Heat transfer structure

Abstract

This heat transfer structure is disposed along a principal surface of a heating element and includes: a facing surface that faces the principal surface; a side part that extends from the facing surface in a normal direction of the principal surface; and an end surface opposite the facing surface. The heat transfer structure has a porous body immersed in a liquid medium, and changes the phase of the liquid medium that has passed through the inside of the porous body into a gas phase. The porous body extends from the end surface along a normal line and includes: a core part through which the liquid medium passes from the end surface side to the facing surface side; and a vaporization part which covers the core part and comes into contact with the liquid medium, thereby changing the liquid medium that has passed through the core part into a gas phase.

Description

Heat Transfer Structure

[0001] The present invention relates to a heat transfer structure including a wick made of a porous structure.

[0002] Heat transfer structures are widely used in cooling devices for electronic devices, heat pipes, boilers, cooling parts for laser devices, cooling parts for nuclear fusion targets in neutron therapy, etc. Here, a heat transfer structure has been proposed in which a wick made of a porous structure is used to provide three-dimensional vapor and liquid paths for the purpose of promoting heat transfer under high heat flux conditions.

[0003] For example, Patent Document 1 discloses a heat transfer structure having multiple convex portions (wicks) made of a porous material on a plate-shaped portion in thermal contact with a heating element. The convex portions are made of a porous material so that the average porosity is higher in the outer portion than in the inner portion. A liquid-phase working fluid flows from the outer portion of the convex portions to the inner portion. Heat transferred from the heating element to the convex portions causes the working fluid to change phase from liquid to gas, generating a gas-phase working fluid that flows toward the outside. The gas-phase working fluid generated in the convex portions is temporarily retained in the porous material constituting the outer portion, causing bubbles to grow and flow upward, reducing the likelihood of collision with the liquid-phase working fluid flowing toward the inner portion. As a result, the working fluid reflux is less likely to be impeded by collisions between the gas-phase working fluid and the liquid-phase working fluid, thereby improving the heat transport performance of the heat transfer member.

[0004] Japanese Patent Application Laid-Open No. 2021-188890

[0005] When implementing heat transfer structures in various types of actual equipment and systems, they must be made smaller without compromising heat transfer performance. For example, when cooling electronic devices, they must be housed within a single server unit, approximately 20 mm in height. Similarly, they must also be used in limited spaces, such as automotive inverters and autonomous driving ECUs, which require consideration of separating gas-liquid paths in smaller spaces and expanding the solid-gas-liquid three-phase boundary where evaporation occurs.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a heat transfer structure including a wick made of a porous structure that can be made smaller without compromising heat transfer performance.

[0007] The heat transfer structure according to the present invention is a heat transfer structure that is arranged along the main surface of a heating element and includes an opposing surface opposing the main surface, a side portion extending from the opposing surface in the normal direction to the main surface, and an end surface that is the opposite side to the opposing surface, and has a porous body immersed in a liquid medium, and causes the liquid medium that passes through the inside of the porous body to change into a gas phase, the porous body extending along the normal from the end surface and including a core portion through which the liquid medium passes in the direction from the end surface side to the opposing surface side, and a vaporization portion that covers the core portion and comes into contact with the liquid medium and changes the liquid medium that has passed through the core portion into a gas phase, and is characterized in that the heat transfer structure operates in response to the heating element so that the outer surface of the porous body becomes higher than the phase change temperature of the liquid medium to a gas phase, and the core portion becomes lower than the phase change temperature.

[0008] According to this feature, a flow of the liquid medium can be formed in the heat transfer structure made of a porous body, and the liquid medium can be changed into a gas phase without impairing the heat transfer performance, thereby making it possible to make the main body more compact.

[0009] In the above-described invention, the vaporizing section may have a lower porosity than the core section, which allows the heat transfer structure made of a porous body to change the liquid medium into a gas phase without impairing the heat transfer performance, thereby enabling further miniaturization.

[0010] In the above-described invention, the core portion may have voids larger than those of the vaporizer portion. With this feature, the heat transfer structure made of a porous body can change the liquid medium into a gas phase without impairing the heat transfer performance, and can be made smaller.

