A vapor chamber with a condensation directional reflux channel and a manufacturing method thereof

Abstract

This invention discloses a vapor chamber with a directional reflux channel for condensation and its preparation method. The vapor chamber includes an upper shell, a lower shell, and a liquid-absorbing core disposed within the cavity enclosed by the upper and lower shells. A gas-liquid coplanar flow space is formed within the cavity, and the liquid-absorbing core occupies a portion of this space, with areas on its sides reserved for vapor diffusion and condensate reflux. Several directional reflux channels for condensation, connected to the liquid-absorbing core, are arranged laterally on the inner surface of the upper shell. These directional reflux channels have a directional effect along the direction pointing towards the liquid-absorbing core, causing the condensate within them to move towards the liquid-absorbing core under a driving force acting in that direction. This invention constructs a directional flow path from the condensation end to the liquid-absorbing core region. Compared to relying solely on capillary reflux from the liquid-absorbing core and only focusing on local migration of surface droplets, this invention can better organize the directional reflux of condensate, improve the reflux efficiency, and thus improve the efficiency of internal gas-liquid circulation.

Description

Technical Field

[0001] This invention relates to a heat transfer component and its preparation method, and more particularly to a heat spreader with a condensation directional reflux channel and its preparation method. Background Technology

[0002] A vapor chamber is a type of thermal management device that achieves efficient heat transfer based on the phase change cycle of the working fluid. It is widely used in thermal management of high-power-density electronic devices. Its structure typically includes a sealed housing, a working chamber, a wick, and the working fluid. During operation, the working fluid absorbs heat and vaporizes at the evaporation end. The vapor diffuses to the condensation end, releases heat, and liquefies. The condensate then flows back through the capillary force of the wick, forming a continuous cycle. In recent years, electronic devices have become increasingly thinner and more integrated, leading to a continuous reduction in the thickness of vapor chambers. For ultra-thin vapor chambers, the thinner working chamber restricts vapor diffusion and increases flow resistance; the thickness and arrangement space of the wick are also reduced, decreasing the liquid reflux capacity.

[0003] Existing technologies primarily focus on improvements such as wick strengthening, patterned surface transport, and gas-liquid coplanar structure design. Wick strengthening enhances the wick's ability to absorb, conduct, or retain liquid by optimizing pore, groove, and composite capillary structures. It mainly addresses the transport of condensate within the wick after it enters, but cannot solve the problems of disordered spreading, random aggregation, or retention of condensate before it arrives. Another approach uses hydrophilic / hydrophobic patterns, wettability gradients, and wedge-shaped biomimetic patterns to achieve droplet spreading, aggregation, removal, or localized directional migration. This can even weaken or eliminate the traditional high-capillary-performance wick, allowing the patterned surface to directly handle the working fluid transport. While this approach can improve localized droplet migration and removal behavior on the wall, or replace the wick's main reflux function with a patterned surface, it may suffer from insufficient long-distance transport capacity, limited resistance to drying out, insufficient long-term reflux stability, and difficulty in balancing steam channel space allocation for ultrathin vapor chambers operating under high heat loads, complex orientations, and long-term circulation conditions. The gas-liquid coplanar structure allows the vapor flow region and the liquid return region to be arranged within the same thickness plane, expanding the lateral steam flow space and reducing steam flow resistance within a limited thickness, thus better meeting the development needs of ultra-thin vapor chambers. However, this structure usually requires sacrificing some space for the wick, so that the wick no longer continuously covers the condensation area over a large area. As a result, the condensate often needs to spread randomly on the wall surface, coalesce and grow until it can contact or be captured by the wick before it can rely on the capillary force of the wick to complete the return flow, resulting in untimely return flow and reduced efficiency. Retained liquid may also form large droplets, liquid bridges or local liquid plugs, covering the condensation surface, increasing local thermal resistance, and encroaching on the steam flow space and hindering steam diffusion, thereby reducing the efficiency of the evaporation-condensation cycle.

[0004] To alleviate condensate retention in gas-liquid coplanar structures, existing solutions typically employ drainage structures such as equal-width grooves, or use drainage channels as boundary superposition hydrophilic / hydrophobic designs. For example, equal-width drainage channels can be used as pattern boundaries to divide areas into wedge-shaped or strip-shaped alternating hydrophilic / hydrophobic regions, promoting droplet spreading and coalescence on the vapor channel wall, followed by adsorption by the side wicks. The core of these solutions remains providing a low-resistance spreading path or inducing local droplet migration using wettability differences, followed by droplet coalescence and adsorption by the wicks. Furthermore, equal-width grooves themselves struggle to generate a definite directional driving force, and the alternating hydrophilic / hydrophobic regions primarily represent patterned wettability boundaries, not necessarily providing continuous condensate movement along the wick direction. Therefore, such structures typically require shorter wicking distances and denser or multiple wick arrangements to ensure timely reflux; simultaneously, their reflux stability and multi-angle applicability are limited under varying placement angles, orientation changes, or fluctuations in condensate generation. Furthermore, hydrophilic and hydrophobic patterns rely on coatings, surface modifications, or selective etching to form a stable wettability contrast. However, under long-term phase change cycles, condensation erosion, encapsulation contamination, or high-temperature environments, issues such as wettability decay, pattern boundary degradation, or insufficient stability may arise.

[0005] Therefore, there is an urgent need to construct a directional reflux structure for condensate that does not rely on external energy input, so that the condensate can reflux quickly and stably, making it more suitable for increasingly thinner and lighter applications such as portable electronic devices, foldable devices, and highly integrated electronic devices. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a gas-liquid coplanar heat exchanger with a directional reflux channel for condensation. Under the premise that the ultra-thin heat exchanger does not rely on external energy input and the space for wicking is limited, a directional reflux channel for condensate is constructed between the condensing end and the wicking core, forming a composite reflux path of "directional transport at the condensing end - capillary relay reflux at the wicking core - liquid replenishment at the evaporating end". Furthermore, the coordinated distribution relationship between the wicking core space and the gas-liquid circulation space is optimized, thereby improving the internal gas-liquid circulation efficiency and the heat transfer performance of the heat exchanger.

