Capillary wick and method of manufacturing the same, evaporator, loop heat pipe, cooling device

Abstract

The present invention relates to a capillary core, an evaporator, a loop heat pipe, a cooling device, an electronic device, and a capillary core manufacturing method. The present invention aims to provide a capillary core, an evaporator, a loop heat pipe, a cooling device, an electronic device, and a capillary core manufacturing method that can improve the long-term stability of the hydrophilicity of the capillary core. The capillary core of the present invention is a capillary core of a porous elastomer that is permeated by a working fluid in a liquid phase, which is provided inside an evaporator that changes the working fluid in the liquid phase to a gas phase. The porous elastomer includes composite voids having communication holes at portions where a plurality of spherical voids partially overlap each other. The surface of the voids of the porous elastomer is coated with a hydrophilic polymer having a betaine group and a molecular weight of 10,000 or more of a polymer brush structure.

Description

TECHNICAL FIELD

[0001] The present application relates to a capillary wick, an evaporator, a loop heat pipe, a cooling device, an electronic device, and a capillary wick manufacturing method. BACKGROUND

[0002] Conventionally, a capillary wick of a porous elastomer, through which a working fluid in a liquid phase penetrates, provided inside an evaporator that changes the working fluid in the liquid phase to a gas phase, is known.

[0003] In Patent Literature 1, as the capillary wick, a foamed silicone rubber of a porous elastomer is described. In addition, in Patent Literature 1, water is described as the working fluid.

[0004] [Patent Literature 1] Japanese Patent Application Publication No. 2020-20495 SUMMARY

[0005] However, in the case of using water or a hydrophilic fluid as the working fluid, there is room for improvement in the long-term stability of the hydrophilicity of the capillary wick.

[0006] To solve the above problem, the capillary wick of the present application is a capillary wick of a porous elastomer, through which a working fluid in a liquid phase penetrates, provided inside an evaporator that changes the working fluid in the liquid phase to a gas phase, characterized in that:

[0007] the porous elastomer includes a composite void having a communication hole at a portion in which a plurality of spherical voids partially overlap each other,

[0008] a surface of the void of the porous elastomer is covered with a hydrophilic polymer film.

[0009] The effects of the present application are described below.

[0010] According to the present application, it is possible to improve the long-term stability of the hydrophilicity of the capillary wick. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic explanatory view showing one example of a loop heat pipe 1 to which the present embodiment relates.

[0012] Figure 2 is a view showing an imaginary cross section when the a-a cross section indicated by a dashed line in Figure 1 is cut.

[0013] Figure 3 is a schematic explanatory view of a conventional general loop heat pipe.

[0014] Figure 4 is a schematic explanatory view showing another example of a loop heat pipe provided in an electronic device to which the present embodiment relates.

[0015] Figure 5 FIG. 1 is a diagram showing various factors and test results of samples of examples and comparative examples for cooling performance tests.

[0016] Figure 6 FIG. 2 is a diagram showing the state of bubbles (photograph) of the capillary core sample of Example 1 observed with a laser microscope.

[0017] Figure 7 FIG. 3 is a graph showing one example of a bubble diameter distribution.

[0018] Figure 8 FIG. 4 is a diagram showing one example of an image of a sample of the capillary core of Example 1 observed with a scanning electron microscope.

[0019] Figure 9 FIG. 5 is a graph showing the change in hydrophilicity of the capillary core of Example 1 and Comparative Examples 1, 3, and 4 from the initial to 3 months.

[0020] DETAILED DESCRIPTION

[0021] Hereinafter, as a cooling means provided with an evaporator and a condenser in which a capillary core according to the present application is provided inside, one embodiment of a loop heat pipe (hereinafter referred to as loop heat pipe 1) will be described with appropriate reference to the accompanying drawings.

[0022] Herein, in each of the drawings used to describe the present embodiment, components and constituent elements having the same function or shape, and the like are denoted by the same reference numerals as long as they can be distinguished. In addition, for the constituent elements denoted by the same reference numerals, the description thereof will be appropriately omitted after the description thereof is given once.

[0023] Figure 1 FIG. 1 is a diagram showing one example of a schematic configuration of the loop heat pipe 1 to which the present embodiment is directed. Figure 2 FIG. 2 is a diagram showing an imaginary cross section when the a-a cross section indicated by a dashed line in FIG. 1 is cut. Figure 1

[0024] Figure 1 The loop heat pipe 1 shown in FIG. 1 has a working fluid composed of a condensable fluid enclosed inside, and includes the following parts. The loop heat pipe 1 includes an evaporation section 2 that absorbs heat from a heat generating section to evaporate the working fluid from a liquid phase to a gas phase, and a condensation section 3 that condenses the working fluid in the gas phase introduced from the evaporation section 2 to the liquid phase. In addition, it also includes a vapor pipe 4 that causes the working fluid in the gas phase to flow from the evaporation section 2 to the condensation section 3, and a liquid pipe 5 that causes the working fluid in the liquid phase to flow from the condensation section 3 to the evaporation section 2.

[0025] The evaporation section 2 is composed of a heat receiving section 7 in which a capillary core 6 is accommodated inside, and a storage section 8 that stores the working fluid in the liquid phase.

[0026] ​The heated portion 7 has one end of the vapor pipe 4 connected thereto, and the storage portion 8 has one end of the liquid pipe 5 connected thereto. Further, the other ends of the vapor pipe 4 and the liquid pipe 5 are connected to the condensing portion 3. The condensing portion 3 is composed of a pipe 31 made of stainless steel having a plurality of thin plate-shaped fins 32 provided on the outer peripheral surface.

[0027] The capillary core 6 is a porous body. Further, a plurality of grooves 10 are provided on the bottom surface of the capillary core 6 from the end portion on the side of the vapor pipe 4 to the opposite side direction. Figure 1

[0028] The plurality of grooves 10 are shown in Fig. 2 as imaginary cross sections when the a-a cross section indicated by a broken line in Fig. 1 is cut. The grooves 10 are provided at equal intervals on the bottom of the capillary core 6. Here, in Fig. 2, the dimensions of the grooves 10 are drawn in a scale larger than the actual dimensions. Further, the thickness of the capillary core 6 is set to a dimension slightly larger than the inner dimension of the case of the heated portion 7. Figure 2 Figure 1 Figure 2

[0029] By setting the thickness of the capillary core 6 as described above, the capillary core 6 is in close contact with the inner surface of the heated portion 7 in a state in which the capillary core 6 is accommodated in the heated portion 7. Further, since the capillary core 6 is in close contact with the heated portion 7, the heat of the heating portion is efficiently transmitted to the capillary core 6 through the case of the heated portion 7. On the other hand, in the portion in which the grooves 10 are provided, a space portion is formed between the heated portion 7 and the case.

