Thermal management medium filled with open porous material

Abstract

Disclosed is a thermal management medium having functions of heat exchange, transfer, absorption and storage and impact mitigation, the thermal management medium being characterized by comprising: an open porous material, the pore surface of which has been hydrophilically treated; a film housing attached to the outside of the open porous material and sealing the open porous material in a vacuum state; and a working fluid filled in pores of the open-type porous material, the open-type porous material having a structure that fills an inner space divided by a thin film housing and functioning as both a liquid and gaseous working fluid moving medium. The heat management medium not only can play a role of an ultra-lightweight structural material capable of bearing internal vacuum pressure and external load, but also can realize various heat management functions related to rapid heat exchange, transfer, absorption and storage and heat shock mitigation, and the various functions can be autonomously controlled, and as a result, the heat management medium can be used for heat exchange, heat transfer, heat absorption and heat shock mitigation. The heat management medium has the advantages of being beneficial to miniaturization and light weight of products or enabling appearance design of the products to be free.

Description

TECHNICAL FIELD

[0001] The present application relates to a heat management medium, which various heat management functions of exchange, transfer, absorption, and even storage and thermal shock mitigation are achieved by phase change and flow of working fluid contained in a vacuum chamber. In particular, the heat management medium is a structure in which an open porous material, which is hydrophilic-treated, is sealed in a vacuum state by a thin film type shell, and is a lightweight medium in a state in which the working fluid is injected to an internal space of the vacuum state by 10 to 80%. BACKGROUND

[0002] As an example of a heat transfer medium that does not depend on simple conduction heat transfer and forced or natural convection, there is a heat pipe. The heat pipe is designed for efficient heat transfer, and is not only used for various industrial heat exchangers, but is also widely used for connecting electronic devices such as computers, which are particularly near a heat source, narrow spaces, and cooling devices that are difficult to attach cooling devices to the outside. Figure 1 A heat pipe in the most widely used form at present is shown. For the heat pipe in Figure 1 The heat pipe in the above-described

[0003] The operation of the heat pipe shown in the above-described Figure 1 will be described as follows: When the evaporator is in contact with a high-temperature heat source, the liquid working fluid stored in the wick is vaporized. The gaseous working fluid is pushed to the opposite condenser along the central empty space channel of the passage portion as the pressure rises and moves. Since the temperature of the condenser is relatively lower than that of the evaporator, the gaseous working fluid is condensed and reconverted into a liquid. The liquid working fluid is recovered to the original evaporator along the wick provided on the wall surface of the passage portion by capillary phenomenon. The thermodynamic cycle of moving between the two ends of the heat pipe is completed in the process of repeating the vaporization and condensation of the working fluid, so that the heat transfer is much faster than simple conduction. Therefore, the temperature difference in the length direction of the heat pipe becomes small. The heat pipe that operates on such a principle is called a capillary-driven heat pipe because the liquid working fluid returns to the origin along the wick by capillary phenomenon, or a vacuum chamber type heat pipe because the phase change of vaporization / condensation is easily achieved at a lower temperature due to the decrease in internal pressure.

[0004] In this type of capillary-driven heat pipe, the liquid working fluid is stored using a wick as a medium or moves via capillary action. Traditionally, such as Figure 2 As shown, such wicks are mainly provided in three types: sintered powder metal, metal fabric (textile or mesh), and grooves machined on the wall surface. However, for most conventional capillary-driven heat pipes, the heat pipe is designed with the wick simply as a storage and transport medium for the liquid working fluid. Specifically, although conventional heat pipe wicks have pores small enough to generate good capillary action, the porosity, which accounts for about 10% to 50% of the internal empty space, is also limited. Furthermore, they are manufactured such that when the working fluid is completely liquefied, its volume is about 20% of the total internal space of the heat pipe. This results in a very small amount of working fluid being introduced into the interior, which limits the improvement of the transferable heat capacity, a key performance indicator of heat pipes.

[0005] On the other hand, in situations where a large amount of heat is generated in a confined area, such as a computer's CPU or GPU, although it is possible to... Figure 3 The method shown uses multiple ordinary rod-shaped heat pipes to transfer heat to a large-capacity forced convection heat exchanger, but this method suffers from problems such as complex design and large footprint. Therefore, a different approach can be adopted. Figure 4 The flat-plate vapor chamber replaces Figure 3 Multiple rod-shaped heat pipes are used. In the following text, unless otherwise stated in this specification, the vapor chamber refers to such a... Figure 4 The diagram shows a "flat plate type." Vapor chambers are widely used to sequentially transfer heat from a heat source to a wider area, and then to a large-capacity forced convection heat exchanger. Such a vapor chamber can be considered as extending the one-dimensional heat transfer of a heat pipe to two dimensions. That is, the vapor chamber functions to transfer heat from a single point to a wide surrounding area. Figure 4 (a) is a schematic diagram of the working principle of the vapor chamber. Figure 4 (b) shows an example of a vapor chamber attached to a heat sink with the same bottom surface area.

