Wick, evaporator, loop type heat pipe, cooling device, electronic device, and wick manufacturing method

Abstract

To provide a wick capable of enhancing long-term stability of wick hydrophilicity, and to provide a looped heat pipe, a cooler, an electronic device, and a wick manufacturing method.SOLUTION: A wick is a porous elastic body that is provided inside an evaporator that changes liquid-phase working fluid to a vapor phase, and through which the liquid-phase working fluid penetrates. The porous elastic body has a composite void having a communication hole in a portion where a plurality of spherical voids partially overlap each other. Also, the surfaces of the voids of the porous elastic body are coated with a hydrophilic polymer having a betaine group of a polymer brush structure and a molecular weight of 10,000 or more.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Conventionally, a wick made of a porous elastic body provided inside an evaporator that changes a liquid-phase working fluid into a gas phase and into which the liquid-phase working fluid penetrates is known.

[0003] Patent Document 1 describes using foamed silicone rubber, which is a porous elastic body, as the wick. Further, Patent Document 1 describes using water as the working fluid.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when water or a hydrophilic fluid is used as the working fluid, there is room for improvement in the long-term stability of the hydrophilicity of the wick.

Means for Solving the Problems

[0005] In order to solve the above-described problems, the present invention provides a wick made of a porous elastic body provided inside an evaporator that changes a liquid-phase working fluid into a gas phase and into which the liquid-phase working fluid penetrates. The porous elastic body has a composite void having communication holes in a portion where a plurality of spherical voids partially overlap each other. The surface of the voids of the porous elastic body has been subjected to a surface treatment that forms radicals, and the surface of the voids where the radicals are formed is coated with a hydrophilic polymer film. The porosity of the porous elastic body is 70 % and is characterized by the above.

Effects of the Invention

[0006] According to the present invention, the long-term stability of the wick hydrophilicity can be enhanced.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0008] Hereinafter, as a cooling means including an evaporator provided with a wick to which the present invention is applied and a condenser, an embodiment of a loop heat pipe (hereinafter referred to as loop heat pipe 1) will be described with reference to the drawings as appropriate. Here, in each drawing for explaining the present embodiment, components such as members and components having the same function or shape are given the same reference numerals as much as possible for discrimination. Also, for the components given the same reference numerals, the description will be omitted as appropriate after being explained once. Fig. 1 is a schematic explanatory diagram showing an example of the loop heat pipe 1 according to the present embodiment, and Fig. 2 is a diagram showing a virtual cross-section when cut along the a-a cross-section indicated by the dashed line in Fig. 1.

[0009] The loop heat pipe 1 shown in Fig. 1 has a working fluid made of a condensable fluid enclosed therein and comprises the following components. The loop heat pipe 1 includes an evaporation section 2 that absorbs heat from a heat generating section and evaporates the working fluid from the liquid phase to the gas phase, and a condensation section 3 that condenses the gas-phase working fluid guided from the evaporation section 2 into the liquid phase. It also includes a vapor pipe 4 that allows the gas-phase working fluid to flow from the evaporation section 2 to the condensation section 3, and a liquid pipe 5 that allows the liquid-phase working fluid to flow from the condensation section 3 to the evaporation section 2.

[0010] The evaporation section 2 is composed of a heat receiving section 7 in which a wick 6 is accommodated and a reservoir section 8 that stores the liquid-phase working fluid. One end of the vapor pipe 4 is connected to the heat receiving section 7, and one end of the liquid pipe 5 is connected to the reservoir section 8. Also, the other ends of the vapor pipe 4 and the liquid pipe 5 are both connected to the condensation section 3. The condensation section 3 is composed of a stainless steel pipe 31 provided with a large number of thin aluminum fins 32 on its outer peripheral surface.

[0011] The wick 6 is a porous body. Also, a plurality of grooves 10 are provided on the bottom surface of the wick 6 in Fig. 1 in the direction from the end on the vapor pipe 4 side to the opposite side. The plurality of grooves 10 are provided at equal intervals at the bottom of the wick 6 as shown in Fig. 2, which shows a virtual cross-section when cut along the a-a cross-section indicated by the dashed line in Fig. 1. Here, in Fig. 2, the dimensions of the grooves 10 are drawn at a ratio larger than the actual size. Also, the thickness of the wick 6 is set to a dimension slightly larger than the inner dimension of the housing of the heat receiving section 7 of the evaporation section 2.

[0012] By setting the thickness of the wick 6 as described above, when the wick 6 is accommodated in the heat receiving section 7, the wick 6 is in close contact with the inner surface of the heat receiving section 7. Also, because the wick 6 is in close contact with the heat receiving section 7, the heat of the heat generating section is efficiently transmitted to the wick 6 through the housing of the heat receiving section 7. On the other hand, in the portion where the grooves 10 are provided, a space is formed between the housing of the heat receiving section 7.

[0013] Since the wick 6 is composed of a porous body, that is, a porous material, the liquid-phase working fluid stored in the reservoir portion 8 penetrates into the wick 6 by capillary action. Due to this capillary action, the wick 6 also serves as a pump that sends the liquid-phase working fluid from the condensation portion 3 to the evaporation portion 2.

[0014] As the working fluid, condensable fluids such as water, alcohol, acetone, and alternative refrigerants are used. In particular, by using water with a high latent heat as the working fluid, high cooling performance can be obtained, which is preferable. Also, the working fluid is preferably one with good wettability with the wick 6 so that it can easily penetrate into the wick 6. The wettability can be measured by the contact angle between the wick 6 and the working fluid. If the contact angle is 40 [°] or more, the working fluid cannot penetrate into the wick 6, so the contact angle needs to be less than 40 [°]. If the contact angle is less than 10 [°], more preferably 5 [°] or less, the capillary action becomes more effective, which is more preferable.

[0015] In the loop heat pipe 1 according to the present embodiment, when the heat from the heat-generating portion is transmitted to the liquid-phase working fluid in the wick 6 through the housing of the evaporation portion 2 (heat-receiving portion 7), the working fluid evaporates and changes to the gas phase due to that heat. The evaporated working fluid that has changed to the gas phase is sent to the vapor pipe 4 through the groove 10. Then, the gas-phase working fluid is sent to the condensation portion 3 through the vapor pipe 4.

