A radiator based on bionic tree-shaped flow channel and plum blossom-shaped variable-diameter needle rib composite

Abstract

The application discloses a radiator based on a bionic tree-shaped flow channel and a plum-blossom-shaped variable-diameter needle rib composite, comprising a substrate, a needle rib array arranged at the center of the substrate, and a plurality of fractal flow channels arranged around the needle rib array; wherein the needle rib array comprises an extremely dense nuclear center, an intermediate transition zone located outside the extremely dense nuclear center, and an outermost peripheral zone located outside the intermediate transition zone. By using vein fractal flow channels on a macro scale to achieve low-resistance and high-efficiency liquid supply and gas discharge, and by using a variable-diameter needle rib array on a micro scale to strengthen nucleate boiling and regulate bubble behavior, cross-scale synergistic optimization of heat transfer enhancement and flow organization is realized, the critical heat flux density, the heat exchange coefficient and the temperature uniformity are effectively improved, and the problem that heat exchange enhancement and flow regulation are mutually disjointed in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of chip heat dissipation technology, and in particular to a heat sink based on a combination of biomimetic tree-like flow channels and plum blossom-shaped variable diameter pin ribs. Background Technology

[0002] With the rapid development of high-power-density chips such as data center processors and 3D integrated chips, traditional air cooling and single-phase liquid cooling are no longer sufficient to meet heat dissipation requirements. Two-phase immersion cooling technology, which utilizes the latent heat of the working fluid for efficient heat exchange, has become an important development direction. In two-phase cooling, high heat flux density easily leads to the aggregation of bubbles on the heated surface, forming a gas film that hinders liquid replenishment and causes localized drying and overheating, causing the CHF (critical heat flux density) to be reached prematurely. Therefore, how to achieve efficient separation and transport of the gas and liquid phases while enhancing nucleation boiling through the structural design of the heat sink is a core problem that urgently needs to be solved.

[0003] Currently, the industry's enhanced structures for chip heat dissipation are mainly divided into two categories: one is the pin-rib array structure that focuses on strengthening the microscopic interface, and the other is the biomimetic fractal flow channel structure that focuses on macroscopic fluid distribution.

[0004] In terms of enhancing the microscopic interface, researchers often use ordinary micro-sized needle-rib arrays to increase the nucleation point density and promote the evaporation of thin liquid films. For example, studies by Wan et al. and Yang et al. have shown that micro-sized needle-rib structures can improve the critical heat flux density and heat transfer coefficient. However, such dense, uniform needle-rib arrays are prone to causing extremely high flow resistance and are very likely to cause bubbles to stagnate and accumulate locally.

[0005] In terms of macroscopic fluid distribution, besides academic research, biomimetic structures are increasingly being applied to heat sink patent designs. For example, patent CN104617062A discloses an impact-type water-cooled chip heat sink with biomimetic plant leaf vein fractal microchannels, which improves coolant distribution and enhances chip heat dissipation performance by constructing leaf vein-shaped fractal microchannels. Patent CN224264115U proposes a liquid-cooled plate heat dissipation structure that mimics the distribution of leaf veins, using leaf vein-like flow channels to achieve uniform transport of coolant in the heat source area. Patent CN119314960A discloses an interlaced leaf vein-shaped embedded microchannel heat sink, which improves flow field distribution and enhances heat transfer efficiency through leaf vein bifurcation structure and interlaced flow channel layout. Summary of the Invention

[0006] The purpose of this invention is to provide a heat sink based on a combination of biomimetic tree-like flow channels and plum blossom-shaped variable diameter needle ribs, which solves the problem that existing chip heat dissipation structures are difficult to balance heat transfer enhancement and flow organization under high heat flux density, resulting in easy bubble retention, large system pressure drop, and easy local drying.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The present invention provides a heat sink based on a combination of biomimetic tree-shaped flow channels and plum blossom-shaped variable diameter needle ribs, including a substrate, a needle rib array disposed at the center of the substrate, and a plurality of fractal flow channels disposed around the needle rib array; The needle-rib array, from the inside out, includes an extremely dense nucleation center, an intermediate transition region located outside the extremely dense nucleation center, and an outermost region located outside the intermediate transition region. The extremely dense nucleation center includes a matrix of peripheral region needles and ribs; the intermediate transition region includes multiple transition region needles and ribs located on the sides of the extremely dense nucleation center; the outermost region includes multiple peripheral region needles and ribs located outside the intermediate transition region. The outer diameter of the peripheral area needle rib is larger than the outer diameter of the transition area needle rib, and the outer diameter of the transition area needle rib is larger than the core area needle rib. The depth of the fractal flow channel is the same as the height of the needle rib array; the fractal flow channel includes multiple k-level fractal (k+1) level flow channels; where k is 2, 3, 4, 5, 6; as the level flow channels on the fractal flow channel move away from the needle rib array, the width of the level flow channels decreases.

