Intercooler overall three-dimensional numerical simulation method in local non-thermal balance state

Abstract

The invention relates to the technical field of heat exchangers, in particular to an integral three-dimensional numerical simulation method for an intercooler in a local non-thermal balance state, which comprises the following steps: S1, extracting a periodic repeated infinitesimal structure of the intercooler as a simulation research object; s2, under the given inlet and outlet conditions, the heat exchange amount qr of the infinitesimal structure, the viscous resistance coefficient Dh and the inertial resistance coefficient Ch of the hot side fins and the viscous resistance coefficient Dc and the inertial resistance coefficient Cc of the cold side fins are calculated; s3, establishing a periodic infinitesimal model for removing hot side fins, and solving the equivalent porosity epsilon e, h of a hot side channel; s4, establishing a periodic infinitesimal model without a cold side fin, replacing the periodic infinitesimal model with a porous medium local heat balance model, and solving the equivalent porosity epsilon e, c of a cold side channel; and S5, an overall three-dimensional simplified model is established, and the overall pressure loss and heat exchange amount of the heat exchanger under the specified inlet and outlet conditions are solved. The simulation method provided by the invention can accurately simulate the performance of the complex heat exchanger in the non-heat-balance state.

Description

Technical Field

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

[0002] Traditional heat exchanger design methods have long design cycles and high costs. In recent years, with the rapid development of computational fluid dynamics (CFD) and the rapid improvement of computer performance, more and more studies have been conducted on numerical simulation of heat exchangers using CFD software. At present, in countries with more developed vehicle fields, most of the intercoolers used are compact and efficient tube-belt intercoolers. In order to increase the heat dissipation area of ​​the intercooler and enhance the disturbance of the fluid in the tube, complex structures such as louvers are often added to the fins of the intercooler, which greatly increases the difficulty of predicting the heat transfer and resistance performance of such intercoolers. The fins of the intercooler are closely distributed, and the thickness generally does not exceed 0.1mm. If the entire intercooler is directly meshed, the number of mesh units generally reaches billions, and the amount of calculation is still difficult for general computers to complete within a limited time. Therefore, based on the existing computer capabilities, it is crucial to appropriately simplify the intercooler model and obtain an accurate overall intercooler simulation method.

[0003] At present, the main methods for overall simulation of heat exchangers such as intercoolers are distributed method and porous media method. Among them, the distributed method includes two methods: finite difference method based on discrete control volume and finite difference method based on thermal resistance concept. Although the distributed method has been proven to be able to effectively predict the heat transfer performance of intercoolers, the solution process requires the use of experimental correlation equations for estimation, which not only requires a lot of preliminary work but also has a narrow scope of use. The porous media method can greatly reduce the number of required grids by utilizing the effect of porous media equivalent fins on fluid flow and heat transfer, and has therefore become the most common method for studying heat exchangers such as intercoolers. And research has shown that on the basis of a simple porous media method, a multi-scale coupling method is used, that is, first using a fine grid 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, a higher solution accuracy can be obtained.

[0004] The heat transfer process in porous media can be divided into a local thermal equilibrium (LTE) model or a local thermal non-equilibrium (LTNE) model, depending on whether the fluid temperature at the fluid-solid interface is equal to the solid temperature. For models in thermal equilibrium, the heat transfer in the porous medium is treated as pure heat conduction, so the heat transfer can be accurately calculated by simply specifying the porosity. For models in non-thermal equilibrium, the convective heat transfer caused by the temperature difference at the fluid-solid interface must also be calculated, so the convective heat transfer coefficient of the fluid-solid interface must be additionally set. In most cases, heat exchangers such as intercoolers must use non-thermal equilibrium models to accurately simulate their heat transfer processes. This also causes researchers to spend a lot of time and effort to extract the convective heat transfer coefficient or heat flux density of the model fluid-solid interface when dealing with such problems, and the calculation accuracy is affected. To this end, based on the porous medium thermal equilibrium state equation, an efficient processing method is proposed, which greatly simplifies the calculation of the intercooler heat transfer process, and the effectiveness of the method is verified using test report data.

