Plate-fin precooler performance two-dimensional calculation method

Abstract

The invention relates to a two-dimensional calculation method for the performance of a plate-fin precooler, and the method comprises the steps: S1, building a geometric model of the plate-fin precooler, and dividing Nh * Nc heat transfer calculation units; s2, constructing a heat transfer calculation model and a pressure drop calculation model; s3, setting structural parameters, initial cold fluid physical parameters and initial hot fluid physical parameters; s4, assigning the initial thermal fluid physical parameters to the heat transfer calculation unit (i, 1), and assigning the initial cold fluid physical parameters to the heat transfer calculation unit (1, j); s5, assigning i = j = 1; s6, calculating the heat transfer coefficient of the heat transfer calculation unit; s7, the cold and hot fluid heat exchange amount and pressure drop of the heat transfer calculation unit are calculated, and cold and hot fluid physical parameters of the heat transfer calculation unit (i, j + 1) are obtained; s8, updating the assignment j to be equal to j + 1, and repeating the steps S6 to S7 until j is equal to Nc; and S9, updating the assignment i = i + 1, j = 1, and repeating the steps S6 to S8 until i = Nh to complete solution.

Description

Technical Field

[0001] The invention relates to the technical field of precoolers, and in particular to a two-dimensional calculation method for performance of a plate-fin precooler. Background Art

[0002] In order to design a high-performance precooler, it is necessary to design the precooler structure. For a precooler with a specific structure, engineers often use two quick methods: logarithmic mean temperature difference method and heat exchange efficiency-heat transfer unit number ( ) method. These two methods are based on the average temperature of the cold and hot fluids inside the heat exchanger, ignoring the changes in the physical properties of the fluid during the heat exchange process, and therefore belong to zero-dimensional calculation methods. In recent years, in order to further improve the performance of the precooler, cryogenic fluids are often used as ideal coolants. For example, the temperature of liquid nitrogen can reach as low as 77K, which has excellent cooling performance. In addition, cryogenic fluids often undergo phase changes during the heat transfer process, and the convective heat transfer coefficient is greatly improved, which can achieve better cooling effects. Therefore, cryogenic working fluids are receiving more and more attention and have been widely used in engineering fields, such as ATREX engines, LACE engines, and SABRE engines. However, under flow boiling conditions, the physical properties of the cold fluid change dramatically, and the zero-dimensional calculation method cannot be applied to the performance evaluation of precoolers under flow boiling conditions.

[0003] At the same time, three-dimensional numerical simulation methods can also be used to design and optimize the precooler structure. The three-dimensional calculation method can not only predict the performance of the precooler, but also provide detailed flow field structure, such as bubble morphology information generated by flow boiling. At present, for the flow boiling heat transfer calculation of the precooler, the widely used boiling models include the volume of fluid model (VOF model), the mixture model and the Eulerian model. Among these models, the VOF model and the mixture model are the most widely used. The VOF model can capture the gas-liquid interface generated by the flow boiling process and provides an effective way to understand the instability of two-phase flow and the dynamic characteristics of bubbles. However, the application of the VOF model is usually limited to relatively simple geometric shapes, such as single tubes or parallel pipes. For research objects with complex structures, such as heat exchangers, the mixture model is more suitable. However, this model needs to be compared with the experimental results of specific objects to correct the empirical coefficients, which undoubtedly increases the difficulty. Therefore, although the three-dimensional numerical simulation method can provide richer information, its disadvantage is that the processing and calculation time is too long, and it is impossible to quickly evaluate the performance of the precooler under different working conditions and structural conditions.

[0004] In general, the research on the design and performance evaluation of heat exchange devices is relatively rich, but there are still two outstanding issues that need attention. As for the zero-dimensional calculation method, it is often based on the average temperature calculation of the hot and cold fluids inside the precooler, which cannot reveal the flow field structure of the precooler. In addition, cryogenic fluids as ideal coolants (such as liquid nitrogen, liquid hydrogen and liquid methane) are receiving more and more attention, but cryogenic fluids often undergo phase changes during the heat transfer process, and the physical properties change dramatically. Therefore, the performance evaluation of the precooler must consider the physical property changes of the fluid inside the precooler. As for the three-dimensional calculation method, it involves steps such as meshing, flow field calculation, and heat transfer model selection. The performance calculation of the precooler is very complicated. Although it can reveal the flow field structure, it cannot form a fast and effective performance evaluation method.

[0005] Therefore, it is particularly important to develop a rapid performance evaluation method that takes into account the changes in physical properties of the fluid at different locations in the heat exchange device. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a two-dimensional calculation method for the performance of a plate-fin precooler.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a two-dimensional calculation method for plate-fin precooler performance, comprising the following steps: S1. Establish a geometric model of the plate-fin precooler and mesh the geometric model to obtain N h × N c heat transfer calculation unit; among them, the heat exchange mode of the plate-fin precooler is cross type; S2. constructing a heat transfer calculation model and a pressure drop calculation model for the heat transfer calculation unit; S3. Setting the structural parameters of the plate-fin precooler, the initial cold fluid physical parameters of the cold flow inlet, and the initial hot fluid physical parameters of the hot flow inlet; S4. Encode the heat transfer calculation unit in a two-dimensional coordinate format, and assign the initial hot fluid physical parameters to the heat transfer calculation unit coded as (i, 1), and assign the initial cold fluid physical parameters to the heat transfer calculation unit coded as (1, j), where 1≤i≤ N h , 1≤j≤ N c ; S5. Assigning the code of the heat transfer calculation unit to i=1, j=1; S6. Calculate the heat transfer coefficient of the heat transfer calculation unit coded as (i, j) based on the heat transfer calculation model; S7. Based on the initial cold fluid physical parameters, the initial hot fluid physical parameters, the heat transfer coefficient and the pressure drop calculation model, respectively calculate the cold and hot fluid heat exchange and pressure drop of the heat transfer calculation unit coded as (i, j) to obtain the cold fluid physical parameters and hot fluid physical parameters of the heat transfer calculation unit coded as (i, j+1); S8. Update the code assignment j=j+1 of the heat transfer calculation unit, and repeat steps S6 to S7 to iteratively solve until j= N c ; S9. Update the code assignment of the heat transfer calculation unit to i=i+1, j=1, and repeat steps S6 to S8 to iteratively solve until i= N h , to obtain the physical field inside the plate-fin precooler.