[0030] Since the capillary core 6 is composed of a porous body, i.e., a porous material, the working fluid in the liquid phase stored in the storage portion 8 penetrates into the capillary core 6 due to the capillary phenomenon. Due to this capillary phenomenon, the capillary core 6 also functions as a pump that transports the working fluid in the liquid phase from the condensing portion 3 to the evaporating portion 2.

[0031] As the working fluid, water, ethanol, acetone, a condensing fluid that substitutes for freon, or the like can be used. In particular, by using water having a high latent heat as the working fluid, a high cooling performance can be obtained. Further, in order to make the working fluid easily penetrate into the capillary core 6, a working fluid having good wettability with the capillary core 6 can be used. The wettability can be measured by the contact angle of the capillary core 6 with the working fluid. If the contact angle is greater than or equal to 40°, the working fluid cannot penetrate into the capillary core 6, and therefore, the contact angle must be less than 40°. The contact angle is preferably less than 10°, and more preferably 5° or less, and the capillary phenomenon is more effective.

[0032] ​​​​In the loop-type heat pipe 1 of this embodiment, if heat from the heating element is transferred through the shell of the evaporation section 2 (heated section 7) to the liquid working fluid in the capillary wick 6, the heat causes the working fluid to evaporate and change into a gaseous phase. The evaporated working fluid, now in a gaseous phase, is then sent to the vapor pipe 4 through the tank 10. Finally, the gaseous working fluid is sent to the condenser section 3 through the vapor pipe 4.

[0033] In the condenser section 3, the heat from the working fluid inside (pipe 31) is discharged to the outside via the heat sink 32, causing the working fluid temperature to drop and condense, changing from a gas phase to a liquid phase. The liquid working fluid moves to the evaporator section 2 through the liquid pipe 5, and due to capillary action, it permeates again from the storage section 8 into the capillary wick 6 located inside the heating section 7. Through this circulation of the working fluid, the heat from the heating section is continuously dissipated to the outside, and the object being cooled is cooled.

[0034] Here, with reference to the attached diagram, we will first explain the problems with the conventional loop-type heat pipes that have a capillary wick inside the evaporator.

[0035] Figure 3 This is a simplified diagram of a typical loop-type heat pipe 100.

[0036] Generally speaking, such as Figure 3 As shown, the loop-type heat pipe 100 includes an evaporation section 102 that receives heat from the outside, causing the working fluid to evaporate from the liquid phase to the gas phase, and a condensation section 103 that dissipates heat to the outside, causing the working fluid to condense from the gas phase to the liquid phase. Furthermore, it includes a vapor pipe 104 that allows the gaseous working fluid to flow from the evaporation section 102 to the condensation section 103, and a liquid pipe 105 that allows the liquid working fluid to flow from the condensation section 103 to the evaporation section 102.

[0037] Inside the evaporation section 102, a capillary wick 106 made of a porous material is housed. The liquid working fluid delivered from the liquid pipe 105 permeates through the micropores of the capillary wick 106 due to capillary action and seeps to the outer surface of the capillary wick 106. At this time, heat from the heating element (the object being cooled) in contact with the evaporation section 102 is transferred to the capillary wick 106 through the shell of the evaporation section 102, causing the working fluid to evaporate and become a gaseous phase. Then, the gaseous working fluid moves to the condensation section 103 through the vapor pipe 104.

[0038] In the condenser section 103, the heat of the working fluid dissipates to the outside, causing the temperature of the working fluid to drop and turn into a liquid phase. Then, the liquid working fluid moves through the liquid pipe 105 to the evaporator section 102 and permeates back into the capillary wick 106. In this way, in the loop-type heat pipe 100, the phase change of the working fluid is utilized to circulate the working fluid, transferring the heat absorbed in the evaporator section 102 to the condenser section 103, thereby effectively cooling the object being cooled.

[0039] Here, in order to improve the cooling efficiency, it is necessary to ensure the close contact with the evaporation section 102, to circulate the working fluid by the capillary force of the capillary 106, and to minimize the pressure loss, and therefore the capillary 106 needs to have high permeability.

[0040] As the capillary, for example, a porous sintered body formed by filling aluminum fibers, and a porous elastomer such as foamed silicone rubber can be used. In the case where the capillary is composed of a porous sintered body, high dimensional accuracy is required in order to ensure the close contact with the case, and therefore the cost is high. For this reason, it is preferable that the capillary 6 be composed of a porous elastomer. Since the capillary 6 is composed of a porous elastomer, high elastic force can be obtained, and therefore even if the dimensional accuracy is not high, the capillary 6 can be in close contact with the case (heated section 7) of the evaporation section 2. The cost of the device can be reduced. In addition, since the capillary 6 is composed of a porous elastomer, high close contact can be obtained. As a result, the heat transfer efficiency from the case of the evaporation section 2 to the capillary 6 is good, and the cooling performance of the loop heat pipe 1 is improved.

[0041] In addition, as described above, the high close contact of the capillary and the suppression of the collapse of the local voids at the time of post-processing can be achieved by the countermeasure of making the capillary 6 a porous elastomer alone. Therefore, if the post-processing of the delivery groove (channel) of the groove 10 or the like for delivering the working fluid (evaporated refrigerant) can be omitted, the manufacturing cost can be further reduced.

[0042] However, in the case where the loop heat pipe 1 is used in an application requiring high cooling performance, it is preferable to use water having high latent heat as the working fluid. However, when water is used as the working fluid, the hydrophilicity of the porous elastomer such as foamed silicone rubber is not sufficient. Therefore, in order to make it hydrophilic, surface treatment is usually performed, but the hydrophilicity can deteriorate over time due to the disappearance or insertion of a segment containing a hydrophilic group, and the cooling performance can decrease.

[0043] Therefore, in the present embodiment, the surface of the void of the porous elastomer is covered with a hydrophilic polymer. By covering the surface of the void with a hydrophilic polymer as the hydrophilic polymer, the hydrophilicity can be stabilized for a long period of time, and the high cooling performance can be maintained. Even in the case where a fluid having hydrophilicity as water, such as alcohol having a hydrophilic substituent, is used, the working fluid can be efficiently circulated. The above-mentioned so-called polymer refers to a polymer having a molecular weight of 10,000 or more.

[0044] Next, an example of the capillary 6 as a feature of the present embodiment will be described in detail.

[0045] As described above, the capillary 6 for the loop heat pipe 1 according to the present embodiment is composed of a porous elastomer such as foamed silicone rubber.

[0046] The manufacturing method of the capillary core composed of such a porous elastomer having elasticity can be considered variously, and the porous elastomer in the present embodiment can be obtained by applying, for example, a technology proposed as a water-blown silicone rubber.