[0006] A typical vapor chamber is composed of a flat plate-shaped envelope, like a common heat pipe, with a wick arranged on the inner face of the envelope, and in order to prevent the flat plate-shaped envelope from collapsing, a structure in which a support element such as a pillar, a rib, or the like is additionally formed inside it. In addition, like a heat pipe, the wick of a vapor chamber also widely uses sintered metal (see references [1] X. Ji, J. Xu, A. M. Abanda, "Foam-copper-based vapor chamber for high heat flux dissipation", Exp. Therm. Fluid Sci., 2012, vol. 40, pp. 93-102; [3] M. Wang, W. Cui, Y. Hou, "Thermal spreading resistance of a grooved vapor chamber heat spreader", Appl. Therm. Eng., 2019, vol. 153, pp. 361-368).

[0007] Recently, there has been an increasing demand for a flat plate-shaped heat pipe, even a vapor chamber, much thinner than ever before, in order to achieve cooling of mobile devices. In this context, Ji et al. proposed a vapor chamber with a structure in which a simple flat plate is placed on top of a pin-fin formed by regularly arranging a cone on a flat plate using a powder composed of copper particles with a diameter of about 1 micrometer (pm) (see Fig. 1 of reference [2] Ji, X. B.; Xu, J. L.; Li, H. C; Huang, G. H. Nucleation and convective switching heat transfer mechanism realization by matching wettability of evaporator and condenser of heat pipe: effect of nanostructured surface. Nanoscale Energy 2017, vol. 38, pp. 313-325). Figure 5 Figure 5 In addition, Yang et al. proposed a structure in which a simple flat plate is placed on top of a pin-fin regularly arranged in a pattern (array) on a silicon wafer in which parallel grooves have been dug out using MEMS technology (see Fig. 1 of reference [3] Yang, K. S.; Lin, C. C; Shyu, J. C; Tseng, C. Y.; Wang, C. C. Performance and two-phase flow pattern of micro-flat-plate heat pipes. Int. J. Heat Mass Transfer 2014, vol. 77, pp. 1115-1123).

[0008] As described above, the vapor chamber has a structure in which a simple flat plate is placed on top of a pin-fin regularly arranged in a pattern (array) on a silicon wafer in which parallel grooves have been dug out using MEMS technology (see Fig. 1 of reference [3] Yang, K. S.; Lin, C. C; Shyu, J. C; Tseng, C. Y.; Wang, C. C. Performance and two-phase flow pattern of micro-flat-plate heat pipes. Int. J. Heat Mass Transfer 2014, vol. 77, pp. 1115-1123). Figure 5 ​As a similar example of an extremely thin flat plate type heat pipe or even a vapor chamber, Lewis et al. proposed a structure with a total thickness of 0.5 mm, in which a copper fabric is arranged on a flat thin plate, and a unique thin plate in which copper pillars are arranged in a regular pattern is formed using MEMS technology and an electroplating process (Reference [4] Lewis, R.; Xu, S. S.; Liew, L. A.; Coolidge, C; Yang, R. G.; Lee, Y. C. Thin flexible vapor chamber: fabrication and characterization of size properties. J. Microelectromech. Syst. 2015, 24, 2040-2048); Tang et al. proposed a structure with an estimated wick thickness of 0.24 mm and a total thickness of 0.5 mm, in which a copper fabric woven into a tubular shape is pressed and placed in the central portion of a copper tube that is also pressed, so that the copper fabric simultaneously functions as a wick and a support for a flat plate, and the space on both sides of the copper fabric functions as a vapor movement channel (Reference [5] Tang, Y.; Tang, H.; Li, J.; Zhang, S. W.; Zhuang, B. S.; Sun, Y. L. Experimental study on capillary force of novel sintered copper mesh wick for ultra-thin heat pipe. Appl. Therm. Eng. 2017, 115, 1020-1030). In 2021, Luo et al. proposed a flat plate heat pipe: this structure forms a dendritic structure layer with a thickness of 100 pm on one surface of two copper thin plates by electroplating, arranges the two thin plates in a face-to-face manner, and arranges a support plate with a plurality of parallel strip-shaped openings therebetween, in which the dendritic structure plating layer functions as a wick, and the strip-shaped openings of the support plate function as a vapor channel, and the total thickness of this flat plate heat pipe is 0.5 mm (Reference [6] J. L. Luo, D. C. Mo, Y. Q. Wang, and S. S. Lyu, Biomimetic copper forest wick enables high thermal conductance ultra-thin heat pipe. ACS Nano 2021, 15, 6614-6621). However, since this method uses an electroplating process, the formation of dendritic structures can be sensitive depending on the distance between the electrodes and the arrangement, and there is a problem that it cannot be applied when the shape of the wick in the heat pipe is not flat.

[0009] However, the vapor chambers of the above-described structures are all manufactured by combining a separately prepared envelope with a wick, or by combining separately prepared upper and lower plates each having an envelope and a wick, and thus are disadvantageous in terms of manufacturing cost and time. In addition, in order to prevent the flat plate-type envelope from collapsing due to the negative pressure generated by the vacuum, a support element needs to be additionally provided, or the wick needs to be designed to have the function of the support element, resulting in a high manufacturing cost and making it difficult to manufacture the product into an arbitrary shape.