[0005] The existing Chinese patent document CN202210609536.8 discloses a heat exchange process analysis method for a fin tube sodium-air heat exchanger, the method comprising: modeling the fin tube sodium-air heat exchanger to obtain a heat exchanger model; gridding the heat exchanger model to generate a grid model; selecting a calculation model and an algorithm adapted to the calculation model; and calculating the grid model using the algorithm to obtain the temperature field state and / or flow field state of the heat exchanger; wherein, modeling the fin tube sodium-air heat exchanger comprises: modeling the fin heat exchange tube bundle of the fin tube sodium-air heat exchanger, and modeling the fins of each heat exchange tube of the fin heat exchange tube bundle as an equivalent porous medium model. However, the above invention only mentions the use of a porous medium model instead of a fin for simulation, and does not indicate that the existing porous medium simulation method has been improved, and cannot solve the problem of whether the model is in thermal equilibrium for simulation.

[0006] Porous media models are divided into two types: thermal equilibrium and non-thermal equilibrium models. Therefore, it is necessary to determine the thermal equilibrium state at the fluid-solid interface of the model before use. Existing studies generally use thermal equilibrium models for calculations without special instructions, even though the model is in a non-thermal equilibrium state, which will cause large errors in the calculations. The comparative document does not indicate which porous media model is used for calculations, so it is probably a thermal equilibrium porous media model, even though it is not certain whether the model is in a thermal equilibrium state.

[0007] When the model is in thermal equilibrium, the thermally balanced porous media model is selected for calculation. At this time, it is only necessary to input the porosity of the porous media region. The porosity is equal to the solid volume / total channel volume, and the solution process is simple.

[0008] When the model is in a non-thermal equilibrium state, a non-thermal equilibrium porous media model is selected for calculation. At this time, it is necessary to input the porosity of the porous media area and the convective heat transfer coefficient of the fluid-solid interface. Among them, the commonly used method for the convective heat transfer coefficient is to solve it through an empirical formula, so the scope of application is narrow and the error is large. In order to avoid the errors caused by using empirical formulas, researchers have currently disclosed a method for calculating heat flux density, which replaces the convective heat transfer coefficient with heat flux density, aiming to improve the calculation accuracy of the non-thermal equilibrium porous media model. However, the calculation process is more complicated and the amount of calculation is large.

[0009] It is generally difficult for a heat exchanger to be completely in thermal equilibrium, so a non-thermal equilibrium porous medium model is required. In view of the problem that the solution process of the non-thermal equilibrium model is complicated or the error is large, this paper proposes an efficient and convenient simulation method for heat exchangers in any thermal equilibrium state based on the thermal equilibrium state equation, and performs error analysis and effectiveness verification. Summary of the invention

[0010] The purpose of the present invention is to provide a three-dimensional numerical simulation method for an intercooler under a local non-thermal equilibrium state. Under 20 calculation conditions, the maximum difference in heat exchange 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] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0012] A three-dimensional numerical simulation method for an intercooler under a local non-thermal equilibrium state comprises the following steps:

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

[0014] S2: Under given inlet and outlet conditions, calculate the heat transfer q of the micro-element structure r , Viscous drag coefficient D of 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 .

[0015] S3: Establish a periodic microelement model without the hot side fins and replace it with a local thermal balance model of porous media. By adjusting the porosity, the heat transfer capacity of the model is adjusted to e,h The actual heat exchange rate qr Equal, that is: q e,h =q r , thereby determining the equivalent porosity ε of the hot side channel e,h .

[0016] 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 .

[0017] 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.

