A heat flow simulation method for refrigerant flow boiling in plate heat exchangers

Abstract

The present application relates to a kind of plate heat exchanger refrigerant flow boiling heat flow simulation method and the prediction system of the method is executed, by based on nucleation point approximation Poisson distribution and dryout region wall heat flow partition model, nucleation point distribution and its influence on heat transfer are characterized, while through the wall surface partition design of space-time two dimensions, wall heat flow partition model covering full boiling condition is built, in combination with the multi-item coupling calculation of total heat flow and the fine modeling of dryout region, the prediction interval of boiling heat transfer is effectively widened, can realize nucleate boiling, critical heat flow and the accurate calculation of wall heat flow of transition boiling full working condition.

Description

Technical Field

[0001] This invention belongs to the field of plate heat exchanger simulation technology, and more specifically, relates to a heat flow simulation method for refrigerant flow and boiling in a plate heat exchanger, and a plate heat exchanger refrigerant flow and boiling heat transfer prediction system for implementing the simulation method. Background Technology

[0002] With the increasing demand for industrial heat exchange, traditional single-phase cooling technology can no longer meet the requirements of efficient heat exchange. Boiling heat exchange has become an important solution due to its excellent heat transfer performance. In the boiling heat exchange process, accurate prediction of wall heat flux is of great significance for heat exchanger design and optimization. This requires the establishment of an accurate wall heat flux partitioning model to describe the complex bubble behavior and heat transfer mechanism.

[0003] Currently, there has been considerable research on numerical simulation methods for boiling heat transfer, forming a simulation technology system that adapts to different operating conditions and accuracy requirements, covering multiple core application scenarios such as conventional two-phase flow boiling, microchannel flow boiling, subcooled boiling, and critical heat flux density solution.

[0004] However, existing wall heat flux partitioning models still have many limitations in practical applications. First, the prediction range of existing models is limited, making it difficult to cover the entire operating range from nucleation boiling to critical heat flux and transitional boiling, especially with low prediction accuracy in the critical heat flux and transitional boiling regions. Second, existing models do not accurately describe bubble merging behavior, lack in-depth analysis of the lateral bubble merging mechanism, and fail to fully consider the impact of bubble merging on the nucleation point density distribution and heat transfer characteristics. Third, existing models are not comprehensive in their description of spatiotemporal distribution, failing to establish a complete wall heat flux partitioning model covering the spatiotemporal distribution, thus limiting their predictive ability for complex boiling phenomena. In addition, existing models simplify the treatment of the evaporation region, lacking accurate calculations of the proportion of the evaporation region and steam convection heat transfer, affecting the prediction accuracy of the model under high heat flux density conditions. These problems make existing models significantly limited in the simulation of actual heat exchangers, making it difficult to meet the accuracy requirements of engineering applications. Summary of the Invention

[0005] To address the limitations of existing wall heat flux partitioning models, which have limited prediction ranges and cannot cover the entire operating range from nucleation boiling to critical heat flux and transitional boiling, lack sufficient modeling of bubble sliding growth behavior and fail to consider its impact on nucleation point density and heat transfer characteristics, and have incomplete spatiotemporal distribution descriptions, while also exhibiting simplified and low-precision heat transfer calculations in the evaporation region, these models struggle to accurately simulate refrigerant phase changes, temperature, dryness fraction, and pressure distribution when applied to plate heat exchanger refrigerant flow boiling simulations. Consequently, the heat transfer prediction accuracy fails to meet engineering application requirements. This invention provides a heat flux simulation method for refrigerant flow boiling in plate heat exchangers and a heat transfer prediction system that implements this method. The aim is to broaden the boiling heat transfer prediction range of wall heat flux partitioning models, improve the simulation and heat transfer prediction accuracy of refrigerant flow boiling in plate heat exchangers, accurately characterize bubble sliding and growth behavior, spatiotemporal partitioned heat transfer characteristics, and heat transfer laws in the evaporation region, and accurately simulate the refrigerant phase changes and heat transfer characteristics within the plate heat exchanger.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows:

[0007] In a first aspect, the present invention provides a heat flow simulation method for refrigerant flow and boiling in a plate heat exchanger. Using a mixed multiphase flow model as a framework, an approximate Poisson distribution of nucleation points and a wall heat flow partitioning model are embedded at the refrigerant-solid interface. This method numerically simulates the refrigerant phase change, temperature distribution, dryness distribution, pressure distribution, and heat transfer characteristics within the plate heat exchanger. Specifically, it includes the following steps:

[0008] 1) Divide the original nucleation points N into n groups, and the number of nucleation points allocated to each group is approximately distributed according to a Poisson distribution;

[0009] 2) In the spatial dimension, the wall is divided into non-bubble-affected area, nucleation point area, bubble sliding area and evaporation area. In the temporal dimension, bubble behavior is divided into waiting time, generation time, transient heat transfer-dominated time and single-phase heat transfer-dominated time, and a wall heat flux partitioning model covering the spatiotemporal distribution is constructed.