[0010] Recently, the present inventors have proposed an ultra-light heat pipe (Patent Literature 1) Figure 6 , which is manufactured by 3D printing or other methods to produce a polymer template having a free shape and size, forming a non-permeable first electroless plating layer having a uniform thickness on the surface of the template, etching the polymer inside to produce an ultra-light thin film structure composed of the first electroless plating layer as an envelope, on the other hand, forming a porous second electroless plating layer on the surface of the envelope, and performing a hydrophilic treatment such as blackening treatment on the porous second electroless plating layer to form a wick Figure 6 of the heat pipe, and it has been confirmed that the heat pipe based on this model can have a capillary force sufficient to be applied to a capillary-driven heat pipe. Figure 6 (a) and (b) of Figure 6 are schematic diagrams showing the process of manufacturing the above-described ultra-light heat pipe from a rod-shaped and hole-shaped polymer template having a circular cross-section, Figure 6 (c) compares the heat pipe manufactured by this method with a commercial product manufactured by the existing method and shows the comparison. The heat pipe manufactured in this way is not only simple and easy to manufacture, but also can be miniaturized, lightened, and made into a free shape because a uniform and extremely thin electroless plating layer is used as the material of the envelope and the wick regardless of the position and direction in three-dimensional space, and thus can be advantageously applied to mobile devices (Reference Literature [7] Lee Yong-ju, "Ultra-light heat pipe using electroless plating", Graduate School of Chonnam National University, Master's Thesis, 2023). However, the heat pipe of this structure still has problems: since the envelope is extremely thin, if the cross-section is not circular, it cannot withstand the internal vacuum pressure, and thus it is difficult to manufacture the heat pipe into a flat plate type or other free shapes.

[0011] Moreover, the conventional heat pipe, needless to say, and the vapor chamber of the various structures as mentioned above and known in the art have the common limitation that the manufacturing process is complicated and that they simply serve to rapidly transfer heat, so that a cooling product and an external fan or the like heat dissipation device by forced convection are ultimately required. Furthermore, with the high performance of small components such as CPUs and GPUs of computers, and the increased use of high heat sources such as large-capacity secondary batteries and fuel cells in a narrow area, the devices for cooling them and the housings for accommodating them are also showing a tendency to be large and heavy, which is becoming a major obstacle to the miniaturization and light weight of electronic products such as mobile devices. SUMMARY

[0012] PROBLEM TO BE SOLVED BY THE INVENTION

[0013] The present application has been made to solve the problems of the prior art as described above, and aims to provide a novel concept of a thermal management medium which can serve as a super-lightweight structural material capable of withstanding internal vacuum pressure and external loads, and which can achieve various thermal management functions such as rapid heat exchange, transfer, absorption, and storage, and thermal shock mitigation.

[0014] TECHNICAL SOLUTION

[0015] In this context, the present inventors and others have recently discovered and recognized the following three main facts as the basis of the present invention in the course of studying the heat transfer characteristics of a foamed metal and a structure sealed with a thin film envelope on the outer surface thereof.(1) First, according to the structure, if an open-cell foamed metal having an appropriate cell size is subjected to a chemical treatment to impart hydrophilicity thereto, the foamed metal can not only function as a wick and a storage space for a liquid working fluid, but also function as a flow passage for a gaseous working fluid.(2) Second, according to the structure, if an envelope having a thickness of several tens of micrometers is laminated on the outer surface of the foamed metal, a super-lightweight structural material capable of sufficiently withstanding vacuum and vapor pressure acting on the inside and an externally applied load can also be realized.(3) Third, conventionally, in heat pipes and vapor chambers, a working fluid is simply used as a medium for heat transfer; however, in the above structure, the higher specific heat characteristics of a liquid working fluid compared to a solid, and the higher latent heat characteristics thereof during a phase change can be utilized, and thus the structure can be expanded to a heat absorbing and even storing use. Based on such discoveries and recognitions, the present inventors and others have finally proposed a new type of heat management medium that can not only function as a super-lightweight structural material, but also realize various heat management functions such as heat exchange, transfer, absorption, and even storage and impact mitigation, and can minimize the additional use of forced convection cooling devices, thereby being able to comply with the recent trend of product miniaturization and lightening, and the gist thereof is the same as that described in the claims, and is as follows.

[0016] (1) A heat management medium having heat exchange, transfer, absorption, and even storage and impact mitigation functions, the heat management medium characterized by comprising: an open-cell porous material having a hydrophilic-treated pore surface; a thin film envelope attached to the outside of the open-cell porous material and sealing the open-cell porous material in a vacuum state; and a working fluid filled in the pores of the open-cell porous material, the open-cell porous material being a structure that fills the internal space divided by the thin film envelope and simultaneously functioning as a moving medium for a liquid and gaseous working fluid.

[0017] (2) The heat management medium according to the above (1), characterized in that the working fluid is filled to 10 to 80% of the internal space divided by the thin film envelope in a liquid state.

[0018] (3) The heat management medium according to the above (1), characterized in that the open-cell porous material is any one of an open-cell foamed metal, a microstructure material, a three-dimensional truss-type porous material, and a woven metal material.