[0047] Specifically, a water-blown silicone rubber composition using an active agent or a water-phase additive is used so as to become a composite bubble, and a cross section obtained when a formed foam is cut is stirred as described below. The bubbles present in the cross section are made to be in a size range of 1 μm or more and 50 μm or less, and bubbles in a size of 5 μm or more and 10 μm or less are present most.

[0048] More specifically, the above porous elastomer is prepared by mixing a catalyst, a surfactant, and a cross-linking agent in a commercially available two-liquid type liquid silicone rubber. Here, an additive, a filler, a dispersant, and the like are mixed in water (ethanol is added as needed) to make a mixed solution having a viscosity equivalent to that of the liquid silicone rubber, and the mixed solution is stirred to prepare an emulsion composition. The liquid silicone rubber is preferably 1.00 to 1.05 g / cm3 in specific gravity in consideration of emulsifiability with water. 3 .

[0049] Here, the mixing ratio of the liquid silicone rubber to the mixed solution varies depending on the desired porosity. For example, if the mixing ratio of the liquid silicone rubber to the mixed solution is 1:1, water in the form of fine particles in the emulsion evaporates to form voids, and thus a foam having a porosity of 50% or more can be obtained.

[0050] The emulsion is stirred using a homogenizer or a stirrer with ultrasonic treatment as needed, and various stirring conditions such as the stirring means, the stirring time, the stirring speed (for example, 300 to 1500 rpm), and the like are adjusted in order to obtain a bubble diameter distribution satisfying the above conditions.

[0051] Then, the prepared emulsion composition is filled into a mold, and primary heating is performed by heating without evaporating the water in the emulsion composition to harden the silicone rubber.

[0052] Here, the heating temperature is in the range of 80 to 130°C, and the heating time is in the range of 30 to 120 minutes. The heating temperature is preferably 90 to 110°C, and the heating time is preferably 60 to 90 minutes. Next, secondary heating is performed in order to remove the water from the foam after the primary heating. The heating temperature is in the range of 150 to 300°C, and the heating time is in the range of 1 to 24 hours. The heating temperature is preferably 200 to 250°C, and the heating time is preferably 3 to 8 hours. By performing such secondary heating, the water is removed from the porous elastomer, the composite bubbles formed by the spherical bubbles locally overlapping each other are connected, the bubbles are set to be connected-bubble type, and the final curing of the silicone rubber is completed.

[0053] Then, the outer surface of the capillary core is ground by several μm to several mm as needed for the purpose of improving accuracy or removing the surface layer. For example, removal by grinding with a grinding wheel or with a belt sander, etc. Then, cleaning is performed for the purpose of removing chips or impurities. For example, ultrasonic cleaning or baking, etc.

[0054] Further, for the purpose of imparting hydrophilicity, hydrophilic treatment is performed. As the hydrophilic treatment, for example, there are treatments such as corona, plasma, UV ozone, etc. The treatment is performed not only on the outer surface of the silicone rubber but also on the surface of the path through which the working fluid passes, including the voids in the interior. Further, for the purpose of achieving stable hydrophilicity over time, after the surface treatment, a hydrophilic polymer, which is a polymer having a betaine group, is applied by immersion or the like. As needed, heat treatment is performed to fix the hydrophilic polymer. The hydrophilic polymer can be, for example, a polymer having a polymer brush structure of a betaine group such as phosphobetaine, carboxybetaine, sulfobetaine, etc.

[0055] The so-called polymer brush structure refers to a structure in which a plurality of polymer chains extend in the vertical direction with respect to the surface of the base material (the surface of the porous elastomer). By providing the polymer chains with a hydrophilic group, as shown in the verification test described later, it is possible to maintain hydrophilicity stably over a long period of time. In particular, by providing the hydrophilic group with a betaine group such as phosphobetaine, carboxybetaine, sulfobetaine, etc., it is possible to obtain very high hydrophilicity.

[0056] Next, the water-blown silicone rubber, which is the porous elastomer that is the final hardening end, is cut, and the specification parameters (specifications, conditions at the time of manufacture) of the cross section that can be obtained at the time of cutting are described in further detail.

[0057] (Bubble diameter peak value)

[0058] The porous elastomer for the capillary core 6 moves the working fluid by the capillary force thereof and assumes the function of driving the loop-type heat pipe 1, and therefore, it is preferable that the diameter of the bubbles of the porous elastomer be small so as to obtain a greater capillary force.

[0059] The diameter of the bubbles of the porous elastomer for the capillary core 6 (radius of the bubbles of the capillary core: rwick) and the capillary force (capillary pressure: ΔPcap) are represented by the following formula 1.

[0060] ΔPcap = 2σcosθ / rwick (Formula 1)

[0061] where σ is the surface tension of the working fluid, and θ is the contact angle of the capillary core and the working fluid.

[0062] As is clear from the above formula 1, the smaller the radius of the bubbles of the capillary core, the greater the capillary pressure. Further, in order for the loop-type heat pipe 1 to operate, the capillary force (capillary pressure: ΔPcap) and the total pressure loss: ΔPtotal should satisfy the following formula 2:

[0063] ΔPcap > ΔPtotal (Equation 2)

[0064] Further, the total pressure loss: ΔPtotal can be calculated by Equation 3 below.

[0065] ΔPtotal = ΔPwick + ΔPgroov + ΔPVL + ΔPcond + ΔPIL + ΔPgrav (Equation 3)

[0066] where ΔPwick is the pressure loss of the capillary wick, ΔPgroov is the pressure loss of the groove, ΔPVL is the pressure loss of the vapor tube, ΔPcond is the pressure loss of the condenser, ΔPIL is the pressure loss of the liquid tube, and ΔPgrav is the pressure loss due to gravity.

[0067] As described above, in order to obtain a greater capillary force, it is preferable that the maximum diameter of the bubbles of the porous elastomer be small, and specifically, 50 μm or less is desirable. If the maximum diameter of the bubbles is greater than 50 μm, it is difficult to obtain a capillary force sufficient to drive the loop heat pipe. It is preferable that the maximum diameter of the bubbles be 30 μm or less, and more preferably, the maximum diameter of the bubbles be 10 μm or less.

[0068] When the thickness of the capillary wick is extremely thin, the maximum diameter of the bubbles can function even if it is 1 μm or less or 0.1 μm or less, but as a lower limit value, it is preferable to be 0.1 μm or more.

[0069] Here, the maximum diameter of the bubbles can be calculated by taking an image of a cross section of the porous elastomer using a laser microscope, and measuring the area of the pores by image processing of the image.

[0070] (Porosity)

[0071] The higher the porosity of the porous elastomer used for the capillary wick 6, the more advantageous it is for driving the loop heat pipe 1. Specifically, the porosity of the porous elastomer is preferably 20% or more. If the porosity is less than 20%, it becomes difficult to drive the loop heat pipe 1. More preferably, the porosity is 50% or more. The porosity can be calculated by Equation 4 below.