[0016] In the condensation portion 3, the heat of the working fluid passing through the inside (pipe 31) is released to the outside through the fins 32, so that the temperature of the working fluid decreases and it condenses, changing from the gas phase to the liquid phase. The working fluid that has changed to the liquid phase moves to the evaporation portion 2 through the liquid pipe 5 and penetrates again into the wick 6 provided inside the heat-receiving portion 7 from the reservoir portion 8 by capillary action. By such circulation of the working fluid, the heat of the heat-generating portion is continuously released to the outside, and the object to be cooled is cooled.

[0017] Here, regarding the problem of a loop heat pipe with a wick provided inside a conventional evaporator, an explanation will be given using a figure. FIG. 3 is a schematic explanatory diagram of a conventional general loop heat pipe 100. Generally, as shown in FIG. 3, the loop heat pipe 100 includes an evaporation section 102 that receives heat from the outside and evaporates the working fluid from the liquid phase to the gas phase, and a condensation section 103 that dissipates heat to the outside and condenses the working fluid from the gas phase to the liquid phase. Further, it also 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-phase working fluid to flow from the condensation section 103 to the evaporation section 102.

[0018] Inside the evaporation section 102, a wick 106 made of a porous body (porous material) is accommodated, and the liquid-phase working fluid sent from the liquid pipe 105 penetrates the fine pores of the wick 106 by capillary action and oozes out to the outer surface of the wick 106. At this time, the heat from the heat-generating section (object to be cooled) in contact with the evaporation section 102 is transmitted to the wick 106 through the housing of the evaporation section 102, and the working fluid evaporates and changes to the gas phase due to that heat. Then, the working fluid that has changed to the gas phase moves to the condensation section 103 through the vapor pipe 104.

[0019] In the condensation section 103, the heat of the working fluid is released to the outside, so that the temperature of the working fluid decreases and changes to the liquid phase. Then, the working fluid that has changed to the liquid phase moves to the evaporation section 102 through the liquid pipe 105 and penetrates into the wick 106 again. In this way, in the loop heat pipe 100, by utilizing the phase change of the working fluid, circulating the working fluid, and transferring the heat absorbed in the evaporation section 102 to the condensation section 103, the object to be cooled can be efficiently cooled. Here, in order to improve the cooling efficiency, it is necessary to ensure the adhesion to the evaporation section 102, circulate the working fluid by the capillary force of the wick 106, and the wick 106 requires high permeability in order to minimize the pressure loss.

[0020] As the wick, for example, a porous sintered compact formed by filling aluminum fibers and a porous elastic body such as foamed silicone rubber can be used. When the wick is constituted by a porous sintered compact, high dimensional accuracy is required to ensure adhesion to the housing, resulting in high costs. Therefore, it is preferable that the wick 6 is constituted by a porous elastic body. By constituting the wick 6 with a porous elastic body, a high elastic force can be obtained, so that even if the dimensional accuracy is not high, it can be satisfactorily adhered to the housing (heat receiving part 7) of the evaporation part 2, and the cost of the device can be reduced. Further, by constituting the wick 6 with a porous elastic body, high adhesion can be obtained. As a result, the heat transfer efficiency from the housing of the evaporation part 2 to the wick 6 is favorably obtained, and the cooling performance of the loop heat pipe 1 is improved.

[0021] Also, as described above, ensuring the high adhesion of the wick 6 and suppressing the collapse of local pores during post-processing can be achieved only by making the wick 6 a porous elastic body. For this reason, if post-processing of a transport groove (groove) such as the groove 10 for transporting the working fluid (evaporating refrigerant) can be omitted, further reduction of the manufacturing cost is possible.

[0022] Incidentally, when the loop heat pipe 1 is used for applications that require high cooling performance, it is preferable to use water with high latent heat as the working fluid. However, when water is used as the working fluid, a porous elastic body such as foamed silicone rubber lacks hydrophilicity. Therefore, surface treatment is generally performed to impart hydrophilicity, but there is a risk that the hydrophilicity deteriorates over time due to reasons such as the disappearance and infiltration of segments containing hydrophilic groups, resulting in a decrease in cooling performance.

[0023] Therefore, in the present embodiment, the surface of the voids of the porous elastomer is coated with a hydrophilic polymer. By coating the surface of the voids with a hydrophilic polymer as the hydrophilic polymer, hydrophilicity can be stabilized over a long period of time, and high cooling performance can be maintained. In addition, even when a fluid having hydrophilicity similar to water, for example, an alcohol such as ethanol having a hydrophilic substituent is used, the working fluid can be circulated efficiently. The above-mentioned polymer refers to a polymer having a molecular weight of 10,000 or more.

[0024] Hereinafter, an example of the wick 6 which is a characteristic part of the present embodiment will be described in detail. As described above, the wick 6 used in the loop heat pipe 1 according to the present embodiment is composed of a porous elastomer such as foamed silicone rubber. Although various manufacturing methods of the wick composed of such an elastic porous elastomer can be considered, the porous elastomer in the present embodiment can be obtained by applying, for example, the technology proposed as water-foamed silicone rubber.

[0025] Specifically, a water-foamed silicone rubber composition in which an activator or an aqueous phase additive is selected so as to form composite bubbles is used, and stirring is performed so that the spherical voids (bubbles) present in the cross section obtained when the foam formed by taking is cut exist as follows. Stirring is performed so that the bubbles present in the cross section have a size in the range of 1 [μm] or more and 50 [μm] or less, and the largest number of bubbles having a size in the range of 5 [μm] or more and 10 [μm] or less are present.

[0026] More specifically, the above-mentioned porous elastomer is obtained by mixing a catalyst, a surfactant, and a crosslinking agent with a commercially available two-component liquid silicone rubber. Therein, a mixed solution in which additives, fillers, dispersants, etc. are mixed with water (alcohol is added as necessary) to have the same viscosity as the liquid silicone rubber is combined and stirred to prepare an emulsion composition. The liquid silicone rubber is preferably considered for emulsifiability with water and has a specific gravity of 1.00 to 1.05 [g / cm 3 is preferred.

[0027] Here, the blending ratio of the liquid silicone rubber and the mixed solution varies depending on the desired porosity. For example, when the blending ratio of the liquid silicone rubber and the mixed solution is 1:1, fine particulate water in the emulsion evaporates to form voids, so a foam with a porosity of 50% or more can be obtained.

[0028] For the emulsion, a homogenizer or a stirrer with ultrasonic treatment as required is used, and various stirring conditions such as stirring means, stirring time, and stirring speed (for example, 300 - 1500 [rpm]) are adjusted so as to obtain a bubble size distribution that satisfies the above-mentioned conditions. Thereafter, the prepared emulsion composition is filled into a mold, and primary heating is performed to cure the silicone rubber without evaporating the water in the emulsion composition by heating.