[0008] Furthermore, the thickness of the substrate is greater than the height of the pin array.

[0009] Furthermore, the fractal flow channel adopts a first fractal flow channel or a second fractal flow channel similar to plant leaf veins; the first fractal flow channel is a third-level fractal fourth-level flow channel; the second fractal flow channel is a second-level fractal third-level flow channel; The main flow channel of the fractal flow channel is close to the heating center, and the terminal branches of each level extend to the four corner edges of the substrate.

[0010] Furthermore, the first fractal flow channel includes a third-level fractal first-level flow channel extending to the needle rib array, two third-level fractal second-level flow channels respectively connected to the ends of the third-level fractal first-level flow channel, two third-level fractal third-level flow channels respectively connected to the ends of the third-level fractal second-level flow channels, and a third-level fractal fourth-level flow channel respectively connected to the ends of the third-level fractal third-level flow channels.

[0011] Furthermore, the second fractal flow channel includes a secondary fractal primary flow channel extending to the needle rib array region, two secondary fractal secondary flow channels communicating with the secondary fractal primary flow channel, and secondary fractal tertiary flow channels communicating with the ends of the secondary fractal secondary flow channels respectively.

[0012] Furthermore, the main channels of adjacent fractal channels are not physically connected, and a stepped disconnection design is adopted.

[0013] Furthermore, in practical applications, the bifurcation angle of the fractal flow channel is designed and determined based on the physical dimensions of the substrate and the number of bifurcation stages of the flow channel. As the flow channel extends outward and the number of bifurcation stages increases, the bifurcation angle of each stage of the flow channel can be set to different values ​​to adapt to the coverage requirements of the target heat exchange area and the limitations of the substrate boundary space. To reduce the impact of changes in bifurcation angle on flow characteristics, the fractal flow channel is equipped with a rounded transition structure at all bifurcation nodes, so that adjacent flow channels are smoothly connected, reducing flow separation and local resistance loss of the working fluid at the bifurcation nodes, guiding the working fluid to flow continuously along the flow channel wall, improving the uniformity of the flow field, and maintaining a stable flow state of the working fluid during the splitting and merging processes.

[0014] Furthermore, the width of the fractal flow channel gradually decreases as it extends outward with each branching stage, and the scaling ratio of each stage follows Murray's Law, which minimizes fluid resistance. To minimize the increase in hydraulic resistance when cold liquid branches from the main channel to the sub-channel, the equivalent hydraulic diameter of the channel must satisfy the following relationship: Physical meaning of the parameters: : Indicates the characteristic width (or equivalent hydraulic diameter) of the parent channel (the channel above it). : represents the characteristic width (or equivalent hydraulic diameter) of the i-th sub-channel (next-level channel) branching off from the main channel; n: represents the number of branches.