[0072] Porosity (%) = (solid specific gravity - specific gravity of the porous elastomer) / (solid specific gravity) x 100 (Equation 4)

[0073] (Interconnected pore diameter)

[0074] The communication hole of the capillary core 6 is a portion of the inter-bubble (inter-cell) communication, and is a portion in which the capillary force acts to drive the working fluid. In order to obtain the cooling performance, the diameter of the communication hole (communication hole diameter) is preferably 10 μm or less, and more preferably 5 μm or less. In addition, the average pore diameter of the communication hole is preferably 3 μm or less, and the capillary core 6 itself can more suitably have both a high capillary force and a good permeability.

[0075] However, in the case where the capillary core 6 is extremely thin, the diameter of the communication hole can function even if it is 1 μm or less or 0.1 μm or less.

[0076] The pore diameter of the communication hole is measured by the bubble point method, and the maximum pore diameter obtained is taken as the communication hole diameter.

[0077] Here, the pressure at which the appearance of a bubble is observed is taken as the bubble point by applying air pressure to the porous elastomer which is completely immersed in the test liquid. In addition, by using a test liquid of which the surface tension is known, the communication hole diameter (maximum diameter) is calculated using the following equation 5.

[0078] d = 4σcosθ / ΔP (Equation 5)

[0079] where d is the communication hole diameter (maximum diameter), σ is the surface tension of the working fluid, θ is the contact angle of the capillary core and the working fluid, and ΔP is the pressure loss (bubble point pressure).

[0080] The average diameter of the communication hole can also be obtained by the bubble point method. The average diameter of the communication hole can be obtained by obtaining the pressure (ΔP) at which the pressure-flow curve in the state where the porous elastomer is immersed and the pressure-flow curve (half-dry curve) obtained in the dry state intersect, using the above equation 5.

[0081] (Evaluation of Hydrophilicity)

[0082] The hydrophilicity of the capillary core 6 is measured by the contact angle of water, and is calculated by the θ / 2 method. The long-term stability is evaluated by being left under the atmosphere.

[0083] (Cooling Performance Test)

[0084] The cooling performance test performed on the examples in the main numerical range of the conditions of the above capillary core 6, and the comparative examples outside the numerical range will be described below with reference to the drawings.

[0085] (1) Description of an electronic device (projector) 20 in which a capillary core suitable for use in the cooling performance test is incorporated.

[0086] Figure 4 is a schematic explanatory view showing another example of the loop type heat pipe 1 incorporated in the electronic device 20 according to the present embodiment.

[0087] In addition, Figure 4 Another example of the loop heat pipe 1 shown in FIG. 1 is different from the example shown in FIG. 1 in that a capillary core having an inner diameter slightly larger than that of the cylindrical inner space in the housing (box body) of the evaporator 2 is pressed into the housing of the evaporator. Figure 1

[0088] However, as a cooling means of the electronic device according to the present embodiment, the loop heat pipe 1 shown in FIG. 1 can be used instead of the loop heat pipe shown in FIG. 1, but in the tests of the cooling performance of each of the embodiments and comparative examples described later, the loop heat pipe shown in FIG. 1 was used. Figure 1 Figure 4 Figure 4

[0089] Figure 4 The electronic device 20 shown in FIG. 1 is a projector having an optical unit 21, and is an example of the electronic device to which the present embodiment is applied.

[0090] Here, the electronic device to which the loop heat pipe 1 according to the present embodiment is applied is not limited to the projector. In addition to the projector, it can be applied to various electronic devices such as an image forming apparatus such as a printer, a copier, a facsimile, or a multifunction peripheral thereof, a personal computer, a server, an electronic whiteboard, a television, a Blu-ray recorder, a game machine, and the like.

[0091] In addition, the loop heat pipe 1 and the cooling device according to the present embodiment can also be applied to other than electronic devices. For example, a cooling device that cools a chemical plant having a reaction furnace or the like, or a container attached to an electronic device such as a server rack or a building can also apply the loop heat pipe 1 and the cooling device according to the present embodiment.

[0092] Figure 4 The evaporator 2 (particularly, the heat receiving portion 7) of the loop heat pipe 1 shown in FIG. 1 is arranged in contact with the heat generating portion of the optical unit 21. The evaporator 2 cools the cooling target (the heat generating portion, the optical unit, or the projector) by absorbing heat from the heat generating portion.

[0093] The condenser 3 is arranged in the vicinity of an exhaust fan 22 provided on the side surface of the housing of the projector main body. The exhaust fan 22 discharges air to the outside, and generates an air current around the condenser 3, which cools the condenser 3 and improves the heat dissipation effect of the condenser 3.

[0094] In addition, a supply port 23 is provided on the side surface opposite to the side surface of the housing on which the exhaust fan 22 is provided, and air taken in from the supply port 23 is discharged from the exhaust fan 22 through the projector. In Figure 4 ​​​​In the illustrated example, as the cooling device for cooling the projector, the loop heat pipe 1 and the exhaust fan 22 for improving the heat dissipation effect of the loop heat pipe 1 are provided, and instead of the exhaust fan 22, an air supply fan for supplying air toward the condenser 3 can be provided. In addition, the cooling device can be provided with only the loop heat pipe 1 without the fan.

[0095] (2) Detailed examples and comparative examples are described.

[0096] Figure 5 are explanatory diagrams of various specifications of samples of examples and comparative examples for cooling performance tests, and test results.

[0097] In this test, as shown in Figure 5 , a sample of the example in which the capillary core 6 is made of water-blown silicone rubber. In addition, a sample of the comparative example in which the capillary core 6 is made of water-blown silicone rubber for each of the continuous bubble (composite) and the single bubble, and aluminum for sintering the connection therebetween. Then, as shown in Figure 4 , the manufactured sample is used for a cooling performance test for the loop heat pipe 1 of the projector.

[0098] The bubble shape is observed (photographed) by a laser microscope to confirm the bubble state, and in the case where the bubbles are adjacent to become a composite shape, it is evaluated as "composite", and when it cannot be confirmed, it is evaluated as "single bubble". Figure 6 is a diagram of the bubble state of the sample of the capillary core 6 of Example 1 observed (photographed) by a laser microscope, and it can be confirmed that the bubbles are formed in an adjacent composite shape. Therefore, the bubble state of Example 1 is "composite". Such evaluation is performed for Example 1, 2, Comparative Example 1, 2, 3, 4, 5, 6.

[0099] The diameter range of the bubble and the most frequent value of the bubble diameter are calculated from the bubble diameter distribution and the like by image processing of the image observed by the laser microscope.