[0019] (4) The thermal management medium according to the above (3), wherein the working fluid is water, and the open-cell porous material is a foamed metal having a porosity of 90% or more.

[0020] (5) The thermal management medium according to the above (3), wherein the working fluid is water, and the open-cell porous material is a foamed metal having a pore size of 0.3 to 1.5 mm.

[0021] (6) The thermal management medium according to the above (1), wherein the housing is a sheet attached by resin bonding, welding, brazing or soldering.

[0022] (7) The thermal management medium according to the above (1), wherein the housing is composed of a plating layer formed on the outside of the open-cell porous material in a state where the pores of the open-cell porous material are filled with a temporary filling material of a polymer material, the temporary filling material being removed after the formation of the plating layer.

[0023] (8) The thermal management medium according to the above (1), wherein the housing is made of a metal.

[0024] Effects of the Invention

[0025] The thermal management medium of the present application has the following advantageous effects:

[0026] First, the thermal management medium has a structure in which a sheet housing surrounds the outside of an open-cell porous material, and thus can achieve an extremely lightweight structure material, and can ensure a sufficient structural strength against a high internal vacuum pressure and an external load. Accordingly, even if the thermal management medium has a flat plate-type two-dimensional shape similar to a conventional vapor chamber, it does not need to have a separate support element such as a pillar or a column in the inside thereof to prevent collapse or narrowing due to a high internal vacuum pressure, and thus is easy to manufacture and can have a free product shape.

[0027] Second, the heat management medium has an extremely thin shell thickness, so it can not only achieve rapid heat transfer through conduction with the outside, but also can serve as a moving medium for both liquid and gaseous working fluids due to the predetermined uniform size of the pores of the open porous material and the hydrophilic treatment of the surface. Accordingly, the exchange, transfer, absorption, and even storage of heat of the heat management medium can be autonomously determined according to the operating environment related to the size and shape of the heat management medium, the amount and location of heat input, and the like, thereby maximizing the utilization rate of the internal space of the heat management medium and allowing a high degree of freedom in the design of the product without the need for differential or separate design of each part of the heat management medium to achieve each function.

[0028] Third, the heat management medium can accommodate much more working fluid inside and has a high heat transfer capacity, so it can effectively alleviate the thermal shock caused by instantaneous heat input. Even in operating environments with high heat capacity requirements, the heat management medium can effectively suppress the dryout or depletion problem caused by insufficient working fluid. As a result, the heat management medium not only has the functions of heat exchange and transfer as a conventional heat pipe, but also has applications in heat absorption, storage, and shock mitigation, and its use efficiency can be improved.

[0029] Fourth, as described above, the heat management medium has the structural characteristics mentioned in the first and second points, so the shape of the product can be freely made without compromising the functions of the heat management medium. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structural diagram of a conventional capillary-driven heat pipe.

[0031] Figure 2 is an example diagram of the wick structure of a conventional capillary-driven heat pipe.

[0032] Figure 3 is an example diagram of the application of a conventional capillary-driven heat pipe to electronic components.

[0033] Figure 4 is a schematic diagram of the working principle of a conventional vapor chamber and an application example photo.

[0034] Figure 5 is a structural diagram of a vapor chamber in other conventional examples.

[0035] Figure 6 is a schematic diagram showing the manufacturing process of a capillary-driven heat pipe in a conventional example and a product comparison photo.

[0036] Figure 7A sample photograph of a heat management medium according to an embodiment of the present application.

[0037] Figure 8 A structural diagram and a sample photograph of an open-cell foamed metal according to an embodiment of the present application.

[0038] Figure 9 A device and a method for measuring water absorption capacity of an open-cell foamed metal after hydrophilic treatment, and a comparative chart of water absorption capacity.

[0039] Figure 10 A general process conceptual diagram of a manufacturing process of a heat management medium according to an embodiment of the present application, including a method of using plating in forming a thin film shell.

[0040] Figure 11 A chart showing temperature changes of a heat management medium corresponding to temperature changes of a heat source by comparing cases where amounts of a working fluid are different, according to an embodiment of the present application.

[0041] Figure 12 A chart showing a measurement method of heat transfer characteristics and results thereof, with respect to a heat management medium made of a rod-shaped sample according to an embodiment of the present application.

[0042] Figure 13 A chart showing specifications and characteristics of a heat management medium made of a flat plate-shaped sample according to an embodiment of the present application, compared with a conventional flat plate-shaped steam chamber.

[0043] Figure 14 A chart showing product appearance and heat transfer characteristics of a heat management medium made of a hexahedral sample according to an embodiment of the present application.

[0044] Figure 15 A chart showing Figure 14 A chart showing temperature changes of a sample over time when an injection amount of a working fluid is changed, among the samples shown in FIG. 8.