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

[0019] Beneficial effects of the present invention:

[0020] Traditional full-scale model numerical simulation requires extremely large computing resources when calculating high-precision networks. This is partly due to the complex structure and dense distribution of the intercooler fins, which leads to a huge number of grid units in direct simulation. The present invention extracts a periodically repeated micro-element structure and uses a porous medium model to approximate the actual fin structure, greatly reducing the number of required grid units, thereby reducing the dependence on computing resources.

[0021] Traditional numerical simulation requires gridding of the complex structure of the entire intercooler, which is computationally intensive and time-consuming. The present invention uses an advanced porous medium local thermal balance model to replace the actual intercooler fin structure. The present invention facilitates setting parameters, such as porosity, viscous drag coefficient, and inertial drag coefficient. By adjusting these parameters to match the actual heat transfer and fluid resistance, the complexity of the model is greatly reduced, the model is simplified, and the calculation speed is accelerated.

[0022] In actual working conditions, heat exchangers are often in a state of local non-thermal equilibrium, and directly using a thermal equilibrium model will introduce large errors. The present invention takes into account the non-thermal equilibrium state in actual heat exchangers, and can more accurately simulate and predict the performance of heat exchangers under actual working conditions. This is because when performing micro-element structure simulation, the heat transfer and resistance coefficient can be accurately calculated, and these data are used for the calculation of the overall model, ensuring the accuracy and reliability of the simulation results.

[0023] When designing and optimizing heat exchangers, it is very costly and time-consuming to obtain performance data through actual testing. The present invention provides an efficient numerical simulation method, which establishes a microelement periodic calculation model containing all details and uses its heat transfer calculation results as the actual heat transfer value q r , and use this to determine the equivalent thermal conductivity k eff,e Finally, the equivalent thermal conductivity k eff,e The values ​​are assigned to the full-scale porous medium model to complete the heat transfer calculation of the full-scale model. The designer is allowed to simulate on the computer and quickly obtain the performance of the heat exchanger under different design schemes. In this way, the designer can evaluate and select multiple design schemes without actually manufacturing and testing the heat exchanger, which significantly reduces the time and cost of design and testing. At the same time, by comparing with experimental data, the effectiveness of the present invention has been verified, ensuring the accuracy of the simulation.

[0024] In summary, the present invention accurately simulates the performance of complex heat exchangers under non-thermal equilibrium conditions, while greatly improving calculation efficiency and reducing design costs. It is extremely valuable and has market potential, and provides a new and efficient tool for the design and optimization of heat exchange equipment such as intercoolers.

[0025] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

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

[0028] Figure 2 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 louvered fins outside the flat tube;

[0029] Figure 3This is a schematic diagram of a small-scale periodically repeated micro-element structure of the present invention;

[0030] Figure 4 It is a schematic diagram of a full-scale simulation model of the present invention;

[0031] Figure 5 It is a schematic diagram of the micro-element structure calculation model of the present invention;

[0032] Figure 6 It is a schematic diagram of the overall calculation model of the intercooler of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] The present embodiment provides a method for three-dimensional numerical simulation of an intercooler under a local non-thermal equilibrium state, comprising the following steps:

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

[0037] S2: Under given inlet and outlet conditions, calculate the heat transfer q of the micro-element structure r , Viscous drag coefficient D of 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 .

[0038] S3: Establish a periodic microelement model without the hot side fins and replace it with a local thermal balance model of porous media. By adjusting the porosity, the heat transfer capacity of the model is adjusted to 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 .

[0039] 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: qe,c =q r , thus 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 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.