[0008] According to one aspect of the present invention, in step S1, in the step of establishing a geometric model of a plate-fin precooler, a precooler configuration of the plate-fin precooler is obtained, and the geometric model is established with the precooler configuration; The precooler is configured as a partition-type structure, and comprises: a plurality of heat exchange plates arranged at intervals, and fins arranged between adjacent heat exchange plates; Between adjacent heat exchange plates, a plurality of fins are arranged at equal intervals; The fins and the heat exchange plates are fixedly connected to each other, and adjacent fins and adjacent heat exchange plates form a hot fluid flow channel for the hot fluid to flow; A plurality of cold fluid flow channels arranged at intervals are provided in the heat exchange plate; The axial direction of the hot fluid flow channel is arranged to intersect with the axial direction of the cold fluid flow channel.

[0009] According to one aspect of the present invention, in step S1, the geometric model is meshed to obtain N h × N c In the step of a heat transfer calculation unit, the hot fluid flow channel is divided into equal intervals along the axial direction N c A first dividing line is formed along the axial direction of the cold fluid flow channel to divide the cold fluid flow channel into equal intervals. N h The heat transfer calculation unit is constructed by the area enclosed by the first dividing line and the second dividing line to obtain N h × N c Heat transfer calculation unit; The number of the first dividing lines is greater than the number of the cold fluid channels, and the first dividing lines are arranged at the middle position of the fins dividing the cold fluid channels; The number of the second dividing lines is greater than the number of the thermal fluid channels, and the second dividing lines are arranged at the middle position of the fins dividing the thermal fluid channels.

[0010] According to one aspect of the present invention, in step S2, the step of constructing a heat transfer calculation model for the heat transfer calculation unit includes: S21. Constructing the heat transfer between the hot fluid and the cold fluid based on the precooler configuration The expression of , and it is expressed as: ; in, is the heat transferred between the hot fluid and the cold fluid, and are the temperatures of the hot and cold fluids, respectively, and are the total heat transfer area on the hot fluid side and the total heat transfer area on the cold fluid side, respectively. is the solid heat transfer area, and are the convective heat transfer coefficients of the hot and cold fluids, respectively, represents the wall thickness, is the thermal conductivity of the wall, and They are the total efficiency of the fins on the cold fluid side and the total efficiency of the fins on the hot fluid side respectively; S22. Construction for calculating the total efficiency of the cold fluid side fins and the total efficiency of the fins on the hot fluid side Total fin efficiency The expression of is expressed as: ; ; ; ; in, is the flat wall area between fins, is the protruding area between fins, is the cold fluid side fin efficiency or the hot fluid side fin efficiency, is the intermediate function, is the equivalent fin height, is the fluid heat transfer coefficient, is the fin height; S23. Construct a method for calculating the convective heat transfer coefficient of thermal fluids and the convective heat transfer coefficient of the cold fluid Convective heat transfer coefficient To complete the construction of the heat transfer calculation model.

[0011] According to one aspect of the present invention, in step S23, a convective heat transfer coefficient for calculating the thermal fluid is constructed. and the convective heat transfer coefficient of the cold fluid Convective heat transfer coefficient In the step of the expression of Expression of If the different phase fluids are liquid phase fluid and gas phase fluid, and they are in a turbulent state, including: S23a1. The Nusselt number is calculated based on the Gnielinski formula and is expressed as: ; ; in, is the Nusselt number, is the flow friction coefficient, is the Reynolds number, is the Prandtl number; S23a2. Constructing the Nusselt number and convective heat transfer coefficient in turbulent state The relationship is used to solve the convective heat transfer coefficient ; Among them, the Nusselt number and the convective heat transfer coefficient in the turbulent state The relationship is expressed as: ; ; ; in, is the thermal conductivity of the fluid, is the hydraulic diameter of the channel, is the fluid density, is the fluid flow rate, is the fluid dynamic viscosity, is the specific heat of the fluid at constant pressure; If the different phase fluids are liquid phase fluid and gas phase fluid, and they are in a laminar flow state, including: S23b1. The Nusselt number is calculated based on the Sieder-Tate formula and is expressed as: ; in, is the Nusselt number, is the convection heat transfer length, is the Reynolds number, is the Prandtl number, is the hydraulic diameter of the channel; S23b2. Constructing Nusselt number and convective heat transfer coefficient under laminar flow The relationship is used to solve the convective heat transfer coefficient ; Among them, the Nusselt number and the convective heat transfer coefficient under laminar flow The relationship is expressed as: ; ; ; in, is the thermal conductivity of the fluid, is the hydraulic diameter of the channel, is the fluid density, is the fluid flow rate, is the fluid dynamic viscosity, is the specific heat of the fluid at constant pressure; When the fluid is a single phase of gas or liquid, the fluid density and fluid dynamic viscosity Using the NIST database, when the fluid is a two-phase gas phase and a liquid phase, the fluid density and fluid dynamic viscosity Obtained using a homogeneous model, where the fluid density when the fluid is two-phase and fluid dynamic viscosity Respectively expressed as: ; ; in, is the two-phase flow dryness, is the liquid density, is the gas phase density, is the liquid phase dynamic viscosity, is the gas phase dynamic viscosity.

