Wick

Abstract

To provide a looped heat pipe capable of maintaining cooling performance.SOLUTION: A looped heat pipe comprises an evaporator that changes the state of liquid-phase working fluid to vapor-phase working fluid, a condenser that changes the state of the vapor-phase working fluid to the liquid-phase working fluid, and a vapor pipe and a liquid pipe connected to the evaporator and the condenser, where stress due to compressive deformation of an elastic wick, which is housed in the evaporator in a compressively deformed state and forms a boundary part between the liquid-phase working fluid and the vapor-phase working fluid, is larger than pressure loss that occurs when the working fluid circulates from the vapor-phase side of the boundary part to the liquid-phase side of the boundary part via the condenser.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention , Ru This relates to a wick for use in a loop-type heat pipe. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there is known a loop heat pipe that includes an evaporator that changes the phase of a working fluid from a liquid phase to a gas phase, and a condenser that changes the phase of the working fluid from the gas phase to a liquid phase.

[0003] Patent Document 1 describes a loop heat pipe that has an elastic porous wick inside the evaporator. The wick housed inside the evaporator is configured so that the air bubbles contained in the porous body have a size within a certain range. Summary of the Invention [Problem to be solved by the invention]

[0004] However, the loop heat pipe described in Patent Document 1 has room for improvement in terms of maintaining cooling performance. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention The wick is a wick used in a loop type heat pipe, the wick being a porous elastic body that allows a working fluid to penetrate into its interior and elastically deforms due to stress, and the maximum stress at which the porous elastic body can be elastically deformed due to compressive deformation is greater than the capillary pressure of the working fluid in the porous elastic body. Effect of the Invention

[0006] According to the present invention, the cooling performance of the loop heat pipe can be maintained. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing an example of a loop heat pipe according to an embodiment of the present invention. [Diagram 2] 2 is a diagram showing a virtual cross section taken along the dashed line aa in FIG. 1. [Diagram 3]FIG. 3 is a diagram for explaining the compressive deformation of the wick in FIG. 2. [Figure 4] FIG. 2 is a diagram illustrating the elastic range of the wick and the maximum stress at which the wick can be elastically deformed. [Diagram 5] FIG. 2 is a diagram for explaining the system pressure loss of a loop heat pipe. [Figure 6] Photograph showing the communicating holes of the wick of Example 1. [Figure 7] FIG. 1 is a schematic explanatory diagram showing an example of an electronic device equipped with a loop heat pipe according to an embodiment of the present invention. [Figure 8] FIG. 2 is an explanatory diagram showing the specifications of samples of examples and comparative examples used in a cooling performance test, and test results. [Figure 9] FIG. 2 shows the results of tensile evaluation of the wick of Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A loop heat pipe and a configuration in which the loop heat pipe is applied to a cooling device for electronic devices will be described below. In the loop heat pipe of the embodiment, a compressively deformed elastic wick is housed inside an evaporator.

[0009] In the drawings for explaining the present embodiment, components such as members and components having the same function or shape are given the same reference numerals as far as they can be distinguished. Furthermore, once a component with the same reference numerals is explained, the explanation thereof may be omitted as appropriate.

[0010] FIG. 1 is a schematic diagram showing the configuration of a loop heat pipe to which the present invention can be applied, and FIG. 2 is a diagram showing a virtual cross section taken along the dashed line a-a in FIG.

[0011] The loop heat pipe 1 shown in Fig. 1 is filled with a working fluid made of a condensable fluid, and includes an evaporator 2 that absorbs heat from a heat generating part and evaporates the working fluid from liquid phase to gas phase, and a condenser 3 that condenses the gas phase working fluid introduced from the evaporator 2 to liquid phase. It also includes a vapor pipe 4 that passes the gas phase working fluid from the evaporator 2 to the condenser 3, and a liquid pipe 5 that passes the liquid phase working fluid from the condenser 3 to the evaporator 2.

