Data fitting method of heat exchange tube of gas-liquid blending heat exchanger and simulation method and system of heat exchanger

Abstract

The invention relates to the technical field of heat exchangers, and discloses a data fitting method of a heat exchange tube of a gas-liquid allocation heat exchanger and a simulation method and system of the heat exchanger, and the method comprises the following steps: constructing a heat exchange tube part model of the gas-liquid allocation heat exchanger, and dividing the heat exchange tube part model into a plurality of infinitesimal segments; dividing each infinitesimal section into a two-phase section and an overheating section; if the working medium is the two-phase section, calculating the heat exchange amount of the working medium in the infinitesimal section; iteratively calculating the outlet dryness of the heat exchange tube, and calculating the pressure drop and the outlet pressure of the infinitesimal section; if the micro-element section is an overheating section, calculating the maximum heat exchange amount, the thermal resistance, the heat exchange amount, the outlet temperature, the pressure drop and the outlet pressure of the working medium of the micro-element section, calculating the next micro-element section, fitting into a database, calling data of the database to simulate heat exchange of a heat exchange tube, and realizing simulation of the gas-liquid blending heat exchanger. The problem that in the prior art, the simulation is not accurate due to the fact that the pressure drop between the adjacent tube passes is not considered is solved, and the method has the advantage that numerical simulation of the gas-liquid blending heat exchanger can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchangers, and more specifically to a data fitting method for heat exchange tubes of a gas-liquid mixing heat exchanger, and a simulation method and system for the heat exchanger. Background Art

[0002] Heat exchangers are devices that realize heat transfer of fluids at different temperatures. Their heat transfer performance has an important impact on the energy efficiency of thermal systems. Therefore, some scholars have proposed to improve the performance of heat exchangers by changing the dryness distribution in heat exchangers by adjusting the liquid phase. This type of heat exchanger is called a gas-liquid adjustment heat exchanger. The header-small hole type gas-liquid adjustment unit has become one of the mainstream liquid distribution structures of gas-liquid adjustment heat exchangers due to its simple structure, good separation performance, and the advantages of being integrated into the heat exchanger. Gas-liquid adjustment heat exchangers are divided into two types: liquid separation condensers and liquid distribution evaporators. Liquid separation condensers reduce the thickness of the liquid film and the heat transfer resistance by discharging the liquid phase in time, thereby enhancing the heat transfer during the condensation process. During the evaporation process, the heat transfer coefficient increases first and then decreases with the increase of dryness. The liquid distribution evaporator improves the overall dryness distribution of the evaporator by separating part of the liquid phase at the low inlet dryness to increase the inlet dryness, and replenishing this part of the liquid phase to the high dryness area to reduce its dryness, thereby improving its efficient heat transfer area.

[0003] Therefore, the discharge volume of the liquid separation hole is crucial to the performance of the gas-liquid mixing heat exchanger. However, the discharge volume of the liquid separation hole is not only affected by the structure of the header-small hole type gas-liquid mixing unit, but also related to the pressure drop between adjacent tubes. At the same time, unreasonable structural design will cause leakage of the liquid separation hole and even cause the performance of the heat exchanger to deteriorate.

[0004] The prior art has a simulation calculation method for the working condition of a heat exchanger system, wherein the heat exchanger system includes a heat exchanger group composed of a plurality of heat exchanger units, and the simulation calculation method includes the following steps: establishing a three-dimensional simulation model of the heat exchanger unit; performing dimensional simulation calculation on the three-dimensional simulation model to obtain heat exchange characteristic information of the heat exchanger unit; wherein the heat exchange characteristic information includes flow characteristic information and temperature characteristic information; establishing a one-dimensional simulation model of the heat exchanger group; performing simulation calculation on the one-dimensional simulation model based on the heat exchange characteristic information to obtain the flow distribution result of the heat exchanger group; and performing three-dimensional simulation calculation on each heat exchanger unit in the heat exchanger group according to the flow distribution result to obtain the simulation calculation result of the heat exchanger system. Thus, the present invention can reduce the simulation calculation cost and improve the simulation calculation efficiency.

[0005] However, the existing simulation of gas-liquid allocation heat exchanger mainly simulates the performance of gas-liquid allocation heat exchanger by assuming the liquid separation amount. At the same time, the existing model also assumes that the flow distribution of each tube is uniform, and does not consider the deterioration of heat exchange performance caused by uneven flow distribution. Therefore, how to invent a method that can accurately simulate the flow and heat exchange in the gas-liquid allocation heat exchanger is a technical problem that urgently needs to be solved in this technical field. Summary of the invention

[0006] In order to solve the problem that the prior art does not consider the pressure drop between adjacent tube passes, resulting in inaccurate simulation, the present invention provides a data fitting method for heat exchange tubes of a gas-liquid mixing heat exchanger, a simulation method and system for the heat exchanger, which have the characteristic of being able to realize numerical simulation of the gas-liquid mixing heat exchanger.

[0007] In order to achieve the above-mentioned purpose of the present invention, the technical scheme adopted is as follows:

[0008] A data fitting method for a heat exchange tube of a gas-liquid mixing heat exchanger comprises the following specific steps:

[0009] Construct a heat exchange tube model of the gas-liquid mixing heat exchanger, and divide the heat exchange tube model into several micro-element segments; based on the set inlet dryness, divide each micro-element segment into a two-phase segment and a superheat segment;

[0010] For each microelement segment:

[0011] If it is a two-phase section, calculate the heat transfer of the working fluid in the micro-element section; iteratively calculate the outlet dryness of the heat exchange tube based on the heat transfer, and further calculate the pressure drop and outlet pressure of the micro-element section; use the outlet pressure, flow rate and dryness as the inlet conditions of the next micro-element section to calculate the next micro-element section;

[0012] If it is a superheated section, the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element section are calculated, and the outlet pressure, flow rate and temperature are used as the inlet conditions of the next micro-element section to calculate the next micro-element section;

[0013] The heat transfer, pressure drop and outlet dryness of the heat exchange tubes at different inlet flow rates and drynesses are fitted into a database.

[0014] Preferably, the heat exchange tube part model of the gas-liquid mixing heat exchanger is constructed, and the specific steps are as follows:

[0015] Obtain the heat exchange tube structural parameters including tube length, tube number, tube spacing, outer diameter, inner diameter and thermal conductivity;

[0016] If it is an internally threaded pipe, the number of grooves, groove bottom width, tooth height, tooth top angle and helix angle are also obtained;

[0017] If there are fins installed externally, the input fin parameters are also obtained;

[0018] The ε-NTU method is used to simulate the heat exchange tube section and construct a one-dimensional heat exchange tube partial model.

[0019] Furthermore, based on the set inlet dryness, each micro-element segment is divided into a two-phase segment and a superheat segment. Specifically, the micro-element segment with an inlet dryness less than 1 is divided into a two-phase segment, and the micro-element segment with an inlet dryness equal to 1 is divided into a superheat segment.