[0012] According to one aspect of the present invention, in step S2, the step of constructing a pressure drop calculation model for the heat transfer calculation unit includes: S201. Constructing the pressure drop of the thermal fluid in the thermal fluid flow channel The expression is used to calculate the total pressure drop of the hot fluid flowing through the plate-fin precooler, and to construct the pressure drop of the cold fluid in the cold fluid flow channel. The expression is used to calculate the total pressure drop of the cold fluid flowing through the plate-fin precooler, wherein the pressure drop of the hot fluid in the hot fluid flow channel is It is expressed as: ; in, is the pressure drop of the thermal fluid in the thermal fluid flow channel, is the friction pressure drop of the thermal fluid in the thermal fluid flow channel, is the gravity pressure drop of the thermal fluid in the thermal fluid flow channel, is the local pressure drop of the thermal fluid in the thermal fluid flow channel; The pressure drop of the cold fluid in the cold fluid flow channel It is expressed as: ; in, is the pressure drop of the cold fluid in the cold fluid flow channel, is the friction pressure drop of the cold fluid in the cold fluid flow channel, is the gravity pressure drop of the cold fluid in the cold fluid flow channel, is the local pressure drop of the cold fluid in the cold fluid flow channel, is the accelerated pressure drop of the cold fluid in the cold fluid flow channel; S202. Construct a method for calculating the friction pressure drop of cold fluid in the cold fluid flow channel and the friction pressure drop of the hot fluid in the hot fluid flow channel Friction pressure drop Expression, and is represented as: ; in, Indicates dense flow, is the flow friction coefficient, is the fluid density, is the hydraulic diameter of the channel, is the convection heat transfer length; S203. Construct a method for calculating the local pressure drop of the cold fluid in the cold fluid flow channel and the local pressure drop of the hot fluid in the hot fluid flow channel Local pressure drop Expression, and is represented as: ; in, is the local resistance coefficient; S204. Construct a method for calculating the local pressure drop of the cold fluid in the cold fluid flow channel and the accelerated pressure drop of the hot fluid in the hot fluid flow channel Acceleration pressure drop Expression, and is represented as: ; ; in, is the heat exchange length, is the two-phase flow dryness, is the cavitation fraction of the two-phase flow in the homogeneous model, is the liquid density, is the gas phase density.

[0013] According to one aspect of the present invention, the initial cold fluid physical parameters include: cold fluid flow, cold fluid pressure, cold fluid temperature, and dryness; The initial thermal fluid physical parameters include: thermal fluid flow, thermal fluid pressure, and thermal fluid temperature; The structural parameters include: the length, width and height of the hot fluid flow channel, the length, width and height of the cold fluid flow channel, the number of hot fluid flow channels, the number of cold fluid flow channels, and the length, width and height of the plate-fin precooler.

[0014] According to one aspect of the present invention, step S3 further includes: Assumptions for two-dimensional calculation of the performance of the plate-fin precooler are set; wherein the assumptions include: the mass flow rate of the cold fluid is evenly distributed in the cold fluid flow channel, the mass flow rate of the hot fluid is evenly distributed in the hot fluid flow channel, the fluid at the outlet of the plate-fin precooler is evenly mixed, axial heat transfer of the fluid is ignored, and internal heat conduction of the solid is ignored.

[0015] According to one solution of the present invention, the precooler performance calculation method of the present invention can take into account the coupled heat exchange of cold fluid-solid-hot fluid, and effectively reveal the flow field structure inside the precooler.

[0016] According to one solution of the present invention, the precooler performance calculation method of the present invention can consider the cold fluid flow boiling heat transfer calculation, which provides a new idea for the performance evaluation of the precooler.

[0017] According to one scheme of the present invention, the precooler performance calculation method of the present invention divides the precooler into several heat transfer calculation units, and the physical properties inside the units are considered to be constant, thereby achieving precise control of the calculation, especially by controlling the size of the heat transfer calculation unit to further make the calculation accuracy flexible and controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flowchart of a two-dimensional calculation method for plate-fin precooler performance according to an embodiment of the present invention; Figure 2 A calculation flow chart of a two-dimensional calculation method for plate-fin precooler performance according to an embodiment of the present invention; Figure 3 is a structural diagram of a precooler according to an embodiment of the present invention, wherein: Figure 3 (a) is a three-dimensional structural diagram of a precooler, wherein: is the length of the precooler, is the height of the precooler, is the width of the precooler, Figure 3 (b) indicates Figure 3 (a) is an enlarged view of position A, where is the thickness of the heat exchange plate, is the cross-sectional width of the hot fluid flow channel, is the cross-sectional length of the hot fluid flow channel, is the fin thickness, Figure 3 (c) indicates Figure 3 (a) is an enlarged view of position B, where is the spacing thickness between adjacent cold fluid channels, is the cross-sectional width of the cold fluid flow channel, is the cross-sectional length of the cold fluid flow channel, is the wall thickness between the cold fluid flow channel and the hot fluid flow channel; Figure 4 Schematic diagram of grid division and heat transfer of a precooler according to an embodiment of the present invention, wherein: Figure 4 (a) The division diagram of the heat transfer calculation unit of the precooler. Figure 4 (b) shows the heat transfer diagram on the hot fluid side, where: represents the heat of the thermal fluid, Figure 4 (c) shows the heat transfer diagram of the cold fluid side, where: Indicates the heat of the cold fluid; Figure 5 The flow field structure diagram of a two-stage precooler according to an embodiment of the present invention is shown in FIG. Figure 5 (a) represents the temperature distribution diagram of the thermal fluid, Figure 5 (b) shows the temperature distribution diagram of the cold fluid. DETAILED DESCRIPTION

[0019] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not therefore limited to the following embodiments.

[0020] For the plate-fin precooler, there are two fluids inside, one is the hot fluid and the other is the cold fluid. Among them, the cold fluid refers to the fluid with a lower temperature, which is used to cool the hot fluid; the hot fluid refers to the fluid with a higher temperature. The goal of the precooler is to lower the temperature of the hot fluid.