[0045] Figure 16 A use state schematic diagram of a flat plate-shaped heat management medium according to another embodiment of the present application, which can be used as a housing structure material. DETAILED DESCRIPTION

[0046] The present application will be described in detail below by way of examples. Before doing so, the terms or words used in the specification and claims should not be interpreted in the light of the meanings generally or in dictionaries, but should be interpreted in the light of the meanings and concepts in accordance with the technical idea of the present application, based on the principle that the inventors can define the concepts of terms appropriately in order to describe their own inventions by the most optimal methods. Therefore, the constitution of the examples described in the specification is only the most preferred one of the present application, and does not represent the entire technical idea of the present application, and thus it should be understood that at the point of filing of the present application, there can be a variety of equivalents and modifications which can replace these examples. On the other hand, in the drawings, the same or equivalent parts are marked with the same or similar reference numerals; and in addition, throughout the specification, when a certain part is referred to as "comprising" a certain constituent element, this does not mean that other constituent elements are excluded unless specifically stated to the contrary, but means that other constituent elements can be further included.

[0047] (Structure and operation of the thermal management medium)

[0048] Figure 7 (a) of FIG. 1 shows a sample of a thermal management medium according to an embodiment of the present application. Here, as an example of an open-cell porous material, an open-cell foam material is used. The thermal management medium includes an open-cell porous material whose pore surface is hydrophilically treated, a film envelope attached to the outside of the open-cell porous material and sealing the open-cell porous material in a vacuum state, and a working fluid injected into the pores of the open-cell porous material. In this case, the injection amount of the working fluid can be varied to the extent of occupying 10 to 80% of the internal space, i.e., the internal space divided by the film envelope. The material of the open-cell porous material and the envelope is not particularly limited, and can be composed of the same or different materials, and is preferably composed of a metal material having excellent thermal conductivity such as copper. Referring to Figure 7 (b) and Figure 7 (c) of FIG. 1, it can be confirmed that the open-cell foam material and the envelope are attached to each other in good condition.

[0049] Open porous material treated with hydrophilicity

[0050] Figure 8 (a) of FIG. 2 shows a structure diagram and a sample photograph of an open-cell copper foam material composed of a copper material according to an embodiment of the present application. Here, an open-cell copper foam material, which is one of open-cell porous materials, is used. Referring to Figure 8 (a) of FIG. 2, the open-cell copper foam material preferably has a porosity of 90% or more and a pore size (d poreIf the porosity is below 90%, it will lead to a meaningless increase in weight, so it is not preferred. However, it should be noted that while higher porosity is more beneficial for weight reduction, if the porosity is extremely high, such as above 99%, the yield strength will be lower than 0.1 MPa, making it unable to withstand the pressure generated by the internal vacuum, resulting in collapse and narrowing, so it is also not preferred. Furthermore, if the pore size exceeds 1.5 mm, even after hydrophilic treatment of the open-pore material, the capillary force will not be strong enough to fully function as a flow channel (i.e., a liquid wick) for liquid fluid; conversely, if the pore size is less than 0.3 mm, the flow resistance of the working fluid in gaseous state will increase, so it is also not preferred. However, it should be noted that such porosity and pore size are only limited to the case of using water as the working fluid in copper foam metal, and can vary depending on the type of open-pore material, its microstructure, and the type of working fluid.

[0051] To improve the hydrophilicity of the above-mentioned open-cell foamed material, it was immersed in an aqueous solution of K2S2O8 (1.5 g / L) and NaOH (7.5 g / L) for 24 hours to form copper oxide (CuO) on the surface (Reference [8] Jingchun Min, Xiaomin Wu, Lifeng Shen, Frank Gao, Hydrophilic treatment of copper finned tube evaporators, Purdue University International Conference on Refrigeration and Air Conditioning, July 14-17, 2008). Since such treatment makes the surface black after treatment, it is called blackening treatment. Figure 8 (b) and Figure 8 (c) shows the fine structure after hydrophilic treatment.

[0052] Figure 9 Apparatus and methods for measuring the water absorption capacity of hydrophilically treated materials, specifically rod-shaped hydrophilically treated open-cell foamed metal, are shown. Figure 9 (a) and a comparison chart of water absorption capacity ( Figure 9 (b)). See reference. Figure 9 (b) The open-cell copper foam material of the present invention has a pore size of 0.713 mm, which is much larger than the pore size of 20 to 50 μm of copper powder sintered bodies that have been widely used as liquid absorbers in the past (Reference [9] K. Leong, C. Liu, G. Lu, Characterization of sintered copper liquid absorbers for heat pipes, Journal of Porous Materials, Vol. 4, pp. 303-30, 1997). Nevertheless, it can be confirmed that its water absorption capacity over time is superior to that of conventional copper powder sintered bodies.

[0053] In the above embodiments, open-cell foam was used as an example of an open-cell porous material, but other porous materials with different microstructures but similar pore sizes can also be used. For example, microstructured materials or three-dimensional truss porous materials (Reference

[10] Fleck, NA, Deshpande, VS & Ashby, MF “Microstructured Materials: Past, Present and Future”, Proceedings of the Royal Society A, Vol. 466, pp. 2495-2516, 2010), woven metal (Reference

[11] KJ Kang, “Woven Porous Metal Materials: Present and Future”, Progress in Materials Science, Vol. 69, pp. 213-307, 2015) or woven metal materials can be used instead of the open-cell foam of the embodiments.