[0020] Furthermore, if it is a two-phase section, the heat transfer of the working fluid in the micro-element section is calculated; the outlet dryness of the heat exchange tube is iteratively calculated based on the heat transfer, and the pressure drop and outlet pressure of the micro-element section are further calculated. The specific steps are:

[0021] Assume that the outlet dryness of the micro-element segment is:

[0022] x i,out,a =x i,in +0.01

[0023] Where: x i,out,a is the outlet dryness assumed for the ith microelement segment, x i,in is the inlet dryness of the ith microelement segment;

[0024] Take the average dryness of the inlet and outlet to determine the working fluid properties, and calculate the average dryness x of the i-th microelement segment i :

[0025]

[0026] The heat flux q is calculated by the inlet dryness and outlet dryness as follows:

[0027]

[0028] Where G is the refrigerant flow rate, ΔH is the latent heat of the refrigerant, D is the outer diameter of the heat exchange tube, and L is i is the length of the heat exchange tube microelement segment, mesh is the number of microelement segments;

[0029] Calculate the refrigerant side heat transfer coefficient h by heat transfer correlation r and the heat transfer coefficient h outside the tube a Then calculate the total thermal resistance UA:

[0030]

[0031] Where d is the inner diameter of the heat exchange tube, and λ is the thermal conductivity of the heat exchange tube wall;

[0032] Then calculate the number of heat transfer units NTU:

[0033]

[0034] Among them, C min is the specific heat capacity of the fluid with the smallest specific heat capacity among the fluids inside and outside the tube;

[0035] Calculate the heat transfer effectiveness ε:

[0036] ε=1-e -NTU

[0037] Calculate the theoretical maximum heat transfer Q max :

[0038] Q max =C min (T a,dry,in -T i,in )

[0039] Among them, T a,dry,in is the air side dry bulb temperature, T i,in is the refrigerant inlet temperature of the micro-element segment;

[0040] Calculate the heat transfer Q under the assumed outlet dryness according to ε i And the corresponding outlet dryness:

[0041] Q i =ε·Q max

[0042]

[0043] Among them, Q i is the heat transfer of the microelement segment, x i,out,c is the calculated outlet dryness;

[0044] Determine whether the assumed outlet dryness and the calculated outlet dryness converge:

[0045]

[0046] If it does not converge, the calculated outlet dryness x i,out,c Assume that the outlet dryness x is the new i,out,a , return to the step of calculating the average dryness of the i-th microelement segment, and iterate repeatedly until convergence;

[0047] If convergence occurs, the pressure drop ΔP of the microelement segment is calculated according to the two-phase flow pressure drop correlation formula: i And the outlet pressure of the micro-element segment P i,out , and use the exit condition as the entry condition of the next micro-element segment.

[0048] Furthermore, if it is a superheating section, the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element section are calculated. The specific steps are:

[0049] Calculate the maximum heat transfer of the micro-element segment:

[0050] Q max =C min (T a,dry,in -T i,in )

[0051] C min =min(C r ,C a )

[0052] Among them, C r is the specific heat capacity of the refrigerant, C a is the specific heat capacity of air;

[0053] Calculate the heat transfer coefficient h of the refrigerant side in the superheat section according to the heat transfer correlation formula r , and then calculate the total thermal resistance UA and the number of heat transfer units NTU:

[0054]

[0055] The heat transfer effectiveness ε is calculated based on the ε-NTU correlation formula for cross flow without phase change:

[0056]

[0057] C max =max(C r ,C a )

[0058]

[0059] Calculate the heat transfer Q under the assumed outlet dryness according to ε i And the outlet temperature:

[0060] Q i =ε·Q max

[0061]

[0062] Calculate the pressure drop ΔP of the micro-element section according to the correlation formula of the pressure drop of the superheat section i And the outlet pressure of the micro-element segment P i,out , and use the exit condition as the entry condition of the next micro-element segment.

[0063] Furthermore, the heat transfer, pressure drop and outlet dryness of the heat exchange tube at different inlet flow rates and drynesses are fitted into a database. The specific steps are: divide the flow range into several flow rates according to the set step size, calculate the heat transfer, pressure drop and outlet dryness of each flow rate at several inlet drynesses, fit the relationship between the pressure drop and flow rate at each inlet dryness, and the relationship between the outlet dryness and flow rate, and use the fitted correlation equation as the database.

[0064] A simulation method for a gas-liquid mixing heat exchanger, based on the data fitting method of the heat exchange tube, comprises the following specific steps:

[0065] Construct the header model of the gas-liquid mixing heat exchanger;

[0066] The simulation of the gas-liquid mixing heat exchanger is realized by simulating the flow in the manifold using three-dimensional fluid mechanics calculations: the outlet flow and dryness of the inlet manifold are monitored in each simulation, and the outlet dryness and pressure drop of the heat exchange tube after heat exchange in the heat exchange tube are called up in the database according to the outlet flow and dryness of the inlet manifold. The outlet flow and outlet dryness are used as the inlet conditions of the outlet manifold, and the inlet pressure of the outlet manifold is monitored at the same time, and the pressure plus the pressure drop of the heat exchange tube is used as the outlet pressure of the inlet manifold.

[0067] Preferably, when constructing the manifold part model of the gas-liquid mixing heat exchanger, a three-dimensional physical model including several manifolds is constructed; for the three-dimensional physical model of each manifold, structured mesh division is performed, and if the manifold part has a orifice plate, the mesh at the liquid separation hole of the orifice plate is encrypted.

[0068] Furthermore, the flow in the manifold is simulated by using three-dimensional fluid mechanics calculations to simulate the gas-liquid mixing heat exchanger. Specifically, ANSYS fluent software is used to put the inlet manifold and the outlet manifold into the same case for simulation, and a custom equation UDF is used to replace the flow and heat transfer of the heat exchanger. In ANSYS fluent, the velocity inlet boundary condition is used at the manifold inlet, and the pressure outlet boundary condition is used at the manifold outlet. When UDF is used to replace the heat exchanger, the outlet parameters of the inlet manifold are monitored, and the heat transfer and pressure drop are calculated based on the database to obtain the outlet parameters of the heat exchanger tube as the inlet condition of the outlet manifold. The inlet pressure of the outlet manifold is monitored, and the pressure drop of the heat exchanger tube is added based on the database as the outlet pressure boundary condition of the inlet manifold.