[0010] 3) Decompose the total wall heat flow into single-phase convective heat transfer, bubble sliding transient heat transfer, evaporative heat transfer, quenching heat transfer and steam heat transfer in the drying zone, and establish a coupled calculation formula for the total heat flow.

[0011] In step 1), the probability density function of the nucleation point distribution follows a binomial distribution, which approximates a Poisson distribution.

[0012]

[0013] in, The original nucleation point density is calculated based on the RPI nucleation point density model. It is a non-negative number and satisfies .

[0014] In step 3), the total heat flux coupling calculation formula satisfies the following formula:

[0015]

[0016] in, For the total wall heat flux, For the single-phase convective heat transfer in the non-bubble-affected region within the i-th group, For transient heat transfer caused by sliding bubbles in the i-th group, For the evaporative heat transfer during bubble growth in the i-th group, The heat transfer caused by the rapid cooling of bubbles leaving the nucleation point in the i-th group. For heat transfer of steam in the drying zone, This represents the percentage of the area that has been evaporated.

[0017] Evaporative heat transfer during bubble growth in the i-th group Simultaneously considering both bubble evaporation and condensation at the bubble top, the expression is:

[0018]

[0019] in , , , , , , , , , These are, respectively, vapor density, bubble departure frequency, latent heat of vaporization, bubble departure diameter, condensation heat transfer coefficient, liquid saturation temperature, mainstream temperature, area of ​​contact between bubble and subcooled liquid, bubble growth time, and condensation start time.

[0020] The rapid cooling and heat transfer caused by the bubbles leaving the nucleation point in the i-th group Based on the transient heat transfer established by supercooled liquid covering the dry spot after bubble detachment, the expression is:

[0021]

[0022] in , , , These are the density of the heating surface material, specific heat capacity, liquid volume carried away by bubbles, and temperature difference between the cold fluid and the heating wall surface, respectively.

[0023] The transient heat transfer caused by the sliding bubble in the i-th group The sliding process can be simplified to a one-dimensional unsteady heat conduction process on a semi-infinite plate, expressed as:

[0024]

[0025] in, This represents the time during which transient heat transfer dominates in the region influenced by the sliding bubble during the bubble's sliding process. , , as well as These are the time for one bubble nucleation cycle, the liquid's thermal conductivity, the liquid's thermal diffusivity, and the convective heat transfer coefficient, respectively. This is the corrected nucleation point density;

[0026] The proportion of the drying area From average steam volume fraction relative to the initial volume fraction of drying A joint decision, when When steam convection heat transfer is initiated, the expression is:

[0027]

[0028] in , , , , , These are, respectively, steam density, steam specific heat capacity at constant pressure, steam friction velocity, steam dimensionless temperature, wall temperature, and steam temperature. The average vapor volume fraction over the entire bubble layer thickness. This represents the vapor volume fraction at the wall drying breakpoint or at the start of drying. Represented as: ,

[0029] The coefficient is used to calculate the proportion of the evaporated area. .

[0030] Secondly, the present invention also provides a plate heat exchanger refrigerant flow boiling heat transfer prediction system. The system is used in the plate heat exchanger refrigerant flow boiling simulation method of the present invention, and includes a nucleation point Poisson distribution calculation module, a wall heat flux partition coupling calculation module, and a plate heat exchanger refrigerant flow boiling simulation prediction module that are connected in sequence via communication.

[0031] The Poisson distribution calculation module for nucleation points completes the preset assumptions based on the Poisson distribution of nucleation points, establishes an approximate Poisson distribution model for nucleation points, and outputs the calculation results of the probability density function of the nucleation point distribution.

[0032] The wall heat flux partitioning coupled calculation module includes a wall spatiotemporal partitioning unit, a single-phase convective heat transfer calculation unit, a bubble sliding transient heat transfer calculation unit, an evaporation heat transfer calculation unit, a quenching heat transfer calculation unit, a steam heat transfer calculation unit in the drying region, and a total heat flux coupled solution unit.