[0011] In the above-described invention, the vaporizing portion may be made of a material having a higher thermal conductivity than the core portion. With this feature, the liquid medium can be changed into a gas phase without impairing the heat transfer performance of the heat transfer structure made of a porous body, and the heat transfer structure can be made smaller.

[0012] In the above-described invention, the porous body may have a base including the opposing surface and a plurality of columnar or plate-shaped protrusions with a rectangular cross section extending from the base in the normal direction, the vaporizer covers the side surfaces of the protrusions, and the core is filled inside the protrusions covered by the vaporizer. According to this feature, the liquid medium can be efficiently guided to the vaporizer, and the heat transfer structure made of the porous body can be made smaller without impairing the heat transfer performance.

[0013] In the above-described invention, the porous body may have a plurality of holes extending in a normal direction from the opposing surface, the vaporizer covers the inner surfaces of the holes and the side of the porous body, and the core is filled inside the porous body covered by the vaporizer. According to this feature, the liquid medium can be efficiently guided to the vaporizer, and the heat transfer structure made of the porous body can be made smaller without impairing the heat transfer performance.

[0014] In the above invention, the porous body may be a sintered body, which allows for further miniaturization without reducing manufacturability.

[0015] FIG. 1 is (a) a cross-sectional view of a heat transfer structure as a comparative example, and (b) a diagram showing the flow of a liquid medium and heat. FIG. 2 is (a) a cross-sectional view of a heat transfer structure according to an embodiment, and (b) a diagram showing the flow of a liquid medium and heat. FIG. 3 is a cross-sectional view showing several examples of the structure of a protrusion of a heat transfer structure according to an embodiment. FIG. 4 is (a) a perspective view and (b) a cross-sectional view showing an example of a heat transfer structure according to an embodiment. FIG. 5 is (a) a perspective view and (b) a cross-sectional view showing another example of a heat transfer structure according to an embodiment. FIG. 6 is a perspective view showing yet another example of a heat transfer structure according to an embodiment. FIG. 7 is a photograph showing a heat transfer structure used in an actual measurement test. Here, (a) is an overall photograph, (b) is an enlarged photograph of the joint between a core portion (SUS) and an outer portion (Cu), and (c) is an enlarged photograph of the core portion. FIG. 8 is a diagram of an apparatus used in the actual measurement test. FIG. 9 is a graph showing the wall superheat ΔT in the actual measurement test. ｓａｔ [K] versus heat flux q [kW / m ２]. Fig. 10 is a graph showing the heat flux q [kW / m ２ ] to the heat transfer coefficient h [kW / m ２ .W].

[0016] Hereinafter, a heat transfer structure according to one mode for carrying out the invention (hereinafter also referred to as one embodiment or embodiment) will be described with reference to the drawings. The configuration of the following embodiment is an example, and the present heat transfer structure is not limited to the configuration of the embodiment. Furthermore, unless otherwise specified, the dimensions, materials, shapes, relative positions, and the like of the components disclosed in this embodiment are not intended to limit the technical scope of the invention to only those.

[0017] Before describing the heat transfer structure and the heat transfer method according to the embodiment, a heat transfer structure and a heat transfer method according to a comparative example will be described first.

[0018] As shown in FIG. 1 , the heat transfer structure 50 includes a base 52 made of a porous material with a communicating pore structure, the bottom surface of which is disposed along the main surface 51a of the heating element 51. The base 52 also includes a protruding portion 53 made of a porous material of the same shape and material protruding from the bottom surface (main surface 51a) in a normal direction. The protruding portion 53 is a so-called wick. It is heated by thermal conduction from the heating element 51 and is immersed in a liquid medium. It exchanges heat with the surrounding liquid medium, causing the liquid medium to change phase from liquid to gas (vapor). In other words, it boils the liquid medium. Examples of liquid media include pure water, alcohol, and fluorocarbon-based refrigerants. In particular, the protruding portion 53 is made of a porous material, which allows the liquid medium to be contained in its pores, promoting heat exchange, and allowing the vapor generated by boiling to be discharged from the pores to the outside. The liquid medium is supplied from the tip of the protruding portion 53 while moving downward through the interior. Meanwhile, the vapor generated within the protruding portion 53 moves outward through the pores and is discharged further outside the protruding portion 53. In other words, an upward flow of steam is generated around the protruding portion 53 .