[0069] A gas-liquid mixing heat exchanger simulation system is used to execute the simulation method of the gas-liquid mixing heat exchanger, including a modeling module, a heat exchange tube simulation module, a database fitting module, and a gas-liquid mixing heat exchanger simulation module:

[0070] The modeling module is used to construct a heat exchange tube part model and a header part model of a gas-liquid mixing heat exchanger;

[0071] The heat exchange tube simulation module is used to divide the heat exchange tube part model into several micro-element segments; based on the set inlet dryness, each micro-element segment is divided into a two-phase segment and a superheat segment; for each micro-element segment: if it is a two-phase segment, the heat transfer of the working fluid in the micro-element segment is calculated; the outlet dryness of the heat exchange tube is iteratively calculated based on the heat transfer, and the pressure drop and outlet pressure of the micro-element segment are further calculated; the outlet pressure, flow rate and dryness are used as the inlet conditions of the next micro-element segment to calculate the next micro-element segment; if it is a superheat segment, the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element segment are calculated, and the outlet pressure, flow rate and temperature are used as the inlet conditions of the next micro-element segment to calculate the next micro-element segment;

[0072] The database fitting module is used to fit the heat transfer, pressure drop and outlet dryness of the heat exchange tube under different inlet flow rates and dryness into a database;

[0073] The gas-liquid mixing heat exchanger simulation module is used to simulate the flow in the manifold by adopting three-dimensional fluid mechanics calculation to realize the simulation of the gas-liquid mixing heat exchanger: each simulation monitors the outlet flow and dryness of the inlet manifold, and calls the outlet dryness and heat exchange tube pressure drop after heat exchange in the heat exchange tube in the database according to the outlet flow and dryness of the inlet manifold, and uses the outlet flow and outlet dryness as the inlet conditions of the outlet manifold, and monitors the inlet pressure of the outlet manifold at the same time, and uses the pressure plus the heat exchange tube pressure drop as the outlet pressure of the inlet manifold.

[0074] The beneficial effects of the present invention are as follows:

[0075] The present invention discloses a simulation method for a gas-liquid mixing heat exchanger, which divides the gas-liquid mixing heat exchanger into two parts, namely a header and a heat exchange tube, and divides the heat exchange tube part model into a plurality of micro-element segments for simulation in the heat exchange tube part, fits the heat exchange amount, pressure drop and outlet dryness of the heat exchange tube under different inlet flow rates and drynesses obtained into a database, and constructs a header part model, and simulates the gas-liquid mixing heat exchanger based on the database and the header part model; thereby, the present invention realizes accurate simulation of the flow distribution in a header-small hole type gas-liquid mixing unit with less calculation amount, considers the coupling relationship between the heat exchange tube pressure drop and the header flow distribution, and can realize numerical simulation of the gas-liquid mixing heat exchanger, accurately and efficiently calculates the working fluid distribution, heat transfer performance and pressure drop of the heat exchanger under different working conditions and structures, provides technical support for the optimization of the gas-liquid mixing heat exchanger, and reduces the research and development cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 The present invention is a flow chart of a method for fitting data of heat exchange tubes of a gas-liquid mixing heat exchanger.

[0077] Figure 2 This is a schematic diagram of the structure of the gas-liquid blending heat exchanger in Example 1.

[0078] Figure 3 This is a simulation schematic diagram of the heat exchange tube in Example 1.

[0079] Figure 4 This is a simulation flow chart of the heat exchange tube in Example 1.

[0080] Figure 5 This is a flow chart of the simulation method of the gas-liquid blending heat exchanger in Example 2.

[0081] Figure 6 This is a schematic diagram of the simulation of the gas-liquid blending heat exchanger in Example 2.

[0082] Figure 7 This is a specific flow chart for simulating the gas-liquid blending heat exchanger in Example 2.

[0083] Figure 8 This is a schematic diagram of the structure of the gas-liquid mixing evaporator in Example 3.

[0084] Fig. 9 This is the phase distribution diagram of the upper half of the gas-liquid blending evaporator in Example 3.

[0085] Fig.10 This is the phase distribution diagram of the lower half of the gas-liquid blending evaporator in Example 3.

[0086] Fig.11 This is the flow distribution diagram of the gas-liquid blending evaporator pipeline in Example 3.

[0087] Fig.12 This is the heat exchange diagram of the gas-liquid blending evaporator pipeline in Example 3.

[0088] In the figure, 1 is a fin, 2 is a heat exchange tube, 3 is an inlet of the heat exchange tube, 4 is a liquid separation orifice plate, 5 is an outlet of the heat exchange tube, and 6 is a blind plate. DETAILED DESCRIPTION

[0089] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0090] Example 1

[0091] like Figure 1 As shown, a data fitting method for a heat exchange tube of a gas-liquid mixing heat exchanger comprises the following specific steps:

[0092] Construct a heat exchange tube model of the gas-liquid mixing heat exchanger, and divide the heat exchange tube model into several micro-element segments; based on the set inlet dryness, divide each micro-element segment into a two-phase segment and a superheat segment;

[0093] For each microelement segment:

[0094] If it is a two-phase section, calculate the heat transfer of the working fluid in the micro-element section; iteratively calculate the outlet dryness of the heat exchange tube based on the heat transfer, and further calculate the pressure drop and outlet pressure of the micro-element section; use the outlet pressure, flow rate and dryness as the inlet conditions of the next micro-element section to calculate the next micro-element section;

[0095] If it is a superheated section, the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element section are calculated, and the outlet pressure, flow rate and temperature are used as the inlet conditions of the next micro-element section to calculate the next micro-element section;

[0096] The heat transfer, pressure drop and outlet dryness of the heat exchange tubes at different inlet flow rates and drynesses are fitted into a database.

[0097] In this embodiment, the structure of the gas-liquid mixing heat exchanger is as follows: Figure 2 As shown, the gas-liquid mixing heat exchanger realizes liquid phase mixing in different pipe passes by setting an orifice plate in the header or other methods. The liquid separation amount of the orifice plate is related to the pressure drop of the intermediate pipe pass. The gas-liquid mixing heat exchanger is divided into two types: liquid separation condenser and liquid mixing evaporator. The liquid separation condenser reduces the thickness of the liquid film by discharging the liquid phase in time, reduces the heat transfer resistance, and thus enhances the heat transfer in the condensation process. During the evaporation process, the heat transfer coefficient increases first and then decreases with the increase of dryness. The liquid mixing evaporator improves the overall dryness distribution of the evaporator by separating part of the liquid phase at the low inlet dryness and replenishing the part of the liquid phase to the high dryness area to reduce its dryness, thereby improving its efficient heat transfer area. Therefore, the working medium flow area in the gas-liquid mixing evaporator can be divided into two parts, one part is the header-small hole type gas-liquid mixing unit for gas-liquid mixing of the working medium, and the other part is the heat exchange pipe section for heat exchange with the heat source. The simulation of the gas-liquid mixing evaporator can be decomposed into the simulation of these two parts. Since the two-phase flow in the header is very complex, three-dimensional CFD is used to simulate the header. For the heat exchange tube section, the main focus is on the heat transfer, pressure drop and outlet parameters of the working fluid, and it is not necessary to know the specific flow state in the heat exchange tube. At the same time, many scholars have studied the heat transfer process of the heat exchange tube and obtained high-precision empirical formulas, which can be used to calculate the heat transfer and pressure drop of the working fluid in the heat exchange tube. Therefore, considering the simulation accuracy and calculation amount, a one-dimensional heat exchange tube model is established, and the ε-NTU method is used to simulate the heat exchange tube section to calculate the heat transfer coefficient, heat transfer, pressure drop and outlet parameters of the heat exchange tube.

