Heat exchanger design method based on mixed TPMS structure

Abstract

The invention provides a heat exchanger design method based on a mixed TPMS structure, and relates to the technical field of heat exchange, and the method comprises the following steps: 1, combining a sigmoid function to realize smooth transition of two original typical TPMS structure curved surfaces so as to construct a flexible mixed TPMS lattice structure mathematical expression; 2, lattice units are output in three-dimensional modeling software according to the obtained flexible mixed TPMS lattice structure mathematical expression; thirdly, periodic arrays of the target lattice units in a space coordinate system are achieved according to the structural requirements of a heat exchanger shell, independence of a hot flow basin and a cold flow basin is achieved by sealing opposite fluid areas at a hot fluid inlet and a cold fluid outlet respectively, and finally a flexible mixed heat exchange core structure is obtained and filled into the heat exchange shell to obtain the heat exchanger; and 4, flow and heat transfer characteristic analysis is carried out on the TPMS heat exchanger with different flexible mixing so as to obtain the optimal design. And by adopting the flexible TPMS structural design, the heat exchange area can be increased under the condition that the size is kept unchanged, so that the heat exchange performance is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of heat exchange, and in particular relates to a heat exchanger design method based on a hybrid TPMS structure. Background Art

[0002] In energy conversion systems in many fields such as industrial engineering, microelectronics engineering, automotive engineering, and chemical engineering, waste heat resources account for about 17% to 67% of their total fuel consumption, of which the recoverable rate is 60%. There is a large room for improving the waste heat utilization rate and huge energy-saving potential. Industrial waste heat recovery and utilization is considered to be a "new energy source". However, low-grade and low-energy low-temperature waste heat is often not effectively utilized, resulting in a waste of limited resources.

[0003] In the energy conversion process of waste heat recovery, heat exchangers play a vital role due to their rapid heat exchange characteristics. The utilization of low-temperature waste heat by heat exchange technology equipment is an energy-consuming process that directly transfers waste heat energy to its own process through heat exchange equipment. It is one of the direct and efficient methods of waste heat recovery. However, under low-grade waste heat recovery conditions, traditional partition-type heat exchangers such as shell and tube, plate-fin, spiral, and printed circuit heat exchangers are often unable to effectively recover waste heat due to the limitations of manufacturing capabilities and their shape and structure. Therefore, designing a high-performance heat exchanger structure suitable for low-grade waste heat recovery conditions to improve heat exchange efficiency and ensure the independence of heat exchange channels has become an urgent problem to be solved.

[0004] With the development of additive manufacturing technology, more and more structures with complex geometric shapes can be manufactured, and among them, the three-periodic minimal surface topological structure (TPMS) with continuous surfaces and high surface area to volume ratio characteristics has attracted widespread attention. The TPMS structure is defined as a continuous smooth surface with zero average curvature at all points on the surface, and its geometric shape shows periodic changes in three-dimensional space. The overall structure can be accurately described and controlled by mathematical equations, and its key parameters such as surface area and relative density can be flexibly adjusted through mathematical functions to meet specific application requirements. Due to the smooth surface modeling and continuous hole geometry, the TPMS structure has a high surface area to volume ratio and a curved flow channel without sharp edges inside, which shows extremely excellent flow and heat transfer performance. At the same time, it has good self-supporting and lightweight potential advantages, which can make the TPMS structure fully play a role in the field of heat exchange.

[0005] As a company with a wide influence in the field of additive manufacturing, nTopology of the United States has a leading level in the development and processing of design software for minimum surface heat exchangers. Using the TPMS structure, nTopology has optimized and improved the shell and tube heat exchanger. nTopology has given a design process for optimizing the traditional heat exchanger using TPMS: (1) Determine the outer contour of the design object; (2) Select the minimum surface model; (3) Fill the fluid domain space with TPMS; (4) Set baffles to close the fluid domains on both sides. Since the optimization process first determines the outer contour of the design object and then selects the minimum surface model, there is no direct constraint relationship between the selection of the minimum surface model and the outer contour of the heat exchanger. The designed internal structure of the heat exchanger cannot achieve a high air ratio. In particular, the internal gap of the TPMS structure cannot be maximized, so it cannot effectively increase the heat exchange area or improve the heat exchange performance per unit volume. Summary of the invention

[0006] In view of this, the present invention proposes a heat exchanger design method based on a hybrid TPMS structure to solve the problem that the traditional TPMS structure cannot maximize the heat transfer rate per unit volume in the limited space of the heat exchanger.

[0007] The technical solution of the present invention is implemented as follows: The present invention provides a heat exchanger design method based on a hybrid TPMS structure, comprising the following steps:

[0008] Step 1: Based on the mathematical implicit equation of the original typical TPMS lattice structure, the sigmoid function is combined to realize the smooth transition of the two original typical TPMS structure surfaces to construct the mathematical expression of the flexible hybrid TPMS lattice structure;

[0009] Step 2: outputting lattice units in a three-dimensional modeling software according to the obtained mathematical expression of the flexible hybrid TPMS lattice structure;

[0010] Step 3: According to the requirements of the heat exchanger shell structure, the target lattice unit is formed into a periodic array in the spatial coordinate system, and the hot and cold flow domains are separated by closing the areas of the opposing fluids at the inlet and outlet of the hot and cold fluids, so as to finally obtain a flexible hybrid heat exchange core structure, which is then filled into the heat exchange shell to obtain a heat exchanger;

[0011] Step 4: Analyze the flow and heat transfer characteristics of TPMS heat exchangers with different flexible mixtures to obtain the optimal design.

