coefficient D of the hot side fin h and the inertial drag coefficient C h , Viscous drag coefficient D of cold side fin c and the inertial drag coefficient C c ; S3: Establish a periodic microelement model without the hot side fins and replace it with a local thermal balance model of porous media; adjust the porosity to make the heat transfer q e,h The actual heat exchange rate q r Equal, that is: q e,h =q r , thereby determining the equivalent porosity ε of the hot side channel e,h ; S4: Establish a periodic microelement model without the cold side fins and replace it with a local thermal equilibrium model of porous media; keep the porosity of the hot side channel at a fixed value ε e,h , adjust the porosity of the cold side channel to make the heat transfer rate of the model q e,c The actual heat exchange rate q r Equal, that is: q e,c =q r , thus obtaining the equivalent porosity ε of the cold side channel e,c ; S5: Establish an overall three-dimensional simplified model, remove the heat dissipation fins of the cold and hot side channels, and use the porous medium local thermal equilibrium model instead; the porous medium area parameter setting applies the viscous resistance coefficient D of the microelement structure h , inertial drag coefficient C h , Viscous drag coefficient D of cold side fin c , inertial drag coefficient C c , hot side channel porosity ε e,h and the cold side channel porosity ε e,c ; Solve the overall pressure loss and heat transfer capacity of the heat exchanger under specified inlet and outlet conditions.

2. Application of the method as claimed in claim 1 in heat exchanger design optimization.

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