[0012] The evaporator 2 is composed of a heat receiving section 7 that houses a wick 6 therein, and a reservoir section 8 that stores a liquid phase working fluid. One end of a steam pipe 4 is connected to the heat receiving section 7, and one end of a liquid pipe 5 is connected to the reservoir section 8. The other ends of the steam pipe 4 and the liquid pipe 5 are each connected to the condenser 3. The condenser 3 is composed of a stainless steel pipe 31 having a large number of thin aluminum fins 32 provided on its outer circumferential surface.

[0013] Since the wick 6 is made of a porous elastic body, that is, a porous material, the liquid phase working fluid stored in the reservoir 8 permeates into the wick 6 by capillary action. Due to this capillary action, the wick 6 also functions as a pump that sends the liquid phase working fluid from the condenser 3 to the evaporator 2.

[0014] Furthermore, a plurality of grooves 10 are provided on the bottom surface (the lower surface in Figs. 1 and 2) of the heat receiving portion 7 of the wick 6 from the end on the steam pipe 4 side toward the opposite end. The plurality of grooves 10 are provided at equal intervals on the bottom of the wick 6, as shown in the a-a cross section of Fig. 2. In Fig. 2, the dimensional ratio of the grooves 10 to the wick 6 is drawn larger than actual size in order to clearly show the structure.

[0015] The wick 6 is porous and elastic. The thickness of the wick 6 is set to be slightly larger than the inner dimensions of the housing of the heat receiving part 7 of the evaporator 2. By setting the thickness of the wick 6 in this way, when the wick 6 is housed in the heat receiving part 7, the wick 6 undergoes compressive deformation and adheres to the inner surface of the heat receiving part 7 with stress. However, in the portion where the groove 10 is provided, a space is formed between the wick 6 and the housing of the heat receiving part 7. Similarly, the wick 6 also adheres to the inner surface of the heat receiving part 7 on the reservoir part 8 side with stress due to compressive deformation.

[0016] The stress due to the compressive deformation of the wick 6 can be set by the elastic modulus of the wick 6 and the distortion when housed in the heat receiving part 7. In FIG. 3, the cross-sectional view of the heat receiving part 7 shows the shape of the wick 61 before it is housed in the heat receiving part 7 with a dashed line. The thickness of the wick 61 before it is housed in the heat receiving part 7 is t [mm]. The thickness of the wick 6 housed in the heat receiving part 7 while being compressed in the thickness direction is thinner by Δt [mm] than the thickness of the wick 61 before it is housed. The distortion ε [%] due to the compressive deformation at this time is ε [%] = Δt / t × 100. The stress σ [Pa] due to the compressive deformation in this state is calculated using the bulk modulus E [Pa] and the distortion ε [%] due to the compressive deformation, σ=E×ε / 100 It becomes.

[0017] The stress σ [Pa] due to compressive deformation of the wick 6 is set to a range smaller than the maximum stress σmax at which the wick 6 can be elastically deformed (σ<σmax). Figure 4 shows a schematic diagram of the relationship between the strain ε [%] and the stress σ [Pa] due to compressive deformation when the wick is compressively deformed in the thickness direction. The stress σ [Pa] versus the strain ε has an approximately linear relationship within the range of elastically deformable strain. This range of strain at which elastic deformation is possible is generally referred to as the elastic range. As the stress and strain due to compressive deformation of the wick 6 contained in the heat receiving part 7 are within the elastic range, the wick 6 can be stably adhered to the inner surface of the heat receiving part 7.

[0018] On the other hand, in the region where the strain is larger than the elastically deformable region, the wick undergoes plastic deformation, so the relationship between stress σ and strain ε is not linear. This range of strain is generally called the plastic region. In this plastic region, that is, when the wick 6 is compressed and deformed by a stress larger than the maximum elastically deformable stress σmax, and is placed in the heat receiving part 7, the wick 6 undergoes plastic deformation and is no longer able to adhere to the heat receiving part 7 with the necessary stress.