[0021] Combination Figure 1 and Figure 2 As shown, according to one embodiment of the present invention, a two-dimensional calculation method for plate-fin precooler performance of the present invention comprises the following steps: S1. Establish the geometric model of the plate-fin precooler and mesh the geometric model to obtain N h × N c heat transfer calculation unit; among them, the heat exchange mode of the plate-fin precooler is cross type; S2. constructing a heat transfer calculation model and a pressure drop calculation model for a heat transfer calculation unit; S3. Setting the structural parameters of the plate-fin precooler, the initial cold fluid physical parameters of the cold flow inlet, and the initial hot fluid physical parameters of the hot flow inlet; S4. Encode the heat transfer calculation unit in a two-dimensional coordinate format, and assign the initial hot fluid physical parameters to the heat transfer calculation unit coded as (i, 1), and assign the initial cold fluid physical parameters to the heat transfer calculation unit coded as (1, j), where 1≤i≤ N h , 1≤j≤ N c ; S5. Assign the code of the heat transfer calculation unit to i=1, j=1; S6. Calculate the heat transfer coefficient of the heat transfer calculation unit coded as (i, j) based on the heat transfer calculation model; S7. Based on the initial cold fluid physical parameters, the initial hot fluid physical parameters, the heat transfer coefficient and the pressure drop calculation model, respectively calculate the cold and hot fluid heat exchange and pressure drop of the heat transfer calculation unit coded as (i, j) to obtain the cold fluid physical parameters and the hot fluid physical parameters of the heat transfer calculation unit coded as (i, j+1); S8. Update the code assignment j=j+1 of the heat transfer calculation unit, and repeat steps S6 to S7 to iteratively solve until j= N c ; S9. Update the code assignment of the heat transfer calculation unit to i=i+1, j=1, and repeat steps S6 to S8 to iteratively solve until i= N h to obtain the physical fields inside the plate-fin precooler.

[0022] like Figure 3 As shown, according to one embodiment of the present invention, in step S1, in the step of establishing the geometric model of the plate-fin precooler, the heat exchange mode of the plate-fin precooler is a cross type, which can maximize the average temperature difference between the cold and hot fluids; then, the precooler configuration of the plate-fin precooler is obtained, and the geometric model is established with the precooler configuration; wherein the precooler configuration is a partition wall structure, thereby allowing the cold fluid and the hot fluid to exchange heat through the wall surface, thereby achieving instant and long-term cooling of the hot fluid.

[0023] Furthermore, the plate-fin precooler includes: a plurality of heat exchange plates 1 arranged at intervals, and fins 2 arranged between adjacent heat exchange plates; wherein, between adjacent heat exchange plates, a plurality of fins 2 are arranged at equal intervals; further, the fins 2 and the heat exchange plates 1 are fixedly connected to each other, and adjacent fins 2 and adjacent heat exchange plates 1 form a hot fluid flow channel for the flow of heat fluid; a plurality of cold fluid flow channels arranged at intervals are arranged in the heat exchange plate 1; wherein, the portion used to divide the cold fluid flow channel can also be referred to as a cold fluid flow channel fin or simply a fin. In this embodiment, the axial direction of the hot fluid flow channel is arranged to intersect with the axial direction of the cold fluid flow channel. Thus, the hot fluid and the cold fluid are heat exchanged through the heat exchange plate.

[0024] In this embodiment, the cold fluid can be dispersed from the top into several cold fluid flow channels through the cold fluid flow channels provided in each heat exchange plate 1, so that the cold fluid is regularly distributed in the entire heat exchange plate 1; further, the hot fluid passes through the regular hot fluid flow channels formed between the heat exchange plate 1 and the fins 2 from front to back, so as to achieve the cross distribution of the cold fluid flow direction and the hot fluid flow direction. Therefore, the hot fluid and the cold fluid can not only achieve heat exchange through the wall surface of the heat exchange plate 1, but also achieve heat exchange through the fins 2 accordingly.

[0025] Combination Figure 3 and Figure 4 As shown, according to one embodiment of the present invention, in step S1, the geometric model is meshed to obtain N h × N c In the step of heat transfer calculation unit, the hot fluid flow channel is divided into equal intervals along the axial direction. N c The first dividing line L1 is divided into two equal-spaced lines along the axial direction of the cold fluid flow channel. N h The second dividing line L2 is used to construct a heat transfer calculation unit in the area surrounded by the first dividing line L1 and the second dividing line L2 to obtain N h × N cheat transfer calculation units. In this embodiment, the number of first dividing lines L1 is greater than the number of cold fluid channels (specifically, the number of first dividing lines L1 is one more than the number of cold fluid channels), and the first dividing line L1 is set at the middle position of the fins that divide the cold fluid channels; thus, when the first dividing line L1 is between two adjacent cold fluid channels, the cold fluid channels can be symmetrical on the opposite sides of the first dividing line L1. In this embodiment, the number of second dividing lines L2 is greater than the number of hot fluid channels (specifically, the number of second dividing lines L2 is one more than the number of hot fluid channels), and the second dividing line L2 is set at the middle position of the fins that divide the hot fluid channels; thus, when the second dividing line L2 is between two adjacent hot fluid channels, the hot fluid channels can be symmetrical on the opposite sides of the second dividing line L2. The above-mentioned setting is used to realize that the constructed multiple heat transfer calculation units can fully cover all channel areas. In this embodiment, inside the heat transfer calculation unit, it is considered that the physical properties of the fluid such as temperature, pressure, dryness, etc. are the same.