[0019] The liquid medium supplied to the tip of the protrusion 53 is heated by heat exchange with the porous body as it moves downward. Then, when it reaches the phase change temperature at which it changes into gas, it changes into vapor. In other words, a temperature gradient of the liquid medium is generated in the vertical direction, and the position at which the temperature at which the liquid medium moving downward through the protrusion 53 changes into gas becomes the solid-gas-liquid three-phase boundary (see FIG. 1( b ) in particular). Therefore, in a heat transfer method using such a heat transfer structure, the solid-gas-liquid three-phase boundary inside the protrusion 53 is formed in a cross-sectional portion that crosses the protrusion 53 approximately horizontally at a predetermined height.

[0020] Next, an example of a heat transfer structure and a heat transfer method according to an embodiment will be described.

[0021] As shown in FIG. 2 , the heat transfer structure 10 is made of a porous material having an overall interconnected void structure. The base 12 is made of a porous material that includes interconnected voids in a network-like, capillary-like configuration. The base 12 has a bottom surface that is arranged along the main surface 11a of the heating element 11. The base 12 also includes a protruding portion 13 made of a similar porous material that protrudes from the bottom surface (main surface 11a) in a normal direction. That is, the protruding portion 13 is provided on the base 12 in a continuous manner. The protruding portion 13 has an axis and may be, for example, approximately cylindrical. The protruding portion 13 includes a core portion 13b and a vaporizing portion 13a located on the outer surface side of the core portion 13b. The core portion 13b is located inside the vaporizing portion 13a and extends from the tip of the protruding portion 13 along its axis, i.e., in the normal direction of the bottom surface (main surface 11a), to the vicinity of the heating element 11. The core portion 13b is exposed from the vaporizing portion 13a at the tip of the protruding portion 13. The protrusions 13 are, for example, so-called wicks, which are heated by heat conduction from the heating element 11 and exchange heat with the surrounding liquid medium to boil the liquid medium. In the heat transfer structure 10 of FIG. 2 , the bottom surface of the base 12 can also be referred to as the "opposing surface facing the main surface of the heating element," the protrusions 13 can also be referred to as the "side portion extending from the opposing surface in the normal direction to the main surface," and the tip of the protrusions 13 can also be referred to as the "end surface opposite the opposing surface." The immersed liquid medium passes through the core portion 13b of the protrusions 13 from the end surface side toward the opposing surface side. The vaporizing portion 13a covers the core portion 13b, comes into contact with the liquid medium, and converts the liquid medium that passes through the core portion 13b into a gas phase.

[0022] At this time, the temperature of the outer surface of the vaporizing portion 13a is set higher than the phase change temperature at which the liquid medium changes to the gas phase, and the temperature of the core portion 13b is set lower than the phase change temperature.

[0023] By operating with such a temperature distribution, for example, the liquid medium is heated while flowing from the tip of the protrusion 13 through the core 13b toward the main surface 11a of the heating element 11 below. The liquid medium heated in the core 13b is then guided to the vaporizer 13a on the outer surface side, where it is further heated and vaporized near the outer surface (evaporation surface). The generated vapor is then discharged further outside the protrusion 13 through the voids in the porous body and moves upward due to buoyancy. In other words, an upward flow of vapor is generated outside the protrusion 13. The liquid medium that has flowed through the core 13b to the lowest level is vaporized near the high-temperature heating element 11.