[0019] By making the stress due to compressive deformation of the wick 6 smaller than the maximum stress σmax at which the wick can be elastically deformed, even if a change in temperature causes a change in the volume of the wick 6 or a change in the inner dimensions of the heat receiving part 7, the elastic deformation of the wick allows the wick 6 to maintain its intimate contact with the inner surface of the heat receiving part 7, thereby stabilizing the thermal contact between the heat receiving part 7 and the wick 6 and allowing the loop type heat pipe to operate stably.

[0020] (Working fluid) As the working fluid, a condensable fluid such as water, alcohol, acetone, or alternative fluorocarbon is used. In particular, by using water, which has a high latent heat, as the working fluid, high cooling performance can be obtained, which is preferable. In addition, the working fluid should have 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°, the capillary phenomenon becomes more effective, which is more preferable.

[0021] (Operation of loop heat pipe) In the loop heat pipe 1 according to this embodiment, when heat from the heat generating part is transferred to the liquid phase working fluid in the wick 6 through the housing of the evaporator 2 (heat receiving part 7), the working fluid evaporates due to the heat and changes into a gas phase. When the liquid phase working fluid changes into a gas phase working fluid, the pressure of the gas phase working fluid in the groove 10 increases according to the vapor pressure at the temperature of the working fluid. Due to this pressure increase, the working fluid that has changed into a gas phase is sent through the groove 10 to the vapor pipe 4. Then, the gas phase working fluid is sent through the vapor pipe 4 to the condenser 3.

[0022] In the condenser 3, the heat of the working fluid passing through the inside (pipe 31) is released to the outside through the fins 32, causing the temperature of the working fluid to drop and condense, changing the state of the working fluid from gas phase to liquid phase. The working fluid that has changed to liquid phase moves through the liquid pipe 5 to the evaporator 2, and permeates again from the reservoir 8 into the wick 6 provided inside the heat receiving part 7 due to capillary action. By circulating the working fluid in this way, the heat of the heat generating part is continuously released to the outside, and the object to be cooled is cooled.

[0023] When the working fluid inside the heat receiving portion 7 changes state from liquid to gas, the pressure of the gas phase working fluid increases. This causes a pressure difference between the gas phase working fluid in the heat receiving portion 7 and the liquid phase working fluid in the heat receiving portion 7, causing the working fluid to flow in one direction from the groove 10 to the reservoir portion 8 via the condenser 3. In order to allow the working fluid to flow in one direction, the wick 6 functions as a check valve that prevents the working fluid from flowing back from the groove 10 to the reservoir portion 8 without passing through the condenser 3.

[0024] (The boundary between the liquid and gas phases of the wick) Because the wick 6 is a porous body, the liquid phase working fluid stored in the reservoir 8 permeates into the inside, forming a boundary 62 between the liquid phase working fluid and the gas phase working fluid on the surface or inside of the wick 6. Microscopically, the boundary 62 is an interface between the liquid phase and the gas phase formed by surface tension in the pores of the porous body. This interface is formed by capillary pressure Pcap in the direction from the liquid phase side to the gas phase side. The capillary pressure Pcap at the boundary 62 prevents the gas phase working fluid from flowing back inside the wick.

[0025] The capillary pressure Pcap at the boundary portion 62 of the wick 6 can be expressed by the following equation (1) using the surface tension T of the liquid working fluid, the contact angle θ of the liquid working fluid with respect to the wick, and the pore radius rwick of the wick. Pcap = 2T × cosθ / rwick (1)

[0026] The capillary pressure can be increased by increasing the wettability so as to reduce the contact angle of the working fluid with the wick and by decreasing the pore radius. The capillary pressure can also be adjusted by adjusting the pore diameter of the wick 6. By making the capillary pressure Pcap larger than the pressure difference between the working fluid on the gas phase side and the liquid phase side of the boundary 62, it is possible to prevent the working fluid on the gas phase side of the boundary 62 from flowing back to the liquid phase side of the boundary 62.

[0027] (System Pressure Loss) The pressure difference occurring between the liquid phase side and the gas phase side of the boundary 62 corresponds to the system pressure loss ΔPtotal occurring when the working fluid circulates once from the gas phase side of the boundary 62 through the condenser 3 to the liquid phase side of the boundary 62.