[0026] According to an embodiment of the present invention, in step S2, the step of constructing a heat transfer calculation model for the heat transfer calculation unit includes: S21. Construct the heat transfer between hot fluid and cold fluid based on the precooler configuration The expression of , and it is expressed as: ; in, is the heat transferred between the hot fluid and the cold fluid, and are the temperatures of the hot and cold fluids, respectively, and They are the total heat transfer area on the hot fluid side (for plate-fin precoolers, the total heat transfer area on the hot fluid side is the total wall area of ​​the hot fluid flow channel through which the hot fluid flows, that is, the sum of the fin area through which the hot fluid flows and the flat wall area between the fins) and the total heat transfer area on the cold fluid side (for plate-fin precoolers, the total heat transfer area on the cold fluid side is the total wall area of ​​the cold fluid flow channel through which the cold fluid flows, that is, the sum of the fin area through which the cold fluid flows and the flat wall area between the fins), is the solid heat transfer area (for the plate-fin precooler, the solid heat transfer area is the total heat transfer area of ​​the cold and hot fluids flowing through the plate-fin precooler, which includes the sum of the fin area and the flat wall area between the fins), and are the convective heat transfer coefficients of the hot and cold fluids, respectively, represents the wall thickness, is the wall thermal conductivity, and They are respectively the total efficiency of the fins on the cold fluid side (i.e. the total efficiency of the fins on the opposite sides of the cold fluid flow channel through which the cold fluid flows) and the total efficiency of the fins on the hot fluid side (i.e. the total efficiency of the fins on the opposite sides of the hot fluid flow channel through which the hot fluid flows); S22. Construction for calculating the total efficiency of the cold fluid side fins and the total efficiency of the fins on the hot fluid side Total fin efficiency The expression of is expressed as: ; ; ; ; in, is the flat wall area between fins, is the protruding area between fins, is the cold fluid side fin efficiency or the hot fluid side fin efficiency, is the intermediate function, is the equivalent fin height, is the fluid heat transfer coefficient, is the fin height; S23. Construct a method for calculating the convective heat transfer coefficient of thermal fluids and the convective heat transfer coefficient of the cold fluid Convective heat transfer coefficient To complete the construction of the heat transfer calculation model.

[0027] According to one embodiment of the present invention, in step S23, a convective heat transfer coefficient for calculating the thermal fluid is constructed. and the convective heat transfer coefficient of the cold fluid Convective heat transfer coefficient In the step of the expression of Expression of If the different phase fluids are liquid phase fluid and gas phase fluid, and they are in a turbulent state, including: S23a1. The Nusselt number is calculated based on the Gnielinski formula and is expressed as: ; ; in, is the Nusselt number, is the flow friction coefficient, is the Reynolds number, is the Prandtl number; S23a2. Constructing the Nusselt number and convective heat transfer coefficient in turbulent state The relationship is used to solve the convective heat transfer coefficient ; Among them, the Nusselt number and the convective heat transfer coefficient in the turbulent state The relationship is expressed as: ; ; ; in, is the thermal conductivity of the fluid, is the hydraulic diameter of the channel, is the fluid density, is the fluid flow rate, is the fluid dynamic viscosity, is the specific heat of the fluid at constant pressure; If the different phase fluids are liquid phase fluid and gas phase fluid, and they are in a laminar flow state, including: S23b1. The Nusselt number is calculated based on the Sieder-Tate formula and is expressed as: ; in, is the Nusselt number, is the convection heat transfer length, is the Reynolds number, is the Prandtl number, is the hydraulic diameter of the channel; S23b2. Constructing Nusselt number and convective heat transfer coefficient under laminar flow The relationship is used to solve the convective heat transfer coefficient ; Among them, the Nusselt number and the convective heat transfer coefficient under laminar flow The relationship is expressed as: ; ; ; in, is the thermal conductivity of the fluid, is the hydraulic diameter of the channel, is the fluid density, is the fluid flow rate, is the fluid dynamic viscosity, is the specific heat of the fluid at constant pressure; When the fluid is a single phase of gas or liquid, the fluid density and fluid dynamic viscosity Using the NIST database, when the fluid is a two-phase gas phase and a liquid phase, the fluid density and fluid dynamic viscosity Obtained using a homogeneous model, where the fluid density when the fluid is two-phase and fluid dynamic viscosity Respectively expressed as: ; ; in, is the two-phase flow dryness, is the liquid density, is the gas phase density, is the liquid phase dynamic viscosity, is the gas phase dynamic viscosity.

[0028] Based on this, for two-phase fluids, different fluids have different flow heat transfer relationships, taking liquid nitrogen and water as examples. When water is used as the cold fluid, the flow boiling heat transfer relationship of water in a microchannel summarized by Li et al. is used, and the expression is as follows: ; ; ; in, is the boiling number, is the Bond number, is the heat flux density, For dense flow, is the latent heat of vaporization, is the acceleration due to gravity, is the liquid phase Reynolds number, is the density of the liquid phase in the two-phase flow, is the gas phase density in two-phase flow, is the surface tension coefficient, is the hydraulic diameter of the channel.

[0029] When liquid nitrogen is used as the cold fluid, the convective heat transfer coefficient is calculated using the experimental relationship of the flow boiling test of the micro-channel low-temperature working fluid. The expression is as follows: ; ; ; ; ; in, is the dryness, We is the Weber number, is the dimensionless pressure parameter, is the Martinelli number, is the gas phase dynamic viscosity, is the liquid phase dynamic viscosity, is the static pressure, is the hydraulic diameter of the channel.