[0033] Among them, the wall spatiotemporal partitioning unit is used to receive the calculation results of nucleation points and bubble sliding growth behavior, complete the wall partitioning in the spatial dimension and the bubble behavior stage division in the temporal dimension, and construct a wall heat flux partitioning model covering spatiotemporal distribution;

[0034] The single-phase convective heat transfer calculation unit, the bubble sliding transient heat transfer calculation unit, the evaporation heat transfer calculation unit, the quenching heat transfer calculation unit, and the steam heat transfer calculation unit in the drying zone are used to complete the sub-item calculations for single-phase convective heat transfer, bubble sliding transient heat transfer, evaporation heat transfer, quenching heat transfer, and steam heat transfer in the drying zone, respectively.

[0035] The total heat flux coupled solution unit is used to complete the coupled solution of the total wall heat flux based on the calculation results of each component heat flux.

[0036] The plate heat exchanger refrigerant flow boiling simulation prediction module is used to embed the solved wall heat flow partition model into the mixed multiphase flow model framework, and to perform numerical simulation of refrigerant phase change, temperature distribution, dryness distribution, pressure distribution and heat transfer characteristics in the plate heat exchanger, and output the temperature, pressure, dryness and heat flux distribution results.

[0037] The beneficial effects of this invention are as follows: The simulation method of this invention establishes a wall heat flux partitioning model based on the approximate Poisson distribution of nucleation points and the evaporation region, accurately simulating the distribution of nucleation points and their impact on heat transfer. At the same time, through the spatiotemporal dual-dimensional wall partitioning design, a wall heat flux partitioning model covering the entire boiling condition is constructed. Combined with the multi-component coupled calculation of total heat flux and the refined modeling of the evaporation region, the prediction range of boiling heat transfer is effectively broadened, and accurate calculation of wall heat flux under all conditions of nucleation boiling, critical heat flux, and transition boiling can be achieved. When this model is embedded into the mixed multiphase flow framework and applied to the simulation of refrigerant flow and boiling in plate heat exchangers, the phase change, temperature, dryness, and pressure distribution of the refrigerant in the heat exchanger can be accurately simulated, greatly improving the simulation accuracy. The heat transfer prediction system of this invention adopts a modular and pipelined design, with each module's function corresponding one-to-one with the technical steps of the simulation method. This achieves the integration of nucleation point distribution calculation, wall heat flux partition coupling solution, and heat exchanger simulation prediction, enabling efficient execution of the aforementioned simulation methods and rapid output of accurate heat transfer prediction results. The system's wall heat flux partition coupling calculation module incorporates multiple types of heat transfer calculation units, realizing independent calculation of each component's heat flux and coupling with the total heat flux, further ensuring the accuracy and efficiency of heat transfer prediction. Experimental verification shows that the simulation method and prediction system of this invention have small deviations from experimental values ​​in predicting the refrigerant inlet and outlet pressures, outlet temperature, superheat, and water-side outlet temperature within the plate heat exchanger. It can accurately predict the distribution of the low-dryness region of the refrigerant and the phase change process, proving its high accuracy and feasibility in actual engineering simulation of plate heat exchangers. It can provide reliable numerical tools and system support for the design optimization and performance evaluation of plate heat exchangers. Attached Figure Description

[0038] Figure 1 This is a schematic diagram illustrating the Poisson distribution assumption of nucleation points in this invention;

[0039] Figure 2 This is a schematic diagram of the different regions divided in the spatiotemporal dimension of the wall heat flow partitioning model of the present invention;

[0040] Figure 3 This is a schematic diagram of the bubble growth process of the present invention;

[0041] Figure 4 This is a schematic diagram of bubble merging according to the present invention;

[0042] Figure 5 This is a schematic diagram of the nucleation point spacing distribution of the present invention;

[0043] Figure 6 This invention provides a visual representation of the temperature distribution of the refrigerant in the flow direction within a plate heat exchanger.

[0044] Figure 7 This invention provides a visualization of the refrigerant's dryness distribution along the flow direction within a plate heat exchanger. Detailed Implementation

[0045] The technical features of the present invention will be clearly and completely described below in conjunction with the technical solutions in the embodiments of the present invention. All embodiments are based on the core technical solutions of the present invention and are not intended to limit the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0046] To better understand the embodiments provided by the present invention, the technical content involved in the present invention will first be introduced.

[0047] This invention establishes a heat flux partitioning model based on the approximate Poisson distribution of nucleation points and the wall surface of the evaporation region. The specific method is as follows:

[0048] The heating surface is divided into n regions, and the number of nucleation points in each of the n regions follows a Poisson distribution, as shown in the attached figure. Figure 1 As shown, the probability density function of the nucleation point is:

[0049] ,in, The original nucleation point density is calculated based on the RPI nucleation point density model. It is a non-negative number and satisfies .