[0007] Technical Solution: The vapor chamber with directional reflux channels for condensation described in this invention includes an upper shell, a lower shell, and a liquid-absorbing core disposed within the cavity enclosed by the upper and lower shells; a gas-liquid coplanar flow space is formed within the cavity; characterized in that the liquid-absorbing core occupies a portion of the working cavity in the horizontal direction, with its sides having areas for vapor diffusion and condensate reflux; several directional reflux channels for condensation are arranged laterally on the inner surface of the upper shell, communicating with the liquid-absorbing core, so that the condensate formed at the condensation end flows back to the liquid-absorbing core through the directional reflux channels, and continues to flow back to the evaporation end from the liquid-absorbing core; the direction pointing towards the liquid-absorbing core is defined as the positive direction, and the directional reflux channels for condensation are constructed with directional action features along the positive direction, so that the condensate located in the directional reflux channels for condensation is subjected to a driving force along the positive direction, and moves towards the liquid-absorbing core under the action of the driving force; the directional action features include one or a combination of two or more of the following: differences in interfacial energy / apparent wettability, differences in structural curvature, and differences in structural anisotropy.

[0008] The aforementioned directional features can be used individually or in combination, their combined effect being to transform the disordered migration of condensate before it reaches the wick into directional migration towards the wick. The interfacial energy / apparent wettability difference includes at least one of the following: surface chemical composition difference, surface modification difference, hydrophilic / hydrophobic pattern, wettability gradient, roughness gradient, and roughness pattern. This interfacial energy / apparent wettability difference is used to cause the condensate to move from a low surface energy region to a high surface energy region, and / or from a relatively hydrophobic region to a relatively hydrophilic region, and to directionally flow back to the wick along the positive direction. The structural curvature difference includes variations in the outline, characteristic dimensions, cross-sectional dimensions, channel boundaries, radius of curvature, etc., of the condensate directional return channel. At least one of the following: effective hydraulic radius variation; the structural curvature difference is used to make the condensate form liquid surfaces with different curvatures at different locations and be driven by a Laplace pressure difference pointing towards the wick; the structural anisotropy difference includes at least one of oriented microstructure, asymmetric microstructure, ratchet structure, groove structure, ridge structure, columnar structure, inclined structure, and re-entry structure; the structural anisotropy difference is used to make the contact line pinning, spreading resistance, adhesion resistance, and / or capillary spreading ability of the condensate different in different directions, thereby causing it to flow back to the wick in the positive direction.

[0009] The directional reflux channel for condensation is a directional reflux channel formed based on differences in structural curvature. This directional reflux channel has continuously or discontinuously varying external contours, characteristic dimensions, cross-sectional dimensions, equivalent hydraulic radii, and / or structural unit arrangements to generate a Laplace pressure difference driving force and / or capillary pressure gradient driving force acting in the positive direction. The directional reflux channel is not used for non-directional drainage in equal-width trenches. Instead, through changes in structural dimensions or asymmetrical arrangements of structural units in the positive direction, it allows the condensate to obtain a driving force pointing towards the wick outside the wick, thereby reducing dependence on hydrophilic or hydrophobic chemical coatings or surface modification layers. This reduces the risk of reflux failure due to long-term phase change cycling, condensation erosion, encapsulation contamination, or wettability decay and pattern boundary degradation under high-temperature environments.

[0010] The condensation directional reflux channel is selected from one or more of the following: wedge-shaped channel, triangular channel, conical channel, truncated conical channel, spindle-shaped channel, gourd-shaped channel, star-shaped channel, arrow-shaped channel, V-shaped channel, arc-shaped channel, fan-shaped channel, teardrop-shaped channel, fishbone-shaped channel, dendritic channel, asymmetric groove channel, asymmetric channel, eccentric annular channel, asymmetric annular channel, ratchet-shaped channel, oriented microgroove channel, oriented ridge-shaped channel, oriented column array channel, inclined column array channel, re-entry structure channel, continuous variable diameter channel, discontinuous variable diameter channel, periodic variable diameter channel, S-shaped variable diameter channel, channel formed by arranging multiple tapered units, channel formed by arranging multiple expanding units, channel formed by arranging multiple wedge-shaped units, channel formed by arranging multiple triangular units, channel formed by arranging multiple conical units, channel formed by arranging multiple spindle-shaped units, channel formed by arranging multiple ratchet-shaped units, channel formed by arranging multiple V-shaped units, channel formed by arranging multiple eccentric ring units, and channel formed by arranging multiple variable diameter units.

[0011] The key point of this invention is to match the directional reflux channel with the wick in terms of spatial position and reflux function. Thus, the condensate is pre-captured before entering the wick and guided into it along the shortest vertical path in the direction pointing towards the wick. The wick then completes capillary reflux within the wick and replenishes the evaporator end, thereby establishing a spatially coordinated relationship between the directional reflux path of the condensate, the capillary reflux path of the wick, and the working chamber of the overall heat exchanger.

[0012] The condensation directional reflux channel is a wedge-shaped channel. The width of the wedge-shaped channel gradually increases along the positive direction, and the end of the wedge-shaped channel near the wick is connected to or in contact with the wick. The wedge-shaped channel creates a difference in geometric constraint along the path by gradually increasing the channel width along the positive direction, so that the condensate droplets or liquid bridges located in the wedge-shaped channel have different liquid surface curvatures at different positions. The difference in liquid surface curvature creates a Laplace pressure difference inside the condensate droplets or liquid bridges, thereby generating a driving force acting along the positive direction to guide the condensate to the wick, and from the wick, it continues to flow back to the evaporation end.

[0013] The wedge angle α of the condensation directional reflux channel ranges from 2° to 15°; the interval between the wide ends of adjacent condensation directional reflux channels is 0 to 2 mm.

[0014] The liquid-absorbing core can be made of sintered powder, metal mesh, hydrophilic fabric, porous metal, multi-level grooved, or other reinforced capillary structure. The liquid-absorbing core can be one, two, or more arranged parallel to the length of the heat spreader, or arranged in a grid, radial, or partitioned pattern. Correspondingly, the wide ends of the condensation directional reflux channels are all configured to point towards and connect to, be adjacent to, or contact the corresponding liquid-absorbing core. When the number, width, or position of the liquid-absorbing cores changes, the length, wedge angle, spacing, arrangement density, and orientation of the condensation directional reflux channels are adjusted synchronously, so that the condensate is driven by the directional force of the liquid-absorbing cores before entering them and is guided into the liquid-absorbing cores. The above-mentioned types and layouts of liquid-absorbing cores can be matched with the aforementioned condensation directional reflux channels of different morphologies to adapt to heat spreaders of different sizes, heat source distributions, and steam channel layouts. Therefore, this invention does not replace the wick with a patterned surface, but instead uses a condensation directional reflux channel to carry out directional transport from the condensation end to the wick, and uses the wick to carry out subsequent long-distance capillary reflux and liquid replenishment at the evaporation end.