[0012] On the basis of the above technical solution, preferably, the smooth transition of the two original typical TPMS structure surfaces is achieved by a Sigmoid function, as shown in the following formula:

[0013]

[0014] Where M and N are transition functions, their value range is in the interval (0,1) and satisfy the relationship M+N=1, f(x,y,z)=0 is used to control the shape of the transition area, parameter k (k>0) defines the width of the transition area, and e is an exponential function with the natural constant e as the base;

[0015] Typical original TPMS structures include: Primitive structure, Gyroid structure and Diamond structure, and the corresponding generated hybrid TPMS structures include: Primitive-Gyroid structure, Primitive-Diamond structure and Gyroid-Diamond structure. The flexible hybrid TPMS unit is expressed as follows:

[0016]

[0017] and Represent the mathematical expressions of two different typical original TPMS unit structures. X, Y, and Z refer to the coordinates of the lattice unit in three-dimensional space. When M and N change from 0 to 1, the TPMS unit to Hybrid structural transformation of TPMS unit.

[0018] On the basis of the above technical solution, preferably, when the transition functions M and N change from 0 to 1, TPMS unit to The method of transforming the hybrid structure of the TPMS unit to obtain a hybrid TPMS structure includes:

[0019] When M and N are constants, a different formula can be obtained from TPMS unit and A new unit structure of the TPMS unit, which is called a uniform structure;

[0020] When M and N are not constants, the transition zone of the hybrid structure is designed according to the Sigmoid function. The shape of the transition zone is controlled by designing the function f(x, y, z). The resulting hybrid structure has the same dimension as the periodic lattice and maintains the same size.

[0021] On the basis of the above technical solution, preferably, when M and N are not constants, the transition zone of the hybrid structure is designed according to the Sigmoid function, and the shape of the transition zone is controlled by designing the function f(x, y, z), including:

[0022] For the linear transition region, set f(x,y,z)=x, and the mathematical expression of the hybrid structure is:

[0023]

[0024] For the circular transition region, set f(x,y,z)=x 2 +y 2 -8, the mathematical expression of the mixed structure is:

[0025]

[0026] For the elliptical transition zone, set The mathematical expression of the hybrid structure is:

[0027]

[0028] in, and They represent two different typical original TPMS unit structures.

[0029] On the basis of the above technical solutions, preferably, during the design process, the flow performance and heat transfer efficiency of different transition zone design schemes under different flow conditions are compared through numerical simulation or experimental testing, and then the most suitable transition zone design scheme is selected according to the fluid flow rate, temperature gradient, flow pattern and other conditions in the actual working conditions to optimize the overall performance of the heat exchanger.

[0030] Based on the above technical solution, preferably, step two includes inputting the dimensional parameters of the TPMS lattice unit in the three-dimensional modeling software, wherein the dimensional parameters include the porosity, wall thickness, unit size and lattice arrangement of the unit lattice; wherein the porosity and wall thickness are selected based on the design requirements, fluid characteristics and heat exchange performance of the heat exchanger, and the optimal value is determined through simulation or experimental testing to ensure the optimization of the performance of the heat exchanger under working conditions.

[0031] On the basis of the above technical solution, preferably, in the step three, the method for realizing a periodic array of the target lattice units in the spatial coordinate system according to the requirements of the heat exchanger shell structure is: arraying the target lattice in three dimensions of length, width and height based on the requirements of the heat exchanger shell structure; the method for realizing the independence of the hot and cold flow domains by respectively closing the areas of opposing fluids at the inlets and outlets of the hot and cold fluids is: closing the area where the cold fluid is located at the inlet and outlet side of the hot fluid, and closing the area where the hot fluid is located at the inlet and outlet side of the cold fluid.

[0032] On the basis of the above technical solution, preferably, according to the working conditions and fluid characteristics of the heat exchanger, by optimizing the array arrangement of the lattice units, the distance, arrangement and direction between the lattice units are adjusted to optimize the kinetic energy loss and heat exchange efficiency of the fluid under different flow and heat transfer conditions, thereby improving the overall performance of the heat exchanger.

[0033] On the basis of the above technical solution, preferably, step four also includes analyzing the flow and heat transfer characteristics of different TPMS heat exchanger structures to obtain the following parameters, including heat transfer efficiency, heat transfer rate per unit volume, and dimensionless parameters Nusselt number (Nu) and Fanning friction coefficient (f).

[0034] On the basis of the above technical solution, preferably, the flexible hybrid heat exchange core structure is processed as a whole by a 3D printing method.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The heat exchanger design method based on the hybrid TPMS structure proposed in the present invention can achieve more efficient porosity distribution and fluid channel design by using a flexible hybrid TPMS structure. Compared with the traditional heat exchanger structure, the flexible TPMS structure design can increase the heat exchange area while keeping the volume unchanged, thereby improving the heat exchange performance, successfully overcoming the shortcomings of the traditional TPMS structure, and has significant advantages in improving the heat transfer performance per unit volume of the heat exchanger and increasing the heat exchange area, providing an efficient, optimized, and manufacturable heat exchanger design solution.

[0037] 2. The hybrid TPMS structure optimizes the surface distribution morphology by combining two original TPMS structures (such as Gyroid and Diamond) in a smooth transition. Different TPMS structures have different surface properties. After mixing, they form a multifaceted surface with complex geometric properties, which greatly increases the surface area. At the same time, its special spatial geometric structure creates a shear effect of fluids in multiple places, enhancing heat exchange. Designers can choose a combination of different TPMS structures (such as Primitive-Diamond hybrid or Gyroid-Diamond hybrid) according to the shape and needs of the internal space of the heat exchanger, so as to maximize the coverage of the internal surface area of ​​the heat exchanger.

[0038] 3. By introducing the Sigmoid function, a smooth transition can be achieved between two typical TPMS structures, avoiding sudden or discontinuous transition. The transition functions M and N can be adjusted according to needs to achieve a mixture of different TPMS structures to meet the design requirements in different application scenarios. By combining the Primitive, Gyroid and Diamond structures, different types of hybrid TPMS structures can be generated. The structure of the heat exchanger can be flexibly designed according to actual needs to cope with different fluid flow, heat exchange requirements and other conditions.