[0098] In this embodiment, the heat exchange fluid outside the tube is air. Under steady-state conditions, air and refrigerant exchange heat. The heat exchange tube is the core of the heat exchange. The gas-liquid two-phase distribution in the header will affect the heat exchange amount and pressure drop of the heat exchange tube. At the same time, the pressure drop of the heat exchange tube will in turn affect the liquid separation amount of the liquid separation hole in the header, thereby affecting the two-phase distribution of each heat exchange tube. Therefore, the present invention divides the gas-liquid mixing heat exchanger into two parts: the header and the heat exchange tube. First, a one-dimensional model of the heat exchange tube is established, and the relationship between the outlet dryness, pressure drop and inlet flow rate and dryness of the heat exchange tube is fitted into a correlation equation. Then, a three-dimensional model of the left header and the right header is established. Fluent is used to simulate and calculate it. The inlet and outlet parameters of the header are monitored by UDF. The correlation equation obtained by the heat exchange tube model is used for processing to obtain the corresponding parameters as new boundary conditions, so as to achieve the modeling of the heat exchange tube part replaced by UDF in Fluent, and a gas-liquid mixing heat exchanger model with small calculation amount and high precision is established.

[0099] In a specific embodiment, a heat exchange tube part model of a gas-liquid mixing heat exchanger is constructed, and the specific steps are as follows:

[0100] Obtain the heat exchange tube structural parameters including tube length, tube number, tube spacing, outer diameter, inner diameter and thermal conductivity;

[0101] If it is an internally threaded pipe, the number of grooves, groove bottom width, tooth height, tooth top angle and helix angle are also obtained;

[0102] If there are fins installed externally, the input fin parameters are also obtained, such as fin thickness, fin width, fin height, number of fins, fin spacing and fin thermal conductivity, etc.;

[0103] The ε-NTU method is used to simulate the heat exchange tube section and construct a one-dimensional heat exchange tube partial model. This one-dimensional heat exchange tube partial model is mainly suitable for cross-flow or large heat capacity of the heat exchange fluid outside the tube, and the corresponding physical property parameters of the heat exchange fluid outside the tube are also required.

[0104] In this embodiment, the heat exchange tube model is divided into several micro-element segments such as Figure 3 As shown, each micro-element segment includes an air side inlet, an air side outlet, a working fluid side inlet, and a working fluid side outlet; the inlet dryness is given by simultaneously giving the air side inlet and the working fluid side inlet dryness.

[0105] In a specific embodiment, based on the set inlet dryness, each micro-element segment is divided into a two-phase segment and a superheat segment, specifically: the micro-element segment with an inlet dryness less than 1 is divided into a two-phase segment, and the micro-element segment with an inlet dryness equal to 1 is divided into a superheat segment.

[0106] In a specific embodiment, Figure 4As shown, if it is a two-phase section, the heat transfer of the working fluid in the micro-element section is calculated; the outlet dryness of the heat exchange tube is iteratively calculated based on the heat transfer, and the pressure drop and outlet pressure of the micro-element section are further calculated. The specific steps are:

[0107] Assume that the outlet dryness of the micro-element segment is:

[0108] x i,out,a =x i,in +0.01

[0109] Where: x i,out,a is the outlet dryness assumed for the ith microelement segment, x i,in is the inlet dryness of the ith microelement segment;

[0110] Take the average dryness of the inlet and outlet to determine the working fluid properties, and calculate the average dryness x of the i-th microelement segment i :

[0111]

[0112] The heat flux q is calculated by the inlet dryness and outlet dryness as follows:

[0113]

[0114] Where G is the refrigerant flow rate, ΔH is the latent heat of the refrigerant called by refprop according to the refrigerant inlet pressure, D is the outer diameter of the heat exchange tube, L is i is the length of the heat exchange tube microelement segment, mesh is the number of microelement segments;

[0115] Calculate the refrigerant side heat transfer coefficient h by heat transfer correlation r and the heat transfer coefficient h outside the tube a Then calculate the total thermal resistance UA:

[0116]

[0117] Where d is the inner diameter of the heat exchange tube, and λ is the thermal conductivity of the heat exchange tube wall;

[0118] Then calculate the number of heat transfer units NTU:

[0119]

[0120] Among them, C min is the specific heat capacity of the fluid with the smallest specific heat capacity among the fluids inside and outside the tube, which is air here;

[0121] Calculate the heat transfer effectiveness:

[0122] ε=1-e -NTU

[0123] Calculate the theoretical maximum heat transfer Qmax :

[0124] Q max =C min (T a,dry,in -T i,in )

[0125] Among them, T a,dry,in is the air side dry bulb temperature, T i,in is the refrigerant inlet temperature of the micro-element segment called by refprop according to the refrigerant inlet pressure;

[0126] Calculate the heat transfer Q under the assumed outlet dryness according to ε i And the corresponding outlet dryness:

[0127] Q i =ε·Q max

[0128]

[0129] Among them, Q i is the heat transfer of the microelement segment, x i,out,c is the calculated outlet dryness;

[0130] Determine whether the assumed outlet dryness and the calculated outlet dryness converge:

[0131]

[0132] If it does not converge, the calculated outlet dryness x i,out,c Assume that the outlet dryness x is the new i,out,a , return to the step of calculating the average dryness of the i-th microelement segment, and iterate repeatedly until convergence;

[0133] If convergence occurs, the pressure drop ΔP of the microelement segment is calculated according to the two-phase flow pressure drop correlation formula: i And the outlet pressure of the micro-element segment P i,out , and use the exit condition as the entry condition of the next micro-element segment.

[0134] In a specific embodiment, if it is a superheating section, the maximum heat transfer capacity, thermal resistance, heat transfer capacity, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element section are calculated, and the specific steps are:

[0135] Calculate the maximum heat transfer of the micro-element segment:

[0136] Q max =C min (T a,dry,in -T i,in )

[0137] C min =min(Cr ,C a )

[0138] Among them, C r is the specific heat capacity of the refrigerant, C a is the specific heat capacity of air;

[0139] Calculate the heat transfer coefficient h of the refrigerant side in the superheat section according to the heat transfer correlation formula r , and then calculate the total thermal resistance UA and the number of heat transfer units NTU:

[0140]

[0141] The heat transfer effectiveness ε is calculated based on the ε-NTU correlation formula for cross flow without phase change:

[0142]

[0143] C max =max(C r ,C a )

[0144]

[0145] Calculate the heat transfer Q under the assumed outlet dryness according to ε i And the outlet temperature:

[0146] Q i =ε·Q max

[0147]

[0148] Calculate the pressure drop ΔP of the micro-element section according to the correlation formula of the pressure drop of the superheat section i And the outlet pressure of the micro-element segment P i,out , and use the exit condition as the entry condition of the next micro-element segment.

