A method for generating hierarchical porous structures to enhance boiling heat transfer

Abstract

This invention discloses a method for generating a hierarchical porous structure to enhance boiling heat transfer. Based on MATLAB software, a hierarchical porous structure model is generated. A first-order porous structure is generated on the heating surface, and based on this first-order porous structure, second-order and third-order porous structures with different pore sizes are obtained. The resulting hierarchical porous structure, under low heat flux density, can increase the solid-liquid heat transfer area, increase vaporization nuclei, strengthen flow field disturbance, and improve boiling heat transfer. Under high heat flux density, the number of bubbles increases significantly. The hierarchical porous structure can utilize small-sized channels to enhance capillary liquid replenishment capacity and reduce the bubble detachment diameter, promoting bubble detachment. The pores of the first-order porous structure can provide low-resistance channels for bubble escape.

Description

Technical Field

[0001] This invention relates to the field of computer-aided heat transfer enhancement technology, and in particular to a method for generating a hierarchical porous structure for enhancing boiling heat transfer. Background Technology

[0002] With the continuous development of the microelectronics technology industry, electronic devices, as core components, are also moving towards large-scale, highly integrated, and high-power applications. Due to efficiency limitations, most of the energy consumed by electronic devices is ultimately converted into heat. The thermal failure caused by untimely heat dissipation will pose a severe challenge to the stable operation and safe functioning of the device.

[0003] Traditional air cooling and single-phase liquid cooling methods have low heat transfer capacity and cannot meet the ever-increasing heat dissipation demands. Liquid boiling phase change processes can utilize the latent heat of phase change to absorb a large amount of heat with relatively small temperature changes, achieving superior cooling effects. To meet the increasing heat transfer requirements of high-tech fields, it is necessary to further improve the heat transfer coefficient and critical heat flux density, leading to the development of various boiling heat transfer enhancement technologies. Surface structures can adjust various factors such as wettability, heat transfer area, vaporization nuclei, and capillary liquid supply capacity, making them a relatively effective means to enhance boiling heat transfer performance. Researchers have proposed a variety of surface structures, achieving significant improvements in heat transfer capacity. However, their heat transfer performance still falls far short of the theoretical heat transfer limit, and the rapidly increasing power density urgently demands further enhancement of boiling phase change heat transfer performance.

[0004] By utilizing micro- and nano-surface structures to reduce the superheat required for bubble nucleation and increase vaporization nuclei, the growth and detachment of numerous bubbles can disturb the flow field and enhance heat transfer, significantly improving the boiling heat transfer coefficient. However, at high heat flux densities, the increased number of bubbles accelerates steam accumulation, which then covers the heat transfer surface, causing a severe deterioration in heat transfer performance. Summary of the Invention

[0005] This invention provides a method for generating a hierarchical porous structure to enhance boiling heat transfer, thereby overcoming the aforementioned technical problems.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for generating hierarchical porous structures to enhance boiling heat transfer. This method generates hierarchical porous structure models based on MATLAB software, and specifically includes the following steps:

[0008] S1: Based on the equation of the first and third period minimal surface, obtain the first and third period minimal surface entity to generate a first-order porous structure entity on the heating surface, providing a low flow resistance channel for vapor-liquid transport.

[0009] S2: Obtain the second and third period minimum surface entity according to the equation of the second and third period minimum surface, and generate the second-order porous structure entity according to the first-order porous structure entity.

[0010] S3: Obtain the third three-period minimum surface entity according to the third three-period minimum surface equation, and generate the third-order porous structure entity according to the second-order porous structure entity.

[0011] The relationship between the parameters in the implicit functions of the first three-period minimum surface equation, the second three-period minimum surface equation, and the third three-period minimum surface equation is as follows:

[0012]

[0013] in, The wavelength of the first three-period minimum surface; The wavelength of the second and third periodic minimum surface; The wavelength of the third periodic minimum surface.

[0014] Furthermore, the method for generating a first-order porous structure on a heated surface is as follows:

[0015] Based on the equation of the first three-period minimum surface, the isosurface of the first three-period minimum surface is generated on the heated surface;

[0016] The first and third periodic minimum surface isosurfaces are used to generate a first-order porous structure with a thickness of C, where C is a parameter that determines the porosity of the porous structure.

[0017] Furthermore, the method for generating second-order porous structures is as follows:

[0018] Based on the equation of the second and third period minimum surface, obtain the isosurface of the second and third period minimum surface;

[0019] Generate the structural entity of the second and third period minimal surface based on the isosurface of the second and third period minimal surface;

[0020] Perform a Boolean operation between the first-order porous structure entity and the second and third periodic minimal surface structure entity to obtain the second-order porous structure entity.