[0029] Here, the heating temperature is in the range of 80 - 130 [°C], and the heating time is in the range of 30 - 120 minutes. A heating temperature of 90 - 110 [°C] and a heating time of 60 - 90 minutes are desirable. Next, secondary heating is performed to remove water from the foam after the primary heating. The heating temperature is in the range of 150 - 300 [°C], and the heating time is in the range of 1 - 24 hours. A heating temperature of 200 - 250 [°C] and a heating time of 3 - 8 hours are desirable. By performing such secondary heating, water is removed from the porous elastic body, and composite bubbles formed by spherical bubbles partially overlapping each other are connected to make the bubbles of the interconnected type, and at the same time, the final curing of the silicone rubber is completed.

[0030] Next, for the purpose of achieving dimensional accuracy and removing the skin layer as required, the outer surface of the wick is ground by several [μm] to several [mm]. For example, it is ground by grinding with a grindstone or tape polishing. Thereafter, cleaning is performed for the purpose of removing grinding dust and impurities. For example, there is ultrasonic cleaning or baking.

[0031] Furthermore, in order to impart hydrophilicity, a hydrophilic treatment is performed. Examples of the hydrophilic treatment include treatments such as corona, plasma, and UV ozone. The treatment is performed so that hydrophilicity is imparted not only to the outer surface of the silicone rubber but also to the surface of the internal voids through which the working fluid passes. Furthermore, in order to realize stable hydrophilicity over time, after the surface treatment, a hydrophilic polymer, which is a hydrophilic macromolecule, is coated by dipping or the like. If necessary, a heat treatment is performed to fix the hydrophilic polymer. Examples of the hydrophilic polymer include those having a polymer brush structure with a betaine group such as phosphobetaine, carboxybetaine, and sulfobetaine.

[0032] Note that the polymer brush structure is a structure in which a plurality of polymer chains extend in a direction perpendicular to the surface of the base material (the surface of the porous elastomer). By using a polymer chain as a hydrophilic group, hydrophilicity can be stably maintained over a long period as shown in the verification experiment described later. In particular, by using a betaine group such as phosphobetaine, carboxybetaine, or sulfobetaine as the hydrophilic group, very high hydrophilicity can be obtained.

[0033] Next, the specifications (specifications, conditions during manufacturing) of the cross-section that can be obtained when cutting the water-expanded silicone rubber, which is a porous elastomer after the final curing, will be described in more detail.

[0034] (Bubble diameter peak) Since the porous elastomer used for the wick 6 is responsible for the function of moving the working fluid by its capillary force and driving the loop heat pipe 1, it is preferable that the diameter of the bubbles in the porous elastomer is smaller so that a larger capillary force can be obtained. The diameter of the bubbles in the porous elastomer used for the wick 6 (the radius of the bubbles in the wick: rwick) and the capillary force (capillary pressure: ΔPcap) are expressed using the following formula 1. ΔPcap = 2σcosθ / rwick ··· (Formula 1) Here, σ is the surface tension of the working fluid, and θ is the contact angle between the wick and the working fluid.

[0035] As can be seen from Equation 1 described above, the smaller the radius of the bubbles in the wick, the greater the capillary pressure. Also, in order to operate the loop heat pipe 1, the capillary force (capillary pressure: ΔPcap) and the total pressure loss: ΔPtotal must satisfy the following Equation 2. ΔPcap≧ΔPtotal ···(Equation 2)

[0036] Furthermore, the total pressure loss: ΔPtotal is obtained using the following Equation 3. ΔPtotal = ΔPwick + ΔPgroov + ΔPVL + ΔPcond + ΔPLL + ΔPgrav ···(Equation 3) Here, ΔPwick is the pressure loss of the wick, ΔPgroov is the pressure loss of the groove, ΔPVL is the pressure loss of the vapor pipe, ΔPcond is the pressure loss of the condensation section, ΔPLL is the pressure loss of the liquid pipe, and ΔPgrav is the pressure loss due to gravity.

[0037] As described above, in order to obtain a larger capillary force, the maximum diameter of the bubbles in the porous elastic body is preferably smaller, specifically 50 [μm] or less. This is because when the maximum diameter of the bubbles is larger than 50 [μm], it becomes difficult to obtain sufficient capillary force to drive the loop heat pipe. Preferably, the maximum diameter of the bubbles is 30 [μm] or less, and more preferably 10 [μm] or less.

[0038] When the thickness of the wick is extremely thin, the loop heat pipe can function even when the maximum diameter of the bubbles is 1 [μm] or less or 0.1 [μm] or less, but the lower limit value is preferably 0.1 [μm] or more. Here, the maximum diameter of the bubbles can be obtained by photographing the cross-section of the porous elastic body with a laser microscope, processing the obtained image, and measuring the area of the pores.

[0039] (Porosity) The higher the porosity of the porous elastic body used for the wick 6, the more advantageous it is to drive the loop heat pipe 1. Specifically, the porosity of the porous elastic body is preferably 20% or more. When 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 the following formula 4. Porosity (%) = (Specific gravity of solid - Specific gravity of porous elastic body) / (Specific gravity of solid) × 100 ··· (Formula 4)

[0040] (Pore diameter of connecting holes) The connecting holes of the wick 6 refer to the portions where the spaces between bubbles (cells) communicate, and are the portions where the capillary force for driving the working fluid acts. In order to obtain cooling performance, the diameter of the connecting holes (pore diameter of connecting holes) is preferably 10 μm or less, and more preferably 5 μm or less. Also, it is preferable to set the average pore diameter of the connecting holes to 3 μm or less, so that the wick 6 itself can more suitably achieve both high capillary force and permeability. However, when the thickness of the wick 6 is extremely thin, the diameter of the connecting holes can function even at 1 μm or less or 0.1 μm or less.

[0041] The pore diameter of connecting holes is measured by the bubble point method, and the maximum diameter obtained is taken as the pore diameter of connecting holes. Here, a gas pressure is applied to the porous elastic body completely immersed in the test liquid, and the pressure when the appearance of bubbles is observed is defined as the bubble point. Also, by using a test liquid with known surface tension, the pore diameter of connecting holes (maximum diameter) is calculated using the following formula 5. d = 4σcosθ / ΔP ··· (Formula 5) Here, d is the pore diameter of connecting holes (maximum diameter), σ is the surface tension of the working fluid, θ is the contact angle between the wick and the working fluid, and ΔP is the pressure loss (bubble point pressure).