[0024] The liquid medium passing through the core portion 13b is heated to a temperature lower than the phase change temperature and therefore maintains its liquid phase. Meanwhile, when the liquid medium is guided to the vaporizing portion 13a, it is further heated to a temperature higher than the phase change temperature and vaporizes. In other words, a temperature gradient of the liquid medium is generated from the inside to the outside of the protruding portion 13, forming a vertically extending solid-gas-liquid three-phase boundary in the vaporizing portion 13a, where the liquid medium can reach the phase change temperature. This results in a cross-sectionally U-shaped solid-gas-liquid three-phase boundary, including the vicinity of the heating element 11. In other words, compared to the comparative heat transfer structure 50 shown in FIG. 1 , the heat transfer structure 10 allows for a three-dimensional expansion of the solid-gas-liquid three-phase boundary. This allows for the separation of gas-liquid paths in a smaller space and the expansion of the solid-gas-liquid three-phase boundary during evaporation, resulting in high heat transfer performance. This also allows for a smaller heat transfer structure without sacrificing heat transfer performance.

[0025] By maintaining this temperature distribution, the liquid medium flows downward through the core portion 13b, as described above, and forms a flow that is discharged laterally from the vaporizing portion 13a. Therefore, the ascending vapor flow does not interfere with the flow of liquid medium descending through the core portion 13b. In other words, the liquid medium is maintained within the protruding portion 13 while controlling the location of vapor generation to prevent stagnation of the liquid medium flow. This ensures a stable supply of liquid medium to the protruding portion 13, preventing dryout of the liquid phase and burnout due to a sudden increase in temperature on the heat transfer surface of the protruding portion 13, even when heat is conducted from the heating element 11 to the protruding portion 13 at a high heat flux. If a high heat flux occurs near the heating element 11, the actual liquid supply will be insufficient compared to the required amount. In this case, a transition to film boiling occurs, in which the surface vicinity is covered with a generated vapor film, causing the temperature near the surface to rise. However, the porous material promotes heat conduction, maintaining heat flow to a position slightly away from the surface. This reduces the temperature at a distance from the surface, and also increases the heat exchange area with the fluid, reducing the effective heat flux. In other words, boiling heat transfer is maintained, reducing the risk of a sudden and unsteady temperature rise in the heating element 11 and the associated burnout.

[0026] In this way, the heat transfer structure 10 obtains the above-described solid-gas-liquid three-phase boundary by obtaining a temperature distribution in which the temperature of the outer surface, which is the evaporation surface of the vaporizing section 13 a, is made higher than the phase change temperature and the temperature of the core section 13 b is made lower than the phase change temperature. Such a temperature distribution can be adjusted, for example, by the thermal conductivity and porosity of the porous bodies of the vaporizing section 13 a and the core section 13 b.

[0027] For example, it is also preferable that the porous body constituting the core portion 13b have coarse pores larger than the fine pores of the porous body constituting the vaporizer portion 13a. The liquid medium fills the relatively large space of the coarse pores of the core portion 13b as a liquid phase with a higher specific heat than vapor, and lowers the temperature of the core portion 13b through heat exchange. On the other hand, in the vaporizer portion 13a having fine pores, the liquid medium is quickly heated and boiled by heat exchange over the relatively large surface area of ​​the fine pores, thereby maintaining a high temperature in the vaporizer portion 13a. The porous body of the core portion 13b is preferably designed to obtain the maximum flow rate. For example, when the liquid medium is water, the pore size of the coarse pores is preferably approximately 10 to 100 μm. In this case, the pore size of the fine pores of the porous body of the vaporizer portion 13a is preferably approximately 1 to 30 μm, for example, taking into account the balance with the coarse pores to obtain the temperature distribution described above.

[0028] It is also preferable that the thermal conductivity of the porous material constituting the vaporizing portion 13a be greater than that of the porous material constituting the core portion 13b, which makes it easier to maintain the temperature of the vaporizing portion 13a higher than the phase change temperature and the temperature of the core portion 13b lower than the phase change temperature in the protruding portion 13 heated by the heat from the heating element 11.

[0029] As shown in Figure 3, the temperature distribution described above can also be controlled by the shape of the protrusion 13. In Figure 3(a), protrusion 13-1 with a constant diameter is provided substantially perpendicular to the main surface 11a of the heating element 11. In contrast, in Figure 3(b), protrusion 13-2 is provided with a taper that increases in diameter toward the top. Furthermore, in Figure 3(d), protrusion 13-4 is provided with a taper that decreases in diameter toward the top. By adjusting the taper in this way, it is possible to control the balance between the amount of liquid medium supplied to the protrusion and the evaporation rate, which is the amount of vapor discharged from the protrusion. In other words, the temperature distribution described above can be stably maintained.