[0039] 4. In the design of hybrid TPMS structure, the Sigmoid function makes the transition between two different TPMS units smoother and more seamless by adjusting the shape of the transition zone. By designing the function f(x, y, z): This function defines the shape of the transition zone. Through different function forms, the geometric shape of the transition area of ​​the hybrid structure can be controlled to achieve different types of transition effects. By adjusting the shape of the transition zone, the local performance of the heat exchanger can be flexibly optimized, while ensuring the smoothness and functional optimization of the overall structure, thereby improving the overall efficiency and performance of the heat exchanger.

[0040] 5. According to the working conditions and fluid characteristics of the heat exchanger, optimize the array arrangement of the lattice units to improve the uniformity of fluid flow and heat exchange efficiency. By adjusting the distance, arrangement and direction between the lattice units, the overall performance of the heat exchanger can be optimized under different flow and heat transfer conditions, and the flow stability, heat transfer efficiency, energy saving effect, etc. can be improved. This method not only improves the performance of the heat exchanger, but also enhances its adaptability and stability under different working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0042] Figure 1 It is a flow chart of the heat exchanger design method based on the hybrid TPMS structure disclosed in the present invention;

[0043] Figure 2 The three typical TPMS structures disclosed in the present invention and the hybrid TPMS structure after two-by-two fusion;

[0044] Figure 3 It is a structural diagram of the transition zone of the hybrid TPMS structure disclosed in the present invention;

[0045] Figure 4 It is a schematic diagram of the structure of the TPMS heat exchanger disclosed in the present invention;

[0046] Figure 5 It is a cross-sectional schematic diagram of the TPMS heat exchanger disclosed in the present invention;

[0047] Figure 6 A volume heat exchange rate variation diagram of the TPMS heat exchanger disclosed in the present invention and a traditional cross-flow heat exchanger;

[0048] Figure 7 The curve function changes with the parameter f at different k values ​​disclosed in the present invention;

[0049] Figure 8 This is a velocity cloud diagram of the fluid region inside the Gyroid-Diamond hybrid TPMS structure disclosed in the present invention. DETAILED DESCRIPTION

[0050] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] like Figure 1 , combined with Figure 2-5 As shown, the embodiment of the present invention discloses a heat exchanger design method based on a hybrid TPMS structure, comprising the following steps:

[0052] Step 1: Based on the mathematical implicit equation of the original typical TPMS lattice structure, the sigmoid function is combined to achieve a smooth transition between the two original typical TPMS structure surfaces to construct a mathematical expression of the flexible hybrid TPMS lattice structure.

[0053] The TPMS structure (periodic porous media structure) is a structural form commonly used for heat transfer and fluid flow optimization, with uniform pores and good flow characteristics. Traditional TPMS structures may have obvious boundaries and different geometric features, but this structure is often not flexible enough and cannot adapt well to various design requirements. By combining the Sigmoid function to smooth the transition between the two original TPMS structures, the sudden or discontinuous geometry in the traditional design is avoided, making the structure smoother and more flexible. This flexible structure helps to increase the surface area and improve the heat exchange efficiency.

[0054] By using the sigmoid function to control the transition mode between different TPMS units, a hybrid TPMS lattice structure with flexible transition characteristics is generated. Each TPMS structure adjusts its geometry and porosity as needed to provide more heat exchange area in the heat exchanger. The combination and transition of different TPMS structures can create a larger effective surface area within a limited volume, thereby improving the heat exchange capacity per unit volume of the heat exchanger.

[0055] Through innovative mathematical expressions and flexible design, a larger heat exchange area can be achieved without increasing the volume, and the inherent defects of traditional structures can be avoided. In this way, the heat exchange performance per unit volume of the heat exchanger has been significantly improved.

[0056] Step 2: Output the lattice unit in the three-dimensional modeling software according to the obtained mathematical expression of the flexible hybrid TPMS lattice structure.

[0057] This step uses 3D modeling software (such as SolidWorks, AutoCAD, PROE, Catia, Blender, etc.) to output the 3D modeling of the flexible hybrid TPMS lattice structure according to the above mathematical expression. The 3D modeling software can accurately reflect the geometric shape and internal channel layout of the structure, providing a basis for subsequent actual design and manufacturing. The required lattice unit model is automatically generated by the software. This method can greatly improve the efficiency and accuracy of the design and avoid the errors that may be caused by manual drawing or human operation. In addition, 3D modeling can intuitively display the lattice structure, which is convenient for subsequent optimization and adjustment.

[0058] Step 3: According to the requirements of the heat exchanger shell structure, the target lattice unit is realized in a periodic array in the spatial coordinate system, and the hot and cold fluid inlets and outlets are closed to realize the independence of the hot and cold flow domains, and finally a flexible hybrid heat exchange core structure is obtained and filled into the heat exchange shell to obtain a heat exchanger.

[0059] According to the space requirements of the heat exchanger shell, the generated flexible hybrid TPMS lattice units are periodically arranged in three-dimensional space. This periodic array can form a three-dimensional continuous lattice structure and ensure uniform heat exchange effect throughout the working space of the heat exchanger. In this way, the effective heat exchange surface area can be maximized inside the heat exchanger. The independent design of hot and cold fluid areas avoids heat exchange interference between fluids and ensures that each fluid area can exchange heat under optimal conditions, thereby improving the overall heat transfer efficiency.

[0060] Step 4: Analyze the flow and heat transfer characteristics of TPMS heat exchangers with different flexible mixtures to obtain the optimal design.

[0061] After the design is completed, the flow and heat transfer characteristics are analyzed, which is usually carried out through numerical simulation (such as CFD, finite element analysis, etc.) or experimental testing. The goal of this step is to verify the fluid flow, heat transfer performance and pressure loss of the designed flexible hybrid TPMS structure under different working conditions. Through simulation analysis, the temperature distribution, flow velocity distribution, heat flux density and other parameters of the heat exchanger under working conditions can be obtained, so as to further optimize the design and improve the thermal efficiency and fluidity of the heat exchanger.