[0028] Figure 5 shows a schematic diagram of the pressure of the working fluid in the flow path of a loop heat pipe. The horizontal axis corresponds to each configuration of the working fluid flow, and the working fluid flows from left to right in the figure. Since the flow path is configured in a loop, the right side of the liquid pipe in the figure is connected to the left side of the reservoir in the figure.

[0029] The pressure P1 on the gas phase side of the boundary 62 corresponds to the pressure generated by the working fluid changing from the liquid phase to the gas phase. The working fluid on the gas phase side of the boundary flows through the groove 10 toward the steam pipe 4, and a pressure loss ΔPgroove occurs according to the flow rate of the working fluid and the fluid resistance of the groove 10, and the pressure drops to P2. The working fluid flows through the steam pipe 4 toward the condenser 3, and a pressure loss ΔPVL occurs according to the flow rate of the working fluid and the fluid resistance of the steam pipe 4, and the pressure drops to P3. The working fluid flows through the pipe 31 of the condenser 3 toward the liquid pipe 5, and a pressure loss ΔPcond occurs according to the flow rate and fluid resistance of the working fluid, and the pressure drops to P5. The pressure loss ΔPcond is the sum of the pressure loss in the gas phase and the pressure loss in the liquid phase. Since the density of the working fluid in the liquid phase is smaller than the density of the working fluid in the gas phase, the flow rate of the working fluid in the liquid phase is significantly smaller than the flow rate of the working fluid in the gas phase. Therefore, the pressure loss in the liquid phase state is relatively small.

[0030] The working fluid flows through the liquid pipe 5 toward the reservoir 8, and generates a pressure loss ΔPLL, causing the pressure to drop to P6. ΔPLL includes the pressure loss according to the flow rate and fluid resistance of the working fluid, and the pressure loss due to gravity. The pressure loss due to gravity corresponds to the pressure difference due to the head difference between the inlet and outlet of the liquid pipe. When the working fluid flows against gravity in the liquid pipe, ΔPLL includes a positive pressure loss due to the head difference. When the working fluid flows along gravity in the liquid pipe, ΔPLL includes a negative pressure loss due to the head difference. The head difference can be calculated from the difference in height between the liquid level at the inlet and outlet of the liquid pipe, the density of the working fluid, and the gravity constant. The working fluid flows from the reservoir 8 toward the wick 6 of the evaporator 2, and generates a pressure loss ΔPres according to the flow rate, fluid resistance, and head difference of the working fluid, causing the pressure to drop to P7. The working fluid further permeates the wick 6 and flows within the wick 6 toward the boundary portion 62, causing a pressure loss ΔPwick according to the flow rate of the working fluid, the fluid resistance of the wick, and the head difference, and decreasing to a pressure P8.

[0031] The system pressure loss ΔPtotal that occurs when the working fluid circulates once corresponds to the sum of the pressure losses in each flow path and is given by: ΔPtotal=ΔPgroove+ΔPVL+ΔPcond+ΔPLL+ΔPres+ΔPwick (2)

[0032] The system pressure loss ΔPtotal depends on both the amount of heat that the loop heat pipe processes and the configuration of the loop heat pipe. It is generally known that the mass flow rate Lm [kg / s] of the working fluid generated when the loop heat pipe processes the amount of heat Q [W] is expressed as follows: Lm=Q / η (3) Here, η [J / kg] is the latent heat of vaporization of the working fluid. Equation (3) corresponds to the fact that the larger the amount of heat Q to be processed, the larger the mass flow rate Lm of the working fluid increases.

[0033] Flow rate of working fluid L [m 3 / s] is the mass flow rate Lm [kg / s] and the density ρ [kg / m 3 ], it can be calculated as L = Lm / ρ. The mass flow rate Lm is the same for each flow path of the loop heat pipe, but the flow rate L differs depending on whether the working fluid is in the liquid or gas phase. In the flow paths where the working fluid flows in the gas phase (groove 10, steam pipe 4, and part of the condenser 3), the density ρ of the working fluid is smaller than that of the liquid phase, so the flow rate L is large. On the other hand, in the flow paths where the working fluid flows in the liquid phase (part of the condenser 3, liquid pipe 5, reservoir 8, and wick 6), the density ρ of the working fluid is larger than that of the gas phase, so the flow rate L is small.