[0054] The thermal management medium in embodiments of the present invention, due to the predetermined uniform size of the pores in the open porous material and the hydrophilic surface treatment, can not only realize the functions of a traditional liquid working fluid storage and movement medium, but also operate as a movement medium for gaseous working fluids. Accordingly, the various functions of the thermal management medium, such as exchange, transfer, absorption, and even storage, can be autonomously determined according to the operating environment related to the size and shape of the thermal management medium, the amount and location of heat input, etc., thereby not only optimizing and maximizing the utilization rate of the internal space of the thermal management medium, but also eliminating the need for differentiated or separate design of each part of the thermal management medium to achieve each function, thus providing a high degree of design freedom for the product.

[0055] Thin film shell

[0056] According to embodiments of the present invention, the envelope of the thermal management medium can, for example, be made of copper metal with a thickness of tens of μm. Such an envelope can be formed, for example, using conventional manufacturing processes, namely, attaching a thin plate to the outside of an open porous material via resin bonding, welding, brazing, copper soldering, etc., and sealing the boundary ends of the thin plate. Furthermore, another practical solution for forming the envelope is... Figure 10 As shown, an open porous material can be first immersed in a resin solution and allowed to cure. After the pores are filled, a coating is formed on the outside of the open porous material in this state. Finally, the cured resin inside the pores is removed, and the coating forms the outer shell. In this case, the cured resin, which serves as a temporary filler, can be partially removed by polishing or other methods. With a portion of the coating exposed to the outside along with the inner open porous material, it can be selectively removed by etching, dissolving, or other methods.

[0057] on the other hand, Figure 10A whole process concept diagram related to the manufacturing process of the thermal management medium is shown, including the method of using the plating layer when forming the thin film shell. That is, by sequentially performing the following series of processes in the left-right and up-down directions of the drawing, a thermal management medium having a plating layer configured as a shell is manufactured: manufacturing of an open porous material, impregnation of a resin liquid (e.g., PMMA), curing, outer forming / machining of the open porous material, formation of a plating layer (shell) on the outside of the open porous material, removal of the internal cured resin (PMMA) and hydrophilic treatment (blackening treatment), formation of an internal vacuum, and injection of a working fluid.

[0058] The thermal management medium of the present application can achieve rapid heat transfer with the outside by conduction due to the extremely thin thickness of the shell. In addition, the thermal management medium adopts a structure in which a thin plate shell surrounds the outside of an open porous material, and can achieve an extremely lightweight structural material; however, the innumerable ligaments connected to each other in the open porous material operate as a kind of support element in the form of a truss against external forces applied from the outside, thereby still being able to ensure structural strength sufficient to withstand high internal vacuum pressure and external loads. Accordingly, even though the thermal management medium has a flat plate type two-dimensional shape similar to a conventional vapor chamber, it is different from the conventional vapor chamber in that it does not need to provide a separate support element such as a pillar or column in its interior to prevent collapse or narrowing due to high internal vacuum pressure, and thus is easy to manufacture and enables freedom of the shape of the product.

[0059] Excess working fluid and operation

[0060] In the present application, the type of the working fluid is not particularly limited to distilled water or the like, and the amount of the working fluid injected into the interior is preferably, for example, a state in which it is filled to 10% to 80% of the internal space, and accordingly the thermal management medium of the present application can operate regardless of the amount of the working fluid.

[0061] In the present application, the exchange, transfer, absorption, and even storage and impact mitigation of heat and the like are achieved by the working fluid, and the characteristics thereof are that each of the functions and even the effects are basically autonomously or automatically determined by the uniform fine structure of the open porous material having a predetermined pore size and the hydrophilic treatment of the pore surface, as described above.

[0062] That is, a part of the working fluid can play the role of a first medium that vaporizes in a high-temperature portion near a heat source, moves to a low-temperature portion near a cold source, condenses, and then returns to the high-temperature portion by capillary phenomenon, and repeats the same cycle to rapidly transfer heat; and the remaining part of the working fluid can play the role of a second medium that stores a large amount of heat energy using a high specific heat.

[0063] In this case, the amount and distribution of the working fluid functioning as the first and second medium are automatically or autonomously adjusted, for example, as the externally transferred heat energy increases, the internal temperature and the temperature of the working fluid increase, and thus the proportion of the second medium in the working fluid decreases, and the proportion of the first medium increases accordingly; further, when heat above the critical value flows in, all of the working fluid functions as the first medium, and if necessary, an external cooling device can be required. Conversely, as the externally transferred heat decreases, the working fluid functions automatically by increasing the proportion of the second medium.

[0064] Therefore, for the heat management medium of the present application, since an excess of working fluid can be filled, even if an excess of heat is generated and input instantaneously, a part of the working fluid is easily and quickly absorbed by the specific heat and latent heat (heat of vaporization) during the process of being heated and vaporized, and thus the temperature of the heat source and the heat management medium is effectively moderated or even suppressed from rising sharply, and the thermal shock resulting therefrom is also effectively moderated or even suppressed, and as a result, the need for or operation of an additional cooling device can be minimized.