[0015] Furthermore, the extremely dense nucleation center includes peripheral region needles and ribs arranged in an m×m matrix; the intermediate transition region includes 4×(m-1) transition region needles and ribs located on the sides of the extremely dense nucleation center; and the outermost region includes 4×(m-2) peripheral region needles and ribs located outside the intermediate transition region.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The present invention achieves low-resistance and high-efficiency liquid supply and gas discharge by utilizing leaf vein fractal flow channels on a macroscopic scale, and enhances nucleate boiling and regulates bubble behavior by utilizing variable diameter needle rib arrays on a microscopic scale, thereby achieving cross-scale synergistic optimization of heat transfer enhancement and flow organization, effectively improving critical heat flux density, heat transfer coefficient and temperature uniformity, and optimizing the problem of the separation between enhanced heat transfer and flow regulation in the prior art. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings. Figure 1 A schematic diagram of a heat sink structure based on a combination of a biomimetic tree-shaped flow channel and plum blossom-shaped variable diameter needle ribs; Figure 2 for Figure 1 A schematic diagram of the three-dimensional structure; Figure 3 This is a schematic diagram showing the dimensions of the first fractal flow channel and the needle rib array. Figure 4 This is a schematic diagram of a needle-rib array structure; Figure 5 This is a schematic diagram of the first fractal flow channel structure; Figure 6 This is a schematic diagram of the second fractal flow channel and the needle-rib array structure. Figure 7 A schematic diagram of the second fractal flow channel and the three-dimensional structure of the needle rib array; Figure 8 This is a schematic diagram of the second fractal flow channel structure; Figure 9 This is a schematic diagram showing the dimensions of the second fractal flow channel and the needle rib array.

[0018] Explanation of reference numerals in the attached drawings: 1. Substrate; 2. Pin array; 21. Core region pin; 22. Transition region pin; 23. Peripheral region pin; 3. First fractal flow channel; 31. Third-level fractal primary flow channel; 32. Third-level fractal secondary flow channel; 33. Third-level fractal tertiary flow channel; 34. Third-level fractal quaternary flow channel; 4. Second fractal flow channel; 41. Second-level fractal primary flow channel; 42. Second-level fractal secondary flow channel; 43. Second-level fractal tertiary flow channel. Detailed Implementation

[0019] This embodiment provides a heat sink based on a biomimetic tree-like flow channel and a plum blossom-shaped variable-diameter fin array. Specifically, it proposes a two-phase heat dissipation structure for chips based on partitioned reinforcement and structural gradient control, featuring an overall uniform height design, a substrate size of 30×30mm, and a board thickness of 3mm. This structure is mainly applied to immersion liquid cooling scenarios for high-power chips. By constructing a composite layout of peripheral hierarchical flow channels and a central variable-diameter fin array, it achieves coordinated optimization of the liquid supply path and the bubble discharge path.

[0020] The specific design of this invention is as follows: Boundary Constraints and Region Division: First, the overall substrate boundary of 30×30mm was established, along with a high heat flux density region directly opposite the core heat source (the overall span of this central array region is approximately 8×8mm, and the center span of the outermost needle rib is 7.66mm). To address the pain point of "bubbles and cold liquids converging in opposite directions in the same space, leading to drying out" in traditional designs, the model was divided into two functionally complementary regions on the horizontal plane: the outer "cold liquid guiding zone" and the central "bubble nucleation and exhaust zone".

[0021] Fractal channel generation based on the law of construction: In the peripheral region, to achieve pumping of coolant to the center with minimal pressure drop, fractal geometry of plant veins is introduced. Starting from the four corners of the substrate, the channel is drawn in a gradually expanding branching pattern towards the center. The overall channel depth remains at the same height as the central needle rib.

[0022] Needle rib array arrangement based on pressure gradient: In the central region, the traditional needle ribs with equal diameter and spacing are abandoned. A staggered quincunx array is adopted, and a cylindrical array with radial dimensional gradient is constructed by orthogonal coordinate translation, following the principle of "the central cylinder has a smaller diameter and gradually becomes thicker towards the outside". The ends of the outermost flow channels directly cut into the gaps of the outermost needle ribs.

[0023] This region is primarily responsible for rapidly and with low resistance recirculating the surrounding supercooled liquid working fluid back to the central region with high heat flux density.

[0024] Structural morphology and bifurcation node design: refer to Figure 2 and Figure 7 The system employs a bifurcation structure resembling the veins of a plant leaf, with a secondary fractal tertiary flow channel (or a tertiary fractal quaternary flow channel) and a channel depth of 1.0 mm. The main flow channel is close to the heat generation center, and the terminal branches of each stage extend to the four corners of the radiator. To avoid uneven flow distribution and short-circuiting, the main flow channel is not physically continuous but uses a stepped discontinuous design. The main flow channel terminates at the boundary of the pin-rib array 2, without penetrating or entering the area where the pin-rib array 2 is located. The working fluid flows along the main flow channel to the end and then directly enters the pin-rib array 2 through the channel outlet, continuing to flow within the gaps between the pins and ribs and completing the heat exchange process.