[0062] The heat exchanger design method based on the hybrid TPMS structure proposed in the present invention can achieve more efficient porosity distribution and fluid channel design by using a flexible hybrid TPMS structure. Compared with the traditional heat exchanger structure, the flexible TPMS structure design can increase the heat exchange area while keeping the volume unchanged, thereby improving the heat exchange performance, successfully overcoming the shortcomings of the traditional TPMS structure, and has significant advantages in improving the heat transfer performance per unit volume of the heat exchanger and increasing the heat exchange area, providing an efficient, optimized, and manufacturable heat exchanger design solution.

[0063] The following is an introduction to the Sigmoid function that realizes the smooth transition of two original typical TPMS structures. The mathematical form of the Sigmoid function is as follows:

[0064]

[0065] Where M and N are transition functions, and their value range is between (0,1). When their values ​​vary between 0 and 1, a smooth transition can be achieved between the two typical TPMS structures. Here, M and N are used as transition functions to control the degree of mixing of the two original TPMS structures. In this embodiment, the transition functions M and N satisfy the relationship of M+N=1. When M is close to 1 and N is close to 0, the mixed structure will be more inclined to the first TPMS structure, and when N is close to 1 and M is close to 0, the mixed structure will be more inclined to the second TPMS structure.

[0066] See attached Figure 7 As shown in the figure, the parameter k>0 controls the width of the transition zone. A larger k value means a narrower transition zone, and the transition functions M and N will change rapidly in a smaller area, making the transition between the two TPMS structures more abrupt. A smaller k value will make the transition zone wider, thus achieving a smoother transition.

[0067] The function f(x, y, z) = 0 is used to define the shape of the transition zone. By controlling the function value in space, the position and shape of the transition zone can be flexibly adjusted according to actual needs, further optimizing the design of the hybrid TPMS structure.

[0068] The Sigmoid function ensures a smooth transition between the two original TPMS structures without abrupt structural changes, thus avoiding problems such as fluid resistance or uneven heat transfer caused by uneven transition.

[0069] In a single TPMS structure, typical original TPMS structures include primitive structure, gyroid structure and diamond structure, each TPMS structure has its own specific geometry and characteristics. Figure 2As shown, the original structure (a) is the Primitive structure; (b) is the Gyroid structure; and (c) is the Diamond structure.

[0070] In the flexible hybrid TPMS structure, (d) is Primitive-Diamond, (e) is Primitive-Gyroid, and (f) is Gyroid-Diamond.

[0071] Primitive structure: has good symmetry and high porosity, suitable for applications requiring larger fluid channels and higher flow efficiency.

[0072] The mathematical implicit equation of the primitive structure is:

[0073] Gyroid structure: It has a complex three-dimensional surface and can provide a large surface area, which is suitable for occasions requiring high heat exchange efficiency.

[0074] The mathematical implicit equation of the Gyroid structure is:

[0075] Diamond structure: It has a regular pore structure, suitable for uniform flow and stable heat exchange requirements.

[0076] The mathematical implicit equation of the Diamond structure is:

[0077]

[0078] Where c is a constant value representing the thickness of the lattice unit, and l is the length of the unit cell in the x, y, and z directions.

[0079] The corresponding generated hybrid TPMS structures include: Primitive-Gyroid structure, Primitive-Diamond structure and Gyroid-Diamond structure. The flexible hybrid TPMS unit is expressed as follows:

[0080]

[0081] and The mathematical expressions of two different typical original TPMS unit structures are represented respectively, and X, Y, and Z refer to the coordinates of the lattice unit in the three-dimensional space, which ensures the accurate position and arrangement of the hybrid structure in the three-dimensional space. In this embodiment, the mathematical expression of the TPMS unit structure is the mathematical implicit equation of the TPMS unit structure.

[0082] During the change of M and N, the structure transitions from one typical TPMS unit to another, forming a continuous hybrid TPMS structure with flexible transition characteristics.

[0083] Traditional single TPMS structures (such as Primitive, Gyroid, and Diamond) usually have fixed geometric shapes. Although the surface area is large, it is still limited by the distribution law of a single shape and cannot be further adjusted according to specific needs. In the complex internal space of the heat exchanger, the surface area utilization of a single TPMS structure may be insufficient, resulting in reduced space utilization.

[0084] The hybrid TPMS structure optimizes the surface distribution morphology by combining two original TPMS structures (such as Gyroid and Diamond) in a smooth transition. Different TPMS structures have different surface properties, and after mixing, they form a multifaceted surface with complex geometric properties, which greatly increases the surface area. Designers can choose a combination of different TPMS structures (such as Primitive-Diamond hybrid or Gyroid-Diamond hybrid) according to the shape and needs of the internal space of the heat exchanger, thereby maximizing the coverage of the internal surface area of ​​the heat exchanger.

[0085] A single TPMS structure may form inefficient fluid distribution in certain areas, resulting in reduced local heat transfer efficiency. Among them, the Primitive structure has a small surface area and relatively low heat transfer performance. Although the Gyroid structure has a large surface area, it has a high flow resistance and may cause local fluid retention. The Diamond structure has a high uniformity but insufficient complexity, which may limit the heat exchange area.

[0086] Through hybrid design, the performance shortcomings of a single TPMS structure are made up. For example, in areas where a high surface area is required, Gyroid components can be introduced. In areas where lower flow resistance is required, Primitive components can be mixed in. In areas where uniform performance is required, Diamond components can be mixed in. By utilizing the smooth transition characteristics of the Sigmoid function, the hybrid TPMS structure achieves a balanced distribution of performance in different areas, avoiding the problem of reduced local efficiency caused by uneven performance of a single structure.