[0149] In a specific embodiment, the heat transfer capacity, pressure drop and outlet dryness of the heat exchange tube at different inlet flow rates and drynesses are fitted into a database. The specific steps are: divide the flow range into a range of 0.5g / s-20g / s according to the set step size, and calculate the heat transfer capacity, pressure drop and outlet dryness at each flow rate of 0, 0.1, 0.2, 0.3...0.9, 1 with a step size of 0.1g. The relationship between the pressure drop and the flow rate at each inlet dryness, and the relationship between the outlet dryness and the flow rate are fit, and the fitted correlation equation is used as the database.

[0150] Example 2

[0151] like Figure 5As shown, a simulation method for a gas-liquid mixing heat exchanger is based on the data fitting method of the heat exchange tube, and includes the following specific steps:

[0152] Construct the header model of the gas-liquid mixing heat exchanger;

[0153] The simulation of the gas-liquid mixing heat exchanger is realized by simulating the flow in the manifold using three-dimensional fluid mechanics calculations: the outlet flow and dryness of the inlet manifold are monitored in each simulation, and the outlet dryness and pressure drop of the heat exchange tube after heat exchange in the heat exchange tube are called up in the database according to the outlet flow and dryness of the inlet manifold. The outlet flow and outlet dryness are used as the inlet conditions of the outlet manifold, and the inlet pressure of the outlet manifold is monitored at the same time, and the pressure plus the pressure drop of the heat exchange tube is used as the outlet pressure of the inlet manifold.

[0154] More specifically, in a specific embodiment, when constructing the model of the header part, a three-dimensional physical model including several headers is constructed; for the three-dimensional physical model of each header, structured mesh division is performed, and if the header part has a orifice plate, the mesh at the liquid separation hole of the orifice plate is encrypted.

[0155] In a specific embodiment, Figure 6 As shown, the flow in the header is simulated by three-dimensional fluid dynamics calculation to realize the simulation of the gas-liquid mixing heat exchanger. Specifically, the flow in the three-dimensional physical model of each header is simulated by using ANSYS fluent software. Each simulation puts the left and right headers into the same case for simulation, and uses the custom equation UDF to replace the flow and heat exchange of the heat exchange tube; in ANSYS fluent, the velocity inlet boundary condition is used at the header inlet, and the pressure outlet boundary condition is used at the header outlet; when using UDF to replace the heat exchange tube, the outlet parameters of the inlet header are monitored, and the heat transfer and pressure drop are calculated based on the database, and the outlet parameters of the heat exchange tube are obtained as the inlet conditions of the outlet header, the inlet pressure of the outlet header is monitored, and the pressure drop of the heat exchange tube is added based on the database as the outlet pressure boundary condition of the inlet header;

[0156] like Figure 7As shown, when Fluent is used to simulate the header, since the flows in the left and right headers affect each other, the left and right headers are respectively used as the inlet header and the outlet header for simulation in the same case, and UDF is used to replace the flow heat exchange of the heat exchanger, so as to realize the simulation of the gas-liquid mixing heat exchanger. In Fluent, the velocity inlet boundary condition is used at the header inlet, and the pressure outlet boundary condition is used at the header outlet. When using UDF to replace the heat exchanger, the following functions need to be realized: monitor the outlet parameters of the inlet header (the inlet parameters of the heat exchanger tube), calculate its heat transfer and pressure drop, and obtain the outlet parameters of the heat exchanger tube as the inlet conditions (flow rate, dryness) of the outlet header. Since the pressure drop of the heat exchanger tube will affect the header distribution in the header, it needs to be considered as the key point. The inlet pressure of the outlet header (the outlet pressure of the heat exchanger tube) is monitored by UDF and the pressure drop of the heat exchanger tube is added as the outlet pressure boundary condition of the inlet header (the inlet pressure of the heat exchanger tube). In this way, the calculation using UDF instead of the heat exchanger tube is realized, which greatly reduces the amount of calculation.

[0157] Example 3

[0158] In this embodiment, Figure 8 As shown, the simulation method of the gas-liquid mixing heat exchanger of the present invention is used to simulate a three-pass gas-liquid mixing evaporator with a tube number distribution of 2-2-2; wherein the evaporator is provided with a plurality of fins, liquid is separated at the liquid separation orifice plate 3 of the first tube pass, liquid is replenished at the inlet of the third tube pass, the blind plate 6 is used for flow control, and the heat exchange tube 2 is a tube with an internal thread and an external fin 1. The refrigerant enters from the heat exchange tube inlet 3 above the evaporator, exchanges heat through the three tube passes, and then flows out from the heat exchange tube outlet 5 below the evaporator.

[0159] The gas-liquid mixing evaporator is divided into two parts: the header and the heat exchange tube;

[0160] In this embodiment, a heat exchange tube model of a gas-liquid mixing heat exchanger is constructed, specifically:

[0161] Assuming the inlet flow rate is 7.4g, the inlet dryness is 0.1, and the refrigerant is R134a, the header structural parameters of the physical model are shown in Table 1, the heat exchange tube structural parameters are shown in Table 2, and the fin structural parameters are shown in Table 3.

[0162] Table 1 Header structure parameters

[0163]

[0164]

[0165] Table 2 Heat exchange tube parameters

[0166]

[0167] Table 3 Fin parameters

[0168]

[0169] Based on the above parameters, the heat exchange tube model of the gas-liquid mixing heat exchanger is constructed:

[0170] Tube Thickness:

[0171]

[0172] Cross-sectional area of ​​tooth root circle:

[0173]

[0174] Cross-sectional area of ​​tooth tip circle:

[0175]

[0176] Cross-sectional area of ​​tooth tip circle:

[0177]

[0178] Equivalent diameter (calculated by definition as 4 times the area around the circumference):

[0179]

[0180] Total heat exchange area on the air side:

[0181]

[0182] Heat exchange area on the air side of each micro-element segment:

[0183]

[0184] Heat exchange tube radius:

[0185]

[0186] Equivalent rib radius:

[0187]

[0188] Equivalent rib height:

[0189]

[0190] Root heat exchange area:

[0191]

[0192] Fin surface heat exchange area:

[0193]

[0194] Total rib efficiency:

[0195]

[0196] η: Rib efficiency

[0197] The air inlet temperature on the air side is divided into dry bulb temperature and wet bulb temperature. The dry bulb temperature is:

[0198]

[0199] The air side inlet wet bulb temperature is:

[0200]

[0201] Construct a heat exchange tube model of the gas-liquid mixing heat exchanger and divide the heat exchange tube model into several micro-element segments; based on the set inlet dryness, divide each micro-element segment into a two-phase segment and a superheat segment:

[0202] In this embodiment, the refrigerant is divided into two-phase flow and superheated steam flow in the heat exchange tube. Since the dryness of the two-phase flow increases in the heat exchange tube, and the physical properties change greatly with the dryness, the temperature decreases slightly with the pressure decrease, while the superheated flow absorbs heat in the heat exchange tube to continuously increase the temperature. The state of the two-phase flow is measured by dryness, while the state of the superheated steam flow is measured by temperature. The two-phase flow and the superheated steam flow have different flow patterns, and there are large differences in heat transfer coefficient and pressure drop. Therefore, different empirical formulas should be used for these two flow states. For the heat exchange tube model, the main focus is on the refrigerant heat transfer and pressure drop, so the empirical formula is used to calculate its heat transfer coefficient and pressure drop. The selected heat transfer correlation and pressure drop correlation are shown in Table 4.