[0042] The average diameter of the communication holes can also be determined by the bubble point method. The average diameter of the communication holes is obtained by finding the pressure (ΔP) at which the pressure-flow rate curve in the state where the porous elastic body is immersed intersects with the pressure-flow rate curve (half-dry curve) that is 1 / 2 of the flow rate measured in the dry state, and then using the above formula 5 to obtain the average diameter of the communication holes.

[0043] (Hydrophilicity evaluation) The hydrophilicity of the wick 6 is measured by the contact angle of water, and the calculation is obtained by the θ / 2 method. The long-term stability was carried out by leaving it in the air.

[0044] (Cooling performance test) Next, regarding the test of the cooling performance carried out by setting examples within the main numerical range of the conditions of the wick 6 described above and comparative examples outside the numerical range, it will be described as appropriate with reference to the drawings.

[0045] (1) Description of the electronic device (projector) 20 that can preferably include the wick used in the cooling performance test. FIG. 4 is a schematic explanatory diagram showing another example of the loop heat pipe 1 provided in the electronic device 20 according to the present embodiment. In addition, the another example of the loop heat pipe 1 shown in FIG. 4, different from the example shown in FIG. 1, is one in which a wick slightly larger than the inner diameter of the cylindrical internal space of the housing (case) of the evaporation section 2 is press-fitted into the housing of the evaporator.

[0046] However, as the 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. 4. However, for the tests of the cooling performance of each of the following examples and each comparative example, the one shown in FIG. 4 is used.

[0047] The electronic device 20 shown in FIG. 4 is a projector including an optical unit 21, and this projector is an example of an electronic device to which the present embodiment is applied. Here, the electronic devices to which the loop heat pipe 1 according to the present embodiment can be applied are not limited to projectors. For example, it can be applied to various electronic devices such as printers, copiers, facsimiles, or image forming apparatuses such as multifunction machines thereof, personal computers, servers, electronic blackboards, televisions, Blu-ray recorders, game machines, etc.

[0048] Also, the loop heat pipe 1 and the cooling device according to the present embodiment can be applied to things other than electronic devices. For example, a cooling device for cooling a chemical plant equipped with a reactor, etc., or to a container or building associated with electronic devices such as a server rack, etc., the loop heat pipe 1 and the cooling device according to the present embodiment may be applied.

[0049] The evaporation section 2 (particularly the heat receiving section 7) of the loop heat pipe 1 shown in Fig. 4 is arranged so as to be in contact with the heat generating section of the optical unit 21. The evaporation section 2 absorbs heat from the heat generating section to cool the object to be cooled (the heat generating section, the optical unit or the projector).

[0050] The condensation section 3 is arranged in the vicinity of the exhaust fan 22 provided on the side surface of the housing of the projector main body. When the exhaust fan 22 discharges air to the outside, an air flow is generated around the condensation section 3, and the condensation section 3 is cooled by the air flow, improving the heat dissipation effect in the condensation section 3.

[0051] Also, an air supply port 23 is provided on the side surface opposite to the side surface of the housing where the exhaust fan 22 is provided, and the air sucked in from the air supply port 23 passes through the projector and is discharged from the exhaust fan 22. In the example shown in Fig. 4, as a cooling device for cooling the projector, it includes the loop heat pipe 1 and the exhaust fan 22 for enhancing the heat dissipation effect of the loop heat pipe 1, but instead of the exhaust fan 22, a blower fan for blowing air to the condensation section 3 may be provided. Also, a cooling device having only the loop heat pipe 1 without a fan may be provided.

[0052] (2) Explanation of detailed examples and comparative examples. FIG. 5 is an explanatory diagram of the specifications and test results of the samples of the examples and comparative examples used in the cooling performance test. In this test, as shown in FIG. 5, a plurality of samples of the example of the wick 6 were produced using water-expanded silicone rubber. Further, samples of the comparative example of the wick 6 were produced using water-expanded silicone rubber with interconnected bubbles (composite), single bubbles, and sintered-connected aluminum, respectively. Then, each of the produced samples was used for a cooling performance test on the loop heat pipe 1 mounted on the projector as shown in FIG. 4.

[0053] The bubble morphology was observed (photographed) with a laser microscope. When it was confirmed that the bubbles were adjacent to each other and in a composite shape, it was evaluated as "composite", and when it could not be confirmed, it was evaluated as "single bubble". FIG. 6 is a diagram showing the observation (photographing) of the bubble state of the sample of the wick 6 of Example 1 with a laser microscope, and it can be confirmed that the bubbles are adjacent to each other and in a composite shape. Therefore, the bubble state of Example 1 is "composite". Such an evaluation was performed for Examples 1 and 2 and Comparative Examples 1, 2, 3, 4, 5, and 6.

[0054] The bubble diameter range and the mode value of the bubble diameter were obtained from the bubble diameter distribution calculated by image processing of the image observed with a laser microscope. FIG. 7 is a graph showing an example of the bubble diameter distribution. The thick solid line shows the distribution of the water-expanded silicone rubber of Examples 1 and 2 with composite bubbles, and the thin solid line shows the distribution of the water-expanded silicone rubber of Comparative Example 5 with single bubbles (individual bubbles). Here, the distribution of the bubble diameter [μm] is represented by a probability density function, and there is a relationship between the probability density on the vertical axis Y and the bubble diameter [μm] on the horizontal axis X. The image processing calculates by sieving the number (frequency) of bubbles in a certain bubble diameter range [μm]. Among all the bubbles existing in the image processing range, it is the number (probability) of bubbles existing in a certain bubble diameter range [μm]. The mode value of the bubble diameter is obtained from this bubble diameter distribution.

[0055] In Fig. 7, the bubble diameter distribution up to a bubble diameter of 32 [μm] is shown, but the number of bubbles with a bubble diameter of 32 [μm] or more may also be calculated. The minimum value of the bubble diameter range is obtained based on the calculated bubble diameter distribution, and the maximum value is obtained by measuring the area of the pores by image processing of the image taken with a laser microscope as described above.