[0025] The overall angle of each bifurcation is controlled between 70° and 90°. At all bifurcation points in the flow channels, a smooth transition structure with large curvature rounded corners is introduced. When fluid changes direction in the pipeline, boundary layer separation easily occurs, generating swirling vortices. Large curvature rounded corners guide streamlines to smoothly change direction while adhering closely to the channel wall, effectively preventing dead zones in the node region, significantly reducing local resistance losses, and ensuring a stable laminar flow state when multiple coolant streams converge at the node.

[0026] Gradual Size Variation: The channel width gradually tapers outwards with each branching stage, and the scaling ratio at each stage follows Murray's Law, which minimizes fluid resistance. To minimize the increase in hydraulic resistance when cold liquid branches from the main channel to the sub-channel, the equivalent hydraulic diameter of the channel must satisfy the following relationship: Physical meaning of the parameters: : Indicates the characteristic width (or equivalent hydraulic diameter) of the parent channel (the channel above it). : Represents the characteristic width (or equivalent hydraulic diameter) of the i-th sub-channel (next-level channel) branching off from the main channel.

[0027] n: Represents the number of branches. In this embodiment, each node is a symmetrical two-branch structure, i.e., n=2.

[0028] Specific application of the formula in this invention: When n=2, and assuming the widths of the two symmetrical sub-channels are equal (i.e. The above formula can be simplified to: Therefore, the optimal scaling ratio (i.e., fractal dimension) for the widths of two adjacent flow channels can be derived as follows: Specific embodiment parameters: Based on the above theoretical derivation, and combined with the actual processing accuracy and the overall substrate size constraint of 30×30mm, in the specific embodiment of the two-stage fractal three-stage flow channel of the present invention, the flow channel width is set sequentially from the center outward as follows: main trunk 1.40mm, primary branch 1.11mm, secondary branch 0.88mm (reference). Figure 9 Similarly, in a specific embodiment of a three-stage fractal four-stage flow channel, the channel width is set sequentially from the center outwards as follows: main branch 1.40mm, first-stage branch 1.11mm, second-stage branch 0.88mm, and third-stage terminal branch 0.70mm (reference). Figure 3 ,).

[0029] Non-uniform length distribution and gradient compression mechanism: Unlike traditional equal-length distribution channels, the length of the branch channels in this structure changes non-linearly with a gradient: the closer to the central needle rib heating zone, the shorter the length of a single channel segment.

[0030] In an alternative embodiment of the two-stage fractal three-stage flow channel, the lengths of each flow channel from the center outward are 2.0 mm, 3.0 mm, and 7.0 mm, respectively.

[0031] In a specific embodiment of the three-level fractal four-level flow channel, the lengths of each flow channel from the center outward are 2.0mm, 2.5mm, 3.0mm, and 5.0mm, respectively.

[0032] This design, which compresses the length according to the heat flux density gradient, has a direct physical effect: the main flow channel faces the extremely high heat flux density region, and its shorter length can cross the rib boundary, which can maximize the release of the central space of the substrate for arranging the heat exchange area of ​​the solid ribs, while effectively preventing the steam generated by boiling from flowing back into the flow channel and blocking the coolant supply; while the end narrow flow channel located in the cold area at the edge of the substrate is greatly lengthened and laid out over a large area to collect the subcooled working fluid, and the frictional resistance generated by the narrow channel can effectively prevent the bubbles in the core area from expanding to the outside, ensuring the stability of the coolant replenishment.

[0033] Mechanism of action: External coolant is pumped precisely and rapidly to the hot zone at the center of the chip along the flow channel under the drive of capillary force, continuous dynamic pressure and pressure difference, maintaining a high-speed jet of fluid toward the center.

[0034] For the design of the central variable diameter densification needle rib area: refer to Figure 3 and Figure 4 This region directly faces the chip's heat-generating core and is primarily responsible for massive nucleation and perturbation enhancement. The maximum span of the array in both the horizontal and vertical directions (i.e., the distance between the centers of the top and bottom cylinders) is 7.66 mm, and the distance between the centers of the top and leftmost cylinders is 5.42 mm. The height of the needle ribs in this region is consistent with the height of the leaf vein channel in region A, both being 1.0 mm.