[0203] Table 4 Heat transfer correlation and pressure drop correlation

[0204]

[0205]

[0206]

[0207] For each microelement segment:

[0208] If it is a two-phase section, calculate the heat transfer of the working fluid in the micro-element section; iteratively calculate the outlet dryness of the heat exchange tube based on the heat transfer, and further calculate the pressure drop and outlet pressure of the micro-element section; use the outlet pressure, flow rate and dryness as the inlet conditions of the next micro-element section to calculate the next micro-element section;

[0209] If it is a superheated section, the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element section are calculated, and the outlet pressure, flow rate and temperature are used as the inlet conditions of the next micro-element section to calculate the next micro-element section;

[0210] The heat transfer, pressure drop and outlet dryness of the heat exchange tube at different inlet flow rates and dryness are fitted into a database;

[0211] A three-dimensional physical model including several headers is constructed; for the three-dimensional physical model of each header, structured mesh division is performed, and if the header part has an orifice plate, the mesh at the liquid separation hole of the orifice plate is encrypted.

[0212] Simulate the flow within the 3D physical model of each header:

[0213] When simulating each manifold, the outlet flow and dryness of the inlet manifold are monitored, and the outlet dryness and heat exchange tube pressure drop after heat exchange in the heat exchange tube are called up in the database according to the outlet flow and dryness of the inlet manifold. The outlet flow and outlet dryness are used as the inlet conditions of the outlet manifold. At the same time, the inlet pressure of the outlet manifold is monitored, and the pressure plus the heat exchange tube pressure drop is used as the outlet pressure of the inlet manifold.

[0214] The simulation of the gas-liquid mixing heat exchanger is realized by simulating the flow in the header box by using three-dimensional fluid dynamics calculation. Specifically, ANSYS fluent software is used to simulate the flow in the three-dimensional physical model of each header box. Each simulation puts the left and right header boxes into the same case for simulation, and uses the custom equation UDF to replace the flow and heat exchange of the heat exchanger pipe. In ANSYS fluent, the velocity inlet boundary condition is used at the header box inlet, and the pressure outlet boundary condition is used at the header box outlet. When using UDF to replace the heat exchanger, the outlet parameters of the inlet header box are monitored, and the heat transfer and pressure drop are calculated based on the database to obtain the outlet parameters of the heat exchanger pipe as the inlet condition of the outlet header box, the inlet pressure of the outlet header box is monitored, and the pressure drop of the heat exchanger pipe is added based on the database as the outlet pressure boundary condition of the inlet header box.

[0215] In this embodiment, when ANSYS Fluent is used to simulate the junction box, the Eulerian model is selected for the multiphase flow model, the realizable "k-ε" model is selected for the turbulence model, the non-equilibrium wall function is selected to process the wall, the solver is selected as Pressure-Based, the steady-state solution is selected, the discretization method used is the finite volume method (FVM), the velocity-pressure coupling uses the SIMPLE algorithm, the pressure discretization uses the PRESTO format, and other fluxes use the second-order upwind discretization format.

[0216] In this embodiment, since the loaded UDF monitors data and assigns values ​​at each step, and iterates repeatedly, if the entire evaporator is simulated, there are 12 surfaces loaded with UDF for iteration. In order to improve the convergence speed of the header model, the model is further simplified. Assuming that the pressure at the outlet of the liquid separation hole and the outlet of the second tube pass is the same, the header model is divided into upper and lower parts at the outlet of the second tube pass for simulation. The upper part is the first tube pass, the inlet of the second tube pass and the corresponding header part. The outlet pressure at the liquid separation hole is taken as a constant value, and the inlet pressure of the second tube pass is the outlet pressure of the liquid separation hole plus the pressure drop of the second tube pass. The pressure drop of the second tube pass is obtained by the flow rate and dryness at the inlet of the second tube pass through the association formula in the UDF. Therefore, the boundary conditions of the upper model are determined. After the upper model converges, the pressure difference between the evaporator inlet and the separator hole outlet is the pressure difference of the upper part. The flow rate and dryness of the separator hole and the second pipe pass are taken as the inlet conditions of the lower model. After the lower model converges, the pressure difference between the separator hole and the evaporator outlet is the pressure difference of the lower part. The pressure difference of the two parts is the total pressure drop of the evaporator.

[0217] In this embodiment, the simulation results of the upper evaporator are as follows: Fig. 9 The simulation results of the lower evaporator are shown in Fig.10 As shown in Figure 2, the flow distribution of each pipe is as follows: Fig.11 As shown in the figure, 1 to 6 represent the six heat exchange tubes from top to bottom. Due to the different densities of the gas and liquid phases, the two-phase flow is unevenly distributed in each pipe in the same pipe pass, and the liquid phase is difficult to reach the heat exchange tube above the same pipe pass, resulting in high inlet dryness of the heat exchange tube above each pipe pass, and the outlet is superheated steam, and its heat transfer performance is poor. The heat transfer of each pipe is as follows: Fig.12 As shown in the figure, the inlet dryness of tubes 3 and 5 is too high, and their heat transfer is much smaller than that of other heat exchange tubes, resulting in a decrease in evaporator performance. The liquid separation amount of the liquid separation hole is 1.69g, which can effectively improve the dryness of the first and second tube passes, but the flow rate is also reduced due to the liquid separation. Under the comprehensive influence, the heat transfer rate does not change much. Therefore, when performing gas-liquid allocation, the distribution of the number of pipes in the tube pass needs to be optimized according to the flow change.

[0218] In this embodiment, in order to measure the uneven distribution of pipelines, the difference in heat exchange when assuming uniform distribution of pipe flow is compared with the heat exchange obtained by the coupling model under the same liquid separation amount. When the pipe flow is assumed to be uniformly distributed, the heat exchange of the first pipe pass, the second pipe pass and the third pipe pass of the evaporator are 126.4W, 128.3W and 130.6W respectively. Since it does not consider the uneven distribution of gas and liquid, the heat exchange of the second and third pipe passes obtained by the simulation is much larger than that of the coupling model. The heat exchange obtained by the coupling model is only 69.1% of that when the flow is assumed to be uniformly distributed. Therefore, it is very important to consider the uneven distribution of gas and liquid when modeling and simulating the heat exchanger.