[0100] Figure 7 is a curve showing an example of the bubble diameter distribution. The thick solid line indicates the distribution of the water-blown silicone rubber of Examples 1, 2 of the composite bubble, and the thin solid line indicates the distribution of the water-blown silicone rubber of Comparative Example 5 of the single bubble (single bubble). Here, the distribution of the bubble diameter [μm] is expressed by the probability density function, and with respect to the bubble diameter [μm] of the horizontal axis X, the vertical axis Y becomes the relationship of the probability density. The image processing is calculated by screening the number (frequency) of a certain bubble diameter range [μm]. Among all the bubbles existing in the image processing range, the number (probability) of the bubbles existing in a certain bubble diameter range [μm]. From this bubble diameter distribution, the most frequent value of the bubble diameter is calculated.

[0101] In Figure 7In the case of the above, the bubble diameter distribution of the bubbles having a bubble diameter of 32 μm or less is shown, and the number of bubbles having a bubble diameter of 32 μm or more can also be calculated. The minimum value of the bubble diameter range is obtained from the bubble diameter distribution calculated, and the maximum value is obtained from the image taken by the laser microscope as described above, and the area of the void is measured by image processing.

[0102] The void ratio is calculated from the above-described Equation 4. In addition, the connected pore (maximum) diameter is obtained from the bubble point pressure measured by the bubble point method as described above, and is obtained from Equation 5. Specifically, the diameter of the connected pores can be measured using a gas transmission method pore size distribution measuring device (POROMETER 3G manufactured by ANTON PEARL JAPAN Co., Ltd.) capable of measuring the bubble point method according to JIS K3832. The sample for measurement uses Φ25, and the wetting fluid uses POLOFIL. The average diameter of the connected pores is obtained from the pressure (ΔP) at which the pressure-flow curve measured by the bubble point method and the pressure-flow curve (half-dry curve) measured at a flow rate of 1 / 2 in the dry state intersect, using the above-described Equation 5.

[0103] Figure 8 is an example of an image obtained by observing a sample of the capillary core of Example 1 with a scanning electron microscope. The image is enlarged from the image shown in Figure 8 is an image further enlarged from the image shown in Figure 6 observed with a laser microscope. Figure 8 The black holes in the image are connected pores, and it can be confirmed that these connected pores are 5 μm or less.

[0104] "Performance Evaluation"

[0105] The hydrophilicity is measured by the θ / 2 method described above. Specifically, a contact angle measuring device (Drop Master 500 manufactured by Kyowa Interface Science Co., Ltd.) can be used. The change in the hydrophilicity (contact angle) from the initial to the 3-month period is evaluated.

[0106] Regarding the close contact property, the heat receiving portion 7 provided with the capillary core 6 is observed with an X-ray CT, and if there is no gap between the heat receiving portion 7 (housing) and the capillary core 6, the close contact property is evaluated as "O", and if there is a gap, the close contact property is evaluated as "X".

[0107] As a cooling performance test, the cooling performance, the close contact property of the capillary core, and the heat resistance of the capillary core are evaluated.

[0108] The cooling performance is evaluated by applying 100 W of power to the projector, and measuring the evaporation portion temperature after 10 minutes. This evaluation is repeated for 100 cycles over a period of 3 months, and the evaporation portion temperatures of the 100th cycle are ranked in order from low to high.

[0109] The comprehensive evaluation was made from the viewpoints of cooling performance, adhesion, thermal insulation, and cost, and the results were evaluated as O, Δ, and X.

[0110] (Examples 1 and 2)

[0111] In Examples 1 and 2, water-blown silicone rubber materials selected active agents and polymers were used to form composite bubbles (complexes), and after plasma treatment as a hydrophilic treatment, hydrophilic polymers were impregnated. The hydrophilic polymer was a polymer brush structure, and was a hydrophilic polymer having a betaine group with a molecular weight of 10,000 or more. In Examples 1 and 2, the stirring conditions during emulsion preparation were changed to adjust the maximum pore diameter of the communication holes to 5 μm and 10 μm, respectively.

[0112] In both Examples 1 and 2, very good cooling performance was obtained in the cooling performance test. Moreover, the hydrophilicity did not change from the initial stage after 3 months, and long-term stable hydrophilicity was obtained. In particular, the cooling performance of Example 1, in which the maximum pore diameter of the communication holes was 5 μm, ranked first.

[0113] The reason why such good cooling performance was obtained can be considered to be the following. First, in Example 2, the water-blown silicone rubber was subjected to a dehydration reaction of the water phase while the rubber was crosslinked at the time of secondary heating, and since it was a composite bubble, the communication holes between the bubbles were effectively formed, and the porosity was high. Therefore, the working fluid could be caused to permeate well to the capillary core 6. In addition, the diameter of the communication holes (maximum) in Examples 1 and 2 was 10 μm or less, and therefore, it is considered that a plurality of fine communication holes were formed, and a capillary core having a high capillary force was formed. As a result, the working fluid could be caused to circulate well, the cooling efficiency could be improved, and the cooling performance could be improved. Since the diameter of the communication holes (maximum) in Example 1 was 5 μm, a higher capillary force could be obtained, the cooling efficiency could be improved, and therefore, the cooling performance ranked first.

[0114] Furthermore, by using water, which has a high latent heat, as the working fluid, much heat could be taken away at the time of changing from the liquid phase to the gas phase, and the cooling performance could be improved.

[0115] Further, in Embodiments 1 and 2, the hydrophilic polymer having a polymer brush structure is used as the hydrophilic polymer, and therefore, the deterioration of the hydrophilicity due to the disappearance or the like of the segment containing the hydrophilic group is more suppressed. In addition, since the hydrophilic group is the betaine group, the contact angle with water is 5° or less, and therefore, a very high hydrophilicity is obtained. As a result, the working fluid is circulated well, and a high cooling efficiency is obtained, and the cooling performance after three months is improved.

[0116] Further, the adhesion evaluation of Embodiments 1 and 2 is "O". This can be considered to be because the silicone rubber of the porous elastomer is used as the capillary core, and the inner dimension of the case (housing) of the heating portion 7 of the evaporation portion 2 with respect to the capillary core 6 is slightly large, and therefore, a high adhesion is obtained. In addition, by obtaining a high adhesion, the heat transfer efficiency to the capillary core 6 is improved, and therefore, the cooling efficiency is improved. This can also be considered to be a main reason for improving the cooling performance of Embodiments 1 and 2. Even if the cooling performance and the cost are considered, Embodiments 1 and 2 are comprehensively evaluated as "O".

[0117] (Comparative Example 1)

[0118] In Comparative Example 1, the capillary core uses a hydrophilic polymer which is not a polymer brush structure, and which is a low-molecular polymer having a molecular weight of 10,000 or less and not having a betaine group, and is the same as Embodiment 1 except for this.