[0034] Generally, the pressure loss ΔP caused by the working fluid flowing through a flow path is expressed as ΔP=Ra×L, where L is the flow rate of the working fluid and Ra is the fluid resistance of the flow path. The fluid resistance of the flow path is determined by the physical properties (viscosity, etc.) of the working fluid and the dimensions of the flow path (cross-sectional area and length). The relationship between the pressure loss ΔP, the fluid resistance Ra, and the flow rate L depends on the magnitude of the flow rate, the temperature dependence of the viscosity of the working fluid, and the material and microscopic shape of the flow path surface. Therefore, it is preferable to determine the pressure loss by flowing the working fluid actually used in the loop heat pipe through the flow path to be used at the applicable flow rate and measuring the actual pressure.

[0035] In this way, the flow resistance is determined by the configuration of the loop heat pipe. On the other hand, the flow rate L depends on the amount of heat Q that the loop heat pipe can process. Therefore, the pressure loss ΔP is determined by the amount of heat to be processed and the configuration of the loop heat pipe.

[0036] As described above, since the flow rate of the gas phase working fluid is greater than that of the liquid phase working fluid, the pressure loss due to the flow rate of the gas phase working fluid is often greater than the pressure loss due to the flow rate of the liquid phase working fluid. The pressure loss due to the flow of the working fluid can be reduced by increasing the cross-sectional area of ​​the flow path of the gas phase working fluid and shortening the length, but an appropriate shape can be chosen depending on the size of the loop heat pipe, the layout of the flow path, etc.

[0037] When the amount of heat to be processed by the loop heat pipe increases, the pressure loss due to the fluid resistance of each component increases, and the system pressure loss also increases. Therefore, the maximum value of the system pressure loss ΔPtotal is determined by the maximum amount of heat Q to be processed and the configuration of the flow path and layout of the loop heat pipe.

[0038] As shown in Fig. 5, the system pressure loss corresponds to the pressure difference P8-P1 between the liquid phase side and the gas phase side of the boundary part 62. In order to circulate the working fluid in a fixed direction without backflow, the boundary part 62 needs to be such that backflow does not occur even when a pressure equal to the maximum value of the system pressure loss ΔPtotal (the system pressure loss when processing the maximum amount of heat) is applied. There are two main factors that cause the gas phase working fluid to backflow inside the boundary part 62 and the heat receiving part 7:

[0039] The first factor is that the wick 6 deforms due to the pressure on the gas phase side of the boundary portion 62, causing a gap to form between the inner surface of the heat receiving portion 7 and the wick 6, causing the gas phase working fluid to leak and flow back into the reservoir portion 8.

[0040] The second factor is that the boundary portion 62 of the wick 6 itself cannot withstand the pressure on the gas phase side, causing the gas phase working fluid to flow back inside the wick.

[0041] The countermeasure against the first factor is to make the stress σ [Pa] due to the compressive deformation when the wick 6 is accommodated in the heat receiving portion 7 and the system pressure loss ΔPtotal [Pa] have the following relationship: σ ≥ ΔPtotal (4) Here, ΔPtotal is the system pressure loss when the loop heat pipe processes the maximum heat amount that it can process. By satisfying the relationship of formula (4), the wick 6 is compressed by a stress equal to or greater than the pressure applied by the gas phase working fluid, and is therefore not deformed by the pressure from the gas phase working fluid. This makes it possible to prevent the gas phase working fluid from leaking back to the liquid phase side of the boundary portion 62 due to deformation. Furthermore, even if pressure is applied from the gas phase working fluid, the wick 6 is stably attached to the inner wall of the heat receiving portion 7, so that the thermal contact between the liquid phase working fluid and the heat receiving portion can be stabilized. The basis and verification results will be explained in the embodiment described later using FIG. 8 and the like.