[0219] In summary, the method described in this embodiment is a numerical simulation method for a gas-liquid mixing heat exchanger, which can calculate the two-phase distribution, pressure drop and heat transfer of the gas-liquid mixing heat exchanger quickly and accurately under different working environments and inlet conditions. According to the different functions of the heat exchange tube and the header and existing research, a suitable simplified model is established; first, a heat exchange tube model is established to calculate the heat transfer performance of the heat exchange tube within a certain operating range, and it is fitted into a correlation equation, and then the flow in the header is simulated by Fluent, and the heat transfer and pressure drop of the heat exchange tube are simulated by UDF. First, an inlet pressure of the heat exchange tube is assumed to obtain the two-phase distribution in the header, and then the pressure drop and outlet dryness corresponding to the heat exchange tube under the flow are obtained by UDF, and the flow and outlet dryness are used as the inlet conditions of the outlet header, and the inlet pressure of the outlet header plus the pressure drop of the heat exchange tube are used as the new outlet pressure of the header, and it is repeated until the flow and pressure of each pipeline are stable. This method can accurately and efficiently simulate the two-phase distribution in the manifold, and at the same time simulate the coupling relationship between the pipeline pressure drop and the liquid separation of the separation hole. It has the characteristics of wide application range, high calculation efficiency and good accuracy.

[0220] Example 4

[0221] A gas-liquid mixing heat exchanger simulation system is used to execute the simulation method of the gas-liquid mixing heat exchanger, including a modeling module, a heat exchange tube simulation module, a database fitting module, and a gas-liquid mixing heat exchanger simulation module:

[0222] The modeling module is used to construct a heat exchange tube part model and a header part model of a gas-liquid mixing heat exchanger;

[0223] The heat exchange tube simulation module is used to divide the heat exchange tube part model into several micro-element segments; based on the set inlet dryness, each micro-element segment is divided into a two-phase segment and a superheat segment; for each micro-element segment: if it is a two-phase segment, the heat transfer of the working fluid in the micro-element segment is calculated; the outlet dryness of the heat exchange tube is iteratively calculated based on the heat transfer, and the pressure drop and outlet pressure of the micro-element segment are further calculated; the outlet pressure, flow rate and dryness are used as the inlet conditions of the next micro-element segment to calculate the next micro-element segment; if it is a superheat segment, the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element segment are calculated, and the outlet pressure, flow rate and temperature are used as the inlet conditions of the next micro-element segment to calculate the next micro-element segment;

[0224] The database fitting module is used to fit the heat transfer, pressure drop and outlet dryness of the heat exchange tube under different inlet flow rates and dryness into a database;

[0225] The gas-liquid mixing heat exchanger simulation module is used to simulate the flow in the manifold by adopting three-dimensional fluid mechanics calculation to realize the simulation of the gas-liquid mixing heat exchanger: each simulation monitors the outlet flow and dryness of the inlet manifold, and calls the outlet dryness and heat exchange tube pressure drop after heat exchange in the heat exchange tube in the database according to the outlet flow and dryness of the inlet manifold, and uses the outlet flow and outlet dryness as the inlet conditions of the outlet manifold, and monitors the inlet pressure of the outlet manifold at the same time, and uses the pressure plus the heat exchange tube pressure drop as the outlet pressure of the inlet manifold.

[0226] Obviously, the above embodiments of the present invention are only examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A data fitting method for a heat exchange tube of a gas-liquid mixing heat exchanger, characterized in that: The specific steps include: Construct a heat exchange tube model of the gas-liquid mixing heat exchanger, and divide the heat exchange tube model into several micro-element segments; based on the set inlet dryness, divide each micro-element segment into a two-phase segment and a superheat segment; For each microelement segment: If it is a two-phase section, calculate the heat transfer of the working fluid in the micro-element section; iteratively calculate the outlet dryness of the heat exchange tube based on the heat transfer, and further calculate the pressure drop and outlet pressure of the micro-element section; use the outlet pressure, flow rate and dryness as the inlet conditions of the next micro-element section to calculate the next micro-element section; If it is a superheated section, the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element section are calculated, and the outlet pressure, flow rate and temperature are used as the inlet conditions of the next micro-element section to calculate the next micro-element section; The heat transfer, pressure drop and outlet dryness of the heat exchange tubes at different inlet flow rates and drynesses are fitted into a database.

2. The data fitting method for the heat exchange tube of the gas-liquid mixing heat exchanger according to claim 1 is characterized in that: Construct the heat exchange tube model of the gas-liquid mixing heat exchanger. The specific steps are as follows: Obtain the heat exchange tube structural parameters including tube length, tube number, tube spacing, outer diameter, inner diameter and thermal conductivity; If it is an internally threaded pipe, the number of grooves, groove bottom width, tooth height, tooth top angle and helix angle are also obtained; If there are fins installed externally, the input fin parameters are also obtained; The ε-NTU method is used to simulate the heat exchange tube section and construct a one-dimensional heat exchange tube partial model.

3. The data fitting method for the heat exchange tube of the gas-liquid mixing heat exchanger according to claim 1, characterized in that: Based on the set inlet dryness, each micro-element segment is divided into a two-phase segment and a superheat segment. Specifically, the micro-element segment with an inlet dryness less than 1 is divided into a two-phase segment, and the micro-element segment with an inlet dryness equal to 1 is divided into a superheat segment.

4. The data fitting method for the heat exchange tube of the gas-liquid mixing heat exchanger according to claim 3 is characterized in that: If it is a two-phase section, calculate the heat transfer of the working fluid in the micro-element section; iteratively calculate the outlet dryness of the heat exchange tube based on the heat transfer, and further calculate the pressure drop and outlet pressure of the micro-element section. The specific steps are: Assume that the outlet dryness of the micro-element segment is: x i,out,a =x i,in +0.01 Where: x i,out,a is the outlet dryness assumed for the ith microelement segment, x i,in is the inlet dryness of the ith microelement segment; Take the average dryness of the inlet and outlet to determine the working fluid properties, and calculate the average dryness x of the i-th microelement segment i : The heat flux q is calculated by the inlet dryness and outlet dryness as follows: Where G is the refrigerant flow rate, ΔH is the latent heat of the refrigerant, D is the outer diameter of the heat exchange tube, and L is i is the length of the heat exchange tube microelement segment, mesh is the number of microelement segments; Calculate the refrigerant side heat transfer coefficient h by heat transfer correlation r and the heat transfer coefficient h outside the tube a Then calculate the total thermal resistance UA: Where d is the inner diameter of the heat exchange tube, and λ is the thermal conductivity of the heat exchange tube wall; Then calculate the number of heat transfer units NTU: Among them, C min is the specific heat capacity of the fluid with the smallest specific heat capacity among the fluids inside and outside the tube; Calculate the heat transfer effectiveness ε: e=1-e -NTU Calculate the theoretical maximum heat transfer Q max : Q max =C min (T a,dry,in -T i,in ) Among them, T a,dry,in is the air side dry bulb temperature, T i,in is the refrigerant inlet temperature of the micro-element segment; Calculate the heat transfer Q under the assumed outlet dryness according to ε i And the corresponding outlet dryness: Q i =ε·Q max Among them, Q i is the heat transfer of the microelement segment, x i,out,c is the calculated outlet dryness; Determine whether the assumed outlet dryness and the calculated outlet dryness converge: If it does not converge, the calculated outlet dryness x i,out,c Assume that the outlet dryness x is the new i,out,a , return to the step of calculating the average dryness of the i-th microelement segment, and iterate repeatedly until convergence; If convergence occurs, the pressure drop ΔP of the microelement segment is calculated according to the two-phase flow pressure drop correlation formula: i And the outlet pressure of the micro-element segment P i,out , and use the exit condition as the entry condition of the next micro-element segment.