[0035] Structural features: a dense array of cylindrical needle ribs arranged in a staggered, quincunx pattern to effectively break the fluid flow boundary layer, increase turbulence intensity, and improve the convective heat transfer coefficient.

[0036] Variable diameter and positioning rules: The radius of the needle ribs shows a gradient distribution of "increasing from the center outwards", and the positioning between each level of cylinder is achieved through strict orthogonal translation.

[0037] The specific parameters are as follows: Central core area: As the center of extremely dense nucleation, it adopts a 3×3 matrix arrangement, with a total of 9 cylinders. The diameter of the needle rib is 0.5mm, and the distance between adjacent centers (center distance) is 1.0mm.

[0038] Intermediate transition zone: It radially transitions outwards, with the cylinder diameter increasing to 0.65mm. Its position is based on the cylinder at the corner of the central core area (e.g., the upper right corner), and is translated by 1.31mm and 0.5mm in the horizontal and vertical orthogonal directions, respectively, so that the center distance between the cylinder in this zone and the cylinder in the core area is precisely controlled at 1.4mm.

[0039] Outermost zone: As the exhaust outlet, the cylinder diameter is further increased to 0.72mm. Its position is based on the adjacent cylinder in the intermediate transition zone, and is again translated by 1.52mm and 0.5mm in the horizontal and vertical orthogonal directions, respectively, so that the center distance between the cylinder in this zone and the cylinder in the transition zone is increased to 1.6mm.

[0040] Multi-scale interface coupling: The three-stage end branch of the fractal channel with a depth of 1.0 mm in region A directly cuts into the gap of the outermost large-diameter needle rib, ensuring that the liquid phase enters and the gas-liquid exchange form a transition at the interface, forming a composite mechanism of "fractal channel + reinforced surface".

[0041] Overall dynamic operation process (vapor-liquid synergistic mechanism) Under high heat flux density operating conditions, this structure effectively suppresses bubble retention and drying phenomena through the following continuous physical mechanisms: 1. Nucleation foaming: The extremely fine and dense needle-like ribs in the center provide a massive amount of vaporization nuclei, inducing intense boiling to absorb latent heat.

[0042] 2. Active bubble pumping (Laplace pressure difference mechanism): Due to the gradual gradient change of the needle ribs from the center outwards (diameter increases from 0.5mm to 0.72mm, center distance increases from 1.0mm to 1.6mm), a surface tension-driven Laplace pressure difference is formed at the microscopic level. This physical process follows the Laplace pressure formula: Physical meaning of the parameters: The Laplace pressure difference between the gas pressure inside the bubble and the external liquid pressure.

[0043] : The vapor-liquid surface tension coefficient of a liquid cooling medium at a specific temperature.

[0044] , The two principal radii of curvature at the gas-liquid interface. In the confined space of a micropillar array with a height of 1.0 mm, the radius of curvature of the bubble is mainly limited by the net clearance of the local flow channels between adjacent needle ribs.

[0045] Mechanism Implementation: In the array of this invention, the needle ribs are most densely arranged in the central core area (net gap approximately 0.5 mm). When bubbles are generated here, they are compressed by the extremely narrow space, and their radius of curvature... , Extremely small, resulting in Laplace pressure inside the bubble. The pressure is extremely high; however, as the bubbles grow towards the transition zone and the outermost zone, the net gap gradually widens, the radius of curvature increases, and the pressure relatively decreases. This "Laplace pressure gradient radiating from high pressure to low pressure" induced by the structural gradient creates a pressure difference that actively pushes the bubbles from the extremely dense zone to the outer exhaust outlet, preventing the bubbles from lingering and accumulating into a gas film in the center.

[0046] Gas-liquid separation cycle: While the bubbles are squeezed out of the core area, the fractal flow channel of region A utilizes the low flow resistance characteristics that conform to Murray's law to continuously pump external cold liquid into the center, forming a stable cycle of liquid inlet at the periphery and air outlet at the center, thereby significantly improving the critical heat flux density and temperature uniformity.