[0119] In Comparative Example 1, the contact angle after three months returns to the same degree as before the treatment. Therefore, in the initial stage, the working fluid water enters well into the inside of the capillary core, and the cooling performance is good, but after three months, the water does not enter well into the inside of the capillary core, and in the cooling evaluation after three months, the operation is not possible. As a result, the cooling performance is the lowest, and the comprehensive evaluation is also "X".

[0120] This is because the low-molecular hydrophilic polymer covers the void surface in Comparative Example 1. It can be considered that the low-molecular hydrophilic polymer is low-molecular, and the long-term bleeding occurs, and the long-term stability of the hydrophilicity is poor. Further, the low-molecular hydrophilic polymer does not have a polymer brush structure, and therefore, the long-term stability of the hydrophilicity is poorer.

[0121] (Comparative Example 2)

[0122] In Comparative Example 2, the capillary core is coated with silica instead of the hydrophilic polymer, and is the same as Embodiment 1 except for this.

[0123] Comparative Example 2 also had the same contact angle after 3 months as before the treatment. Therefore, water of the working fluid could not enter the inside of the capillary core, and in the cooling evaluation after 3 months, it could not function, and thus, the cooling performance was the worst, and the comprehensive judgment was also "X".

[0124] It can be considered that this is because in Comparative Example 2, the coating was performed with silica that is not a high-molecular hydrophilic polymer, and thus, unlike the hydrophilic polymer, it peeled off from the surface of the rubber immediately. As a result, the hydrophilicity could not be maintained over time, and the contact angle after 3 months returned to the same degree as before the treatment.

[0125] (Comparative Example 3)

[0126] The hydrophilic treatment of the capillary core of Comparative Example 3 was performed only with plasma treatment, and was the same as Example 1 except for this.

[0127] The contact angle after 3 months of this Comparative Example 3 also returned to the same degree as before the treatment. Therefore, water of the working fluid could not enter the inside of the capillary core, and in the cooling evaluation after 3 months, it could not function, and thus, the cooling performance was the worst, and the comprehensive judgment was also "X".

[0128] It can be considered that this is because in Comparative Example 3, only plasma treatment was performed, and no hydrophilic coating was applied to the surface of the void. Therefore, it can be considered that the disappearance of the segment containing the hydrophilic group due to the plasma treatment, and the return of the hydrophilicity to the original state due to the embedding and the like. As a result, the hydrophilicity could not be maintained over time, and the contact angle after 3 months returned to the same degree as before the treatment.

[0129] (Comparative Example 4)

[0130] The capillary core of Comparative Example 4 was not subjected to hydrophilic treatment, and in addition, ethanol was used as the working fluid. Except for this, it was the same as Example 1.

[0131] In this Comparative Example 4, the cooling efficiency was low compared to the examples, and in the cooling performance test, it was significantly worse compared to the examples. This is because the comparative example used ethanol, which has a smaller latent heat than water, as the working fluid, and thus, less heat was taken away when changing from the liquid phase to the gas phase. Therefore, the cooling efficiency was lower compared to the examples, and in the cooling performance test, it was significantly deteriorated compared to the examples.

[0132] In Comparative Example 4, since ethanol was used as the working fluid, and no hydrophilic treatment was performed, there was no influence caused thereby.

[0133] (Comparative Example 5)

[0134] Comparative Example 5 uses a water-blown silicone rubber material, so that the capillary core becomes a single-bubble bubble (single bubble). The bubble is in the size range of 0.1 μm or more and 50 μm or less, but is not a composite bubble, and the bubble diameter is larger than that of the examples, so that the porosity can only be increased to 60%, which is lower than that of Example 1. Other than this, it is the same as Example 1.

[0135] The contact angle of this Comparative Example 5 also returns to the same degree as before the treatment after 3 months. Therefore, the water of the working fluid cannot enter the inside of the capillary core, and in the cooling evaluation after 3 months, it cannot function, so that the cooling performance is the worst, and the comprehensive judgment is also "X".

[0136] The reason why the contact angle returns to the same degree as before the treatment after 3 months is not certain, but it can be considered that the contact angle returns to the same degree as before the treatment after 3 months due to the following reasons. That is, Comparative Example 5 is a single-bubble bubble, and the porosity is lower than that of the examples. Therefore, the hydrophilic polymer does not sufficiently penetrate into the inside of the capillary core, does not sufficiently penetrate into the inside of the communication hole, and cannot form a hydrophilic film of the polymer brush structure until the inside of the communication hole. The inability to form a hydrophilic film of the polymer brush structure until the inside of the communication hole is related to the peeling of the hydrophilic film, and the contact angle returns to the state before the treatment after 3 months.

[0137] In addition, Comparative Example 5 has a higher evaporation portion temperature than Examples 1 and 2 from the initial stage, and has a poor cooling efficiency. This is because the porosity of Comparative Example 5 is lower than that of Examples 1 and 2, so that the permeability of the working fluid to the capillary core is lower than that of Examples 1 and 2. In addition, the hydrophilic polymer does not sufficiently penetrate into the inside of the capillary core, does not sufficiently penetrate into the inside of the communication hole, and does not form a hydrophilic film inside. Therefore, the hydrophilicity inside is insufficient, and the cooling efficiency is poor compared to Examples 1 and 2.

[0138] (Comparative Example 6)

[0139] Comparative Example 6 uses an aluminum sintered sample (sintered interconnection) as the capillary core. By controlling the sintering conditions or the particle diameter, the same porosity [%] as Example 1 is obtained, and the pore size range is 0.1 μm or more and 50 μm. For Comparative Example 6, it is confirmed that there is a gap between the shell (heated portion 7) and the capillary core 6, and the tightness evaluation is "X". It can be considered that this is due to the fact that both the shell and the capillary core 6 are hard materials. Between such hard materials, in order to make them tightly attached without gaps, very high precision is required for both the shell and the capillary core, and it is very difficult to process in order to eliminate the gap, and in addition, the unit price becomes high in order to mass-produce.

[0140] In addition, Comparative Example 6 was inferior to the results of Examples 1 and 2 even in terms of cooling performance. This is because, as in Comparative Example 3, the contact angle returned to the original degree after 3 months due to the disappearance of the hydrophilic group by only the plasma treatment. As a result, the cooling performance evaluation was inferior to the results of Examples 1 and 2. Moreover, Comparative Example 6 was inferior in the adhesion to the housing, and the cooling efficiency was reduced, which also resulted in the inferior result of the cooling performance evaluation. Therefore, the overall evaluation was "X".

[0141] Figure 9 is a graph showing the change in the hydrophilicity (contact angle) of the capillary core from the initial to 3 months in Examples 1 and Comparative Examples 1, 3, and 4.

[0142] As shown in Figure 9 Comparative Example 3 in which only the plasma treatment was performed deteriorated in the hydrophilicity within several days. In Comparative Example 1 in which the envelope silica was used, the change in the hydrophilicity was deviated. It is considered that this is because the silica peeled from the surface of the rubber, and the hydrophilicity evaluation result was deviated due to the difference in the residual rate of the silica in the measurement site.