[0050] single group The marginal distribution is a binomial distribution:

[0051]

[0052] when Large and When very young (i.e.) (Moderate), the binomial distribution approximates the Poisson distribution:

[0053]

[0054] In the RPI nucleation point density model, the nucleation point density can be expressed as:

[0055]

[0056] in , , , , , These are the dimensionless logarithmic density functions of the average nucleation point density, wall contact angle, wall contact angle scale, cavity length scale, critical cavity radius, and pressure effect, respectively. Where:

[0057]

[0058] in , , , , These are surface tension, liquid pressure, latent heat of vaporization, vapor constant, and liquid saturation temperature, respectively.

[0059] The calculation is as follows:

[0060]

[0061] in:

[0062]

[0063] The standard value of the density function constant is:

[0064]

[0065]

[0066]

[0067] .

[0068] To enable the wall heat flux partitioning model to predict critical heat flux and transitional boiling, this invention introduces bubble sliding and vapor layer heat transfer phenomena. Spatially, the wall is divided into a non-bubble-affected region, a nucleation point region, a bubble sliding region, and a drying region. Temporally, the bubble nucleation-related time is divided into bubble waiting time and bubble generation time, and the bubble sliding process time is divided into transient heat transfer-dominated time and one-way relative heat transfer-dominated time. Finally, an improved wall heat flux partitioning model is proposed, the specific principle of which is as follows: Figure 2 As shown, in Figure 2 Among them For the time when transient heat transfer dominates in the sliding region, This represents the time during which single-phase convective flow dominates within the influence region of the sliding bubble. This classification mechanism can encompass bubble behavior and wall heat transfer mechanisms across different time and space. Based on this, wall heat transfer can be divided into five parts: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] Transient heat transfer caused by sliding bubbles Evaporative heat transfer during bubble growth Single-phase heat transfer in non-bubble-affected regions And steam heat transfer in the drying zone ,and For the single-phase convective heat transfer in the non-bubble-affected region within the i-th group, For transient heat transfer caused by sliding bubbles in the i-th group, For the evaporative heat transfer during bubble growth in the i-th group, The total wall heat flux, representing the heat transfer caused by the quenching of bubbles leaving the nucleation point in group i, is the sum of the heat transfers in all the above regions, expressed as:

[0069]

[0070] in, This represents the percentage of the area that has been evaporated.

[0071] The simulation calculation methods for these different heat transfer methods in this invention will be introduced next:

[0072] [Evaporative heat transfer]

[0073] After bubble nucleation, the bubble diameter increases rapidly in the initial stage, which is called the inertial growth stage. In the early stages of bubble growth, there is a layer of liquid at the bottom of the bubble, about a micrometer thick; this thin layer is called the microliquid layer. As the microliquid layer evaporates, bubble growth gradually slows down, and at this stage, bubble growth mainly stems from the evaporation of the superheated layer. When the bubble height exceeds the thickness of the superheated layer, condensation occurs at the top of the bubble, such as... Figure 3 As shown. Considering the effect of condensation at the top of the bubble on the bubble volume, the evaporative heat transfer during bubble growth in the i-th group. Simultaneously taking into account the evaporation of growing bubbles and the condensation at the top of the bubbles, it is expressed as:

[0074]

[0075] in , , , , , , , , , These are, respectively, vapor density, bubble departure frequency, latent heat of vaporization, bubble departure diameter, condensation heat transfer coefficient, liquid saturation temperature, mainstream temperature, area of ​​contact between bubble and subcooled liquid, bubble growth time, and condensation start time.

[0076] Depend on Calculation, where The height of the overheating layer, The specific calculation process for the bubble growth model is as follows:

[0077]

[0078]

[0079] in , representing experimental calculation results, .

[0080] The first part on the right side of equation (8) represents the heat transfer during bubble growth at the nucleation point, and the second part represents the heat transfer during bubble growth due to condensation at the top.

[0081] in It can be expressed by equation (9):

[0082]

[0083] in Contact angle, This refers to the height of the overheating layer. This can be obtained from the Ranz-Marshall correlation:

[0084]

[0085] in , , These are the thermal conductivity of the liquid, the Reynolds number of the bubble, and the Planck number, respectively.

[0086] [Cold Heat Transfer]

[0087] When the bubble grows to a certain diameter (the bubble breaks away from the diameter) After detaching from its nucleation point, the supercooled liquid rapidly covers the dry spot where the bubble left off, resulting in transient quenching heat transfer. This invention assumes that the bubble carries away a hemispherical vapor with a diameter half the diameter of the bubble as it leaves the nucleation point. Based on this assumption, the quenching heat transfer caused by the bubble leaving the nucleation point in the i-th group... Based on the transient heat transfer established by supercooled liquid covering the dry spot after bubble detachment, the expression is:

[0088]

[0089] in , , , These are the density of the heating surface material, specific heat capacity, liquid volume carried away by bubbles, and temperature difference between the cold fluid and the heating wall; where:

[0090]

[0091] Therefore, the area of ​​the bubble-affected region at the nucleation point can be expressed as: .