[0056] The porosity was calculated based on Equation 4 described above. Also, the maximum diameter of the through-holes was measured by the bubble point method as described above to measure the bubble point pressure, and was obtained based on Equation 5. Specifically, for the measurement of the diameter of the through-holes, a gas permeation method pore size distribution measuring instrument (POROMETER 3G manufactured by Anton Paar Japan Co., Ltd.) that can measure the bubble point method in accordance with JIS K3832 was used. The measurement sample was Φ25, and POLOFIL was used as the wetting fluid. The average pore diameter of the through-holes was obtained by obtaining the pressure (ΔP) at which the pressure-flow rate curve measured by the bubble point method as described above and the pressure-flow rate curve (half-dry curve) that is half of the flow rate measured in the dried state intersect, and was obtained based on Equation 5 above.

[0057] Fig. 8 is a diagram showing an example of an image obtained by observing a sample of the wick of Example 1 with a scanning electron microscope. This Fig. 8 is an image obtained by further magnifying the image observed with the laser microscope shown in Fig. 6. The black holes in Fig. 8 are through-holes, and it can be confirmed that these through-holes are 5 [μm] or less.

[0058] <<Performance Evaluation>> The hydrophilicity was measured by the θ / 2 method described above for the contact angle of water. Specifically, a contact angle measuring instrument (Drop Master500 manufactured by Kyowa Interface Science Co., Ltd.) was used. The change in hydrophilicity (contact angle) from the initial stage to 3 months was evaluated respectively.

[0059] The adhesion of the wick 6 was observed by X-ray CT for the heat receiving part 7 to which the wick 6 was assembled, and if there was no gap between the heat receiving part 7 (case) and the wick 6, the adhesion was evaluated as "〇", and if there was a gap, the adhesion was evaluated as "×".

[0060] As the cooling performance test, the cooling performance, the wick adhesion, and the heat resistance of the wick were evaluated. The cooling performance was evaluated by applying 100 [W] of power to the projector and measuring the temperature of the evaporation section after holding for 10 minutes. This evaluation was repeated 100 cycles over 3 months, and the rankings were given in ascending order of the evaporation section temperature at the 100th cycle. The comprehensive judgment was given as ○, △, or × from the viewpoints of cooling performance, adhesion, heat insulation, and cost.

[0061] (Examples 1 and 2) In Examples 1 and 2, a water-foamed silicone rubber material in which an activator and a polymer were selected to form composite bubbles (composite) was used. After plasma treatment as a hydrophilic treatment, it was impregnated with a hydrophilic polymer. The hydrophilic polymer has a polymer brush structure and is a hydrophilic polymer having a betaine group and a molecular weight of 10,000 or more. In Examples 1 and 2, by changing the stirring conditions during emulsion preparation, the maximum pore diameter of the continuous pores was adjusted to 5 [μm] and 10 [μm], respectively.

[0062] For both Examples 1 and 2, very good cooling performance was obtained in the cooling performance test. In addition, the hydrophilicity after 3 months did not change from the initial state, and stable hydrophilicity could be obtained over a long period. In particular, Example 1 with a maximum pore diameter of the continuous pores of 5 [μm] had the highest cooling performance ranking.

[0063] The reasons for obtaining such good cooling performance are considered as follows. First, the water-foamed silicone rubber of Example 2 causes a dehydration reaction of the water phase simultaneously with the crosslinking of the rubber during secondary heating. Since it has composite bubbles, communication holes between the bubbles are efficiently formed and the porosity is high. Therefore, the working fluid can penetrate well into the wick 6. Also, in Examples 1 and 2, since the (maximum) diameter of the communication holes is 10 [μm] or less, it is considered that a large number of fine communication holes are formed, and it is considered that the wick has a high capillary force. For these reasons, it is considered that the working fluid can be circulated well, the cooling efficiency can be increased, and the cooling performance can be improved. Since the (maximum) diameter of the communication holes in Example 1 is 5 [μm], a higher capillary force was obtained, and the cooling efficiency could be increased. Therefore, it is considered that the cooling performance was ranked first.

[0064] Furthermore, by using water with a high latent heat as the working fluid, it is considered that a large amount of heat can be taken away when changing from the liquid phase to the gas phase, and the cooling performance can be improved.

[0065] Furthermore, in Examples 1 and 2, by coating a hydrophilic polymer with a molecular weight of 10,000 or more having a betaine group with a polymer brush structure, the hydrophilicity of the surface of the communication holes, which is the path of the working fluid in the wick 6, was maintained over a long period. In this way, by making the surface composition a hydrophilic polymer, deterioration of hydrophilicity due to disappearance, penetration, etc. of segments containing hydrophilic groups can be suppressed. In particular, in Examples 1 and 2, since a hydrophilic polymer having a polymer brush structure was used as the hydrophilic polymer, it is considered that deterioration of hydrophilicity due to disappearance, penetration, etc. of segments containing hydrophilic groups could be further suppressed. Also, since the hydrophilic group was a betaine group, very high hydrophilicity with a contact angle of 5° or less with water could be obtained. As a result, it is considered that the working fluid could be circulated well and a high cooling efficiency was obtained, and the cooling performance could also be improved even after 3 months.

[0066] Also, in both Example 1 and Example 2, the adhesion evaluation was "〇". This is considered to be because, as the wick, silicone rubber which is a porous elastic body was used, and the wick 6 was made slightly larger than the inner dimension of the housing (case) of the heat receiving part 7 of the evaporation part 2, resulting in high adhesion. Also, by obtaining such high adhesion, the heat transfer efficiency to the wick 6 can be increased, and the cooling efficiency can be enhanced. This is also considered to be one of the factors that improved the cooling performance of Example 1 and Example 2. Considering both the cooling performance and cost, the comprehensive judgment of Example 1 and Example 2 is [○].

[0067] (Comparative Example 1) The wick of Comparative Example 1 has the same configuration as that of Example 1, except that the hydrophilic polymer is not in a polymer brush structure and a low molecular weight polymer with a molecular weight of 10,000 or less without a betaine group is used. In Comparative Example 1, the contact angle after 3 months has returned to the same level as before the treatment. Therefore, initially, the working fluid water entered well into the wick and the cooling performance was good, but after 3 months, the water could not enter well into the wick, and it could not operate in the cooling evaluation after 3 months. As a result, the cooling performance was the lowest, and the comprehensive judgment was also set as "×".

[0068] This is because in Comparative Example 1, the void surface is covered with a low molecular weight hydrophilic polymer. It is considered that the low molecular weight hydrophilic polymer of the poly low molecular weight causes bleeding over a long period, resulting in poor long-term stability of hydrophilicity. Furthermore, since this low molecular weight hydrophilic polymer is not in a polymer brush structure, it is considered that the long-term stability of hydrophilicity is even worse.