[0087] By introducing the Sigmoid function, a smooth transition can be achieved between two typical TPMS structures, avoiding sudden or discontinuous transition. The transition functions M and N can be adjusted according to needs to achieve a mixture of different TPMS structures to meet the design requirements in different application scenarios. By combining the Primitive, Gyroid and Diamond structures, different types of hybrid TPMS structures can be generated. The structure of the heat exchanger can be flexibly designed according to actual needs to cope with different fluid flow, heat exchange requirements and other conditions.

[0088] In this embodiment, when the transition functions M and N change from 0 to 1, TPMS unit to The method of transforming the hybrid structure of the TPMS unit to obtain the hybrid TPMS structure is as follows.

[0089] Specifically, when M and N are constants, a different formula can be obtained from TPMS unit and A new unit structure of the TPMS unit, which is called a uniform structure.

[0090] When both M and N are constants, the structure does not remain in pure TPMS unit or The state of the TPMS unit is not the same as that of the original TPMS unit, but a completely new hybrid TPMS unit is formed. The morphology of this new structure is composed of a weighted combination of the two original TPMS units in a certain proportion, and this process is controlled by the transition function. Specifically, the constants M and N do not lead to a simple transition state, but directly determine the specific morphology of the final structure, which may be a completely new complex structure with the characteristics of both TPMS units. This new unit structure may contain the fusion area of ​​the two TPMS units, forming a more complex curved structure. Its morphology and performance characteristics will depend on the values ​​of M and N, which determine the local geometric characteristics of the new structure.

[0091] When M and N are not constants, they only represent the transition connection between the two TPMS unit cell structures, which is equivalent to connecting the two TPMS unit cell structures by generating a transition area, integrating the flow and heat transfer characteristics of different TPMS to a greater extent, and optimizing the design of the transition area for demand functions.

[0092] The shape of the transition area can be designed by smooth functions such as the Sigmoid function. At the same time, the function f(x, y, z) plays a key role in this, which is used to accurately control the shape and range of the transition area. The specific form and parameter setting of this function determine the proportion, transition speed and spatial distribution of different TPMS units in the hybrid structure.

[0093] The transition region can smoothly connect two TPMS unit cell structures, and the resulting hybrid structure has the same dimensions as the periodic lattice and maintains the same size. The hybrid structure precisely controls the local transition region, allowing multiple hybrid units to form a periodic structure, in which the size and geometry of each periodic unit cell are exactly the same as the original periodic lattice structure, ensuring that the periodicity and size of the overall structure remain unchanged while optimizing local performance. This design achieves a balance between the functional optimization of the structure in the local area and the global periodic consistency.

[0094] When M and N are not constants, the transition zones of different shapes are designed by using the Sigmoid function, and the shapes of these transition zones are controlled by designing the function f(x, y, z), so as to achieve a smooth transition between two different TPMS unit structures. The specific method is as follows.

[0095] In the design of hybrid TPMS structure, the Sigmoid function makes the transition between two different TPMS units smoother and more seamless by adjusting the shape of the transition zone. By designing the function f(x,y,z): This function defines the shape of the transition zone. Through different function forms, designers can control the geometric shape of the transition area of ​​the hybrid structure to achieve different types of transition effects.

[0096] For the linear transition region, set f(x,y,z)=x, and the mathematical expression of the hybrid structure is:

[0097]

[0098] By setting f(x,y,z)=x, the hybrid structure of the linear transition zone is realized along the x-axis direction in space. TPMS unit to Linear transition of TPMS units. This means that as the x-coordinate changes, the mixing ratio changes linearly, resulting in a smooth transition from one TPMS structure to another.

[0099] For the circular transition region, set f(x,y,z)=x 2 +y 2 -8, the mathematical expression of the mixed structure is:

[0100]

[0101] The design implements a circular transition zone whose shape is determined by x2+y2. This means that as it expands outward from the center, the transition zone changes from TPMS unit gradually changes to TPMS unit, and the rate of transition varies according to the radius of the circle and the distance from the center.

[0102] For the elliptical transition zone, set The mathematical expression of the hybrid structure is:

[0103]

[0104] This design achieves structural mixing through an elliptical transition zone. The elliptical transition zone controls the change from the center to the boundary, making the transition between the two TPMS structures smooth within the elliptical area.

[0105] The Sigmoid function and the design function f(x, y, z) are used to control the shapes of different transition zones, thereby achieving a smooth transition between the two TPMS unit structures. By adjusting the shape of the transition zone, the designer can flexibly optimize the local performance of the heat exchanger while ensuring the smoothness and functional optimization of the overall structure, thereby improving the overall efficiency and performance of the heat exchanger.

[0106] This embodiment lists three typical transition areas, mainly to highlight the functional roles represented by different areas. For example, the linear area has better flow characteristics, and the circular and elliptical areas will produce higher turbulence effects and have better heat transfer characteristics. Different transition areas can be designed according to different actual application requirements, which is more free and adaptable.

[0107] In the design process of heat exchangers, flow performance and heat transfer efficiency are key design parameters. The hybrid TPMS structure adjusts the fluid flow path and heat exchange area through a flexible transition zone design, and different transition zone designs will have different effects on flow characteristics and heat transfer effects. Therefore, it is crucial to choose the most suitable transition zone design.

[0108] Using computational fluid dynamics (CFD) simulation and heat transfer models, designers can simulate the performance of different transition zone solutions under various flow conditions. This includes factors such as fluid velocity, temperature distribution, and flow pattern. Through simulation, key parameters such as pressure drop, flow distribution, and heat transfer coefficient under different design solutions can be predicted, providing data support for design decisions.

[0109] In addition to numerical simulation, experimental tests can also be used to verify the performance of different transition zone designs under actual working conditions. By actually testing the flow performance and heat transfer efficiency in the experimental device, more accurate performance data can be directly obtained, especially under complex flow conditions, where experimental results can often provide more representative feedback.