[0092] [Bubble sliding heat transfer]

[0093] In fluid boiling, bubbles leave their nucleation points and slide along the wall. This process is accompanied by the continuous disruption of the thermal boundary layer near the wall, while supercooled liquid continuously flows towards the thermal boundary layer. This process enhances wall heat transfer, and this heat transfer mechanism is called bubble sliding heat transfer, a crucial component of fluid boiling heat transfer. To establish a transient quenching heat transfer model, this heat transfer process is simplified as a one-dimensional unsteady-state heat conduction problem on a semi-infinite flat plate. Within one bubble nucleation cycle, the transient heat transfer during the bubble sliding process dominates the influence region of the sliding bubble for a period of time. After this time, single-phase convective heat transfer becomes dominant. Therefore, transient heat transfer caused by sliding bubbles in the i-th group... The sliding process can be simplified to a one-dimensional unsteady heat conduction process on a semi-infinite plate, expressed as:

[0094]

[0095] in, This represents the time during which transient heat transfer dominates in the region influenced by the sliding bubble during the bubble's sliding process. , , as well as These are the time for one bubble nucleation cycle, the liquid's thermal conductivity, the liquid's thermal diffusivity, and the convective heat transfer coefficient, respectively. This is the corrected nucleation point density;

[0096] here,

[0097]

[0098] in , , , These are, respectively, liquid density, liquid specific heat capacity at constant pressure, liquid friction velocity, and liquid dimensionless temperature.

[0099] The area of ​​the sliding bubble's influence region is , The sliding average diameter of the bubble. It is the distance the bubble slides, such as Figure 4 As shown, the sliding of bubbles can be divided into two parts: evaporation growth and merging. After the bubbles leave the nucleation point, they slide... (See Figure 5 The distance is such that the heat transfer diameter reaches [a certain value] through evaporation. The growth was determined by the correlation of individual bubbles proposed by Maity in fluid boiling, as shown in Equation (18).

[0100]

[0101] in , , , , Bubble sliding time The diameter after detachment, bubble detachment diameter, bubble sliding time, Jacobian number, and bubble Reynolds number are calculated. Bubbles merge when passing other nucleation points, and the diameter of the merged bubble can be obtained from equation (19):

[0102]

[0103] in , These represent the diameter of the merged bubble and the diameter of the bubble at the nucleation point, respectively. (The path of the sliding bubble is shown.) After one nucleation point, the diameter reaches Then continue sliding independently for a distance. Until the diameter grows to the diameter of the bubble buoyancy. Finally, it detaches from the wall. The distance the bubble slides. Bubble sliding time and the average diameter during bubble sliding It can be expressed by the following formula:

[0104]

[0105] in The velocity of the bubble is used to calculate... .

[0106] After merging with bubbles at other nucleation points, no new bubbles will slide at that nucleation point for the remainder of the bubble cycle. Therefore, Gilman introduces a reduction factor. This yields a new nucleation point density. .

[0107]

[0108] [Steam convection]

[0109] As the wall superheat increases, nucleation sites are continuously activated, and the number of bubbles formed on the wall gradually increases. When the vapor volume fraction near the wall increases to a certain level, the heat transfer mode changes to convective heat transfer between the vapor and the wall, and the flow boiling transitions from nucleation boiling to transition boiling. The convective heat transfer between the wall and the vapor can be expressed as:

[0110]

[0111] in , , , , , These are, respectively, steam density, steam specific heat capacity at isobaric pressure, steam friction velocity, steam dimensionless temperature, wall temperature, and steam temperature. Steam convective heat transfer occurs in the drying region, and the percentage of this region can be expressed as:

[0112]

[0113] in The average vapor volume fraction over the entire bubble layer thickness. This represents the vapor volume fraction at the wall drying breakpoint or at the start of drying. When At this time, steam convection participates in the heat flow across the wall, typically The value is 0.82. It can be represented as:

[0114]

[0115] in:

[0116] The coefficient is used to calculate the proportion of the evaporated area. .

[0117] In this invention, it is assumed that when Once the temperature reaches 0.82, the region transitions from the nucleation boiling stage to the transition boiling stage.