[0069] (Comparative Example 2) The wick of Comparative Example 2 has the same configuration as that of Example 1, except that the hydrophilic polymer is replaced with a silicon dioxide coating. In Comparative Example 2 as well, similar to Comparative Example 1, the contact angle after 3 months returned to the same level as before the treatment. Therefore, the water of the working fluid could not enter inside the wick, and in the cooling evaluation after 3 months, it could not operate, so the cooling performance was at the lowest level and the comprehensive judgment was also marked as "×".

[0070] This is because in Comparative Example 1, since it is coated with silicon dioxide which is not a hydrophilic polymer of a high molecular weight, unlike the hydrophilic polymer, it is considered that it peeled off from the rubber surface immediately. As a result, hydrophilicity could not be maintained over time, and it is considered that the contact angle after 3 months returned to the same level as before the treatment.

[0071] (Comparative Example 3) The wick of Comparative Example 3 has the same configuration as that of Example 1 except that the hydrophilic treatment is only plasma treatment. In this Comparative Example 3 as well, the contact angle after 3 months returned to the same level as before the treatment. Therefore, the water of the working fluid could not enter inside the wick, and in the cooling evaluation after 3 months, it could not operate, so the cooling performance was at the lowest level and the comprehensive judgment was also marked as "×".

[0072] This is because in Comparative Example 3, it is only plasma treatment and no hydrophilic film is applied to the void surface. Therefore, it is considered that the hydrophilicity returned to the original state due to factors such as the disappearance and penetration of the segments containing hydrophilic groups generated by the plasma treatment. As a result, hydrophilicity could not be maintained over time, and it is considered that the contact angle after 3 months returned to the same level as before the treatment.

[0073] (Comparative Example 4) The wick of Comparative Example 4 was not subjected to hydrophilic treatment and ethanol was used as the working fluid. Otherwise, it has the same configuration as that of Example 1. In Comparative Example 4, the cooling efficiency was lower than that of the Examples, and in the cooling performance test, the results were significantly worse compared to the Examples. This is because in the Comparative Example, ethanol with a smaller latent heat than water was used as the working fluid, so less heat was taken away when changing from the liquid phase to the gas phase. Therefore, it is considered that the cooling efficiency became lower compared to the Examples, and in the cooling performance test, it became significantly worse compared to the Examples. In addition, in Comparative Example 4, since ethanol is used as the working fluid, it is considered that there is no influence due to the lack of hydrophilic treatment.

[0074] (Comparative Example 5) In Comparative Example 5, a water-foamed silicone rubber material was used in which the wick was made of single-bubble foam (single bubble). The bubbles are in the size range of 0.1 [μm] or more and 50 [μm] or less, but since they are not composite bubbles and the bubble diameter is larger than that of the Examples, the porosity could only be increased to 60 [%], and the porosity was lower than that of Example 1. Otherwise, it is the same as Example 1.

[0075] In this Comparative Example 5 as well, the contact angle after 3 months returned to the same level as before the treatment. Therefore, the water of the working fluid could not enter the inside of the wick, and in the cooling evaluation after 3 months, it could not operate, so the cooling performance was at the lowest level and the overall judgment was also marked as "×".

[0076] The reason why the contact angle after 3 months returned to the same level as before the treatment is not certain, but it is considered that the contact angle after 3 months returned to the same level as before the treatment for the following reasons. That is, Comparative Example 5 is single-bubble foam and has a lower porosity than the Examples. Therefore, it is considered that the hydrophilic polymer did not sufficiently penetrate to the inside of the communication holes inside the wick, and a hydrophilic film with a polymer brush structure could not be formed inside the communication holes. It is thought that the fact that a hydrophilic film with a polymer brush structure could not be formed inside the communication holes led to the peeling of the hydrophilic film and the contact angle returning to its original value after 3 months.

[0077] Moreover, in Comparative Example 5, the temperature of the evaporation section was higher and the cooling efficiency was worse than in Examples 1 and 2 from the beginning. This is because the porosity of Comparative Example 5 was lower than that of Examples 1 and 2, so the permeability of the working fluid into the wick was lower than that of Examples 1 and 2. Also, the hydrophilic polymer did not sufficiently penetrate to the inside of the communication holes up to the inside of the wick, and a hydrophilic film was not formed even inside. Therefore, the hydrophilicity inside is insufficient, and it is considered that the cooling efficiency is worse than that of Examples 1 and 2.

[0078] (Comparative Example 6) In Comparative Example 6, an aluminum sintered sample (sintered joint) was used as the wick. By controlling the sintering conditions and particle diameter, the same porosity [%] as in Example 1 and a pore diameter range of 0.1 [μm] or more and 50 [μm] were obtained. Regarding Comparative Example 6, a gap was confirmed between the case (heat receiving section 7) and the wick 6, and the adhesion evaluation was "×". This is considered to be because both the case and the wick 6 are hard materials. In the case of such hard materials, to adhere them without gaps, very high precision is required for both the case and the wick, it is difficult to process them so as not to crush the voids, and the unit price becomes high for mass production.

[0079] Also, in Comparative Example 6, the cooling performance was also worse than that of Examples 1 and 2. This is a treatment with only plasma, and similar to Comparative Example 3, the contact angle has returned after 3 months due to the disappearance of the hydrophilic group. As a result, the cooling performance evaluation was worse than that of Examples 1 and 2. Furthermore, it is considered that the cooling performance evaluation was also poor because the cooling efficiency decreased due to the poor adhesion to the case in Comparative Example 6. Therefore, the comprehensive judgment was set as "×".

[0080] Figure 9 is a graph evaluating the change in hydrophilicity (contact angle) of the wicks of Example 1 and Comparative Examples 1, 3, and 4 from the initial stage to 3 months. As shown in Fig. 9, the wick of Comparative Example 3 with only plasma treatment had its hydrophilicity deteriorated in a few days. In Comparative Example 1 with a silicon dioxide coating, the change in hydrophilicity varied. This is considered to be because the silicon dioxide peeled off from the rubber surface, and the difference in the residual rate of silicon dioxide at the measurement locations caused variations in the results of hydrophilicity evaluation.

[0081] In contrast, in Example 1, it can be seen that the hydrophilicity (contact angle) hardly changed even after being left for 3 months, and stable hydrophilicity over time was ensured.