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

[0042] Example 2

[0043] Porous Media Model

[0044] Flow process

[0045] Porous media generally refers to solid materials with many pores inside. Most of the pores in the solid are interconnected, and the fluid can penetrate from one end of the porous medium to the other through the connected 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 porous areas is realized by adding resistance source terms in the flow momentum equation. Initially, Darcy obtained Darcy's law through experiments, but Darcy's law is only applicable to laminar flow with a small Reynolds number. At this time, the flow resistance inside the porous medium mainly comes from the viscosity of the fluid itself, while the inertial force is ignored due to its small proportion. Later, many scholars modified Darcy's law, taking into account the combined effects of the viscous dissipation and flow inertia of the fluid. Among them, the more commonly used one is the Brinkman-Forchheimer correction. The modified momentum equation can still be expressed as adding a momentum source term to 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 fluid dynamic viscosity, α is the permeability, and C is the inertial resistance coefficient. Let:

[0050] D is the viscous resistance coefficient, then:

[0051]

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

[0053] ΔP=S i l (5)

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

[0055]

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

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

[0058] Energy Governing Equations

[0059] For the heat transfer process in porous media, the 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 temperature of the fluid (T s =T f ), that is, the average temperature of the two phases in the characterization element is equal. The thermal equilibrium model is suitable for occasions where the local temperature difference between the porous solid skeleton and the fluid is not large, and its control equation is as follows:

[0060]

[0061] Where ρ is the density, c p is the isobaric specific heat capacity, 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 solid, respectively.

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

[0063] k eff =εk f +(1-ε)k s (8)

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

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

[0066]

[0067] Compared with the local thermal equilibrium model, the local non-thermal equilibrium model introduces the internal convection heat transfer coefficient h between the porous medium solid skeleton and the fluid. sf For heat exchangers, the porosity ε and the volume surface ratio a are not difficult to obtain, so the convective heat transfer coefficient h of the two-phase interface inside the heat exchanger is obtained. sf It is the key to solve the equation. sf Measurement research was carried out and many correlation equations were obtained, but most of these correlation equations are related to the Re and Pr numbers. Therefore, using the correlation equations to solve the convective heat transfer coefficient will introduce additional errors. Using the heat flux density to indirectly solve the convective heat transfer coefficient requires a large amount of calculation work and the process is more complicated.

[0068] The necessity of efficient simulation methods

[0069] From the analysis of the energy control equation, it can be seen that the local non-thermal equilibrium model is more complicated than the local thermal equilibrium model. The use of empirical correlation formulas to solve the internal convection heat transfer coefficient also makes its calculation error greater than 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 of the internal interface is good enough and the local temperature difference between the two phases can be ignored, the use of the local thermal equilibrium model will not cause result deviation. For heat exchangers, the cold and hot fluids attached to both sides of the solid phase generally have a large temperature difference. Especially when the fluid is in a gaseous state, the gas-solid two phases also have a large thermal conductivity difference, which makes it difficult to fully achieve the local thermal equilibrium state. Therefore, directly applying the thermal equilibrium model to calculate the internal heat exchange process of the air-cooled heat exchanger will produce a large error. In this context, it is necessary to explore a simulation method that is suitable for solving non-thermal equilibrium state models and has the efficiency and accuracy of solving thermal equilibrium models.

[0070] Internal mechanism: For porous media models in a non-thermal equilibrium state, if the thermal equilibrium model is used, that is, the temperature of the two-phase interface is assumed to be equal, this will make the temperature gradient in the fluid and solid domains greater than the actual situation, that is, is greater than the actual value, so equation (7) is used to calculate the heat transfer process of the model in a non-thermal equilibrium state, and the calculated heat transfer q e will be greater than the actual heat transfer q r From the right side of equation (7), we can see that if we still want to obtain accurate heat transfer in this case, we can adjust the effective thermal conductivity k eff To complete, there is an equivalent thermal conductivity k eff,e , which can make q e =q r Therefore, we need to first obtain an actual heat transfer amount q r By establishing a micro-element periodic calculation model with full details, the heat transfer calculation results are used as the actual heat transfer q r , and use this to determine the equivalent thermal conductivity k eff,e Finally, the equivalent thermal conductivity k eff,e Assign values ​​to the full-size porous media model to complete the heat transfer calculation of the full-size model.