[0015] The liquid-absorbing core is arranged along the length of the shell. The condensation directional return channel is a groove formed in the inner surface of the upper shell, or it can be a protruding groove or other convex structure that protrudes from the inner surface of the upper shell and is arranged laterally. The condensation directional return channel can either penetrate the area of ​​the liquid-absorbing core that is in contact with the upper shell (i.e., the condensation channel remains continuous, with part of its area covered by the liquid-absorbing core and communicating with it), or it can be independently arranged on both sides of the liquid-absorbing core, preferably symmetrically arranged with the liquid-absorbing core as the axis of symmetry. In this case, the end of the condensation directional return channel near the liquid-absorbing core is at least in contact with the liquid-absorbing core so that the condensate in the channel is absorbed by the liquid-absorbing core. The condensation directional return channel is preferably arranged perpendicular to the direction of the liquid-absorbing core. In this case, the condensation directional return channel formed in the condensation end area on the inner surface of the upper shell is the shortest directional drainage path for the condensate. The positive driving force generated by the condensation directional return channel is directed towards the shortest vertical path of the liquid-absorbing core.

[0016] The ratio of the length L of the condensation directional reflux channel to the width Ww of the suction core, L / Ww, is 0.1 to 10:1. The length L is the projected length of the condensation directional reflux channel from the end furthest from the suction core to the end closest to the suction core along the positive direction. When there is one suction core cooperating with the condensation directional reflux channel, Ww is the width of that suction core in the direction perpendicular to its length. When there are two or more suction cores cooperating with the condensation directional reflux channel, Ww is the width of a single suction core, or the total projected width of multiple suction cores in the direction perpendicular to the length of the cavity. In a cross-section perpendicular to the length of the cavity, the ratio of the total projected width Wwt of the suction core to the effective width Wc inside the cavity, Wwt / Wc, is 0.02 to 0.90:1. Wwt is the sum of the widths of one, two, or more wicks on this cross section, and Wv is the effective width inside the cavity Wc after deducting the width occupied by the wicks and necessary support structures, which is the effective width used for steam flow and condensate return. By using the above ratio range, the capillary return capacity of the wicks and the lateral steam diffusion space can be coordinated under different numbers and layouts of wicks.

[0017] The ratio of the projected area A1 of the condensation directional reflux channel within the corresponding gas-liquid coplanar flow area to the projected area A2 of the gas-liquid coplanar flow area on its side is 0.02~0.90:1; the depth H of the condensation directional reflux channel is 1~500 μm, and / or the ratio H / T of the depth H of the condensation directional reflux channel to the effective height T of the cavity is 0.0005~0.33:1. These parameters are used to limit the extent to which the condensation directional reflux channel occupies the gas-liquid coplanar area in both the planar and thickness directions, ensuring that the directional reflux channel covers the necessary condensate capture area while avoiding excessive weakening of the steam flow space and the shell structure strength.

[0018] In the aforementioned spatial coordination relationship, parameters such as L / Ww, Wwt / Wc, Wv / Wwt, A1 / A2, H / T, and the included angle of the driving force direction are used to define the relative dimensions and spatial relationships between the condensation directional return channel, the wick, and the gas-liquid coplanar flow area. By defining these parameters, the proportional relationship between the space occupied by the wick, the vapor / liquid flow space, and the condensate directional return path can be adjusted under given cavity width and thickness conditions. This allows the condensation directional return channel to assume the directional guiding function outside the wick, rather than replacing the wick in bearing all the long-distance liquid return.

[0019] Specifically, the aforementioned structural parameters are not determined in isolation. If the length, area coverage, or depth of the condensate directional reflux channel is too short, the condensate far from the wick still needs to rely on random aggregation or disordered spreading on the wall to reach the wick, resulting in insufficient capture, spreading, and constraint of the condensate. Conversely, if the length, area coverage, or depth of the condensate directional reflux channel is too long, it may excessively occupy the inner surface of the condenser end and the coplanar flow space of the gas and liquid, weakening the shell structure strength or compressing the effective steam flow space. Similarly, while an excessively large total projected width of the wick is beneficial for increasing the capillary reflux cross-sectional area and anti-drying ability, it will compress the lateral steam diffusion space. An excessively small total projected width of the wick will reduce the condensate capture capacity and the evaporator end replenishment capacity. Therefore, this invention designs the "steam flow space—condensate directional reflux path—wick capillary reflux path" as a unified gas-liquid circulation system. Based on the optimization of each functional unit, the spatial proportion of each functional area can be further coordinated to match the low-resistance diffusion of steam, rapid condensate return and continuous liquid replenishment at the evaporation end, thereby obtaining an ultra-thin heat spreader with better overall heat transfer performance.

[0020] The condensation directional reflux channel exhibits superhydrophilicity, and its hydrophilicity is even stronger than that of the area outside the condensation directional reflux channel. This channel is preferably fabricated by laser etching. The shell is made of metal. The heat spreader is an ultra-thin heat spreader. The condensation directional reflux channel can be integrated in a planar pattern on the inner surface of the condenser end, without significantly increasing the thickness of the heat spreader or requiring additional complex three-dimensional flow guiding components. This makes it suitable for structural integration and large-scale processing within the limited space inside an ultra-thin heat spreader.

[0021] The above-mentioned method for preparing a heat spreader with a directional reflux channel for condensation includes the following steps:

[0022] (A) Preparation of the shell serving as the condenser end and evaporator end of the heat spreader;

[0023] (B) Several condensation directional reflux channels are processed on the inner surface of the condenser end using an etching process;

[0024] (C) Place the suction core in the preset area of ​​the working chamber, so that the condensation directional reflux channel made in step (B) is in contact with the suction core at least;

[0025] (D) Assemble the shells of the condenser end and the evaporator end to form a working chamber, inject working fluid into the working chamber and then seal it.

[0026] The laser etching process parameters are as follows: arc-shaped / loop-shaped / straight laser path, line spacing of 0.01~0.1mm, laser speed of 10~1000mm / s, laser power of 20~100%, laser frequency of 10~100Hz, and 1~10 processing cycles. For micron-level channels or micro / nano rough structures formed by a single laser etching operation, the above range can cover common metal surface etching depths and is easily adjustable according to laser power, scanning speed, and processing cycles.

[0027] Invention principle:

[0028] This invention explores that for ultrathin gas-liquid coplanar heat exchangers, heat transfer performance does not solely depend on the enhancement of a single structure, but rather on the matching relationship between vapor diffusion, condensate reflux, and evaporator-end replenishment within a finite thickness. The wick can provide capillary pressure and bear the main liquid reflux, but if the wick occupies too much space, it will compress the vapor flow cross-section and increase vapor pressure drop; conversely, if the vapor flow space is too large, it will reduce the wick's coverage and liquid trapping range, making it difficult for condensate to enter the wick in a timely manner. Therefore, the key problem that ultrathin gas-liquid coplanar heat exchangers need to solve is not simply improving the capillary transport capacity inside the wick, nor merely making condensate droplets spread, coalesce, or detach on a local wall surface, but rather, after the wick has made way for vapor flow, how to quickly, stably, and directionally guide the condensate generated in the condensation area outside the wick into the wick, and then have the wick continue to complete the evaporator-end replenishment.