[0047] Extended declaration and physical boundary constraints of fractal topological series The present invention uses the "two-level fractal three-level flow channel" and "three-level fractal four-level flow channel" listed above as preferred embodiments, but the present invention is not limited to the specific number of levels mentioned above. According to different chip substrate sizes and heat flux density requirements, this structure can naturally expand to higher-dimensional fractal levels (such as four-level fractal five-level flow channels, etc.) based on the aforementioned Murray's Law contraction formula and heat flux density gradient compression principle.

[0048] However, in practical engineering applications, the design of the number of flow channel stages has performance boundaries in terms of physics and fluid dynamics. For the 30×30mm substrate and 8×8mm central heating area in this embodiment, a three- or four-stage flow channel structure is preferred, mainly based on the following physical constraints: Available space and extreme frictional resistance: The effective straight-line distance from the edge of the central pin rib to the four corners of the substrate is approximately 15 mm. In the three-stage fractal four-stage flow channel, the width of the outermost branch has narrowed to 0.70 mm. If the number of branching stages is further increased, the width of the end microchannel will be sharply reduced to below 0.5 mm. This extremely fine channel not only approaches the tolerance limit of conventional micromilling processes, but also causes the frictional resistance along the flow path to increase exponentially, violating the "low resistance compensation" principle pursued by Murray's Law.

[0049] The flow collection and transport mechanisms converge: the main function of fractal channels in the peripheral region is to capture subcooled liquid and establish a centripetal guidance path. Three- or four-stage channels have already achieved sufficient coverage of the cold zone of the substrate within a limited space. Further increasing the number of bifurcation stages results in a repetitive momentum convergence mechanism in the flow field, failing to bring about a qualitative change in the two-phase boiling heat transfer performance. Instead, excessive bifurcation nodes can cause unnecessary local eddy current losses.

[0050] This invention achieves a synergistic technical effect by coupling the peripheral centripetal flow channel with the central plum blossom-shaped variable diameter needle rib.

[0051] In the outer region, the fractal channels strictly follow Murray's law to calculate the optimal contraction ratio in width, and rounded corners are introduced at the nodes for smooth transition to eliminate streamline separation. These two techniques enable the system to achieve coolant replenishment with low pressure drop along the flow path and locally. In terms of length distribution, equal length distribution is abandoned, and a length gradient design that gradually shortens near the needle ribs is adopted. The extremely short central coarse flow channel effectively prevents bubble backflow and preserves the solid heat transfer area of ​​the core heating zone, while the significantly elongated outer narrow flow channel enhances the coolant collection capacity and suppresses vapor overflow.

[0052] In the central region, the variable-diameter needle-rib array provides a high density of nucleation sites to enhance boiling, and its gradually expanding gap structure from the inside out generates a Laplace pressure difference, enabling the passive directional expulsion of bubbles.

[0053] Ultimately, this composite structure achieves a highly efficient combination of microscopic gas-liquid separation and macroscopic cold liquid transport, significantly delaying the arrival of the critical heat flux density (CHF), reducing the risk of localized drying, and improving the temperature uniformity of high-power chips under extreme thermal loads.

[0054] To quantitatively characterize the fluid transport and boiling heat transfer performance of this composite flow channel structure, theoretical calculations and analyses are conducted below from two aspects: system flow resistance, heat transfer coefficient (HTC), and critical heat flux density (CHF).

[0055] 1. Calculation of system flow resistance Assuming laminar flow within the microchannel, based on Poiseuille's law, the fluid resistance R of a single channel is directly proportional to its length L and inversely proportional to the fourth power of its equivalent diameter d. Because the flow channel adopts a symmetrical bifurcation that divides into two, the flow rate of the i-th branch is 1 / of the total flow rate. The overall equivalent flow resistance weight of the system can be evaluated using the following formula: Substitute the previously established geometric parameters into the dimensionless relative measurement: Second-order fractal tertiary flow channel: Given L = [2.0, 3.0, 7.0] mm, d = [1.40, 1.11, 0.88] mm, then the equivalent flow resistance is: Similarly, the flow resistance of the remaining fractals can be calculated as shown in the table below:

[0056] The calculations above show that, within the limited substrate size, the higher the fractal level, the narrower the width of the end flow channel. According to Poiseuille's law, a narrower channel leads to a sharp increase in the fluid's frictional resistance. If a fractal structure with four or more levels is used, the width of the end microchannels becomes increasingly smaller, generating extremely high flow resistance. This directly blocks the external coolant, preventing it from flowing back to the heat-generating center, ultimately resulting in reduced heat dissipation performance. At the current size, the flow resistance of three-level and four-level flow channels is within a reasonable range, making them suitable structural choices.