[0071] Example 3

[0072] According to the analysis of Example 2, if we want to use the local heat balance model to solve the heat exchange process in the non-local heat balance model, we need to first use a known actual heat exchange capacity q r , obtain the equivalent thermal conductivity k eff，e Therefore, based on the multi-scale coupled porous media model method, this paper proposes a three-dimensional efficient numerical simulation method for heat exchangers such as intercoolers with periodic repetitive structures. The calculation process is as follows: Figure 1 shown.

[0073] The A260110J-DFT00 (8110025100) intercooler is taken as the research object. Its appearance and structure are as follows: Figure 2 As shown in (a), it is mainly composed of an air inlet chamber, an air outlet chamber and a heat dissipation core. When the intercooler is working, the fluid flow inside and outside the tube is a cross-flow mode in which each fluid does not mix. The hot fluid flows from the air inlet into the air inlet chamber, and then is diverted by 8 aluminum flat tubes distributed in parallel along the longitudinal direction. The hot fluid flows along the flat tubes to the air outlet chamber and then flows out of the intercooler from the outlet. In order to increase the heat exchange area of ​​the hot fluid in the tube, equidistant parallel fins are arranged inside the flat tube channel, and each flat tube channel is divided into 31 small channels. The cross-sectional structure view of the flat tube is shown in the figure. Figure 2(b) As shown. Outside the heat dissipation flat tubes, cold air blows through the channels between the flat tubes in a direction perpendicular to the flat tubes. Since the cold fluid often has low speed, low density and low thermal conductivity, in order to increase the heat transfer performance on this side, interruptions and offsets (louvered fins) are set 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 louvered fins outside the flat tubes is shown in Figure 2 (c) All geometric parameters of the intercooler are shown in Table 1.

[0074] Table 1 Intercooler structural parameters

[0075]

[0076] The intercooler contains a large number of thin cooling fins. Due to the limitation of calculation conditions, it is difficult to simulate the complete model. Therefore, the multi-scale coupled porous media model method is used to explore the overall pressure drop and heat transfer performance of the intercooler. Figure 3 The microstructure with periodic repetition marked in purple is used as a small-scale simulation model. The heat dissipation flat tube of the microstructure is 3.3 mm long along the flow direction of the hot fluid. The upper and lower surfaces of the flat tube are connected to the louvered fins. The height of the intercepted louvered fins is half of its total height, that is, 3.6 mm. The full-scale intercooler simulation uses a porous medium model, and the fins of the intercooler are removed, such as Figure 4 shown.

[0077] For the simulation models of the two scales, the computational domains are set as follows: Figure 5 and Figure 6 As shown, the fluid-solid coupling solution is performed. In the micro-element structure calculation model, the four cold 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, the flow rate is 1 / 8 of the intercooler inlet flow rate, the temperature is 423K, and the pressure is 200kpa; since ideal gas is used as the fluid medium in this study, setting the 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 to make the inlet have the corresponding velocity value, the velocity value range is 2 to 6m / s, the temperature is 298K, and the pressure is 101.325kpa; the cold and hot side outlets of the model are set as pressure outlets.

[0078] In the full-scale calculation model of the intercooler, the core fins are removed and replaced by a porous medium model, as shown in the orange and blue-gray areas in the figure. In order to be consistent with the experimental test process conditions, an extension section is set at the cold side fluid inlet and outlet, and it is set as a no-slip wall boundary. The flow rate variation range of the hot side inlet of the intercooler is 0.05-0.125kg / s, and the other boundaries are consistent with the small-scale calculation model.

[0079] Small-scale model simulation results

[0080] Calculate the heat transfer q of the micro-element structure under each test condition r and 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 unit distance pressure drop is fitted into the format of equation (6) using the least squares method, and the result is

[0081] ΔP h =284.18u+8.369u 2 (11)

[0082] The viscous drag coefficient D of the hot side fin is obtained from this h =1.189*10 7 , inertial drag coefficient C h =9.966.

[0083] Similarly, the relationship between the cold side velocity and its unit distance pressure drop 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] The viscous drag coefficient D of the cold side fin is obtained from this c =2.181*107, inertial resistance coefficient C c =70.5.