[0029] To address the aforementioned key issues, this invention proposes a design that integrates directional condensate transport with capillary reflux of the wick. Within a limited thickness, the spatial distribution of the wick, vapor channel, and condensate reflux channel is re-optimized, thereby reducing the risk of condensate retention and liquid encroachment in the vapor channel, and improving the gas-liquid circulation efficiency and heat transfer performance of the ultra-thin gas-liquid coplanar heat exchanger.

[0030] Specifically, this invention arranges a directional reflux channel for condensation on the inner surface of the condensing end and connects it to the wick. For example, the end of the directional reflux channel is connected to or in contact with the wick to achieve communication, enabling it to perform the pre-transport function of "condensate capture—directional collection—introduction to the wick." The wick, in turn, performs the main reflux function of "capillary reflux within the wick—replenishment at the evaporation end." Thus, the reflux process of condensate from the condensing end to the evaporation end is divided into two interconnected segments: the first segment uses the directional reflux channel to organize the liquid in the condensation area outside the wick, preventing it from randomly spreading, coalescing, or stagnating in the steam flow area; the second segment uses the wick to continue providing stable capillary transport and wick supply to the evaporation end. This two-stage reflux path allows the wick, which cannot cover a large area of ​​the condensing end, to obtain reliable condensate replenishment while retaining the necessary steam flow space. Therefore, this invention connects the condensation directional reflux channel with the wick in terms of position and function. The former is responsible for the pre-capture and directional introduction of condensate outside the wick, while the latter is responsible for subsequent capillary reflux within the wick and replenishment at the evaporation end. This creates a synergistic distribution of steam flow, condensate reflux, and wick replenishment within the ultra-thin gas-liquid coplanar space. Compared to reflux methods that rely on random wall spreading, droplet coalescence, or passive capture by the wick, this invention can directionally organize and actively introduce condensate before it enters the wick. This allows the condensate to quickly converge near the wick along a shorter or near-straight path pointing towards it, thus compensating for the insufficient capture range caused by the wick yielding space for steam flow in the gas-liquid coplanar structure. It also reduces condensate detours, retention, random coalescence, and localized liquid film coverage in the condensation area outside the wick, improving condensate reflux speed, flow rate, and efficiency.

[0031] The reason why the directional effect of the condensation directional reflux channel of this invention, constructed in the forward direction, can balance the above contradictions lies in its transformation of the "disordered migration of liquid before reaching the wick" into "ordered directional migration towards the wick." Differences in interfacial energy / apparent wettability allow the condensate to migrate from relatively hydrophobic or low surface energy regions to relatively hydrophilic or high surface energy regions; differences in structural curvature allow droplets or liquid bridges to form different liquid surface curvatures at different locations, thereby generating a Laplace pressure difference or capillary pressure gradient towards the wick; differences in structural anisotropy can cause differences in pinning resistance, spreading resistance, or capillary spreading ability of the liquid in the forward and reverse directions. These effects can be used individually or in combination, with the common goal of providing the condensate with a clear forward driving force before entering the wick.

[0032] Based on the above principles, this invention can allocate a limited cavity space into a low-resistivity vapor diffusion region, a directional condensate return path, and a main wick return region without significantly increasing the thickness of the heat spreader. The length, width, wedge angle, structural dimensions, spacing, and arrangement density of the directional wick return channel can be matched according to the heat spreader size, wick width, number of wicks, vapor channel width, condensate generation, and heat source distribution, ensuring that the vapor channel is not obstructed by excessive wicks and that condensate is not stagnant due to insufficient wick coverage. In other words, the core of this invention lies in utilizing the pre-guided liquid flow advantage of the directional wick return channel to redistribute and optimize the coupling of the vapor phase channel, liquid phase return channel, and wick space within the ultra-thin gas-liquid coplanar heat spreader, thereby improving gas-liquid circulation efficiency and achieving a comprehensive improvement in heat transfer performance.

[0033] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0034] 1. This invention constructs a composite reflux path of "directional transport at the condenser end—capillary relay reflux from the wick—liquid replenishment at the evaporator end." After condensate forms, it can be quickly captured by the directional reflux channel and rapidly refluxed back to the wick along a predetermined vertical straight direction. The wick then completes the subsequent capillary reflux and evaporator end replenishment. Thus, this invention provides a pre-emptive supplement to the capillary reflux capability of the wick, further enhancing the wick's modification and compensating for the insufficient liquid capture range caused by the wick relinquishing space for vapor flow in the gas-liquid coplanar structure.

[0035] 2. This invention achieves a quantitative and coordinated allocation of the wick, steam flow space, and condensate return channel within an ultra-thin cavity. Leveraging the advantages of the directional condensation channel and combining it with a high-capillary-performance wick, further coordinated allocation can be achieved. Within a given ultra-thin cavity, the proportions of functional areas such as the directional condensation return channel, wick, and steam diffusion region can be optimized, ensuring a harmonious match between low-resistance steam diffusion, rapid condensate return, and continuous liquid replenishment at the evaporation end. This results in an ultra-thin heat spreader with superior overall heat transfer performance.

[0036] 3. This invention constructs the shortest, directional condensate return path from the condensation region to the wick, improving the condensate return velocity, flux, and efficiency. In a gas-liquid coplanar structure, if the condensate relies on random spreading on the wall, droplet coalescence, or passive adsorption by the wick, its return path is usually uncertain and may involve detours, stagnation, or local liquid film coverage.

[0037] 4. This invention does not limit itself to a specific channel morphology, but emphasizes the functional connection between the directional channel and the liquid-absorbing core. The focus of this invention is not on a specific channel morphology itself, but on the connection relationship between the channel with directional driving capability and the liquid-absorbing core, and the synergy formed by the two in the gas-liquid coplanar space. The condensation directional reflux channel can adopt various morphologies or composite patterns, thus having a high degree of freedom and adaptability in structural design.

[0038] 5. This invention enhances the heat transfer performance of the heat exchanger by leveraging the rapid liquid guiding advantage of the directional reflux channel. The directional reflux channel increases the condensate reflux rate and flow rate, thereby solving problems such as liquid retention, liquid film coverage, and increased local thermal resistance at the condenser end. It also reduces the risk of vapor channel blockage and allows the wick to receive more stable and timely liquid replenishment, thus enhancing the continuous liquid supply capacity at the evaporator end, reducing the risk of localized drying, improving hot spot temperature and overall temperature uniformity, and ultimately reducing equivalent thermal resistance and improving heat transfer performance.