[0021] The method for generating a third-order porous structure is as follows:

[0022] Based on the equation of the third periodic minimum surface, obtain the isosurface of the third periodic minimum surface;

[0023] Generate a third-third-third-period minimum surface structure entity based on the isosurface of the third-third-period minimum surface;

[0024] Perform Boolean operations on the second-order porous structure entity and the third three-period minimal surface structure entity to obtain a third-order porous structure entity.

[0025] Furthermore, the implicit functional expressions for the first three-period minimum surface equation / the second three-period minimum surface equation / the third three-period minimum surface equation are:

[0026]

[0027] In the formula: φ(r) represents an implicit function; A k The amplitude is represented by h; k represents the number of the lattice vector in reciprocal space; K represents the total number of lattice vectors in reciprocal space; h represents the amplitude of the lattice vector in reciprocal space. k λ represents the k-th lattice vector in reciprocal space; r represents the position vector in Euclidean space; λ k The wavelength of the three-period minimum surface is represented by P. k This indicates the phase shift; C is a parameter that determines the porosity of the porous structure.

[0028] Furthermore, the surface type of the first three-period minimum surface equation, the second three-period minimum surface equation, and the third three-period minimum surface equation can be any one of the following: Gyroid three-period minimum surface equation, Diamond three-period minimum surface equation, Primitive three-period minimum surface equation, or I-WP three-period minimum surface equation.

[0029] Furthermore, after S3, it also includes:

[0030] S4: Based on the aforementioned third-order porous structure entity, generate a digital model of the third-order porous structure entity and export an STL model file;

[0031] S5: Import the STL model file into Magics software for slicing and plan the printing path;

[0032] S6: According to the printing path, the third-order porous structure entity is printed using the selected area laser melting additive manufacturing method;

[0033] S7: Process the printed third-order porous structure, including but not limited to removing residual powder, eliminating residual stress, removing supports, and structural characterization.

[0034] Beneficial effects: The present invention provides a method for generating a hierarchical porous structure to enhance boiling heat transfer. By generating a first-order porous structure on the heating surface, and further obtaining second-order and third-order porous structures with different pore sizes based on the first-order porous structure, the resulting hierarchical porous structure can increase the solid-liquid heat transfer area, increase the number of vaporization nuclei, strengthen the flow field disturbance, and improve the boiling heat transfer effect under low heat flux density. Under high heat flux density, the number of bubbles increases significantly. The hierarchical porous structure can enhance the capillary liquid replenishment capacity by utilizing small-sized channels and reduce the bubble detachment diameter, promoting bubble detachment. The channels of the first-order porous structure can provide low flow resistance channels for bubble escape. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of the method for generating gradient porous structures according to the present invention;

[0037] Figure 2 This is a schematic diagram of the three-period minimum surface isosurface in an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of a porous structure type generated by a Gyroid surface in an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the digital generation method of hierarchical porous structures in an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of the hierarchical porous structure generated in an embodiment of the present invention;

[0041] Figure 6 This is a schematic diagram illustrating the mechanism of pore action at different scales in embodiments of the present invention;

[0042] Figure 7 This is a schematic diagram of the design and processing flow of the three-period minimal surface hierarchical porous structure in an embodiment of the present invention.

[0043] Among them, 101: Gyroid surface; 102: Diamond surface; 103: Primitive surface; 104: I-WP surface; 201: rod-shaped porous structure; 202: sheet-shaped porous structure. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] This embodiment provides a method for generating hierarchical porous structures to enhance boiling heat transfer. It is a MATLAB-based method for generating hierarchical porous structures, such as... Figure 1 and Figure 7 As shown, it includes the following steps:

[0046] S1: Based on the equation of the first and third period minimal surface, obtain the first and third period minimal surface solid to generate a first-order porous structure solid (first-order TPMS structure) on the heating surface; to provide a low flow resistance channel for vapor-liquid transport;

[0047] Preferably, the method for generating the first porous structure entity on the heating surface is as follows: establishing a digital model of the first three-period minimal surface porous structure, generating the first three-period minimal surface isosurface on the heating surface; thickening the first three-period minimal surface isosurface to generate a first-order porous structure entity;

[0048] The thickness of the thickening of the first and third period minima isosurface is determined by the parameter C that determines the porosity of the porous structure.