[0082] From the results of the cooling performance tests using the samples of Examples 1 to 2 and Comparative Examples 1 to 6 described above, depending on the specifications such as the bubbles, through-holes, and combinations of hydrophilic treatments present in the cross-section obtained when cutting the porous body constituting the wick 6 of the present embodiment, the following effects were confirmed.

[0083] First, second, and third specifications: (specifications of Examples 1 and 2) In Examples 1 and 2, the surfaces of the bubbles and through-holes are coated with a hydrophilic polymer having a molecular weight of 10,000 or more, and they are composite bubbles (first specification). Furthermore, the hydrophilic polymer has a polymer brush structure and is a hydrophilic polymer having a molecular weight of 10,000 or more with a betaine group (second specification). Also, the bubbles present in the cross-section have a size in the range of 0.1 [μm] or more and 50 [μm] or less, and among the composite bubbles, the bubbles with a size of 5 [μm] or more and 10 [μm] or less are the most numerous (third specification).

[0084] By having the above first specification, the permeability to the wick when using water as the working fluid can be stably increased over a long period, and further improvement in the cooling performance of the loop heat pipe 1 can be realized. Furthermore, by having the second specification, the hydrophilicity and the long-term stability of hydrophilicity can be further enhanced, and the permeability to the wick when using water as the working fluid can be made more stable over a long period.

[0085] Furthermore, by having the third specifications, the capillary force and the permeability to the wick can be enhanced. As a result, high cooling performance can be obtained in the above-described cooling performance evaluation.

[0086] Here, in Comparative Example 1, the hydrophilic polymer does not have a polymer brush structure, does not have a betaine group, and has a molecular weight of 10,000 or less, deviating from the first specifications. In Comparative Example 2, silicon dioxide is used instead of the hydrophilic polymer, deviating from the first specifications. In Comparative Example 3, only plasma treatment is performed, deviating from the first specifications. Further, in Comparative Example 4, ethanol is used as the working fluid, which is different from those in Examples 1 and 2. In Comparative Example 5, single bubbles are used, deviating from the first specifications. In the case of ethanol in Comparative Example 4, the working fluid still operates even after three months, so Comparative Example 4 ranks third in terms of cooling performance. In Comparative Example 6, the hydrophilicity of the aluminum surface has deteriorated, but since it was originally better than silicone rubber, the cooling performance rank is fourth. Comparative Examples 1, 2, 3, and 5, in which the contact angle has returned to the original state after three months, were ranked at the bottom.

[0087] From these comparisons, it was confirmed that by forming composite bubbles and coating the void surface with a hydrophilic polymer having a molecular weight of 10,000 or more, hydrophilicity can be maintained over a long period, and using a combination of the working fluid with water affects the cooling performance ranking. Furthermore, by providing a betaine group to the hydrophilic polymer of the polymer so as to form a polymer brush structure, higher hydrophilicity and long-term hydrophilicity can be maintained. Also, from Examples 1 and 2 and Comparative Example 5, it was found that composite bubbles can more effectively perform hydrophilic treatment.

[0088] Fourth specifications: (specifications of Examples 1 to 2 and Comparative Examples 1 to 5) The point that the porous body is made of foamed silicone rubber as a porous elastic body, specifically, all of Examples 1 to 2 and Comparative Examples 1 to 5 are composed of water-foamed silicone rubber, is the fourth specification. (Effects of Examples 1 to 2 and Comparative Examples 1 to 5) Since the wick 6 is a porous elastic body such as foamed silicone rubber, the adhesion to the case (heat receiving portion 7) can be ensured. Here, Comparative Example 6 is composed of a metal (aluminum), and has poor elasticity, and high-precision processing is required to improve the adhesion.

[0089] As described above, the present embodiment has been described with reference to the drawings. However, the specific configuration is not limited to the configuration of the loop heat pipe 1 provided with the wick 6 of the present embodiment described above, and design changes and the like within the scope not departing from the gist may be made. For example, the loop heat pipe 1 of the present embodiment described with reference to FIGS. 1, 2, and 4 has all been described with respect to a configuration having one evaporation section 2 and one condensation section 3. However, the configuration of the loop heat pipe of the present embodiment is not limited to such a configuration. It is also applicable to a loop heat pipe having two or more of at least one of the evaporation section 2 and the condensation section 3.

[0090] In addition, the loop heat pipe 1 of the present embodiment described with reference to FIGS. 1, 2, and 4 has all been described with respect to a configuration in which one wick 6 is provided inside the evaporation section 2. However, it is also applicable to a configuration having a plurality of wicks provided in parallel.

[0091] What has been described above is an example, and each of the following aspects has a specific effect. (Aspect 1) A wick of a porous elastic body provided inside an evaporator that changes a liquid-phase working fluid into a gas phase, and the liquid-phase working fluid penetrates. The porous elastic body has a composite void having communication holes in a portion where a plurality of spherical voids partially overlap each other, and the surface of the void of the porous elastic body is covered with a hydrophilic polymer film such as a hydrophilic polymer. According to this, as described in the above-described cooling performance test, a composite void having communication holes in a portion where a plurality of spherical voids partially overlap each other, and by coating the surface of the voids of the porous elastic body with a hydrophilic polymer film, stable hydrophilicity can be obtained on the surface of the porous body and the surface of the voids over a long period of time. As a result, a hydrophilic working fluid such as water can be stably permeated into the wick over a long period of time, and the circulability of the working fluid can be maintained over a long period of time. As a result, the cooling efficiency of the evaporator when using a hydrophilic working fluid can be maintained high over a long period of time.

[0092] (Aspect 2) In Aspect 1, the hydrophilic polymer film such as a hydrophilic polymer of a polymer includes a polymer brush structure having a hydrophilic group. According to this, high hydrophilicity can be stably maintained over time.

[0093] (Aspect 3) In Aspect 2, the hydrophilic group is a betaine group. According to this, as described in the embodiment, high hydrophilicity can be obtained, and a hydrophilic working fluid such as water can be satisfactorily permeated into the wick.

[0094] (Aspect 4) In any one of Aspects 1 to 3, the molecular weight of the hydrophilic polymer is 10,000 or more. According to this, as described in the above-described cooling performance test, since there is no adverse effect due to bleeding, stable hydrophilicity can be obtained over a long period of time, and a hydrophilic working fluid such as water can be satisfactorily permeated into the wick over a long period of time.