[0039] 6. This invention retains the liquid-absorbing core and works in conjunction with the directional reflux channel, resulting in better adaptability to various operating conditions. This invention leverages both the rapid liquid-guiding function of the directional channel and the high capillary performance of the liquid-absorbing core, enabling continuous liquid supply over long distances and exhibiting strong resistance to drying out. Therefore, this invention is suitable for various operating conditions, including different heat loads, placement angles, and long-term circulation.

[0040] 7. This invention offers advantages such as better long-term stability, planar design, and integrability. The directional reflux channel for condensation can be driven directionally through physical structures such as differences in structural curvature and structural anisotropy, reducing reliance on easily decaying chemical modifications. Furthermore, this channel can be integrated into a planar pattern on the inner surface of the condenser end without significantly increasing the thickness of the heat spreader, making it suitable for structural fabrication within the limited space of an ultra-thin heat spreader. Attached Figure Description

[0041] Figure 1 This is an overall schematic diagram of the present invention;

[0042] Figure 2 This is a schematic diagram of the internal structure of the present invention, wherein (a) is a schematic diagram of the inner surface structure of the upper shell, and (b) is a schematic diagram of the inner surface structure of the lower shell;

[0043] Figure 3 This is a schematic diagram of the condensate directional reflux channel in Embodiment 1 of the present invention;

[0044] Figure 4 This invention provides a schematic diagram of the directional reflux channel for condensate in the heat spreader, its working principle, and... Figure 2 Detailed view of point A in the middle;

[0045] Figure 5Several basic directional transport structures verified for this invention are: wedge unit combination, eccentric ring unit combination, and S-shaped variable diameter unit combination;

[0046] Figure 6 This is a comparison diagram of the contact angles of the microstructure surfaces with and without condensation reflux in an embodiment of the present invention. a is the contact angle after laser etching and b is the contact angle before laser etching.

[0047] Figure 7 This is a schematic diagram showing the movement of droplets on different reflux channel surfaces in an embodiment of the present invention;

[0048] Figure 8 This is a schematic diagram of the heat spreader control group setup in an embodiment of the present invention;

[0049] Figure 9 This is a schematic diagram of the heat transfer performance test of the heat spreader in an embodiment of the present invention;

[0050] Figure 10 This is a comparison diagram of the temperature distribution of the heat exchange plates in the embodiments and control groups of the present invention;

[0051] Figure 11 This is a comparison of the equivalent thermal resistance of the heat exchange plates in the embodiments of the present invention and the control group. Detailed Implementation

[0052] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0053] Example 1

[0054] like Figure 1-4As shown, this embodiment provides a heat spreader with directional condensation return channels, including a shell and a liquid-absorbing core 2 placed inside the shell. The liquid-absorbing core 2 is arranged along the length of the shell and occupies a portion of the gas-liquid coplanar flow space inside the shell in the horizontal direction, with areas left on its sides for steam diffusion and condensate return. The shell is formed by an upper shell 1 serving as the condensation end and a lower shell 3 serving as the evaporation end, constituting a working chamber; gas-liquid coplanar flow areas for steam diffusion and condensate return are reserved on both sides of the liquid-absorbing core 2. Several directional condensation return channels 4 are arranged laterally on the inner surface of the condensation end of the upper shell 1, communicating with the liquid-absorbing core, so that the condensate formed at the condensation end flows back to the liquid-absorbing core through the directional condensation return channels, and then continues to flow back to the evaporation end from the liquid-absorbing core. The direction pointing towards the wick is defined as positive. The condensation directional reflux channel 4 is constructed with directional action features along the positive direction, so that the condensate located in the condensation directional reflux channel 4 is driven by a positive driving force and moves towards the wick 2 under the action of the driving force. The directional action features include one or a combination of two or more of the following: interfacial energy / apparent wettability difference, structural curvature difference, and structural anisotropy difference. The differences in interfacial energy / apparent wettability include at least one of the following: differences in surface chemical composition, differences in surface modification, hydrophilic / hydrophobic patterns, wettability gradients, roughness gradients, and roughness patterns. These differences are used to cause the condensate to move from low surface energy regions to high surface energy regions, and / or from relatively hydrophobic regions to relatively hydrophilic regions, and to flow back to the wick in the positive direction. The differences in structural curvature include at least one of the following: changes in the outline of the condensate directional return channel, changes in characteristic dimensions, changes in cross-sectional dimensions, changes in channel boundaries, changes in radius of curvature, and changes in equivalent hydraulic radius. These differences are used to cause the condensate to form liquid surfaces with different curvatures at different locations and to be driven by a Laplace pressure difference pointing towards the wick. The differences in structural anisotropy include at least one of the following: oriented microstructures, asymmetric microstructures, ratchet structures, groove structures, ridge structures, columnar structures, inclined structures, and re-entry structures. These differences are used to cause the condensate to have different contact line pinning, spreading resistance, adhesion resistance, and / or capillary spreading ability in different directions, thereby causing it to flow back to the wick in the positive direction.

[0055] like Figure 3 As shown, the condensation directional reflux channel 4 in this embodiment is a wedge-shaped channel etched into the inner surface of the upper housing, indicated by the black area in the figure. The width of the wedge-shaped channel gradually increases in the positive direction. The narrow end of the wedge-shaped channel is away from the wick 2, and the wide end is close to the wick 2. This wide end is connected to or in contact with the wick 2 to achieve communication, allowing the condensate to be directionally guided to the wick 2 along the wedge-shaped condensation directional reflux channel 4. Its working principle is as follows: Figure 4As shown, before the droplet enters the wedge-shaped channel, the surface of the wedge-shaped channel is more hydrophilic than the surrounding un-laser-etched area. The condensed droplet nucleating and growing near the wedge-shaped channel, once it has grown and spread to a certain extent, will be spontaneously captured and drawn into the more hydrophilic interior of the wedge-shaped channel. After the droplet enters the channel, different liquid surface curvatures are formed near the narrow and wide ends of the droplet. The narrow end has a larger liquid surface curvature and corresponding higher capillary pressure, while the wide end has a smaller liquid surface curvature and corresponding lower capillary pressure. This generates a Laplace pressure difference driving force pointing towards the wide end in the width variation direction. Since the wide end is connected or in contact with the wick 2 to achieve communication, the direction of this driving force is consistent with the positive direction pointing towards the wick 2, causing the condensate to be guided from the condensation area outside the wick along the wedge-shaped channel into the wick 2, where the wick 2 continues to replenish the evaporation end.