[0030] like Figure 1 As shown, according to one embodiment of the present invention, in step S2, the step of constructing a pressure drop calculation model for the heat transfer calculation unit includes: S201. Construct the pressure drop of the thermal fluid in the thermal fluid flow channel respectively Expressions for calculating the total pressure drop of the hot fluid flowing through the plate-fin precooler and constructing the pressure drop of the cold fluid in the cold fluid flow channel The expression is used to calculate the total pressure drop of the cold fluid flowing through the plate-fin precooler, where the pressure drop of the hot fluid in the hot fluid flow channel is It is expressed as: ; in, is the pressure drop of the thermal fluid in the thermal fluid flow channel, is the friction pressure drop of the thermal fluid in the thermal fluid flow channel, is the gravity pressure drop of the thermal fluid in the thermal fluid flow channel, is the local pressure drop of the thermal fluid in the thermal fluid flow channel; Pressure drop of cold fluid in the cold fluid flow path It is expressed as: ; in, is the pressure drop of the cold fluid in the cold fluid flow channel, is the friction pressure drop of the cold fluid in the cold fluid flow channel, is the gravity pressure drop of the cold fluid in the cold fluid flow channel, is the local pressure drop of the cold fluid in the cold fluid flow channel, is the accelerated pressure drop of the cold fluid in the cold fluid flow channel; S202. Construct a method for calculating the friction pressure drop of cold fluid in the cold fluid flow channel and the friction pressure drop of the hot fluid in the hot fluid flow channel Friction pressure drop Expression, and is represented as: ; in, Indicates dense flow, is the flow friction coefficient, is the fluid density, is the hydraulic diameter of the channel, is the convection heat transfer length; S203. Construct a method for calculating the local pressure drop of the cold fluid in the cold fluid flow channel and the local pressure drop of the hot fluid in the hot fluid flow channel Local pressure drop Expression, and is represented as: ; in, is the local resistance coefficient; S204. Construct a method for calculating the local pressure drop of the cold fluid in the cold fluid flow channel and the accelerated pressure drop of the hot fluid in the hot fluid flow channel Acceleration pressure drop Expression, and is represented as: ; ; in, is the heat exchange length, is the two-phase flow dryness, is the cavitation fraction of the two-phase flow in the homogeneous model, is the liquid density, is the gas phase density.

[0031] In this embodiment, the gravity pressure drop of the hot fluid in the hot fluid flow channel is and the gravity pressure drop of the cold fluid in the cold fluid flow channel Can be ignored.

[0032] According to one embodiment of the present invention, the initial cold fluid physical parameters include: cold fluid flow rate, cold fluid pressure, cold fluid temperature, and dryness; the initial hot fluid physical parameters include: hot fluid flow rate, hot fluid pressure, and hot fluid temperature; the structural parameters include: the length, width, and height of the hot fluid flow channel, the length, width, and height of the cold fluid flow channel, the number of hot fluid flow channels, the number of cold fluid flow channels, and the length, width, and height of the plate-fin precooler.

[0033] According to one embodiment of the present invention, step S3 further includes: Assumptions for two-dimensional calculation of plate-fin precooler performance are set; wherein the assumptions include: the mass flow rate of the cold fluid is evenly distributed in the cold fluid flow channel, the mass flow rate of the hot fluid is evenly distributed in the hot fluid flow channel, the fluid at the outlet of the plate-fin precooler is evenly mixed (for example, at the outlets of multiple cold fluid flow channels, the cold fluid mixing parameter properties such as temperature, dryness and other parameters are evenly distributed at the outlets, and at the outlets of multiple hot fluid flow channels, the hot fluid mixing parameter properties such as temperature, dryness and other parameters are evenly distributed at the outlets), axial heat transfer of the fluid is ignored, and internal heat conduction of the solid is ignored.

[0034] Combination Figure 1 , Figure 2 and Figure 4As shown, according to one embodiment of the present invention, step S4. encodes the heat transfer calculation unit in a two-dimensional coordinate manner, wherein the heat transfer calculation unit is encoded in the form of (i, j), wherein 1≤i≤ N h , 1≤j≤ N c ; Further, the initial hot fluid physical parameters are assigned to the heat transfer calculation units coded as (i, 1), that is, the initial hot fluid physical parameters are assigned to the heat transfer calculation units at the entrance of the hot fluid flow channel; Further, the initial cold fluid physical parameters are assigned to the heat transfer calculation units coded as (1, j), that is, the initial cold fluid physical parameters are assigned to the heat transfer calculation units at the entrance of the cold fluid flow channel; Combination Figure 1 , Figure 2 and Figure 4 As shown, according to an embodiment of the present invention, in step S5, the code of the heat transfer calculation unit is assigned to i=1, j=1, that is, the initialization of the heat transfer calculation unit when starting the calculation is realized.

[0035] Combination Figure 1 , Figure 2 and Figure 4 As shown, according to an embodiment of the present invention, in step S6, in the step of calculating the heat transfer coefficient of the heat transfer calculation unit coded as (i, j) based on the heat transfer calculation model, the calculation of the heat transfer coefficient starts from the heat transfer calculation unit (1, 1).

[0036] Combination Figure 1 , Figure 2 and Figure 4 As shown, according to an embodiment of the present invention, in step S7, the heat exchange amount and pressure drop of the cold and hot fluids of the heat transfer calculation unit coded as (i, j) are calculated based on the initial cold fluid physical parameters, the initial hot fluid physical parameters, the heat transfer coefficient and the pressure drop calculation model, so as to obtain the cold fluid physical parameters and the hot fluid physical parameters of the heat transfer calculation unit coded as (i, j+1); in this embodiment, the corresponding cold and hot fluid heat exchange amount and pressure drop can be calculated starting from the heat transfer calculation unit (1, 1), and the cold fluid physical parameters and the hot fluid physical parameters of the next heat transfer calculation unit can be obtained.

[0037] Combination Figure 1 , Figure 2 and Figure 4 As shown, according to one embodiment of the present invention, in step S8, the code assignment j=j+1 of the heat transfer calculation unit is updated, and steps S6 to S7 are repeatedly executed to iteratively solve until j= N c .

[0038] Combination Figure 1 , Figure 2 and Figure 4 As shown in the figure, according to one embodiment of the present invention, in step S9, the code assignment i=i+1, j=1 of the heat transfer calculation unit is updated, and steps S6 to S8 are repeatedly executed to iteratively solve until i= N h , to obtain the physical fields inside the plate-fin precooler (such as temperature, dryness, velocity, pressure and other parameters).