[0042] Furthermore, the stress σ due to the compressive deformation of the wick 6 is set to be smaller than the maximum stress σmax at which the wick 6 can be elastically deformed (σ<σmax). As a result, even if dimensional changes occur due to temperature changes in the heat receiving part 7 or the wick 6, the elastic deformation of the wick 6 allows the heat receiving part 7 and the wick 6 to be stably attached to each other, allowing the loop heat pipe to operate stably.

[0043] The countermeasure for the second factor is to make the capillary pressure Pcap [Pa] of the wick 6 and the system pressure loss ΔPtotal [Pa] have the following relationship: Pcap ≥ ΔPtotal (6) Here, ΔPtotal is the system pressure loss when the loop heat pipe processes the maximum amount of heat it can process. By satisfying the relationship in formula (6), the boundary portion 62 can withstand the pressure from the gas phase working fluid and prevent the gas phase working fluid from flowing back inside the wick.

[0044] Furthermore, it is desirable that the stress σ due to the compressive deformation of the wick 6 and the capillary pressure Pcap satisfy the following relationship. Pcap<σ (7)

[0045] Due to abnormal operation of the equipment to be cooled, the loop heat pipe may be subjected to heat beyond its capacity, resulting in an abnormal situation in which the system pressure loss is excessively high. In such a case, the backflow of the working fluid occurs due to either the first factor or the second factor. The relationship of formula (7) is a relationship that allows the backflow due to the second factor to occur before the backflow due to the first factor. As a result, the gas phase working fluid backflows at the boundary portion 62 of the wick 6 due to the second factor before the first factor causes a leak due to deformation of the wick 6. As a result, the wick 6 can be protected by backflowing the gas phase working fluid at the wick itself to reduce the pressure before the wick 6 reaches an irreparable failure such as plastic deformation.

[0046] In order to deal with the first and second factors, it is effective to use a wick that is elastically deformable against compressive stress and can generate high capillary pressure. An example of such a wick 6 will be described in detail.

[0047] The wick 6 used in the loop heat pipe 1 according to this embodiment is made of a porous elastomer such as foamed silicone rubber. There are various methods for manufacturing a wick made of such an elastic porous elastomer, but the porous elastomer in this embodiment is obtained by applying a technique proposed for water-foamed silicone rubber, for example. Silicone rubber has high heat resistance and high chemical resistance, so it can widen the operating temperature range of the loop heat pipe and prevent deterioration due to the working fluid.

[0048] Specifically, the water-foamable silicone rubber composition is used and agitated so that the bubbles, which are spherical voids present in the cross section obtained when the final foam is cut, are present as follows: Agitation is performed so that the bubbles present in the cross section have a size in the range of 0.1 μm to 50 μm, with the largest number of bubbles being 5 μm to 20 μm.

[0049] More specifically, the porous elastomer described above is prepared by mixing a catalyst, a surfactant, and a crosslinking agent with commercially available two-liquid liquid silicone rubber. The mixture is then mixed with water (with alcohol added as necessary) and a mixed solution with additives, fillers, dispersants, etc., adjusted to the same viscosity as the liquid silicone rubber, and stirred to prepare an emulsion composition. The liquid silicone rubber is selected from those having a specific gravity of 1.00 to 1.05 [g / cm3], taking into consideration the emulsification with water. 3 ] is preferred.

[0050] The blending ratio of the liquid silicone rubber to the mixed solution varies depending on the desired porosity. For example, if the blending ratio of the liquid silicone rubber to the mixed solution is 1:1, the minute water particles in the emulsion evaporate and become voids, resulting in a foam with a porosity of 50%.

[0051] The emulsion is prepared using a homogenizer or, if necessary, an agitator with ultrasonic treatment, and various stirring conditions such as the stirring means, stirring time, and stirring speed (e.g., 300 to 1500 rpm) are adjusted to obtain a bubble size distribution that satisfies the above-mentioned conditions.