5. The data fitting method for the heat exchange tube of the gas-liquid mixing heat exchanger according to claim 4 is characterized in that: If it is a superheated section, calculate the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element section. The specific steps are: Calculate the maximum heat transfer of the micro-element segment: Q max =C min (T a,dry,in -T i,in ) C min =min(C r ,C a ) Among them, C r is the specific heat capacity of the refrigerant, C a is the specific heat capacity of air; Calculate the heat transfer coefficient h of the refrigerant side in the superheat section according to the heat transfer correlation formula r , and then calculate the total thermal resistance UA and the number of heat transfer units NTU: The heat transfer effectiveness ε is calculated based on the ε-NTU correlation formula for cross flow without phase change: C max =max(C r ,C a ) Calculate the heat transfer Q under the assumed outlet dryness according to ε i And the outlet temperature: Q i =ε·Q max Calculate the pressure drop ΔP of the micro-element section according to the correlation formula of the pressure drop of the superheat section i And the outlet pressure of the micro-element segment P i,out , and use the exit condition as the entry condition of the next micro-element segment.

6. The data fitting method for heat exchange tubes of a gas-liquid mixing heat exchanger according to claim 5, characterized in that: The heat transfer, pressure drop and outlet dryness of the heat exchange tubes at different inlet flow rates and drynesses are fitted into a database. The specific steps are: divide the flow range into several flow rates according to the set step size, calculate the heat transfer, pressure drop and outlet dryness of each flow rate at several inlet drynesses, fit the relationship between the pressure drop and flow rate at each inlet dryness, and the relationship between the outlet dryness and flow rate, and use the fitted correlation as the database.

7. A simulation method for a gas-liquid mixing heat exchanger, characterized in that: The data fitting method for the heat exchange tube according to any one of claims 1 to 6 comprises the following specific steps: Construct the header model of the gas-liquid mixing heat exchanger; The simulation of the gas-liquid mixing heat exchanger is realized by simulating the flow in the manifold using three-dimensional fluid mechanics calculations: the outlet flow and dryness of the inlet manifold are monitored in each simulation, and the outlet dryness and pressure drop of the heat exchange tube after heat exchange in the heat exchange tube are called up in the database according to the outlet flow and dryness of the inlet manifold. The outlet flow and outlet dryness are used as the inlet conditions of the outlet manifold, and the inlet pressure of the outlet manifold is monitored at the same time, and the pressure plus the pressure drop of the heat exchange tube is used as the outlet pressure of the inlet manifold.

8. The simulation method of the gas-liquid mixing heat exchanger according to claim 7, characterized in that: When constructing the manifold model of the gas-liquid mixing heat exchanger, a three-dimensional physical model including several manifolds is constructed; for the three-dimensional physical model of each manifold, structured mesh division is performed, and if the manifold has an orifice plate, the mesh at the liquid separation hole of the orifice plate is encrypted.

9. The simulation method of the gas-liquid mixing heat exchanger according to claim 7, characterized in that: The flow in the manifold is simulated by three-dimensional fluid mechanics calculation to realize the simulation of the gas-liquid mixing heat exchanger. Specifically, ANSYSfluent software is used to put the inlet manifold and the outlet manifold into the same case for simulation, and the custom equation UDF is used to replace the flow and heat transfer of the heat exchanger. In ANSYS fluent, the velocity inlet boundary condition is used at the manifold inlet, and the pressure outlet boundary condition is used at the manifold outlet. When UDF is used to replace the heat exchanger, the outlet parameters of the inlet manifold are monitored, and the heat transfer and pressure drop are calculated based on the database to obtain the outlet parameters of the heat exchanger tube as the inlet condition of the outlet manifold. The inlet pressure of the outlet manifold is monitored, and the pressure drop of the heat exchanger tube is added based on the database as the outlet pressure boundary condition of the inlet manifold.

10. A gas-liquid mixing heat exchanger simulation system, characterized in that: The method for simulating a gas-liquid mixing heat exchanger according to any one of claims 6 to 9 comprises a modeling module, a heat exchange tube simulation module, a database fitting module, and a gas-liquid mixing heat exchanger simulation module: The modeling module is used to construct a heat exchange tube part model and a header part model of a gas-liquid mixing heat exchanger; The heat exchange tube simulation module is used to divide the heat exchange tube part model into several micro-element segments; based on the set inlet dryness, each micro-element segment is divided into a two-phase segment and a superheat segment; for each micro-element segment: if it is a two-phase segment, the heat transfer of the working fluid in the micro-element segment is calculated; the outlet dryness of the heat exchange tube is iteratively calculated based on the heat transfer, and the pressure drop and outlet pressure of the micro-element segment are further calculated; the outlet pressure, flow rate and dryness are used as the inlet conditions of the next micro-element segment to calculate the next micro-element segment; if it is a superheat segment, the maximum heat transfer, thermal resistance, heat transfer, outlet temperature of the working fluid, pressure drop and outlet pressure of the micro-element segment are calculated, and the outlet pressure, flow rate and temperature are used as the inlet conditions of the next micro-element segment to calculate the next micro-element segment; The database fitting module is used to fit the heat transfer, pressure drop and outlet dryness of the heat exchange tube under different inlet flow rates and dryness into a database; The gas-liquid mixing heat exchanger simulation module is used to simulate the flow in the manifold by adopting three-dimensional fluid mechanics calculation to realize the simulation of the gas-liquid mixing heat exchanger: each simulation monitors the outlet flow and dryness of the inlet manifold, and calls the outlet dryness and heat exchange tube pressure drop after heat exchange in the heat exchange tube in the database according to the outlet flow and dryness of the inlet manifold, and uses the outlet flow and outlet dryness as the inlet conditions of the outlet manifold, and monitors the inlet pressure of the outlet manifold at the same time, and uses the pressure plus the heat exchange tube pressure drop as the outlet pressure of the inlet manifold.

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