[0049] Specifically, the process involves generating a digital model of the first and third period minimal surface gradient porous structure using either independent programming or modeling software, and then exporting the STL model file.

[0050] S2: Based on the equation of the second and third period minimal surface, obtain the second and third period minimal surface entity, and generate a second-order porous structure entity (second-order TPMS structure) based on the first-order porous structure entity; to enhance liquid rewetting and improve liquid replenishment capacity;

[0051] Preferably, the isosurface of the second and third period minimal surface is obtained according to the equation of the second and third period minimal surface; the structural entity of the second and third period minimal surface is generated according to the isosurface of the second and third period minimal surface; the first-order porous structural entity and the structural entity of the second and third period minimal surface are subjected to Boolean operation, and the structural entity of the second and third period minimal surface is removed from the first-order porous structural entity to obtain the second-order porous structural entity;

[0052] S3: Based on the equation of the third three-period minimum surface, obtain the third three-period minimum surface entity, and generate a third-order porous structure entity (third-order TPMS structure) based on the second-order porous structure entity; to increase the gasification core density and improve the heat transfer coefficient;

[0053] Preferably, the isosurface of the third-third periodic minimum surface is obtained according to the equation of the third-third periodic minimum surface; the isosurface of the third-third periodic minimum surface is generated according to the isosurface of the third-third periodic minimum surface; the second-order porous structure entity and the third-third periodic minimum surface structure entity are subjected to Boolean operation to obtain the third-order porous structure entity.

[0054] The relationship between the parameters in the implicit functions of the first three-period minimum surface, the second three-period minimum surface, and the third three-period minimum surface is as follows:

[0055]

[0056] in, The wavelength of the first three-period minimum surface; The wavelength of the second and third periodic minimum surface; The wavelength of the third periodic minimum surface.

[0057] Based on the expected performance (boiling heat transfer performance and vapor-liquid transport characteristics), this embodiment determines the parameters of the first unit cell size and the first porosity of the first-order porous structure entity, the parameters of the second unit cell size and the second porosity of the second three-period minimal surface entity, and the parameters of the third unit cell size and the third porosity of the third three-period minimal surface entity.

[0058] Specifically, in this embodiment, the implicit function expressions of the first three-period minimum surface equation, the second three-period minimum surface equation, and the third three-period minimum surface equation are programmed in Matlab software.

[0059] The implicit functional expressions for the first three-period minimum surface equation, the second three-period minimum surface equation, and the third three-period minimum surface equation are as follows:

[0060]

[0061] In the formula: φ(r) represents an implicit function; A k The amplitude is represented by h; k represents the number of the lattice vector in reciprocal space; K represents the total number of lattice vectors in reciprocal space; h represents the amplitude of the lattice vector in reciprocal space. k λ represents the k-th lattice vector in reciprocal space; r represents the position vector in Euclidean space; λ k The wavelength of the three-period minimum surface is represented by P. kThis indicates the phase shift; C is a parameter that determines the porosity of the porous structure. In actual solid modeling, the value of C is set manually based on experience.

[0062] Specifically, the first three-period minimum surface equation, the second three-period minimum surface equation, and the third three-period minimum surface equation include various types, all of which can be derived from the implicit function.

[0063] Preferably, the surface type of the first three-period minimum surface equation / second three-period minimum surface equation / third three-period minimum surface equation is any one of the following: Gyroid three-period minimum surface equation, Diamond three-period minimum surface equation, Primitive three-period minimum surface equation, and I-WP three-period minimum surface equation.

[0064] Specifically, the preferred surface types for the first / second / third period minimum surface equations / third period minimum surface equations used to enhance boiling heat transfer in this invention include: Figure 2 The diagram shows four types of three-period minimum surfaces: Gyroid, Diamond, Primitive, and I-WP. The surface types of the equations for the first, second, and third three-period minimum surfaces can be the same or different.

[0065] Specifically, in the embodiments of the present invention,

[0066] Gyroid three-period minimum surface equation:

[0067]

[0068] Diamond's three-period minimum surface equation:

[0069]

[0070] Primitive three-periodic minimum surface equation:

[0071]

[0072] I-WP Three-Period Minimal Surface Equation:

[0073]

[0074] in: Represent the equation of the Gyroid three-period minimum surface; Represent the equation of the Diamond three-period minimum surface; Represents the equation of the Primitive three-periodic minimal surface; The equation for the I-WP three-period minimum surface is given; a is a parameter that determines the unit cell size of the porous structure; C is a parameter that determines the porosity of the porous structure; x, y, and z all represent the coordinates of points on the three-period minimum surface.