[0056] In this embodiment, a liquid-absorbing core 2 is centrally arranged along the length of the shell. The dimensions of the liquid-absorbing core 2 are 100mm × 5mm × 2mm, and the effective width inside the cavity is approximately 30mm. Therefore, in this embodiment, the width Ww of the liquid-absorbing core 2 is 5mm, and the ratio of the liquid-absorbing core 2 to the effective width Wc inside the cavity, Ww / Wc, is approximately 0.17:1. The total width Wv of the gas-liquid coplanar flow area on both sides of the liquid-absorbing core 2 that is not occupied by the liquid-absorbing core is approximately 25mm, and Wv / Ww is approximately 5:1. The condensation directional reflux channel in this embodiment is a number of equally spaced wedge-shaped channels opened on the inner surface of the upper shell. Each wedge-shaped channel is perpendicular to the liquid-absorbing core in the lateral direction. Two sets of condensation reflux channels are symmetrically arranged around this centrally located liquid-absorbing core, and their ends are interconnected. Furthermore, the end connection is covered by the liquid-absorbing core. The wedge angle α of the condensation directional reflux channel 4 is 4°, and the channel length is approximately 15 mm, meaning the ratio of the length L of the condensation directional reflux channel 4 to the width Ww of the absorbent core 2, L / Ww, is approximately 3:1; the spacing between the wide ends of adjacent condensation directional reflux channels 4 is 0.3 mm. The shell material is 316L stainless steel, and the absorbent core 2 is a hydrophilic fabric absorbent core, filled with deionized water. It should be noted that when the number, width, or layout of the absorbent cores 2 changes, the length, wedge angle, spacing, arrangement density, and wide end connection position of the condensation directional reflux channels 4 can be adjusted simultaneously to ensure that the end of the condensation directional reflux channel 4 extending along the positive driving force mates with the corresponding absorbent core 2.

[0057] The above-mentioned method for preparing a heat spreader includes the following steps:

[0058] (1) Preparation of the upper shell 1 and the lower shell 3. The upper shell 1 can serve as the condensation end, and the lower shell 3 can serve as the evaporation end; alternatively, the corresponding shell area can be selected as the condensation end and the evaporation end according to the size of the heat spreader, the number and distribution of the object to be cooled or the heat end, and the actual heat dissipation conditions. In this embodiment, the planar dimensions of the upper shell 1 and the lower shell 3 are both 100 mm × 30 mm, and the effective thickness of the working cavity formed after assembly is about 2 mm. To improve the structural stability after encapsulation, support columns can be symmetrically arranged along the length of the shell on both sides of the liquid absorption core 2 in the slotted area of ​​the lower shell 3 to prevent deformation of the shell after encapsulation.

[0059] (2) Several wedge-shaped condensation directional reflux channels 4 are processed by laser etching on both sides of the preset position of the liquid suction core 2 on the inner surface of the upper shell 1, which serves as the condensation end. Each condensation directional reflux channel 4 is symmetrically arranged with the centrally located liquid suction core 2 as the center. Its wide end is connected to or partially overlaps with the liquid suction core 2, and its narrow end faces away from the liquid suction core 2. In this embodiment, the wedge angle α is 4°, the channel length is about 3 times the width of the liquid suction core 2, and the interval between the wide ends of adjacent wedge-shaped condensation directional reflux channels 4 is 0.3 mm. The laser etching process parameters are: bow-shaped laser path, line spacing 0.05 mm, laser speed 100 mm / s, laser power 50%, and processing times 1. For the single-pass laser etching process in this embodiment, the condensation-oriented reflux channel 4 forms a micrometer-level effective etching depth and a micro / nano rough structure in the thickness direction. Based on an effective depth of 5-50 μm, the H / T ratio is approximately 0.0025-0.025:1 at an effective cavity height of about 2 mm. The specific depth can be determined based on the laser energy density, the number of scans, and the morphology test results. After laser etching, a micro / nano rough structure is formed on the surface of the wedge-shaped condensation-oriented reflux channel 4, such as... Figure 6 As shown, its water contact angle is 0° or close to 0°, exhibiting a superhydrophilic state, which is conducive to the capture, spreading and entry of condensate into the channel.

[0060] (3) Place the liquid-absorbing core 2 along the length of the upper shell 1 and the lower shell 3 in the working chamber, and connect the liquid-absorbing core 2 to the wide end of the wedge-shaped condensation directional reflux channel 4 obtained in step (2). In this embodiment, the liquid-absorbing core 2 is preferably a hydrophilic cloth strip with a size of 100 mm × 5 mm × 2 mm. In this embodiment, a single liquid-absorbing core 2 is used along the length direction; in other embodiments, two or more parallel liquid-absorbing cores can be set according to the size of the heat spreader, the distribution of the heat source and the layout of the steam channel, or a grid-like, radial, or partitioned liquid-absorbing core layout can be adopted, and the arrangement direction and terminal position of the condensation directional reflux channel 4 can be adjusted accordingly.

[0061] (4) Assemble the upper shell 1 and the lower shell 3 to form a working cavity, and inject deionized water working fluid into the working cavity before sealing. In this embodiment, a vapor chamber with a condensation directional reflux channel is prepared by non-vacuum sealing method, but vacuum sealing method can also be used.

[0062] Example 2

[0063] This embodiment is used to verify the long-distance liquid conduction capability of different combinations of directional transport units. Specifically, three basic patterns were selected and linearly combined to form three structures: a wedge-shaped unit combination, an eccentric ring unit combination, and an S-shaped variable diameter unit combination, which were used as experimental objects. The wedge-shaped unit combination creates a difference in liquid surface curvature through the channel width varying along the transport direction; the eccentric ring unit combination creates a continuous liquid migration direction through the geometric asymmetry of adjacent eccentric units; and the S-shaped variable diameter unit combination creates capillary pressure changes through variations in width along the path, local turns, and differences in liquid surface constraints. The above three structures are all specific structural forms that achieve directional transport through differences in structural curvature, asymmetrical arrangement of structural units, and / or local capillary pressure gradients, and can be used as different implementations of the condensation directional reflux channel 4.

[0064] To verify the long-distance fluid conduction capability of different directional transport structures, such as Figure 5 As shown, after the above patterns were set on the surface of the superhydrophobic modified aluminum plate, 10 μL of water droplets were dropped onto the starting end of each pattern, and the time required for the droplets to complete a directional transport distance of 5.8 cm was recorded. The results showed that the transport times for the wedge unit combination, the eccentric ring unit combination, and the S-shaped variable diameter unit combination were 5 s, 1 min 33 s, and 23 s, respectively. This result indicates that without external energy input, these structures can all generate long-distance directional transport, but the transport speeds differ.