[0110] In the design of heat exchangers based on hybrid TPMS structures, numerical simulation or experimental testing is used to compare different transition zone design schemes, so as to select the best design scheme according to actual flow conditions. This process effectively improves the accuracy of the design and the ability to optimize performance, ensures the efficiency and reliability of the heat exchanger in actual applications, and provides effective technical support for the design of heat exchangers under complex working conditions.

[0111] Step 2 also includes inputting the dimensional parameters of the TPMS lattice unit into the 3D modeling software, the dimensional parameters including the porosity, wall thickness, unit size and lattice arrangement of the unit lattice; wherein the porosity and wall thickness are selected based on the design requirements, fluid characteristics and heat exchange performance of the heat exchanger, and the optimal values ​​are determined through simulation or experimental testing to ensure the optimal performance of the heat exchanger under working conditions.

[0112] This step requires the use of 3D modeling software to create a TPMS (topology optimized minimum surface) lattice structure model. 3D modeling can accurately define the geometry of each unit, and through parametric input, designers can flexibly adjust the various dimensional parameters of the TPMS structure.

[0113] In the modeling software, it is necessary to define multiple dimensional parameters that are closely related to the structural performance, including porosity, wall thickness, unit size, and lattice arrangement.

[0114] Among them, the porosity determines the degree of opening of the TPMS lattice, affecting the size of the fluid flow channel and the heat exchange surface area. High porosity generally means larger fluid channels, which helps fluid flow, but may reduce the mechanical strength of the structure. Low porosity may provide stronger structural stability, but increase flow resistance. The choice of porosity must balance thermal conductivity and fluid dynamics.

[0115] The wall thickness determines the strength and thermal conductivity of the lattice. Thinner walls can improve the efficiency of heat transfer, but may affect the mechanical stability of the lattice; thicker walls can provide higher strength, but may limit the efficiency of heat transfer. Therefore, the choice of wall thickness needs to be determined according to the actual use environment and load requirements of the heat exchanger.

[0116] The unit size affects the structural size of the heat exchanger and the uniformity of fluid flow, while the lattice arrangement determines the overall geometry of the lattice, which in turn affects the heat exchange efficiency and the path of fluid flow. Reasonable size and arrangement can effectively increase the heat exchange surface area, while optimizing the flow path and reducing the flow dead zone.

[0117] In order to ensure the optimal performance of the heat exchanger under actual working conditions, simulation and experimental tests are required to evaluate the impact of different dimensional parameters on the performance of the heat exchanger. Through computational fluid dynamics (CFD) and heat transfer simulation, the flow and temperature distribution of the fluid under different parameters such as porosity, wall thickness, and unit size can be predicted. Simulation can help designers optimize parameters and find the best design, especially when faced with complex flow conditions, which can effectively avoid time and cost issues that may be encountered in experiments. Through computational fluid dynamics (CFD) and heat transfer simulation, the flow and temperature distribution of the fluid under different parameters such as porosity, wall thickness, and unit size can be predicted. Simulation can help designers optimize parameters and find the best design, especially when faced with complex flow conditions, which can effectively avoid time and cost issues that may be encountered in experiments.

[0118] In step three, the method for realizing a periodic array of target lattice units in a spatial coordinate system according to the requirements of the heat exchanger shell structure is as follows: arraying the target lattice in three dimensions of length, width and height based on the requirements of the heat exchanger shell structure.

[0119] The target lattice units are repeatedly arranged in space according to a certain pattern to ensure the uniformity and overall performance of the internal structure of the heat exchanger. The arrangement of the three-dimensional array can be optimized according to the actual fluid flow pattern, heat transfer efficiency and load-bearing requirements of the structure. This arraying is usually achieved through three-dimensional modeling software, in which the dimensions of the lattice units (porosity, wall thickness, unit size, etc.) are accurately set to ensure that the arrangement rules of the lattice in different directions meet the design requirements. This process allows the arrangement of the lattice units to be flexibly adjusted according to the geometric dimensions, functional requirements and fluid flow requirements of the heat exchanger. For example, the lattice arrangement in the three-dimensional directions of length, width and height can be different, thereby optimizing the fluid flow path and heat exchange area to achieve better heat transfer performance.

[0120] In the design of heat exchangers, hot fluid and cold fluid often need to flow in the same device, but in order to ensure the heat exchange effect, mutual isolation of hot and cold fluid areas is necessary.

[0121] The method of achieving the independence of hot and cold flow areas by closing the areas of opposite fluids at the inlet and outlet of hot and cold fluids is: close the area where the cold fluid is located at the inlet and outlet of the hot fluid, and close the area where the hot fluid is located at the inlet and outlet of the cold fluid. The opposite closing method ensures that the flow of hot and cold fluids does not cross-interfere, which helps to improve the heat exchange effect of the heat exchanger and the stability of the fluid.

[0122] In heat exchanger design, the arrangement of lattice units directly affects the flow path of the fluid and the heat exchange efficiency. According to the working conditions and fluid characteristics (such as flow rate, temperature gradient, flow pattern, etc.), optimizing the array of lattice units can significantly improve the performance of the heat exchanger. The key factors for optimization include the following.

[0123] Properly adjusting the spacing between lattice units can effectively control the flow path of the fluid and reduce dead zones, uneven flow and other problems. At the same time, reasonable spacing helps to control the turbulence of the fluid and avoid unnecessary pressure drops caused by excessive flow rates. The arrangement of the lattice units determines the flow path of the fluid and the efficiency of heat exchange. Different arrangements (such as sequential arrangement, staggered arrangement, etc.) will affect the flow uniformity and heat exchange effect of the fluid. By optimizing the arrangement, the contact surface area of ​​the fluid can be maximized and the heat exchange efficiency can be improved. The directionality of the lattice unit also has an important influence on the flow pattern of the fluid. For example, lattice units in certain directions may promote fluid turbulence, thereby improving heat transfer efficiency; while arrangements in other directions may be conducive to flow stability. Therefore, selecting the appropriate lattice unit direction according to the characteristics of the fluid and flow conditions is crucial to optimizing the heat exchange effect.