[0057] Calculation of heat transfer coefficient (HTC) and critical heat flux (CHF) The composite heat dissipation structure of this invention integrates macroscopic flow channels and microscopic arrays. Current empirical correlations for single-phase or pool boiling cannot directly calculate the heat transfer extrema of such composite structures. Therefore, this section employs the superposition method of enhancement factors to establish a theoretical benchmark for smooth substrates using classical boiling formulas, and then gradually deduce the HTC and CHF peak values ​​of this invention by combining structural characteristics.

[0058] On a smooth copper surface without any added microstructure, the pool boiling heat transfer extremum of an electronically fluorinated liquid (such as Novec 7100) is determined by the Cooper correlation: In the formula, h is the heat transfer coefficient. For comparison, M is the molar mass and q is the heat flux density. Based on this property formula, the CHF reference value of Novec 7100 on a smooth copper surface is only approximately... HTC's extreme value is approximately Exceeding this heat flux density, a film of air will form on the smooth surface, causing it to dry out.

[0059] The physical characteristics of the heat transfer surface change after the introduction of the central plum blossom-shaped variable-diameter needle ribs. The degree of heat transfer enhancement at this stage is determined by the Rohsenow correlation: The core variable in the formula is the surface-fluid specific constant. The extremely high-density needle-rib array in the central region of this invention significantly increases the wetting area and vaporization core density, leading to... Significantly reduced. Under the cubic relationship of the formula, this microneedle rib structure alone can increase the base CHF by approximately 3.5 times, raising the system CHF to approximately [value missing]. .

[0060] As heat flux density continues to increase, the pure needle-rib structure will trigger the fluid instability limit due to steam blockage. The fractal flow channel at the periphery of this invention overcomes this limit by utilizing the low-resistance characteristics following Murray's law and the capillary suction force of the terminal microchannels through centripetal converging flow. Different flow channel stages correspond to different fluid supply enhancement factors: Example of a two-stage fractal three-stage flow channel: The main trunk length is compressed to 2.0 mm, while the peripheral branches are lengthened to 7.0 mm. This structure provides approximately 1.6 times the macroscopic flow replenishment enhancement factor.

[0061] CHF Base value (20) Needle-rib reinforcement (3.5) Flow channel enhancement (1.6) 112 Assuming safe overheating of the wall For 40K, based on This suggests that HTC's peak power at this time was approximately 2.8. .

[0062] Similarly, the CHF and HTC of the other fractals at each level can be calculated as shown in the table below:

[0063] Quantitative calculations of combined flow resistance and heat transfer limits reveal that the number of fractal channel stages and heat dissipation efficiency are not simply positively correlated. Within the limited physical substrate size, increasing the number of branching stages inevitably leads to channel contraction at the ends. When the number of stages exceeds the structural critical point (e.g., in a four-stage fractal structure or higher), the frictional resistance along the path increases dramatically due to the excessively narrow channels. This physical resistance directly counteracts the capillary force generated by the channel, cutting off the return path of external coolant to the heat-generating core. The core region, due to continuous coolant deficiency, will prematurely dry out, causing a rapid decline in critical heat flux density and heat transfer coefficient. Therefore, the design of the heat dissipation structure is constrained by fluid dynamics boundaries. A three-stage fractal four-stage channel is the optimal solution for balancing fluid pumping and system pressure drop within the current dimensions; blindly increasing the number of fractal stages will actually impair overall heat transfer performance.