[0030] As shown in Figures 1(c) and 1(d), it is preferable to provide a porous body as a flange-shaped base 12 that extends from the lower part of the protrusion on the surface of the heating element 11. In other words, it is also preferable for the wick to include a porous body as the base 12 that covers at least a part of the main surface 11a of the heating element. By providing a base 12 made of a porous body in an area where there are no protrusions, heat exchange can be promoted.

[0031] The shape of the heat transfer structure as described above can be appropriately changed to suit the space in which it is used, and further taking into consideration the balance between the supply amount and evaporation amount of the liquid medium, and can be, for example, as follows.

[0032] For example, as shown in FIG. 4 , the heat transfer structure 10a has a plurality of cylindrical protrusions 13. The vaporizing portions 13a of the protrusions 13 are arranged on the outer periphery of the cylinder and contact the liquid medium with their outwardly convex curved surfaces. This structure makes it easy to increase the evaporation rate relative to the supply rate of the liquid medium, depending on the number of protrusions 13 and the dimensions of each portion. In FIG. 4 , the protrusions 13 are an example of "a base including opposing surfaces and a plurality of columnar or plate-like protrusions with rectangular cross sections extending in the normal direction from the base." Furthermore, the vaporizing portions 13a of the protrusions 13 are an example of "covering the side surfaces of the protrusions," and the core portions 13b are an example of being filled inside the protrusions 13 covered by the vaporizing portions 13a.

[0033] On the other hand, as shown in FIG. 5 , the heat transfer structure 10b has a shape in which a disk-shaped porous body is provided with multiple cylindrical holes 13c extending in the normal direction to the main surface of the heating element 11. The protrusion 13 is the entire disk-shaped body, and the upward flow of steam is achieved through the holes 13c. The core portion 13b is connected throughout the entire disk-shaped body, making it easy to increase the area of ​​its upper end. On the other hand, the vaporization portion 13a is disposed on the inner circumferential side of the holes 13c and on the outer circumferential surface of the disk-shaped body. Depending on the number of holes 13c and the dimensions of each portion, this structure makes it easy to increase the supply rate of liquid medium relative to the evaporation rate. In FIG. 5 , the multiple holes 13c can also be referred to as "multiple holes extending in the normal direction from the opposing surface," and the vaporization portion 13a can also be referred to as "covering the inner surface of the holes and the side of the porous body." It can also be said that the core portion 13b is filled inside the porous body covered by the vaporization portion 13a.

[0034] 6(a), a heat transfer structure 10c may be provided with protruding portions 13 that are rectangular parallelepiped as a whole. The heat transfer structure 10c has a shape obtained by changing the circular shape of the heat transfer structure 10b in top view to a square shape. Also, as shown in FIG. 6(b), a heat transfer structure 10d may be provided in which a plurality of protruding portions 13 made of rectangular plate-like bodies are arranged substantially parallel to each other. In this case, the protruding portions 13 have a structure in which both side surfaces of a rectangular plate-like core portion 13b are sandwiched between vaporizing portions 13a.

[0035] In any of these, the cross-sectional shape is the same as that of the heat transfer structure 10 described above, and a three-dimensionally expanded solid-gas-liquid three-phase boundary line can be obtained, resulting in high heat transfer performance. Furthermore, it is possible to further miniaturize the heat transfer structure without impairing the heat transfer performance.

[0036] [Actual Measurement Test] Next, the results of a boiling test performed on a heat transfer structure will be described.