[0124] According to the working conditions of the heat exchanger and the characteristics of the fluid, the array arrangement of the lattice units is optimized to improve the uniformity of fluid flow and heat exchange efficiency. By adjusting the distance, arrangement and direction between the lattice units, the overall performance of the heat exchanger can be optimized under different flow and heat transfer conditions, and the flow stability, heat transfer efficiency, and energy saving effects can be improved. This method not only improves the performance of the heat exchanger, but also enhances its adaptability and stability under different working conditions.

[0125] Step 4 proposes to evaluate the performance of the heat exchanger by analyzing the flow and heat transfer characteristics and using relevant thermophysical parameters, including heat transfer efficiency, heat transfer rate per unit volume, and dimensionless parameters Nusselt number (Nu) and Fanning friction coefficient (f).

[0126] Heat exchange efficiency is a measure of the ability of a heat exchanger to transfer heat from one fluid to another and is a direct reflection of the performance of the heat exchanger.

[0127] The Nusselt number (Nu) reflects the degree of enhancement of convective heat transfer. It is a dimensionless expression of the ratio of the convective heat transfer coefficient to the thermal conductivity and is often used to evaluate the heat transfer performance of the heat exchanger surface.

[0128] The Fanning friction coefficient (f) represents the pressure drop or flow resistance when a fluid flows through a heat exchanger and is used to evaluate the flow loss of a heat exchanger.

[0129] The heat transfer rate per unit volume measures the heat exchange capacity per unit volume of the heat exchanger and is an important indicator for evaluating structural compactness and performance.

[0130] Through quantitative analysis of thermophysical parameters and corresponding cloud map analysis, the specific impact of different designs on performance can be clarified, reducing design uncertainty; on the basis of balancing heat transfer efficiency and flow loss, it is ensured that the heat exchanger achieves a higher heat exchange capacity per unit volume; by analyzing relevant thermophysical parameters, the adaptability of different TPMS structures under different working conditions can be quickly evaluated and adjusted to meet diverse needs; by replacing some experimental tests with simulation analysis, the development cost and cycle can be reduced, while the structure is optimized to reduce material consumption.

[0131] Due to the limitations of design capabilities and mechanical processing methods, traditional heat exchange equipment cannot effectively increase the heat exchange area to increase the heat exchange per unit volume, and has reached a bottleneck stage in the improvement of heat exchange performance of heat exchangers. The development of 3D printing technology has overcome the limitations of traditional processing methods, making the entire structure of the flexible hybrid heat exchange core completed by 3D printing.

[0132] Some specific experimental examples are disclosed as follows.

[0133] Using the design method of the present invention, a 40mm*40mm*40mm heat exchange core structure based on primitive, Gyroid and Diamond type with a relative density of 20% and the corresponding generated primitive-Gyroid, primitive-Diamond and Gyroid-Diamond type hybrid TPMS structure was established. At the inlet and outlet of the heat exchange core, a 2mm thick irregular baffle was set according to the two fluid area junctions divided by the TPMS heat exchange core to ensure that the two different fluids remain independent in their respective flow channels. At the same time, the transition channel is extended by 200mm at the inlet and outlet to prevent fluid backflow. The physical parameters of different TPMS heat exchange cores are shown in Table 1 below, where the TPMS relative density is defined as the ratio of the area volume occupied by the solid area in the cubic unit to the total cubic unit volume.

[0134]

[0135] By comparing the characteristic parameters of different surface types, the following conclusions are drawn: (1) Diamond-type TPMS heat exchangers have the highest surface area and surface area-to-volume ratio; (2) Primitive-type TPMS heat exchangers have the highest hydraulic diameter. The flow and heat transfer characteristics of different TPMS heat exchanger cores were analyzed, and the flow and heat transfer characteristic parameters of different types of TPMS heat exchangers were extracted, as shown in Table 2.

[0136]

[0137] It can be seen from Table 2 that the unit volume heat exchange rate of the Primitive-Gyroid hybrid TPMS structure is greater than that of the Primitive TPMS structure, but smaller than that of the Gyroid TPMS structure; the unit volume heat exchange rate of the Primitive-Diamond hybrid TPMS structure is greater than that of the Primitive TPMS structure, but smaller than that of the Diamond TPMS structure; the unit volume heat exchange rate of the Gyroid-Diamond hybrid TPMS structure is greater than that of both the Gyroid TPMS structure and the Diamond TPMS structure.

[0138] The enhancement of the heat transfer characteristics of the flexible hybrid TPMS structure does not rely solely on the increase in the heat transfer area. The intermittent acceleration and deceleration of the fluid, the turbulence effect, and the secondary flow vortex will enhance the heat transfer. For example, the Gyroid-Diamond hybrid TPMS structure in the embodiment shows the best heat transfer performance because of the particularity of its internal structure, which leads to the high-speed and violent collision between the internal fluid and the solid wall, and the fluid is split into two opposite streams along the z direction, such as Figure 8 As shown in FIG. 1 , it represents the fluid shear effect inside the Gyroid-Diamond TPMS. The two countercurrents produce a strong fluid shear effect at the junction, which enhances the mixing between the fluids. Therefore, their high heat transfer area mainly exists in the area where the fluid undergoes high-speed convection.