[0064] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A heat sink based on a combination of biomimetic tree-like flow channels and plum blossom-shaped variable-diameter fins, characterized in that: It includes a substrate (1), a pin rib array (2) disposed at the center of the substrate (1), and a plurality of fractal flow channels disposed around the pin rib array (2); The needle-rib array (2) includes, from the inside out, an extremely dense nucleation center, an intermediate transition region located outside the extremely dense nucleation center, and an outermost region located outside the intermediate transition region. The extremely dense nucleation center includes a matrix of peripheral region needles (23); the intermediate transition region includes multiple transition region needles (22) located on the sides of the extremely dense nucleation center; the outermost region includes multiple peripheral region needles (23) located outside the intermediate transition region. The outer diameter of the peripheral area needle rib (23) is larger than the outer diameter of the transition area needle rib (22), and the outer diameter of the transition area needle rib (22) is larger than the outer diameter of the core area needle rib (21). The depth of the fractal channel is the same as the height of the needle rib array (2); the fractal channel includes multiple k-level fractal (k+1) level channels; where k is 2, 3, 4, 5, 6; as the level channels on the fractal channel move away from the needle rib array (2), the width of the level channels decreases.

2. The heat sink based on the combination of biomimetic tree-like flow channel and plum blossom-shaped variable diameter ribs according to claim 1, characterized in that: The thickness of the substrate (1) is greater than the height of the pin array (2).

3. The heat sink based on the combination of biomimetic tree-like flow channel and plum blossom-shaped variable diameter ribs according to claim 1, characterized in that: The fractal flow channel adopts a first fractal flow channel (3) or a second fractal flow channel (4) similar to plant leaf veins; the first fractal flow channel (3) is a third-level fractal fourth-level flow channel; the second fractal flow channel (4) is a second-level fractal third-level flow channel; The main flow channel of the fractal flow channel is close to the heating center, and the terminal branches of each level extend to the four corner edges of the substrate.

4. The heat sink based on the combination of biomimetic tree-like flow channel and plum blossom-shaped variable diameter ribs according to claim 3, characterized in that: The first fractal flow channel (3) includes a three-level fractal primary flow channel (31) extending to the needle rib array (2), two three-level fractal secondary flow channels (32) respectively connected to the ends of the three-level fractal primary flow channel (31), two three-level fractal tertiary flow channels (33) respectively connected to the ends of the three-level fractal secondary flow channels (32), and a three-level fractal quaternary flow channel (34) respectively connected to the ends of the three-level fractal tertiary flow channels (33).

5. The heat sink based on the combination of biomimetic tree-like flow channel and plum blossom-shaped variable diameter ribs according to claim 3, characterized in that: The second fractal flow channel (4) includes a secondary fractal primary flow channel (41) extending to the region of the needle rib array (2), two secondary fractal secondary flow channels (42) connected to the secondary fractal primary flow channel (41), and secondary fractal tertiary flow channels (43) respectively connected to the ends of the secondary fractal secondary flow channels (42).

6. The heat sink based on the combination of biomimetic tree-like flow channel and plum blossom-shaped variable diameter ribs according to claim 3, characterized in that: The main flow channels of adjacent fractal flow channels are not physically connected, and a stepped disconnection design is adopted.

7. The heat sink based on the combination of biomimetic tree-like flow channel and plum blossom-shaped variable diameter ribs according to claim 3, characterized in that: At all bifurcation points of the flow channels, a rounded corner smooth transition structure is introduced.

8. The heat sink based on the combination of biomimetic tree-like flow channel and plum blossom-shaped variable diameter fins according to claim 1, characterized in that: The width of the fractal flow channel gradually decreases as it extends outward from the branching stage, and the scaling ratio of each stage follows Murray's law, which minimizes fluid resistance. To minimize the increase in hydraulic resistance when cold liquid branches from the main channel to the sub-channel, the equivalent hydraulic diameter of the channel must satisfy the following relationship: Physical meaning of the parameters: : Indicates the characteristic width (or equivalent hydraulic diameter) of the parent channel (the channel above it). : represents the characteristic width (or equivalent hydraulic diameter) of the i-th sub-channel (next-level channel) branching off from the main channel; n: represents the number of branches.

9. The heat sink based on the combination of biomimetic tree-like flow channel and plum blossom-shaped variable diameter fins according to claim 1, characterized in that: The extremely dense nucleation center includes peripheral region needles (23) arranged in an m×m matrix; the intermediate transition region includes 4×(m-1) transition region needles (22) located on the sides of the extremely dense nucleation center; the outermost region includes 4×(m-2) peripheral region needles (23) located outside the intermediate transition region.

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