[0065] Example 3: Verification of Droplet Directional Transport

[0066] To verify the movement trend of droplets within the condensation directional reflux channel 4 of this invention, a droplet movement comparison experiment was conducted to observe the final positions of the droplets on the surfaces of the wedge-shaped condensation directional reflux channel (WSSC) in this embodiment and the rectangular condensation reflux trench structure (RSSC) in the control group. The results are as follows: Figure 7As shown in the figure, the horizontal lines indicate the initial landing position of the droplets at the center of each channel along the Y-axis, and the irregular dashed lines delineate the final position of the droplets when they stop moving within the channel. The results show that when droplets land on the wedge-shaped condensation directional reflux channel (WSSC) of this embodiment, they all move towards end A; while when droplets land on the rectangular condensation reflux trench structure (RSSC) of the control group, the direction of movement is random. This result indicates that the wedge-shaped condensation directional reflux channel 4 can provide a more defined directional transport trend for the droplets, which is beneficial for the condensate to converge towards the suction core 2 along a predetermined direction, while the rectangular equal-width trench is difficult to provide a spontaneous driving force with a defined direction.

[0067] Example 4: Verification of heat transfer performance of heat exchanger

[0068] To verify the heat transfer performance of the vapor chamber of this invention, the following comparative experiments were conducted. For example... Figure 8 As shown, the experimental group is the wedge-shaped condensation directional reflux channel heat exchanger with a wedge angle α=4° prepared in this embodiment, denoted as 4°-WSSC. The control group includes: ① a heat exchanger with no condensation reflux microstructure treatment on the inner surface of the condensing end, denoted as Blank-H2O; ② a heat exchanger with a rectangular condensation reflux groove structure RSSC etched on the inner surface of the condensing end, denoted as 0°-RSSC. Figure 9 As shown, during the test, the heat exchange plates of the experimental and control groups were placed horizontally. A 20 mm × 20 mm polyimide heating film was attached to the center area of ​​the lower shell 3 (evaporation end), and a constant heating power was provided by a regulated power supply. A fan-cooled radiator was attached to the upper shell 1 (condensation end). K-type thermocouples were arranged at key positions on both the evaporation and condensation ends. In this embodiment, five thermocouple measuring points were arranged on each end, for a total of ten measuring points: the first group was arranged at the center of the upper and lower shells respectively; the second group was symmetrically arranged at a distance of 20 mm from the center of the upper and lower shells respectively; and the third group was symmetrically arranged at a distance of 40 mm from the center of the upper and lower shells respectively. Temperature data was collected in real time using a temperature recorder and recorded after the temperature stabilized. The equivalent thermal resistance can be calculated by dividing the temperature difference between the corresponding measuring points on the evaporation and condensation ends by the input heating power.

[0069] To examine the adaptability of this invention to different operating conditions, tests were conducted on the 4°-WSSC and the control group under different filling ratios and heating powers. Figure 10 and Figure 11 As shown, regardless of whether the liquid filling ratio is changed under a fixed heating power or the heating power is changed under a fixed liquid filling ratio, under the same experimental conditions, the vapor chamber with the 4°-WSSC structure consistently exhibits the lowest temperature at the center of the evaporation end, and the temperature curves at each measuring point along the length of the plate are more gradual. This indicates that this structure can reduce the hot spot temperature and improve the overall temperature distribution uniformity. Taking a heating power of 1.5 W and a liquid filling ratio of 20 vol% as an example, the thermal resistance of Blank-H2O is 9.8 K·W. -1The 0°-RSSC value is 9.0 K·W. -1 The 4°-WSSC is 6.8 K·W. -1 Compared to the previous two, the thermal resistance of the 4°-WSSC is reduced by 30.6% and 24.4% respectively, and the thermal resistance of the 4°-WSSC reaches its minimum under this condition. When the heating power remains constant at 1.5 W, and the liquid filling ratio is adjusted to 10 vol% or 30 vol%, the 4°-WSSC still maintains a low evaporator end temperature rise and thermal resistance even under conditions of insufficient or excessive liquid filling. For example, at a liquid filling ratio of 30 vol%, the evaporator end center temperature of Blank-H2O and 0°-RSSC rises to 73.6 ℃ and 66.7 ℃ respectively, while that of the 4°-WSSC is only 56.7 ℃, demonstrating the good operational adaptability of this structure under overfilling conditions. Further investigation at low power: keeping the liquid filling ratio constant at 20 vol%, and reducing the heating power to 0.5 W, the thermal resistance of the 4°-WSSC is 7.7 K·W. -1 Under the same operating conditions, the thermal resistance of Blank-H2O is 12.5 K·W. -1 The heat transfer efficiency decreased by 38.4%. In summary, the results show that the structure of this invention maintains superior heat transfer performance under adverse conditions of varying heating power and condensate generation, demonstrating excellent adaptability to different operating conditions.

Claims

1. A heat spreader with a condensation directional reflux channel, comprising an upper shell (1), a lower shell (3), and a liquid-absorbing core (2) disposed within a cavity enclosed by the upper shell (1) and the lower shell (3); wherein a gas-liquid coplanar flow space is formed within the cavity; characterized in that, The wick (2) occupies part of the working chamber in the horizontal direction, and its side has a region for vapor diffusion and condensate return. The inner surface of the upper shell (1) is provided with a number of condensation directional return channels (4) connected to the wick (2) in the horizontal direction, so that the condensate formed at the condensation end returns to the wick (2) through the condensation directional return channels (4), and continues to return to the evaporation end from the wick (2). The direction pointing to the wick (2) is defined as the positive direction. The condensation directional return channels (4) are constructed with directional action features along the positive direction, so that the condensate in the condensation directional return channels (4) is driven by the positive action and moves toward the wick (2) under the action of the driving force. The directional action features include one or a combination of two or more of the following: interfacial energy / apparent wettability difference, structural curvature difference, and structural anisotropy difference.

2. The heat spreader with a condensation directional reflux channel according to claim 1, characterized in that, The interfacial energy / apparent wettability difference includes at least one of the following: surface chemical composition difference, surface modification difference, hydrophilic / hydrophobic pattern, wettability gradient, roughness gradient, and roughness pattern, used to cause the condensate to move from a low surface energy region to a high surface energy region, and / or from a relatively hydrophobic region to a relatively hydrophilic region, and to flow back to the wick (2) in the positive direction; the structural curvature difference includes changes in the outline, characteristic dimensions, cross-sectional dimensions, channel boundary, and radius of curvature of the condensate directional return channel (4). At least one of the equivalent hydraulic radius changes is used to make the condensate form liquid surfaces with different curvatures at different locations and be driven by a Laplace pressure difference pointing towards the wick (2); the structural anisotropy difference includes at least one of oriented microstructure, asymmetric microstructure, ratchet structure, groove structure, ridge structure, column structure, inclined structure, and re-entry structure, used to make the contact line pinning, spreading resistance, adhesion resistance and / or capillary spreading ability of the condensate different in different directions, thereby flowing back to the wick (2) in the positive direction.