[0086] The hot side channel fins of the micro-element structure are removed and replaced by a porous medium model. The viscous resistance coefficient D and inertial resistance coefficient C of the porous medium area refer to the above D h and C h Calculation results. By adjusting the porosity, the heat transfer rate of the porous media model q e,h Equal to the heat transfer q of the micro-element structure model r , thus the equivalent porosity ε of the hot side channel under each test inlet condition is obtained e,h As shown in Table 5.

[0087] Furthermore, the cold side channel fins of the micro-element structure model are also replaced by the 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, 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 is calculated using the results in Table 5, and the porosity of the cold side channel is adjusted to make the heat transfer q of the porous medium model e Equal to the heat transfer q of the micro-element structure model r, thus obtaining the equivalent porosity ε of the cold side channel under each test inlet condition e,c As shown in Table 6.

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

[0089]

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

[0091]

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

[0093]

[0094]

[0095] In the porous media model, the porosity is defined as the ratio of the fluid area 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 as r,h =0.9411, the porosity of the cold side channel ε r,c =0.9294.

[0096] From the calculation results in Tables 5 and 6, it can be seen that the equivalent porosity ε of the hot side channel and the cold side channel under all working conditions is e,h , ε r,h The actual porosity ε r,h , ε r,c are not equal, indicating that the 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 larger the difference between the equivalent porosity and the actual porosity, the more significant the non-local thermal equilibrium characteristics. It can be found from Table 5 that when the hot side flow increases, ε e,h With ε r,h The difference increases, that is, the non-thermal equilibrium characteristics are enhanced, indicating that the increase in the hot side flow rate will increase the temperature difference between the two phases. e,c With ε r,c The difference decreases, that is, the non-thermal equilibrium characteristics weaken, indicating that the increase in the cold side velocity will enhance the convective heat transfer at the interface between the two phases on the cold side and reduce the temperature difference.

[0097] Large-scale model simulation results

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

[0099] Under 20 groups of working conditions, the heat exchange capacity and the pressure drop of the hot and cold sides of the intercooler are calculated and shown in Table 7. The calculated values ​​are compared with the experimental values, and the results are shown in Table 8, where A positive value indicates that the calculated value is greater than the test value, and a negative value indicates that the calculated value is less than the test value. As can be seen from Table 8, the heat exchange of the intercooler calculated by simulation is greater than the test value. Under the 20 working conditions, δ Q,e The maximum value is 4.33%, δ P,e The maximum value is -4.68%, and all are less than 5%, indicating that the simulation method has high accuracy.

[0100] Table 7 Intercooler numerical simulation results

[0101]

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

[0103]

[0104] The porous medium thermal equilibrium model can quickly solve the heat transfer process of the heat exchanger in a local thermal equilibrium state by setting the porosity. However, for the heat exchanger in a local non-thermal equilibrium state, the porous medium non-thermal equilibrium model needs to input the convective heat transfer coefficient at the interface of the two phases of the heat exchanger, which makes the solution process more complicated. For the heat exchanger in local non-thermal equilibrium, if the thermal equilibrium model is directly used, it is assumed that the heat transfer performance of the two-phase interface is better than the actual situation, that is, the temperature of the low-temperature phase surface is increased to be equal to the high-temperature phase surface. This will cause the temperature gradient in the low-temperature phase to be greater than the actual situation, making the calculated heat transfer greater than the actual value. To this end, based on the porous medium thermal equilibrium state equation and the definition of effective thermal conductivity, a calculation method that can efficiently solve the heat transfer process of the heat exchanger in a non-thermal equilibrium state is proposed.

[0105] The simulation method proposed in the present invention is used to perform an overall three-dimensional numerical simulation of the working process of a certain type of intercooler. Under 20 calculation conditions, the maximum difference in heat exchange 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.

[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 do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only 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 capacity 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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