[0065] Figure 11 is a graph showing the temperature change of the heat management medium corresponding to the temperature change of the heat source by comparing cases in which the amount of working fluid is different, according to an embodiment of the present application. Referring to Figure 11 As can be seen, the more the amount of working fluid, the more the working fluid functioning as the above-described second medium, based on the heat management medium, and the heat capacity increases, and thus the function of moderating the thermal shock is also enhanced.

[0066] (Separate implementation and operation-related examples using the heat management medium)

[0067] Hereinafter, examples in which the heat management medium having the basic structure described above is applied in various forms according to each use or use environment, and the corresponding operation contents and performance are more specifically described.

[0068] Case where made in a general rod-shaped heat pipe or flat plate type vapor chamber shape

[0069] Figure 12 A method of measuring the heat transfer characteristics and the results are shown, with the heat management medium made in a rod shape as the object, according to an embodiment of the present application. Referring to Figure 12 (a) of FIG. 11, the heat management medium sample of the embodiment uses a long rod made in a quadrangular cross section, and by making heat flow in from the lower portion of the sample, the heat is transferred to the upper portion, and the temperature distribution of the sample is measured using an infrared camera. Referring to Figure 12 (b) of FIG. 11, the temperature distribution of the sample along the length in the up-and-down direction is very uniform, and it can be said that this indicates that the sample works well as a heat pipe.

[0070] According to Figure 12The heat management medium sample made in a rod shape differs from the conventional heat pipe in that, although the envelope thickness is extremely thin, only several tens of μm, and the cross section is a quadrangle, not a circle, which is disadvantageous in supporting a vacuum, the structure is very strong; in the open porous material, as in the conventional wick, the function of the storage and moving passage of the liquid working fluid and even the portion of the function and the moving passage of the gaseous working fluid are autonomously determined according to the operating environment; and since the working fluid is sufficiently present in excess, even if there is an instantaneous excess heat overloading, the working fluid dryout or depletion is effectively delayed or suppressed.

[0071] On the other hand, when the heat management medium of the present application is made in a thin plate shape, it is expected to provide a medium which can operate in the same manner as Figure 12 the conventional vapor chamber and is similar to the conventional vapor chamber. For example, the sample is made based on the basic structure of the heat management medium of the present application, and it is assumed that the sample has the same size of 90 mm x 90 mm x 3 mm as that of the commercial vapor chamber (Wakefield-Vette Co., VC-90-90-3), as shown in (a) of FIG. 10, Figure 13 the expected weight of the sample is 26 g, which can be significantly reduced to about 20% of the conventional reference, but since the working fluid is filled by more than 7 times, it is expected that the allowable heat input will also be significantly increased. Figure 13 (b) of FIG. 10 shows a structure diagram of the conventional vapor chamber similar to the flat plate type heat management medium of the present application, Figure 13 (c) of FIG. 10 shows a disassembled photograph of the actual product, and it can be confirmed that Figure 13 (b) of FIG. 10 is very similar to Figure 13 (c) of FIG. 10.

[0072] The reason why the conventional commercial vapor chamber product is heavy is that the upper and lower envelopes need to be designed to have a thickness of 1 mm and 0.8 mm in order to have a flat plate shape while being able to withstand the extrusion due to the vacuum, and a large number of support elements such as copper pillars need to be provided inside. Accordingly, for the conventional commercial vapor chamber, the internal space in which the working fluid can be contained and used is only about 1.2 mm high, and the amount of the liquid working fluid that can be absorbed by the wire mesh shaped metal (copper) wick that can be disposed on the inner side surfaces of the upper and lower internal spaces is inevitably greatly reduced.

[0073] Case where made in an outline similar to a three-dimensional hexahedron

[0074] Figure 14are diagrams showing product appearance and heat transfer characteristics of a heat management medium made of a hexahedral test sample according to an embodiment of the present application. Referring to Figure 14 (a), the test sample is a cube with a side length of 50 mm, and after forming a housing with a copper plating layer, a nickel alloy is additionally plated to facilitate brazing and soldering. This shape of test sample is particularly useful for investigating the above-mentioned role of the second medium as a storage of thermal energy because the volume of the internal space is maximized relative to the surface area. Figure 14 (b) and Figure 14 (c) show a thermal imaging diagram and a graph related to temperature distribution when 20 W of heat is input from below in a state where the internal space is filled with 20% of a working fluid, i.e., water, respectively. The temperature distribution is very constant in most areas of the test sample except for the surfaces in contact with the heat source and the outside air, and thus it is confirmed that the test sample achieves excellent heat transfer characteristics as with a conventional heat pipe.

[0075] Figure 15 show the temperature change of the test sample over time when the injection amount of the working fluid is changed in the test sample of Figure 14 Specifically, Figure 15 shows the temperature change of the bottom face of the test sample over time after 20 W of heat is input to the bottom face of the test sample in a state where the test sample of Figure 14 is filled with 20% and 60% of a working fluid, i.e., water, respectively.