[0118] [Single-phase convective heat transfer]

[0119] In the spatial dimension, single-phase convective heat transfer occurs in the non-bubble-affected region, where only single-phase convective heat transfer occurs during the bubble nucleation cycle, and the liquid phase is in direct contact with the superheated wall. Therefore, this study uses the standard wall function to derive the single-phase convective heat transfer coefficient. The single-phase convective heat transfer in the non-bubble-affected region can be expressed as:

[0120]

[0121] The relevant parameters have all been derived or explained in the preceding text.

[0122] In a second aspect, the present invention provides a plate heat exchanger refrigerant flow boiling heat transfer prediction system to implement the aforementioned plate heat exchanger refrigerant flow boiling simulation method. Specifically, it adopts a pipelined modular communication and data flow design, with the functional logic of each module corresponding one-to-one with the technical steps of the simulation method. This achieves integrated execution from bubble nucleation distribution and merging behavior analysis, accurate calculation of wall heat flux, to simulation of the overall flow boiling characteristics of the heat exchanger. Specifically, it includes:

[0123] [Nucleation Point Poisson Distribution Calculation Module]

[0124] The Poisson distribution calculation module for nucleation points serves as the fundamental data output for the entire system. Its execution process relies entirely on the core assumption of the approximate Poisson distribution of bubble nucleation points in the aforementioned simulation method. In specific implementation, it includes a built-in RPI nucleation point density model calculation unit and a nucleation point distribution probability / density model solution unit.

[0125] First, the original nucleation point density N is obtained by substituting basic parameters such as average nucleation point density, wall contact angle, wall contact angle scale, cavity length scale, critical cavity radius, and dimensionless logarithmic density function of pressure effect into the calculation unit of the RPI nucleation point density model.

[0126] Based on the mathematical foundation of the Poisson distribution, the probability distribution of the nucleation point is obtained through the pre-defined formulas (1)-(4). Density distribution of a single group Solving for;

[0127] Finally, the calculation results related to the nucleation point density and the characteristic parameters of bubble merging behavior, such as merging probability and bubble diameter coefficient after merging, are transmitted as core basic data to the next-level wall heat flux partitioning coupled calculation module, providing data support for wall spatiotemporal partitioning and various sub-item heat flux calculations.

[0128] [Wall Heat Fluid Zone Coupling Calculation Module]

[0129] The wall heat flux partitioned coupled calculation module is the core calculation unit of the plate heat exchanger refrigerant flow boiling heat transfer prediction system. It is the key to realizing refined and multi-item coupled calculation of wall heat flux. It adopts the execution logic of "first partitioned modeling, then itemized calculation, and finally coupled solution". The built-in seven units work in a series + parallel combination mode. The specific implementation process is as follows:

[0130] As the entry unit of this module, the wall spatiotemporal partitioning unit first receives the calculation results of nucleation point and bubble merging behavior output by the previous module. Based on the partitioning / segmentation rules of spatial and temporal dimensions in the simulation method, it completes the division of the non-bubble influence area, nucleation point area, bubble sliding area, and evaporation area of ​​the wall, as well as the division of the waiting time, generation time, transient heat transfer dominance time, and one-way relative heat transfer dominance time of bubble behavior. It constructs a wall heat flux partitioning model covering the spatiotemporal distribution and synchronizes the spatial boundary and time node parameters of the partitioning model to the other heat transfer calculation units of this module to define the calculation range for the sub-item heat flux calculation.

[0131] The heat transfer calculation unit includes a single-phase convective heat transfer calculation unit, a bubble sliding transient heat transfer calculation unit, an evaporation heat transfer calculation unit, a quenching heat transfer calculation unit, and a steam heat transfer calculation unit for the evaporation zone. Based on the corresponding calculation formulas in the simulation method, the unit substitutes the partitioning parameters of the wall spatiotemporal partitioning unit, the nucleation point density parameters of the previous module, the refrigerant thermophysical parameters, and the heat exchanger structural parameters to complete the independent calculation of each component's heat flux. The calculation results of each unit are fed back to the overall heat flux coupled solution unit in real time.

[0132] The total heat flux coupling solution unit serves as the outlet unit of this module. It receives the sub-item heat flux results from the five major heat transfer calculation units and calculates them according to the total wall heat flux coupling formula (7), combined with the proportion of the evaporation zone. The solution results complete the total wall heat flow. The coupled solution ultimately integrates and encapsulates the wall heat flow partition model, the heat flow data of each component, and the total heat flow data, and transmits them to the next-level plate heat exchanger refrigerant flow boiling simulation prediction module.