[0143] On the contrary, in Example 1, it was known that the hydrophilicity (contact angle) hardly changed even after 3 months, and the stable hydrophilicity could be ensured over time.

[0144] From the results of the cooling performance test using the samples of Examples 1 and 2 and Comparative Examples 1 to 6, it was confirmed that the following effects were obtained depending on various factors such as the bubbles, the communication holes, and the combination of the hydrophilic treatment present in the cross section obtained when cutting the capillary core 6 constituting the present embodiment.

[0145] First, second, and third elements: (elements of Examples 1 and 2)

[0146] The surface of the bubbles or the communication holes of Examples 1 and 2 was covered with the hydrophilic polymer having a molecular weight of 10,000 or more, and it was a composite bubble (first element). Further, the hydrophilic polymer was in a polymer brush structure, and it was a hydrophilic polymer having a molecular weight of 10,000 or more having a betaine group (second element). In addition, the bubbles present in the cross section were in the size range of 0.1 μm or more and 50 μm or less, and among the composite bubbles, the bubbles having a diameter of 5 μm or more and 10 μm or less were present the most (third element).

[0147] Due to the first element described above, the permeability to the capillary core when water is used as the working fluid can be stably improved over a long period of time, and the cooling performance of the loop type heat pipe 1 can be further improved. Further, by having the second element, the hydrophilicity and the long-term stability of the hydrophilicity can be further improved, and the permeability to the capillary core when water is used as the working fluid can be further stabilized over a long period of time.

[0148] Further, since the third element is provided, the capillary force and the permeability to the capillary wick can be improved. As a result, in the above cooling performance evaluation, a high cooling performance can be obtained.

[0149] Here, the hydrophilic polymer of Comparative Example 1 is not a polymer brush structure, does not have a betaine group, and has a molecular weight of less than 10,000, which deviates from the first element. Comparative Example 2 is not a hydrophilic polymer, but uses silica, which deviates from the first element. Comparative Example 3 deviates from the first element because only plasma treatment is performed. In addition, Comparative Example 4 uses ethanol as the working fluid, which is different from Examples 1 and 2. Comparative Example 5 is a single bubble, which deviates from the first element. In the case of ethanol of Comparative Example 4, even after 3 months of operation of the working fluid, the cooling performance ranked third among Comparative Examples 4. The hydrophilicity of the aluminum surface of Comparative Example 6 deteriorated, but was originally better than that of the silicone rubber, and thus the cooling performance ranked fourth. The contact angle returned to the original after 3 months, and Comparative Examples 1, 2, 3, and 5 were the worst.

[0150] From these comparisons, it can be confirmed that, as a composite bubble, by coating the void surface with a hydrophilic polymer of a high molecule having a molecular weight of 10,000 or more, the hydrophilicity can be maintained for a long period of time, and the combination of the working fluid with water can affect the cooling performance ranking. Furthermore, by having a betaine group, the hydrophilic polymer of a high molecule becomes a polymer brush structure, and the hydrophilicity can be further maintained, and the hydrophilicity can be maintained for a long period of time. In addition, as can be seen from Examples 1 and 2 and Comparative Example 5, the composite bubble can be more effectively subjected to hydrophilic treatment.

[0151] Fourth Element: (Element of Examples 1 to 2 and Comparative Examples 1 to 5)

[0152] The porous body is composed of a foamed silicone rubber, specifically, a water-foamed silicone rubber in Examples 1 to 2 and Comparative Examples 1 to 5, which is the fourth element. (Effects of Examples 1 to 2 and Comparative Examples 1 to 5)

[0153] The capillary wick 6 is a porous elastomer such as a foamed silicone rubber, and can ensure the tightness with the housing (heat receiving portion 7).

[0154] Here, Comparative Example 6 is composed of a metal (aluminum), and lacks elasticity, and in order to make the tightness good, high-precision processing is required.

[0155] The above describes the present embodiment with reference to the drawings, but the specific configuration is not limited to the structure of the loop-type heat pipe 1 provided with the above-described capillary wick 6 of the present embodiment, and design changes and the like can be made within the scope of the gist of the present application.

[0156] For example, a material such as Figure 1 , Figure 2 , Figure 4The loop heat pipes 1 of the illustrated embodiments each have a structure in which one evaporator 2 and one condenser 3 are provided, but the structure of the loop heat pipe of the present embodiment is not limited to this structure. It is also possible to apply a structure in which two or more loop heat pipes are provided in at least one of the evaporator 2 and the condenser 3.

[0157] In addition, a hydrophilic polymer film is used Figure 1 , Figure 2 , Figure 4 The loop heat pipes 1 of the illustrated embodiments each have a structure in which one evaporator 2 and one condenser 3 are provided, but the structure of the loop heat pipe of the present embodiment is not limited to this structure. It is also possible to apply a structure in which two or more loop heat pipes are provided in at least one of the evaporator 2 and the condenser 3.

[0158] The above description is an example, and each of the following embodiments has a unique effect.

[0159] (Embodiment 1)

[0160] A capillary core is a porous elastomer capillary core in which a liquid-phase working fluid is permeated, which is provided inside an evaporator that changes the liquid-phase working fluid into a gas-phase, and in which the porous elastomer includes a composite void having a communication hole at a portion in which a plurality of spherical voids partially overlap each other, and a surface of the void of the porous elastomer is covered with a hydrophilic polymer film.

[0161] As a result, as described in the above cooling performance test, the plurality of spherical voids have the communication hole at the portion in which the plurality of spherical voids partially overlap each other, forming the composite void, and the surface of the porous elastomer and the surface of the void can obtain stable hydrophilicity for a long period of time by covering the surface of the void of the porous elastomer with the hydrophilic polymer film. As a result, the hydrophilic working fluid such as water can be permeated into the capillary core for a long period of time, and the circulation of the working fluid can be maintained for a long period of time. As a result, the evaporator using the hydrophilic working fluid can maintain high cooling efficiency for a long period of time.

[0162] (Embodiment 2)

[0163] In Embodiment 1, the hydrophilic polymer film of the hydrophilic polymer or the like includes a polymer brush structure having a hydrophilic group.

[0164] As a result, high hydrophilicity can be stably maintained over time.

[0165] (Embodiment 3)

[0166] In Embodiment 2, the hydrophilic group is a betaine group.

[0167] As a result, as described in the above embodiments, high hydrophilicity can be obtained, and the hydrophilic working fluid such as water can be well permeated into the capillary core.

[0168] (Embodiment 4)

[0169] In any one of aspects 1 to 3, the hydrophilic polymer has a molecular weight of 10,000 or more.