[0075] Specifically, in this embodiment, after generating corresponding isosurfaces using the first three-period minimum surface, the second three-period minimum surface, and the third three-period minimum surface, these are thickened to generate first-order porous structure entities, second three-period minimum surface entities, and third three-period minimum surface entities, respectively. The first-order porous structure entities, second three-period minimum surface entities, and third three-period minimum surface entities can be... Figure 3 The sheet-like or rod-like structures shown are defined based on characteristic parameters and the solid filling region. For sheet-like structures, the three-dimensional space is defined as follows: and The region between them is the solid region, and the rest is the fluid region; for rod-shaped structures, the definition is... The space is a solid region, smaller than The space is a fluid region.

[0076] In embodiments of the present invention, a hierarchical porous structure is generated by generating a second-order porous structure entity through Boolean operations on a first-order porous structure entity, and then generating a third-order porous structure entity through Boolean operations on the second-order porous structure entity. Figure 4 As shown; the specific process is as follows: First, a first-order porous solid structure is generated on the heated surface using the first three-period minimal surface equation, creating the main framework of the hierarchical porous structure and forming macroscopic-scale pores (macroscopic-scale pores) of the porous structure; then, the parameters of the three-period minimal surface governing equation are changed to generate a smaller-scale second-order three-period minimal surface structure, namely the second three-period minimal surface solid. Boolean operations are performed on the first-order porous solid structure and the second three-period minimal surface solid to remove the second three-period minimal surface solid structure from the first-order porous solid structure, generating mesoscopic-scale pores of the porous structure (second-order porous structure solid); similarly, a smaller-sized third three-period minimal surface solid is removed from the second-order porous structure solid region to obtain microscopic-scale pores, thereby obtaining a multi-scale hierarchical three-period minimal surface porous structure (i.e., a third-order porous structure solid) with precisely controlled dimensions. Figure 5 The diagram shows the macroscopic, mesoscopic, and microscopic pore structures in the hierarchical three-period minimal surface porous structure of this embodiment.

[0077] The mechanism by which the gradient pore structure affects the boiling heat transfer process in this embodiment is illustrated as follows: Figure 6As shown, micropores can lower the nucleation temperature, and combined with the high specific surface area of ​​the three-period minimal curved surface structure, increase the vaporization nucleus density and improve the heat transfer coefficient; mesopores provide capillary replenishment paths, which can enhance liquid rewetting and improve replenishment capacity; macroscopically ordered macropores provide low flow resistance channels for vapor-liquid transport, reduce bubble detachment resistance, and accelerate bubble detachment. By enhancing replenishment capacity and accelerating bubble detachment capacity, the critical heat flux density is increased.

[0078] The S1 mainly includes: determining the required porous structure size a, porosity c, three-period minimum surface structure type, and materials used for processing.

[0079] Preferably, after step S3, the method further includes: S4: Based on the third-order porous structure entity, generate a digital model of the third-order porous structure entity by independent programming or by using modeling software, and export an STL model file.

[0080] S5: Import the STL model file into Magics software for slicing and plan the printing path.

[0081] S6: Based on the printing path, the third-order porous structure is printed using the selective laser melting additive manufacturing method.

[0082] The printing material in the selective laser melting additive manufacturing method in S6 is a high thermal conductivity metal material such as copper alloy, aluminum alloy, or stainless steel.

[0083] S7: Process the printed third-order porous structure, including but not limited to removing residual powder, eliminating residual stress, removing supports, and structural characterization.

[0084] Specifically, in S7, the method for eliminating residual stress is preferably heat treatment, the method for removing the support structure is preferably wire cutting, and the structural characterization includes BET testing, scanning electron microscopy characterization, and permeability testing.

[0085] The purpose of this invention is to address the problem of severely deteriorated boiling heat transfer performance under high heat flux density by proposing a passive boiling heat transfer enhancement hierarchical porous structure. This structure has hierarchical pores of different sizes, which increases the number of vaporization nuclei and enhances flow field disturbance to improve heat transfer performance. Furthermore, the capillary effect of the porous structure enhances the liquid rewetting ability and accelerates bubble detachment.