3. The heat spreader with a condensation directional reflux channel according to claim 1, characterized in that, The condensation directional reflux channel (4) is a directional reflux channel formed based on the difference in structural curvature. The condensation directional reflux channel (4) has a continuously or discontinuously varying external profile, characteristic dimensions, cross-sectional dimensions, equivalent hydraulic radius and / or structural unit arrangement to form a Laplace pressure difference driving force and / or capillary pressure gradient driving force acting in the positive direction.

4. The heat spreader with a condensation directional reflux channel according to claim 1, characterized in that, The condensation directional reflux channel (4) is selected from one or more of the following: wedge channel, triangular channel, conical channel, truncated conical channel, spindle-shaped channel, gourd-shaped channel, star-shaped channel, arrow-shaped channel, V-shaped channel, arc-shaped channel, fan-shaped channel, teardrop-shaped channel, fishbone-shaped channel, dendritic channel, asymmetric groove channel, asymmetric channel, eccentric annular channel, asymmetric annular channel, ratchet-shaped channel, oriented microgroove channel, oriented ridge-shaped channel, oriented column array channel, inclined column array channel, re-entry structure channel, continuous variable diameter channel, discontinuous variable diameter channel, periodic variable diameter channel, S-shaped variable diameter channel, channel formed by arranging multiple tapered units, channel formed by arranging multiple expanding units, channel formed by arranging multiple wedge units, channel formed by arranging multiple triangular units, channel formed by arranging multiple conical units, channel formed by arranging multiple spindle-shaped units, channel formed by arranging multiple ratchet-shaped units, channel formed by arranging multiple V-shaped units, channel formed by arranging multiple eccentric ring units, and channel formed by arranging multiple variable diameter units.

5. The heat spreader with a condensation directional reflux channel according to claim 1, characterized in that, The condensation directional reflux channel (4) is a wedge-shaped channel. The width of the wedge-shaped channel gradually increases along the positive direction, and the end of the wedge-shaped channel close to the wick (2) is connected to or in contact with the wick (2). The wedge-shaped channel forms a difference in geometric constraint along the path by gradually increasing the channel width along the positive direction, so that the condensate droplets or liquid bridges located in the wedge-shaped channel have different liquid surface curvatures at different positions. The difference in liquid surface curvature causes a Laplace pressure difference to be formed inside the condensate droplets or liquid bridges, thereby generating a driving force acting along the positive direction to guide the condensate to the wick (2).

6. The heat spreader with a condensation directional reflux channel according to claim 5, characterized in that, The wedge angle α of the condensation directional reflux channel (4) ranges from 2° to 15°; the interval between the wide ends of adjacent condensation directional reflux channels (4) is 0~2 mm.

7. The heat spreader with a condensation directional reflux channel according to claim 1, characterized in that, The liquid-absorbing core (2) is arranged along the length direction of the heat spreader plate, and a plurality of the condensation directional return channels (4) are perpendicular to the liquid-absorbing core (2) and spaced apart along the length direction of the liquid-absorbing core (2); the ratio of the length L of the condensation directional return channel (4) to the width Ww of the liquid-absorbing core (2) is 0.1 to 10:1; the length L is the projected length of the condensation directional return channel (4) from the end away from the liquid-absorbing core (2) to the end close to the liquid-absorbing core (2) in the positive direction; when there is one liquid-absorbing core (2) that cooperates with the condensation directional return channel (4), Ww is the width of the liquid-absorbing core (2) in the direction perpendicular to its length; when there are two or more liquid-absorbing cores (2) that cooperate with the condensation directional return channel (4), Ww is the width of a single liquid-absorbing core (2), or the total projected width of multiple liquid-absorbing cores (2) in the direction perpendicular to the length of the cavity; On a cross section perpendicular to the length of the cavity, the ratio of the total projected width Wwt of the suction core (2) to the effective width Wc inside the cavity, Wwt / Wc, is 0.02~0.90:1; where Wwt is the sum of the widths of one, two or more suction cores (2) on this cross section, and Wv is the effective width inside the cavity after deducting the width occupied by the suction core (2) and the necessary support structure, which is used for steam flow and condensate return.

8. The heat spreader with a condensation directional reflux channel according to claim 1, characterized in that, The ratio of the projected area A1 of the condensation directional reflux channel (4) in the corresponding gas-liquid coplanar flow area to the projected area A2 of the gas-liquid coplanar flow area on the same side is 0.02~0.90:1; the depth H of the condensation directional reflux channel (4) is 1~500 μm, and / or the ratio H / T of the depth H of the condensation directional reflux channel (4) to the effective height T of the cavity is 0.0005~0.33:1; the positive driving force generated by the condensation directional reflux channel (4) is the shortest vertical path direction pointing to the liquid suction core (2); wherein, the condensation directional reflux channel (4) is used for condensate reflux, and the area in the gas-liquid coplanar flow area not occupied by the condensation directional reflux channel (4) is used to retain steam flow space.

9. The heat spreader with a condensation directional reflux channel according to claim 1, characterized in that, The liquid-absorbing core (2) is one of the following: sintered powder liquid-absorbing core, metal wire mesh liquid-absorbing core, hydrophilic cloth liquid-absorbing core, porous metal liquid-absorbing core, multi-level groove liquid-absorbing core, or other reinforced capillary structure liquid-absorbing core; the liquid-absorbing core (2) is arranged in parallel along the length of the heat spreader, or in a grid, radial, or partitioned manner; the end of the condensation directional reflux channel (4) near the liquid-absorbing core (2) is connected to the corresponding liquid-absorbing core (2); the condensation directional reflux channel (4) exhibits superhydrophilic properties.

10. A method for preparing a heat spreader with a condensation directional reflux channel as described in any one of claims 1 to 9, characterized in that, Includes the following steps: (A) Preparation of the shell serving as the condenser end and evaporator end of the heat spreader; (B) Several condensation directional reflux channels are processed on the inner surface of the condenser end using an etching process; (C) Place the suction core in the preset area of ​​the working chamber, so that the condensation directional reflux channel made in step (B) is in contact with the suction core at least; (D) Assemble the shells of the condenser end and the evaporator end to form a working chamber, inject working fluid into the working chamber and then seal it.

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