[0170] Thus, as described in the cooling performance test above, there is no adverse effect due to bleeding, and therefore, stable hydrophilicity can be obtained for a long period of time, and the hydrophilic working fluid such as water can be caused to permeate into the capillary core for a long period of time.

[0171] (Aspect 5)

[0172] In any one of aspects 1 to 4, the maximum pore diameter of the communication holes is 5 μm or less.

[0173] Thus, as described in the aspects, the capillary force of the capillary core can be increased.

[0174] (Aspect 6)

[0175] In any one of aspects 1 to 5, the average pore diameter of the communication holes is 3 μm or less.

[0176] Thus, as described in the aspects, the capillary force of the capillary core can be increased.

[0177] (Aspect 7)

[0178] In any one of aspects 1 to 6, the spherical voids such as bubbles have a diameter of 0.1 μm or more and 50 μm or less.

[0179] Thus, as described in the aspects, a good capillary force can be obtained.

[0180] (Aspect 8)

[0181] In any one of aspects 1 to 7, the most frequent value in the diameter distribution of the spherical voids such as bubbles is 5 μm or more and 10 μm or less.

[0182] Thus, as described in the aspects, a good capillary force can be obtained.

[0183] (Aspect 9)

[0184] In any one of aspects 1 to 8, the porous elastomer is a water-blown silicone rubber.

[0185] Thus, as described in the aspects, the capillary core can obtain a good capillary force, and can be tightly attached to the housing.

[0186] (Aspect 10)

[0187] An evaporator such as an evaporation section 2, which internally houses a capillary core and causes a working fluid in a liquid phase to change into a gas phase, uses the capillary core described in any one of aspects 1 to 9 as the capillary core.

[0188] Thus, good cooling performance can be obtained.

[0189] (Mode 11)

[0190] A loop heat pipe including:

[0191] An evaporator such as the evaporating section 2, which receives heat from the outside to evaporate the working fluid from the liquid phase to the gas phase; and

[0192] A condenser such as the condensing section 3, which condenses the working fluid in the gas phase discharged from the evaporator to the liquid phase,

[0193] As the evaporator, the evaporator of Mode 10 is used.

[0194] Thus, good cooling performance can be obtained.

[0195] (Mode 12)

[0196] In Mode 11, the working fluid is water.

[0197] Thus, by using water, which has high latent heat, as the working fluid, high cooling performance can be obtained.

[0198] (Mode 13)

[0199] A cooling device provided with a loop heat pipe, as the loop heat pipe, the loop heat pipe of Mode 11 or 12 is used.

[0200] Thus, the cooling object can be cooled well.

[0201] (Mode 14)

[0202] An electronic device 20 such as a projector provided with a cooling means, as the cooling means, the cooling device of Mode 13 is used.

[0203] Thus, the heat generating section of the electronic device 20 such as a projector can be cooled well.

[0204] (Mode 15)

[0205] A capillary core manufacturing method of manufacturing a capillary core of a porous elastomer, which is provided in an evaporator such as the evaporating section 2, which changes the working fluid in the liquid phase to the gas phase, and through which the working fluid in the liquid phase permeates, includes a step of forming a composite void having a communication hole in a portion in which a plurality of spherical voids partially overlap each other in the porous elastomer, and a coating step of coating a hydrophilic polymer film on the surface and the voids of the porous elastomer.

[0206] Thus, the hydrophilicity of the void surface can be stabilized for a long period of time, and a capillary core through which the working fluid of water permeates well can be manufactured.

[0207] (Mode 16)

[0208] In Mode 15, a surface treatment step of forming radicals in the surface and voids of the porous elastomer is included, and after the surface treatment step, a coating step is performed.

[0209] Thus, the hydrophilicity of the void surface can be stabilized for a long period of time, and a capillary core that allows the working fluid of water to permeate well can be produced.

Claims

1. A capillary core provided in the inside of an evaporator that changes a working fluid in a liquid phase to a gas phase, the capillary core being a porous elastomer through which the working fluid in the liquid phase permeates, the capillary core characterized by: the porous elastomer including a composite void having a communication hole in a portion in which a plurality of spherical voids partially overlap each other, a surface of a void of the porous elastomer being subjected to a radical-forming surface treatment, and the surface of the void on which the radical is formed being covered with a hydrophilic polymer film.

2. The capillary core according to claim 1, characterized in that: the hydrophilic polymer film contains a polymer brush structure having a hydrophilic group.

3. The capillary core according to claim 2, characterized in that: the hydrophilic group is a betaine group.

4. The capillary core according to any one of claims 1 to 3, characterized in that: the hydrophilic polymer film has a molecular weight of 10,000 or more.

5. The capillary core according to any one of claims 1 to 3, characterized in that: a maximum pore diameter of the communication hole is 5 μm or less.

6. The capillary core according to any one of claims 1 to 3, characterized in that: an average pore diameter of the communication hole is 3 μm or less.

7. The capillary core according to any one of claims 1 to 3, characterized in that: a diameter of the spherical void is 0.1 μm or more and 50 μm or less.

8. The capillary core according to any one of claims 1 to 3, characterized in that: a most frequent value in a diameter distribution of the spherical void is 5 μm or more and 10 μm or less.

9. The capillary core according to any one of claims 1 to 3, characterized in that: the porous elastomer is a foamed silicone rubber.

10. An evaporator that houses a capillary core in the inside thereof, the capillary core changing a working fluid in a liquid phase to a gas phase, the evaporator characterized by: using the capillary core according to any one of claims 1 to 9 as the capillary core.

11. A loop heat pipe including: an evaporator that receives heat from the outside to evaporate a working fluid from a liquid phase to a gas phase; and a condenser that condenses the working fluid in the gas phase discharged from the evaporator to the liquid phase, the loop heat pipe characterized by: using the evaporator according to claim 10 as the evaporator.

12. The loop heat pipe according to claim 11, characterized in that: the working fluid is water.

13. A cooling device provided with a loop heat pipe, the cooling device characterized by: using the loop heat pipe according to claim 11 or 12 as the loop heat pipe.

14. An electronic device provided with a cooling device, the electronic device characterized by: using the cooling device according to claim 13 as the cooling device.

15. A capillary core manufacturing method that manufactures a capillary core provided in the inside of an evaporator that changes a working fluid in a liquid phase to a gas phase, the capillary core being a porous elastomer through which the working fluid in the liquid phase permeates, the capillary core manufacturing method characterized by including: a step of forming the porous elastomer to have a composite void having a communication hole in a portion in which a plurality of spherical voids partially overlap each other, ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ a surface treatment step of forming radicals in the surface and voids of the porous elastomer, a coating step of coating a hydrophilic polymer film in the surface and voids of the porous elastomer after the surface treatment step, the hydrophilic polymer film includes a polymer brush structure having a hydrophilic group.

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