[0086] Beneficial effects: The present invention provides a method for generating a hierarchical porous structure to enhance boiling heat transfer. By generating a first-order porous structure on the heating surface, and further obtaining second-order and third-order porous structures with different pore sizes based on the first-order porous structure, the resulting hierarchical porous structure can increase the solid-liquid heat transfer area, increase the number of vaporization nuclei, strengthen the flow field disturbance, and improve the boiling heat transfer effect under low heat flux density. Under high heat flux density, the number of bubbles increases significantly. The hierarchical porous structure can enhance the capillary liquid replenishment capacity by utilizing small-sized channels and reduce the bubble detachment diameter, promoting bubble detachment. The channels of the first-order porous structure can provide low flow resistance channels for bubble escape.

[0087] This embodiment proposes a hierarchical porous structure with pores of different scales constructed using a three-period minimal surface. The minimal surface structure is interconnected and regularly ordered, which increases specific surface area, reduces flow resistance, and facilitates rapid bubble escape. The three-period minimal surface can be directly described using mathematical expressions and characteristic parameters, enabling customized design of the hierarchical pores. Combined with additive manufacturing technology, controllable fabrication and one-time molding of the hierarchical porous structure can be achieved, facilitating further optimization of its boiling heat transfer performance.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for generating a hierarchical porous structure to enhance boiling heat transfer, wherein the method is based on MATLAB software to generate a hierarchical porous structure model, characterized in that, Specifically, the steps include the following: S1: Based on the equation of the first and third period minimal surface, obtain the first and third period minimal surface entity to generate a first-order porous structure entity on the heating surface, providing a low flow resistance channel for vapor-liquid transport. The method for generating a first-order porous structure on a heated surface is as follows: Based on the equation of the first three-period minimum surface, the isosurface of the first three-period minimum surface is generated on the heated surface; The first and third period minimum surface isosurfaces are defined with a thickness of... C Generate a first-order porous structure entity. C Parameters that determine the porosity of porous structures; S2: Obtain the second and third period minimum surface entity according to the equation of the second and third period minimum surface, and generate the second-order porous structure entity according to the first-order porous structure entity. The method for generating a second-order porous structure is as follows: Based on the equation of the second and third period minimum surface, obtain the isosurface of the second and third period minimum surface; Generate the structural entity of the second and third period minimal surface based on the isosurface of the second and third period minimal surface; Perform a Boolean operation between the first-order porous structure entity and the second and third periodic minimal surface structure entities to obtain a second-order porous structure entity. S3: Obtain the third three-period minimum surface entity according to the third three-period minimum surface equation, and generate the third-order porous structure entity according to the second-order porous structure entity. The method for generating a third-order porous structure is as follows: Based on the equation of the third periodic minimum surface, obtain the isosurface of the third periodic minimum surface; Generate a third-third-third-period minimum surface structure entity based on the isosurface of the third-third-period minimum surface; Perform a Boolean operation between the second-order porous structure entity and the third three-period minimal surface structure entity to obtain a third-order porous structure entity. The relationship between the parameters in the implicit functions of the first three-period minimum surface equation, the second three-period minimum surface equation, and the third three-period minimum surface equation is as follows: ； in, The wavelength of the first three-period minimum surface; The wavelength of the second and third periodic minimum surface; The wavelength of the third periodic minimum surface.

2. The method for generating a hierarchical porous structure to enhance boiling heat transfer according to claim 1, characterized in that, The implicit function expressions for the equations of the first and third period minimum surfaces, the second and third period minimum surfaces, and the third and third period minimum surfaces are: In the formula: Represents an implicit function; Indicates amplitude; k Indicates the number of the lattice vector in reciprocal space; This represents the total number of lattice vectors in reciprocal space; Represents the k-th lattice vector in reciprocal space; Represents a position vector in Euclidean space; The wavelength of the three-period minimum surface is represented. Indicates phase shift; The parameters that determine the porosity of porous structures.

3. The method for generating a hierarchical porous structure to enhance boiling heat transfer according to claim 1, characterized in that, The surface type of the first three-period minimum surface equation, the second three-period minimum surface equation, and the third three-period minimum surface equation is any one of the following: Gyroid three-period minimum surface equation, Diamond three-period minimum surface equation, Primitive three-period minimum surface equation, and I-WP three-period minimum surface equation.

4. The method for generating a hierarchical porous structure to enhance boiling heat transfer according to claim 1, characterized in that, Following S3, it also includes: S4: Based on the aforementioned third-order porous structure entity, generate a digital model of the third-order porous structure entity and export an STL model file; S5: Import the STL model file into Magics software for slicing and plan the printing path; S6: According to the printing path, the third-order porous structure is printed using the selective laser melting additive manufacturing method; S7: Process the printed third-order porous structure, including but not limited to removing residual powder, eliminating residual stress, removing supports, and structural characterization.

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