[0039] like Figure 5 As shown, the flow field structure of the two-stage plate-fin precooler can be calculated by using the above method of the present invention; for details, see Figure 5 (a) and Figure 5 (b), the initial cold fluid physical parameters are set as follows: cold fluid flow rate is 0.3kg / s, cold fluid pressure is 200kPa, cold fluid temperature is 300K, and dryness is 0; among them, for the two-stage plate-fin precooler, the cold fluid flow rate of each stage of the plate-fin precooler is set to 0.15kg / s, and the other parameters are the same; the initial hot fluid physical parameters are set as follows: hot fluid flow rate is 0.3kg / s, hot fluid pressure is 15kPa, and hot fluid temperature is 1200K; After heat exchange between the cold fluid and the hot fluid, the physical parameters of the cold fluid output by the first-stage plate-fin precooler are changed to: cold fluid flow rate 0.15kg / s, cold fluid pressure 193kPa, cold fluid temperature 393K, dryness 0.161; the physical parameters of the hot fluid output by the first-stage plate-fin precooler are changed to: hot fluid flow rate 0.3kg / s, hot fluid pressure 13.67kPa, hot fluid temperature 882.4K; The physical parameters of the cold fluid output by the second-stage plate-fin precooler are: cold fluid flow rate 0.15kg / s, cold fluid pressure 195kPa, cold fluid temperature 393.3K, dryness 0.009; the physical parameters of the hot fluid output by the second-stage plate-fin precooler are: hot fluid flow rate 0.3kg / s, hot fluid pressure 12.74kPa, hot fluid temperature 698.3K; Depend on Figure 5 (a) and Figure 5 As shown in (b), the method of the present invention fully demonstrates the coupled heat transfer process of cold fluid-solid-hot fluid. It can be seen that the method can not only estimate the performance of the precooler, but also effectively reveal the flow field structure of the precooler.

[0040] The above is only one solution of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A two-dimensional calculation method for plate-fin precooler performance, characterized in that: The following steps are involved: S1. Establish a geometric model of the plate-fin precooler and mesh the geometric model to obtain N h × N c heat transfer calculation unit; among them, the heat exchange mode of the plate-fin precooler is cross type; S2. constructing a heat transfer calculation model and a pressure drop calculation model for the heat transfer calculation unit; S3. Setting the structural parameters of the plate-fin precooler, the initial cold fluid physical parameters of the cold flow inlet, and the initial hot fluid physical parameters of the hot flow inlet; S4. Encode the heat transfer calculation unit in a two-dimensional coordinate format, and assign the initial hot fluid physical parameters to the heat transfer calculation unit coded as (i, 1), and assign the initial cold fluid physical parameters to the heat transfer calculation unit coded as (1, j), where 1≤i≤ N h , 1≤j≤ N c ; S5. Assigning the code of the heat transfer calculation unit to i=1, j=1; S6. Calculate the heat transfer coefficient of the heat transfer calculation unit coded as (i, j) based on the heat transfer calculation model; S7. Based on the initial cold fluid physical parameters, the initial hot fluid physical parameters, the heat transfer coefficient and the pressure drop calculation model, respectively calculate the cold and hot fluid heat exchange and pressure drop of the heat transfer calculation unit coded as (i, j) to obtain the cold fluid physical parameters and hot fluid physical parameters of the heat transfer calculation unit coded as (i, j+1); S8. Update the code assignment j=j+1 of the heat transfer calculation unit, and repeat steps S6 to S7 to iteratively solve until j= N c ; S9. Update the code assignment of the heat transfer calculation unit to i=i+1, j=1, and repeat steps S6 to S8 to iteratively solve until i= N h , to obtain the physical field inside the plate-fin precooler.

2. The two-dimensional calculation method for plate-fin precooler performance according to claim 1 is characterized in that: In step S1, in the step of establishing a geometric model of a plate-fin precooler, a precooler configuration of the plate-fin precooler is obtained, and the geometric model is established with the precooler configuration; The precooler is configured as a partition-type structure, and comprises: a plurality of heat exchange plates arranged at intervals, and fins arranged between adjacent heat exchange plates; Between adjacent heat exchange plates, a plurality of fins are arranged at equal intervals; The fins and the heat exchange plates are fixedly connected to each other, and adjacent fins and adjacent heat exchange plates form a hot fluid flow channel for the hot fluid to flow; A plurality of cold fluid flow channels arranged at intervals are provided in the heat exchange plate; The axial direction of the hot fluid flow channel is arranged to intersect with the axial direction of the cold fluid flow channel.

3. The two-dimensional calculation method for plate-fin precooler performance according to claim 2, characterized in that: In step S1, the geometric model is meshed to obtain N h × N c In the step of a heat transfer calculation unit, the hot fluid flow channel is divided into equal intervals along the axial direction N c A first dividing line is formed along the axial direction of the cold fluid flow channel to divide the cold fluid flow channel into equal intervals. N h The heat transfer calculation unit is constructed by the area enclosed by the first dividing line and the second dividing line to obtain N h × N c Heat transfer calculation unit; The number of the first dividing lines is greater than the number of the cold fluid channels, and the first dividing lines are arranged at the middle position of the fins dividing the cold fluid channels; The number of the second dividing lines is greater than the number of the thermal fluid channels, and the second dividing lines are arranged at the middle position of the fins dividing the thermal fluid channels.

4. The two-dimensional calculation method for plate-fin precooler performance according to claim 3 is characterized in that: In step S2, the step of constructing a heat transfer calculation model for the heat transfer calculation unit includes: S21. Constructing the heat transfer between the hot fluid and the cold fluid based on the precooler configuration The expression of , and it is expressed as: in, is the heat transferred between the hot fluid and the cold fluid, and are the temperatures of the hot and cold fluids, respectively, and are the total heat transfer area on the hot fluid side and the total heat transfer area on the cold fluid side, respectively. is the solid heat transfer area, and are the convective heat transfer coefficients of the hot and cold fluids, respectively, represents the wall thickness, is the wall thermal conductivity, and They are the total efficiency of the fins on the cold fluid side and the total efficiency of the fins on the hot fluid side respectively; S22. Construct a method for calculating the total efficiency of the cold fluid side fins and the total efficiency of the fins on the hot fluid side Total fin efficiency The expression of is expressed as: in, is the flat wall area between fins, is the protruding area between fins, is the cold fluid side fin efficiency or the hot fluid side fin efficiency, is the intermediate function, is the equivalent fin height, is the fluid heat transfer coefficient, is the fin height; S23. Construct a method for calculating the convective heat transfer coefficient of thermal fluids and the convective heat transfer coefficient of the cold fluid Convective heat transfer coefficient To complete the construction of the heat transfer calculation model.