[0133] [Plate Heat Exchanger Refrigerant Flow and Boiling Simulation Prediction Module]

[0134] The plate heat exchanger refrigerant flow and boiling simulation prediction module is the final simulation result output terminal for the entire system. Its core execution logic is to embed the wall heat flux partitioning model solved by the preceding modules into the mixed multiphase flow model framework to predict the refrigerant flow and boiling characteristics of the plate heat exchanger. Specifically, it includes:

[0135] First, the total wall heat flux, each component heat flux, and the wall partition model output by the wall heat flux partition coupling calculation module are embedded into the mixed multiphase flow model as boundary conditions and source terms to complete the coupling reconstruction of the model. The reconstructed model can accurately characterize the heat transfer characteristics of the refrigerant-solid interface in the plate heat exchanger, as well as the influence of key phenomena such as bubble merging and evaporation on the overall flow boiling.

[0136] Based on the coupled mixed multiphase flow model, the structural parameters of the plate heat exchanger, such as plate corrugation form, flow channel size, and metal weld point location, as well as the inlet operating parameters of the refrigerant, such as inlet temperature, pressure, flow rate, and flow direction, are substituted into the numerical simulation method to solve the full flow field of the refrigerant flow and boiling process in the plate heat exchanger.

[0137] After the solution is completed, the simulation results are extracted and visualized. Finally, the core results such as the phase change process characteristics of the refrigerant in the plate heat exchanger, temperature distribution cloud map / data, dryness distribution cloud map / data, pressure distribution cloud map / data, and heat flux distribution data are output, providing direct numerical reference for the design optimization and performance evaluation of the plate heat exchanger.

[0138] Figure 6 and Figure 7These are visualizations of the temperature and dryness distribution of the refrigerant in the flow direction within the plate heat exchanger, as predicted by the present invention.

[0139] Example 1:

[0140] This invention employs a real experimental setup to conduct flow boiling experiments within a heat exchanger. To recreate the phase change process of refrigerant and water in the heat exchanger, the real experimental setup includes extended sections at the refrigerant and water inlets / outlets to simulate fluid flow within the pipes. The refrigerant region inlet is a mass flow rate inlet, and the outlet is a pressure outlet; the water region inlet is also a mass flow rate inlet, and the outlet is a pressure outlet. The interface between the refrigerant, water, and solid regions is a mapped contact interface, and all other surfaces are adiabatic. Specific fluid inlet / outlet boundary conditions are shown in the table below.

[0141]

[0142] The measured results were averaged to obtain the average measured result, which was then compared with the results obtained by the simulation method of refrigerant flow boiling in plate heat exchangers according to the present invention and the results of the RPI model simulation, as shown in the table below:

[0143]

[0144] The results show that the simulated refrigerant outlet temperature, refrigerant pressure drop, and water outlet temperature predicted by the refrigerant flow boiling simulation method of the plate heat exchanger of this invention deviate little from the experimental values ​​and are better than the results predicted by RPI. This demonstrates that the method of using mixed multiphase flow as a framework and embedding a new model to simulate the phase change of refrigerant in a plate heat exchanger has high accuracy and feasibility.

[0145] It should be noted that the above description is only a preferred embodiment of the present invention and is not limited to the description in the specification and embodiments. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this invention should be included within the scope of this patent application.