[0076] It is confirmed that the temperature rise rate is significantly reduced when 60% of water is filled compared to when 20% of water is filled. Thus, the former stabilizes at T steady = 79°C after 1.4 hours, while the latter is still T steady = 77°C after 2 hours, which is still lower than 79°C. In addition, as a comparative object, the result of measuring the bottom temperature when the same amount of heat is input to a commercial steam cavity of Figure 13 is shown. It can be seen that, unlike the cubic test sample of the present application, the bottom temperature rises at a significantly faster rate and reaches a significantly higher 85°C after 1 hour.

[0077] For the hexahedral heat management medium shown in Figure 14 and Figure 15 , the longer the side length, the more the working fluid having the role of the second medium increases in proportion to the cube of the side length, and thus, by virtue of the high specific volume and latent heat, the amount of heat that can be absorbed becomes large, and as a result, the time to reach the saturation temperature is extended, and thus it is possible to achieve, for example, Figure 11The use of the illustrated transient thermal shock mitigation is particularly useful. However, due to the relatively small surface area of the specimen of this shape, if a high thermal input is applied continuously, additional cooling fins and fans for natural and forced convection cooling can be required.

[0078] Furthermore, Figure 14 and Figure 15 The hexahedral-shaped thermal management medium illustrated is composed of a tens-of-μm-thick envelope, an open-cell foam material having a porosity of 90% or more, and a working fluid, and is extremely light in weight relative to volume. For example, as described above, for a copper thermal management medium in the shape of a cube having a side length of 50 mm, composed of an envelope having a thickness of 50 μm, an open-cell foam material having a porosity of 95%, and 50% of the interior space filled with a working fluid, water, the total weight is approximately 124.8 g, which is 37% of the weight of 337.5 g of a block-shaped aluminum of the same volume, and thus the volume-weight ratio is extremely low.

[0079] Case where used as a casing structure

[0080] Figure 16 A use state diagram of a flat-plate-shaped thermal management medium according to another embodiment of the present application is illustrated, which shows the use of the thermal management medium as a structural material. The above-described structural material is, for example, an ultra-lightweight housing structural material used in mobile devices, which can be a typical structural sandwich panel in which a rigid panel is disposed on the upper and lower portions and a porous material is disposed in the middle, and such a housing structural material can be required to have the function of transferring and dissipating heat generated by a plurality of components and elements to the outside in addition to the function of protecting the internal components or systems. Since the thermal management medium of the present application has excellent structural and thermal management properties, when it is made into a large area, flat-plate shape, it is very suitable for use in such applications. Figure 16 In anticipation of such use, a use state of a large-area, flat-plate-shaped thermal management medium operating in a state in which one face thereof is in contact with a plurality of components and the like operating as heat sources is illustrated. At the periphery of each heat source, the amount, range, and even distribution of the working fluid functioning as the first medium are determined in the process of heat exchange and transfer, as in a vapor chamber. In this case, if there is an excess of working fluid, a considerable proportion of the working fluid functioning as the second medium can also be present. On the other hand, when the thermal management medium of the present application is used as a structural material such as a housing, problems that can result in a decrease in the sense of use and stability due to the sloshing of the internal working fluid and the like can be effectively prevented by the complex, non-regular microstructure of the open-cell microstructure.

[0081] The above description relates to specific embodiments of the present application. As described above, the embodiments of the present application are disclosed only for illustrative purposes, and should not be construed as limiting the scope of the present application; those skilled in the art should understand that various changes and modifications can be made without departing from the essence of the present application. Therefore, all such modifications and changes can be understood as falling within the scope of the application disclosed in the patent claims or equivalents thereof.

Claims

1. A thermal management medium having heat exchange, transfer, absorption, storage, and impact mitigation functions, the thermal management medium characterized by comprising: an open-cell porous material having a pore surface treated with hydrophilicity; a thin film shell attached to the outside of the open-cell porous material and sealing the open-cell porous material in a vacuum state; and a working fluid filled in the pores of the open-cell porous material, the open-cell porous material being a structure filling the internal space divided by the thin film shell and simultaneously functioning as a moving medium of the working fluid in liquid and gaseous states.

2. The thermal management medium according to claim 1, characterized in that the working fluid is filled in the internal space divided by the thin film shell to 10 to 80% in a liquid state.

3. The thermal management medium according to claim 1, characterized in that the open-cell porous material is any one of an open-cell foamed metal, a microstructure material, a three-dimensional truss porous material, and a woven metal material.

4. The thermal management medium according to claim 3, characterized in that the working fluid is water and the open-cell porous material is a foamed metal having a porosity of 90% or more.

5. The thermal management medium according to claim 3, characterized in that the working fluid is water and the open-cell porous material is a foamed metal having a pore size of 0.3 to 1.5 mm.

6. The thermal management medium according to claim 1, characterized in that the shell is a thin plate attached by resin bonding, welding, brazing, or soldering.

7. The thermal management medium according to claim 1, characterized in that the shell is composed of a plating layer formed on the outside of the open-cell porous material in a state where the pores of the open-cell porous material are filled with a temporary filling material of a polymer material, the temporary filling material being removed after the plating layer is formed.

8. The thermal management medium according to claim 1, characterized in that the shell is made of metal. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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