5. The two-dimensional calculation method for plate-fin precooler performance according to claim 4, characterized in that: In step S23, a convective heat transfer coefficient for calculating the thermal fluid is constructed. and the convective heat transfer coefficient of the cold fluid Convective heat transfer coefficient In the step of the expression of Expression of If the different phase fluids are liquid phase fluid and gas phase fluid, and they are in a turbulent state, including: S23a1. The Nusselt number is calculated based on the Gnielinski formula and is expressed as: in, is the Nusselt number, is the flow friction coefficient, is the Reynolds number, is the Prandtl number; S23a2. Constructing the Nusselt number and convective heat transfer coefficient in turbulent state The relationship is used to solve the convective heat transfer coefficient ; Among them, the Nusselt number and the convective heat transfer coefficient in the turbulent state The relationship is expressed as: in, is the thermal conductivity of the fluid, is the hydraulic diameter of the channel, is the fluid density, is the fluid flow rate, is the fluid dynamic viscosity, is the specific heat of the fluid at constant pressure; If the different phase fluids are liquid phase fluid and gas phase fluid, and they are in a laminar flow state, including: S23b1. The Nusselt number is calculated based on the Sieder-Tate formula and is expressed as: in, is the Nusselt number, is the convection heat transfer length, is the Reynolds number, is the Prandtl number, is the hydraulic diameter of the channel; S23b2. Constructing Nusselt number and convective heat transfer coefficient under laminar flow The relationship is used to solve the convective heat transfer coefficient ; Among them, the Nusselt number and the convective heat transfer coefficient under laminar flow The relationship is expressed as: in, is the thermal conductivity of the fluid, is the hydraulic diameter of the channel, is the fluid density, is the fluid flow rate, is the fluid dynamic viscosity, is the specific heat of the fluid at constant pressure; When the fluid is a single phase of gas or liquid, the fluid density and fluid dynamic viscosity Using the NIST database, when the fluid is a two-phase gas phase and a liquid phase, the fluid density and fluid dynamic viscosity Obtained using a homogeneous model, where the fluid density when the fluid is two-phase and fluid dynamic viscosity Respectively expressed as: in, is the two-phase flow dryness, is the liquid density, is the gas phase density, is the liquid phase dynamic viscosity, is the gas phase dynamic viscosity.

6. The two-dimensional calculation method for plate-fin precooler performance according to claim 5, characterized in that: In step S2, the step of constructing a pressure drop calculation model for the heat transfer calculation unit includes: S201. Constructing the pressure drop of the thermal fluid in the thermal fluid flow channel The expression is used to calculate the total pressure drop of the hot fluid flowing through the plate-fin precooler, and to construct the pressure drop of the cold fluid in the cold fluid flow channel. The expression is used to calculate the total pressure drop of the cold fluid flowing through the plate-fin precooler, wherein the pressure drop of the hot fluid in the hot fluid flow channel is It is expressed as: in, is the pressure drop of the thermal fluid in the thermal fluid flow channel, is the friction pressure drop of the thermal fluid in the thermal fluid flow channel, is the gravity pressure drop of the thermal fluid in the thermal fluid flow channel, is the local pressure drop of the thermal fluid in the thermal fluid flow channel; The pressure drop of the cold fluid in the cold fluid flow channel It is expressed as: in, is the pressure drop of the cold fluid in the cold fluid flow channel, is the friction pressure drop of the cold fluid in the cold fluid flow channel, is the gravity pressure drop of the cold fluid in the cold fluid flow channel, is the local pressure drop of the cold fluid in the cold fluid flow channel, is the accelerated pressure drop of the cold fluid in the cold fluid flow channel; S202. Construct a method for calculating the friction pressure drop of cold fluid in the cold fluid flow channel and the friction pressure drop of the hot fluid in the hot fluid flow channel Friction pressure drop Expression, and is represented as: in, Indicates dense flow, is the flow friction coefficient, is the fluid density, is the hydraulic diameter of the channel, is the convection heat transfer length; S203. Construct a method for calculating the local pressure drop of the cold fluid in the cold fluid flow channel and the local pressure drop of the hot fluid in the hot fluid flow channel Local pressure drop Expression, and is represented as: in, is the local resistance coefficient; S204. Construct a method for calculating the local pressure drop of the cold fluid in the cold fluid flow channel and the accelerated pressure drop of the hot fluid in the hot fluid flow channel Acceleration pressure drop Expression, and is represented as: in, is the heat exchange length, is the two-phase flow dryness, is the cavitation fraction of the two-phase flow in the homogeneous model, is the liquid density, is the gas phase density.

7. The two-dimensional calculation method for plate-fin precooler performance according to claim 6, characterized in that: The initial cold fluid physical parameters include: cold fluid flow, cold fluid pressure, cold fluid temperature, and dryness; The initial thermal fluid physical parameters include: thermal fluid flow, thermal fluid pressure, and thermal fluid temperature; The structural parameters include: the length, width and height of the hot fluid flow channel, the length, width and height of the cold fluid flow channel, the number of hot fluid flow channels, the number of cold fluid flow channels, and the length, width and height of the plate-fin precooler.

8. The two-dimensional calculation method for plate-fin precooler performance according to claim 7, characterized in that: Step S3 also includes: Assumptions for two-dimensional calculation of the performance of the plate-fin precooler are set; wherein the assumptions include: the mass flow rate of the cold fluid is evenly distributed in the cold fluid flow channel, the mass flow rate of the hot fluid is evenly distributed in the hot fluid flow channel, the fluid at the outlet of the plate-fin precooler is evenly mixed, axial heat transfer of the fluid is ignored, and internal heat conduction of the solid is ignored.

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