[0037] As shown in FIG. 7 , the heat transfer structure 10e used here is provided on a heat transfer plate 15 made of a copper disk. That is, the heat transfer plate 15 is provided so as to cover the bottom surface of the heat transfer structure 10e from below, and the heat transfer structure 10e is composed of a protrusion 13 provided on the heat transfer plate 15. Similar to the heat transfer structures 10b and 10c described above, the protrusion 13 has a plurality of cylindrical holes 13c extending in the normal direction to the bottom surface. That is, the vaporizing portions 13a are cylindrical portions defining the holes 13c, and their inner circumferential surfaces serve as evaporation surfaces. Core portions 13b are arranged to fill the spaces between the plurality of vaporizing portions 13a. The vaporizing portions 13a are made of a porous material obtained by sintering copper (Cu) powder, which has a relatively high thermal conductivity. The core portions 13b are made of a porous material obtained by sintering stainless steel (SUS; "SUS" is a registered trademark) powder, which has a relatively low thermal conductivity. After sintering the vaporizing portion 13a, the gaps except for the holes 13c were filled with stainless steel powder and sintered to form the core portion 13b, thereby obtaining the heat transfer structure 10e.

[0038] Here, the porosity of the copper sintered body used for the vaporizer 13a and the stainless steel sintered body used for the core portion 13b was calculated from the relationship between the dimensions and weight, and was approximately 10% for the copper sintered body and 20-30% for the stainless steel sintered body. The porosity of the core portion 13b was more than twice that of the vaporizer 13a. Therefore, it can be said that the core portion 13b has larger coarse voids than the vaporizer 13a. Due to the relatively low porosity and relatively high thermal conductivity of the material, the vaporizer 13a is thought to have a higher effective thermal conductivity than the core portion 13b.

[0039] In addition to the heat transfer structure 10e in which the periphery of the hole 13c is a double structure (bi-porous) formed by the vaporizing portion 13a and the core portion 13b, a comparative example in which the periphery of the hole is a single structure (mono-porous) was also produced. That is, the heat transfer structure of the comparative example has the periphery of the hole entirely made of a sintered body of stainless steel, and the other shapes are the same as those of the heat transfer structure 10e.

[0040] As shown in FIG. 8 , the test apparatus 20 includes a heating block 22 made of a copper block with an embedded cartridge heater (sheathed heater) 21, and a heat conduction block 23 attached to the heating block 22 to transfer heat. The top surface of the heat conduction block 23 serves as a heating surface having an area of ​​15 mm × 15 mm, and is in contact with the rear surface of the heat transfer plate 15 covering the bottom surface of the heat transfer structure 10e via a 20-60 μm thick silver paste. This allows heat from the heating block 22 to be transferred to the bottom surface of the heat transfer structure 10e. The heat transfer structure 10e is immersed in a test fluid 25 stored in a liquid tank 24 having a horizontal cross section of 120 mm square. The test fluids 25 used were hydrofluoroether (AE-300, manufactured by AGC Inc.) as test fluid A and methyl perfluoropropyl ether (NOVEC 7000 (NOVEC is a registered trademark), manufactured by 3M Japan Ltd.) as test fluid B. Additionally, thermocouples were appropriately placed to measure the temperature of each part, and the heat flux q and heat transfer coefficient h, which will be described later, were determined.

[0041] Heat flux q is defined by the following formula. Here, TC1 and TC2 are the temperatures at two points (two surfaces) in the material where heat flux q is measured, t is the distance between the two points (two surfaces), and k is the thermal conductivity: q = (TC2 - TC1) k / t; Also, the heat transfer coefficient h is defined by the following formula. Here, Tsat is the temperature of the heating element, Tw is the surface temperature of the material that is in contact with the heating element and receives heat from the heating element, and q is the heat flux: h = q / (Tw - Tsat);

[0042] As shown in FIG. 9, the wall superheat ΔT ｓａｔ In the boiling curve based on the relationship between the heat flux q (the difference between the temperature of the test fluid and the wall surface temperature), the critical heat flux (CHF) in the example (bi-porous) using the heat transfer structure 10e was improved by 25 to 44% compared to the comparative example (mono-porous).

[0043] As shown in FIG. 10, in terms of the relationship between the heat flux q and the heat transfer coefficient h, it can be seen that the heat transfer coefficient is higher in the example (bi-porous) using the heat transfer structure 10e than in the comparative example (mono-porous).

[0044] As described above, for both test fluid A and test fluid B, the heat transfer coefficient and critical heat flux in the high heat flux range could be improved by the heat transfer structure of the example (bi-porous).