[0095] (Aspect 5) In any one of Aspects 1 to 4, the maximum pore diameter of the communication hole is 5 [μm] or less. According to this, as described in the embodiment, the capillary force of the wick can be increased.

[0096] (Aspect 6) In any one of Aspects 1 to 5, the average pore diameter of the communication holes is 3 [μm] or less. According to this, as described in the embodiment, the capillary force of the wick can be enhanced.

[0097] (Aspect 7) In any one of Aspects 1 to 6, the diameter of spherical voids such as air bubbles is 0.1 [μm] or more and 50 [μm] or less. According to this, as described in the embodiment, good capillary force can be obtained.

[0098] (Aspect 8) In any one of Aspects 1 to 7, the mode value in the diameter distribution of spherical voids such as air bubbles is 5 [μm] or more and 10 [μm] or less. According to this, as described in the embodiment, good capillary force can be obtained.

[0099] (Aspect 9) In any one of Aspects 1 to 8, the porous elastic body is water-expanded silicone. According to this, as described in the embodiment, the wick can obtain good capillary force and can be well adhered to the case.

[0100] (Aspect 10) An evaporator such as an evaporation unit 2 that houses a wick inside and changes a liquid-phase working fluid into a gas phase, and uses a wick according to any one of Aspects 1 to 9 as the wick. According to this, good cooling performance can be obtained.

[0101] (Aspect 11) In a loop heat pipe including an evaporator such as an evaporation unit 2 that receives heat from the outside and evaporates a working fluid from a liquid phase to a gas phase, and a condenser such as a condensation unit 3 that condenses the gas-phase working fluid discharged from the evaporator into a liquid phase, the evaporator according to Aspect 10 is used as the evaporator. According to this, good cooling performance can be obtained.

[0102] (Aspect 12) In Aspect 11, the working fluid is water. According to this, by using water with high latent heat as the working fluid, high cooling performance can be obtained.

[0103] (Aspect 13) In a cooling device equipped with a loop heat pipe, the loop heat pipe according to Aspect 11 or 12 is used as the loop heat pipe. According to this, the object to be cooled can be cooled well.

[0104] (Aspect 14) In an electronic device 20 such as a projector equipped with a cooling means, the cooling device according to Aspect 13 is used as the cooling means. According to this, the heat generating part of the electronic device 20 such as a projector can be cooled well.

[0105] (Aspect 15) In a wick manufacturing method for manufacturing a wick of a porous body provided inside an evaporator such as an evaporation part 2 that changes a liquid-phase working fluid into a gas phase and into which the liquid-phase working fluid penetrates, the method includes a step of forming a composite void having communication holes in a part where a plurality of spherical voids partially overlap each other in a porous elastic body, and a coating step of coating a hydrophilic polymer film on the surface and inside the voids of the porous elastic body. According to this, the hydrophilicity of the void surface can be stabilized in the long term, and a wick that can allow the working fluid of water to penetrate well can be manufactured.

[0106] (Aspect 16) In Aspect 15, it has a surface treatment step of forming radicals on the surface and inside the voids of the porous elastic body, and after the surface treatment step, the coating step is carried out. According to this, the hydrophilicity of the void surface can be stabilized in the long term, and a wick that can allow the working fluid of water to penetrate well can be manufactured.

Explanation of Signs

[0107] 1 Loop heat pipe 2 Evaporation section 3 Condensation section 4 Steam pipe 5 Liquid pipe 6 Wick 7 Heat receiving section 20 Electronic device (projector)

Prior art documents

Patent documents

[0108]

Patent Document 1

Claims

1. A wick made of a porous elastic material is provided inside an evaporator that changes a liquid phase working fluid into a gas phase, and through which the liquid phase working fluid permeates, the porous elastic body has composite voids having communicating holes at portions where a plurality of spherical voids partially overlap each other, the surfaces of the pores of the porous elastic body are subjected to a surface treatment for forming radicals; the surface of the void in which the radicals are formed is covered with a hydrophilic polymer film; A wick characterized in that the porosity of the porous elastomer is 70%.

2. 10. The wick of claim 1, The wick is characterized in that the hydrophilic polymer membrane includes a polymer brush structure having a hydrophilic group.

3. 3. The wick of claim 2, A wick characterized in that the hydrophilic group is a betaine group.

4. 4. A wick according to any one of claims 1 to 3, A wick characterized in that the molecular weight of the hydrophilic polymer membrane is 10,000 or more.

5. 5. A wick according to any one of claims 1 to 4, comprising: A wick characterized in that the maximum pore diameter of the communicating holes is 5 μm or less.

6. 6. A wick according to any one of claims 1 to 5, A wick characterized in that the average pore diameter of the communicating pores is 3 μm or less.

7. 7. The wick according to claim 1, wherein the diameter of the spherical voids is 0.1 μm or more and 50 μm or less.

8. 8. A wick according to any one of claims 1 to 7, comprising: A wick characterized in that the most frequent value in the distribution of diameters of the spherical voids is 5 μm or more and 10 μm or less.

9. 9. A wick according to any one of claims 1 to 8, comprising: The wick is characterized in that the porous elastic body is foamed silicone rubber.

10. An evaporator that houses a wick therein and changes a liquid-phase working fluid into a gas-phase working fluid, the evaporator comprising the wick according to any one of claims 1 to 9 as the wick.

11. A loop-type heat pipe comprising an evaporator that receives heat from an outside source and evaporates a working fluid from a liquid phase to a gas phase, and a condenser that condenses the gas phase working fluid discharged from the evaporator into a liquid phase, characterized in that the evaporator according to claim 10 is used as the evaporator.

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

13. A cooling device equipped with a loop heat pipe, comprising the loop heat pipe according to claim 11 or 12.

14. In an electronic device equipped with a cooling means, 14. An electronic device using the cooling device according to claim 13 as the cooling means.

15. A wick manufacturing method for manufacturing a wick made of a porous elastic material that is provided inside an evaporator that changes a liquid-phase working fluid into a gas phase and through which the liquid-phase working fluid permeates, comprising the steps of: forming composite voids having communicating holes at portions where the plurality of spherical voids partially overlap each other in the porous elastic body; a coating step of coating a hydrophilic polymer membrane on the surface and in the pores of the porous elastic body; a surface treatment step of forming radicals on the surface and within the pores of the porous elastic body, The coating step is carried out after the surface treatment step, A wick manufacturing method characterized in that the porosity of the porous elastomer is 70%.

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