Claims

1. A heat flow simulation method for refrigerant flow and boiling in a plate heat exchanger, characterized in that, Using a mixed multiphase flow model as a framework, an approximate Poisson distribution of nucleation points and a wall heat flux partitioning model are embedded at the refrigerant-solid interface. Numerical simulations are then performed on the refrigerant phase change, temperature distribution, dryness distribution, pressure distribution, and heat transfer characteristics within a plate heat exchanger. The specific steps include the following: 1) Divide the original nucleation points N into n groups, and the number of nucleation points allocated to each group is approximately distributed according to a Poisson distribution; 2) In the spatial dimension, the wall is divided into non-bubble-affected area, nucleation point area, bubble sliding area and evaporation area. In the temporal dimension, bubble behavior is divided into waiting time, generation time, transient heat transfer-dominated time and single-phase heat transfer-dominated time, and a wall heat flux partitioning model covering the spatiotemporal distribution is constructed. 3) Decompose the total wall heat flux into single-phase convective heat transfer, bubble sliding transient heat transfer, evaporative heat transfer, quenching heat transfer and steam heat transfer in the drying zone, and establish a coupled calculation formula for the total heat flux. In step 1), the probability density function of the nucleation point distribution follows a binomial distribution, which approximates a Poisson distribution: in, The original nucleation point density is calculated based on the RPI nucleation point density model. It is a non-negative number and satisfies ; In step 3), the total heat flux coupling calculation formula satisfies the following formula: in, For the total wall heat flux, For the single-phase convective heat transfer in the non-bubble-affected region within the i-th group, For transient heat transfer caused by sliding bubbles in the i-th group, For the evaporative heat transfer during bubble growth in the i-th group, The heat transfer caused by the rapid cooling of bubbles leaving the nucleation point in the i-th group. For heat transfer of steam in the drying zone, This represents the percentage of the drying area. Evaporative heat transfer during bubble growth in the i-th group Simultaneously taking into account the evaporation of growing bubbles and the condensation at the top of the bubbles, the expression is: in , , , , , , , , , These are, respectively, vapor density, bubble departure frequency, latent heat of vaporization, bubble departure diameter, condensation heat transfer coefficient, liquid saturation temperature, mainstream temperature, area of ​​contact between bubble and subcooled liquid, bubble growth time, and condensation start time. The rapid cooling and heat transfer caused by the bubbles leaving the nucleation point in the i-th group Based on the transient heat transfer established by supercooled liquid covering the dry spot after bubble detachment, the expression is: in , , , These are the density of the heating surface material, specific heat capacity, liquid volume carried away by bubbles, and temperature difference between the cold fluid and the heating wall surface, respectively. The transient heat transfer caused by the sliding bubble in the i-th group The sliding process can be simplified to a one-dimensional unsteady heat conduction process on a semi-infinite plate, expressed as: in, This represents the time during which transient heat transfer dominates in the region influenced by the sliding bubble during the bubble's sliding process. , , as well as These are the time for one bubble nucleation cycle, the liquid's thermal conductivity, the liquid's thermal diffusivity, and the convective heat transfer coefficient, respectively. This is the corrected nucleation site density. The wall temperature, The area affected by the sliding bubble.

2. The method according to claim 1, characterized in that, The proportion of the drying area From average steam volume fraction relative to the initial volume fraction of drying A joint decision, when When steam convection heat transfer is initiated, the expression is: in , , , , , These are, respectively, steam density, steam specific heat capacity at constant pressure, steam friction velocity, steam dimensionless temperature, wall temperature, and steam temperature. The average vapor volume fraction over the entire bubble layer thickness. This represents the vapor volume fraction at the wall drying breakpoint or at the start of drying. Represented as: , The coefficient is used to calculate the proportion of the evaporated area. .

3. A refrigerant flow boiling heat transfer prediction system for plate heat exchangers, characterized in that, The system is used to execute the heat flow simulation method for refrigerant flow and boiling in a plate heat exchanger as described in any one of claims 1 to 2, comprising a nucleation point Poisson distribution calculation module, a wall heat flow partition coupling calculation module, and a plate heat exchanger refrigerant flow and boiling simulation prediction module that are connected in sequence via communication.

4. The system according to claim 3, characterized in that, The Poisson distribution calculation module for nucleation points is used to establish a probability model and a density model for nucleation point distribution based on preset assumptions about the lateral merging behavior of bubbles, calculate the nucleation point density corresponding to bubble growth, and output the calculation results of nucleation points and bubble growth sliding behavior; and The plate heat exchanger refrigerant flow boiling simulation prediction module is used to embed the solved wall heat flow partition model into the mixed multiphase flow model framework, and to perform numerical simulation of refrigerant phase change, temperature distribution, dryness distribution, pressure distribution and heat transfer characteristics in the plate heat exchanger, and output the temperature, pressure, dryness and heat flux distribution results.

5. The system according to claim 3, characterized in that, The wall heat flux partitioning coupled calculation module includes a wall spatiotemporal partitioning unit, a single-phase convective heat transfer calculation unit, a bubble sliding transient heat transfer calculation unit, an evaporation heat transfer calculation unit, a quenching heat transfer calculation unit, a steam heat transfer calculation unit in the drying region, and a total heat flux coupled solution unit. Among them, the wall spatiotemporal partitioning unit is used to receive the calculation results of nucleation points and bubble growth sliding behavior, complete the wall partitioning in the spatial dimension and the bubble behavior stage division in the temporal dimension, and construct a wall heat flux partitioning model covering spatiotemporal distribution; The single-phase convective heat transfer calculation unit, the bubble sliding transient heat transfer calculation unit, the evaporation heat transfer calculation unit, the quenching heat transfer calculation unit, and the steam heat transfer calculation unit in the drying zone are used to complete the sub-item calculations for single-phase convective heat transfer, bubble sliding transient heat transfer, evaporation heat transfer, quenching heat transfer, and steam heat transfer in the drying zone, respectively. The total heat flux coupled solution unit is used to complete the coupled solution of the total wall heat flux based on the calculation results of each component heat flux.

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