[0139] See attached Figure 6 As shown, the flexible hybrid TPMS heat exchange core device based on flexible design adopts the same hot and cold channel inlet temperature, flow rate and pressure as the traditional cross-flow plate heat exchanger, and has excellent heat exchange performance. In particular, the Gyroid-Diamond type hybrid TPMS structure in the embodiment shows the best heat exchange performance, and its heat exchange efficiency is higher than that of the original TPMS heat exchange core structure. The unit volume heat transfer rate is increased by more than 3 times compared with the traditional cross-flow heat exchanger, which greatly reduces the space volume occupancy of the heat exchanger and further improves the heat exchange performance of the contemporary TPMS heat exchanger.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A heat exchanger design method based on a hybrid TPMS structure, characterized in that: The steps include: Step 1: Based on the mathematical implicit equation of the original typical TPMS lattice structure, the sigmoid function is combined to realize the smooth transition of the two original typical TPMS structure surfaces to construct the mathematical expression of the flexible hybrid TPMS lattice structure; Step 2: outputting lattice units in a three-dimensional modeling software according to the obtained mathematical expression of the flexible hybrid TPMS lattice structure; Step 3: According to the requirements of the heat exchanger shell structure, the target lattice unit is formed into a periodic array in the spatial coordinate system, and the hot and cold flow domains are separated by closing the areas of the opposing fluids at the inlet and outlet of the hot and cold fluids, so as to finally obtain a flexible hybrid heat exchange core structure, which is then filled into the heat exchange shell to obtain a heat exchanger; Step 4: Analyze the flow and heat transfer characteristics of TPMS heat exchangers with different flexible mixtures to obtain the optimal design.

2. The heat exchanger design method based on the hybrid TPMS structure according to claim 1, characterized in that: The smooth transition of the two original typical TPMS structure surfaces is achieved through the Sigmoid function, as shown below; Where M and N are transition functions, their value range is in the interval (0,1) and satisfy the relationship M+N=1, f(x,y,z)=0 is used to control the shape of the transition area, parameter k (k>0) defines the width of the transition area, and e is an exponential function with the natural constant e as the base; Typical original TPMS structures include: Primitive structure, Gyroid structure and Diamond structure, and the corresponding generated hybrid TPMS structures include: Primitive-Gyroid structure, Primitive-Diamond structure and Gyroid-Diamond structure. The flexible hybrid TPMS unit is expressed as follows: and Represent the mathematical expressions of two different typical original TPMS unit structures. X, Y, and Z refer to the coordinates of the lattice unit in three-dimensional space. When M and N change from 0 to 1, the Unit to Hybrid structural transformation of the unit.

3. The heat exchanger design method based on the hybrid TPMS structure according to claim 2, characterized in that: When the transition function M, N changes from 0 to 1, Unit to The method of transforming the hybrid structure of the unit to obtain a hybrid TPMS structure includes: When M and N are constants, a different formula can be obtained from Unit and A new unit structure of the unit, which is called a uniform structure; When M and N are not constants, the transition zone of the hybrid structure is designed according to the Sigmoid function. The shape of the transition zone is controlled by designing the function f(x, y, z). The resulting hybrid structure has the same dimension as the periodic lattice and maintains the same size.

4. The heat exchanger design method based on the hybrid TPMS structure according to claim 3, characterized in that: When M and N are not constants, the transition zone of the hybrid structure is designed according to the Sigmoid function, and the shape of the transition zone is controlled by designing the function f(x, y, z), including: For the linear transition region, set f(x,y,z)=x, and the mathematical expression of the hybrid structure is: For the circular transition region, set f(x,y,z)=x 2 +y 2 -8, the mathematical expression of the mixed structure is: For the elliptical transition zone, set The mathematical expression of the hybrid structure is: in, and They represent two different typical original TPMS unit structures.

5. The heat exchanger design method based on the hybrid TPMS structure according to claim 4, characterized in that: During the design process, the flow performance and heat transfer efficiency of different transition zone design schemes under different flow conditions are compared through numerical simulation or experimental testing, and then the most suitable transition zone design scheme is selected according to the fluid flow rate, temperature gradient, flow pattern and other conditions in actual working conditions to optimize the overall performance of the heat exchanger.

6. The heat exchanger design method based on the hybrid TPMS structure according to claim 1, characterized in that: Step 2 includes inputting the dimensional parameters of the TPMS lattice unit into the three-dimensional modeling software, wherein the dimensional parameters include the porosity, wall thickness, unit size and lattice arrangement of the unit lattice; wherein the selection of the porosity and wall thickness is based on the design requirements, fluid characteristics and heat exchange performance of the heat exchanger, and the optimal value is determined through simulation or experimental testing to ensure the optimal performance of the heat exchanger under working conditions.

7. The heat exchanger design method based on the hybrid TPMS structure according to claim 1, characterized in that: In the step three, the method for realizing a periodic array of target lattice units in a spatial coordinate system according to the requirements of the heat exchanger shell structure is: arraying the target lattice in three dimensions of length, width and height based on the requirements of the heat exchanger shell structure; the method for realizing the independence of hot and cold flow domains by closing the areas of opposing fluids at the inlets and outlets of hot and cold fluids respectively is: closing the area where the cold fluid is located at the inlet and outlet side of the hot fluid, and closing the area where the hot fluid is located at the inlet and outlet side of the cold fluid.

8. The heat exchanger design method based on the hybrid TPMS structure according to claim 7, characterized in that: According to the working conditions and fluid characteristics of the heat exchanger, by optimizing the array arrangement of the lattice units, adjusting the distance, arrangement and direction between the lattice units, the kinetic energy loss and heat exchange efficiency of the fluid can be optimized under different flow and heat transfer conditions, thereby improving the overall performance of the heat exchanger.

9. The heat exchanger design method based on the hybrid TPMS structure according to claim 1, characterized in that: Step 4 also includes analyzing the flow and heat transfer characteristics of different TPMS heat exchanger structures to obtain the following parameters, including heat transfer efficiency, heat transfer rate per unit volume, and dimensionless parameters Nusselt number (Nu) and Fanning friction coefficient (f).

10. The heat exchanger design method based on the hybrid TPMS structure according to claim 1, characterized in that: The flexible hybrid heat exchange core structure is processed as a whole by using a 3D printing method.

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