[0045] Although the embodiments of the present invention and modifications based thereon have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims.

[0046] (Others) Embodiments of the present invention include the following aspects (hereinafter referred to as appendices). (Appendix 1) A heat transfer structure in which a liquid medium passing through a porous body using a wick including protrusions, the protrusions being located on a main surface of a heating element and having an axis protruding in a normal direction to the main surface, causes a phase change to a gas phase at the outer surface, the wick including a core made of a porous body extending from a tip of the protrusion along the axis toward the heating element, the heat transfer structure being characterized in that the heating element operates such that the outer surface of the protrusion is higher than the phase change temperature of the liquid medium to a gas phase and the core is lower than the phase change temperature. (Appendix 2) The heat transfer structure according to Appendix 1, in which the wick includes a base made of a porous body covering at least a portion of the main surface of the heating element, and the protrusions are provided on the base. (Appendix 3) The heat transfer structure according to Appendix 1, in which the porous body in the core has coarse pores larger than the fine pores of the porous body on the outer surface side of the protrusions. (Appendix 4) The heat transfer structure according to Appendix 1, wherein the porous body on the outer surface side of the protrusion has a higher thermal conductivity than the porous body in the core portion. (Appendix 5) The heat transfer structure according to any one of Appendices 1 to 4, wherein the liquid medium flows inside the core portion from the tip portion toward the main surface of the heating element. (Appendix 6) A heat transfer method using a heat transfer structure including a wick made of a porous body and including protrusions located on the main surface of the heating element and having an axis protruding in a normal direction to the main surface, causing a liquid medium to pass through the inside of the porous body and change phase to a gas phase at the outer surface, wherein the wick includes a core portion made of a porous body extending from the tip portion of the protrusion along the axis toward the heating element, and wherein the heating element operates such that the outer surface of the protrusion is higher than the phase change temperature of the liquid medium to a gas phase and the core portion is lower than the phase change temperature. (Supplementary Note 7) The heat transfer method according to Supplementary Note 6, wherein the liquid medium flows inside the core portion from the tip portion toward the main surface of the heating element.

[0047] REFERENCE SIGNS LIST 10 Heat transfer structure 11 Heat generating element 12 Base 13 Protrusion 13a Vaporizing portion 13b Core 15 Heat transfer plate

Claims

1. A heat transfer structure that is arranged along the main surface of a heating element and has a porous body immersed in a liquid medium, the porous body including an opposing surface facing the main surface, a side portion extending in the normal direction of the main surface from the opposing surface, and an end surface that is the opposite surface to the opposing surface, and that causes the liquid medium passing through the inside of the porous body to undergo a phase change to a gas phase. The porous body extends along the normal from the end surface, and includes a core portion through which the liquid medium passes in the direction from the end surface side to the opposing surface side, and a vaporization portion that covers the core portion, contacts the liquid medium, and changes the liquid medium that has passed through the core portion to a gas phase. The heat transfer structure is characterized by the above structure.

2. The heat transfer structure according to claim 1, wherein the outer surface of the porous body is higher than the phase change temperature of the liquid medium to a gas phase by the heating element, and the core portion operates to be lower than the phase change temperature.

3. The heat transfer structure according to claim 1, wherein the vaporization portion has a lower porosity than the core portion.

4. The heat transfer structure according to claim 1, wherein the core portion has voids larger than the voids of the vaporization portion.

5. The heat transfer structure according to claim 1, wherein the vaporization portion has a higher thermal conductivity than the core portion.

6. The porous body has a base portion including the opposing surface and a plurality of columnar or plate-like protrusions extending in the normal direction from the base portion, the vaporization portion covers the side surfaces of the protrusions, and the core portion is filled inside the protrusions covered by the vaporization portion. The heat transfer structure according to claim 1.

7. The porous body has a plurality of holes extending in the normal direction from the opposing surface side. The vaporization portion covers the inner surfaces of the holes and the side portions of the porous body, and the core portion is filled inside the porous body covered by the vaporization portion. The heat transfer structure according to claim 1.

8. The heat transfer structure according to claim 1, wherein the porous body is a sintered body.

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