[0052] Thereafter, the prepared emulsion composition is filled into a mold and heated to perform primary heating, which hardens the silicone rubber without evaporating the water in the emulsion composition.

[0053] 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 to remove moisture from the foam after the primary heating. The heating temperature is 150 to 300°C, and the heating time is preferably 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, moisture is removed from the porous elastomer, and the cells are made to be of an open-cell type so that the spherical cells are partially overlapped with each other to form composite cells, and the final hardening of the silicone rubber is completed.

[0054] Next, the surface is ground down by a few μm to a few mm to achieve dimensional accuracy or to remove the skin layer as necessary. For example, this is done by grinding with a grindstone or tape polishing. After that, the surface is cleaned to remove shavings and impurities. For example, ultrasonic cleaning or baking is used.

[0055] Furthermore, a hydrophilic treatment is performed to impart hydrophilicity. Examples of hydrophilic treatment include corona, plasma, UV ozone, and other treatments, and new hydrophilic coatings. Alternatively, an additive that imparts hydrophilicity to the material may be added. Treatment is performed so that hydrophilicity is imparted not only to the surface of the silicone rubber, but also to the path through which the working fluid passes, including the inside. In particular, in order to achieve stable hydrophilicity over time, it is preferable to combine hydrophilic coating after treating the inside with methods such as corona, plasma, and UV ozone.

[0056] Next, the cross-sectional dimensions (specifications, manufacturing conditions) that can be obtained when cutting the water-foamed silicone rubber, which is a porous elastomer that has finally been cured, will be described in more detail.

[0057] In order to stably operate the loop heat pipe, it is preferable that the maximum diameter of the pores in the porous elastic body is small so that a larger capillary pressure can be obtained, specifically, it is preferable that the maximum diameter of the pores is 50 [μm] or less. If the maximum diameter of the pores is larger than 50 [μm], it is difficult to obtain a sufficient capillary pressure to drive the loop heat pipe. The maximum diameter of the pores is preferably 30 [μm] or less, and more preferably 10 [μm] or less.

[0058] (Communication hole diameter) Figure 6 is a micrograph of a cross section obtained when cutting the wick 6. It can be seen that multiple pores overlap and communicate with each other. Such a portion where multiple pores are connected is called a communicating pore.

[0059] The porous elastic material used in the wick 6 has the function of moving the working fluid by its capillary pressure to drive the loop heat pipe 1, so it is preferable that the diameter of the holes in the porous elastic material is small so that a larger capillary pressure can be obtained. As mentioned above, the capillary pressure Pcap needs to be higher than the system pressure loss ΔPtotal. The capillary pressure Pcap can be adjusted to a desired value by adjusting the diameter of the holes using the above-mentioned formula (1).

[0060] In order to obtain a cooling performance, the diameter of the communicating holes (communicating hole diameter) is preferably 20 [μm] or less, and more preferably 5 [μm] or less. In addition, it is preferable to set the average pore diameter of the communicating holes to 3 [μm] or less, so that the wick 6 itself can more suitably achieve both high capillary pressure and permeability.

[0061] If the wick is extremely thin, it can function even if the maximum diameter of the communicating holes is 1 μm or less or 0.1 μm or less, but the lower limit is preferably 0.1 μm or more. If the diameter of the communicating holes is too small, the fluid resistance of the wick to the working fluid increases, increasing the amount of pressure loss in the wick and causing an increase in system pressure.

[0062] The diameter of the communicating pores is measured by a bubble point method, and the maximum diameter obtained is regarded as the maximum diameter of the communicating pores.

[0063] Here, gas pressure is applied to a porous elastic body completely immersed in a test liquid, and the pressure at which the appearance of gas bubbles is observed is defined as the bubble point. In addition, by using a test liquid with a known surface tension, the maximum pore size of the communicating pores is calculated using the following formula. d=4Tcosθ / ΔP (8) Here, d is the maximum pore diameter of the communicating holes, T 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).

[0064] The average pore diameter can also be determined by the bubble point method. The average pore diameter is calculated by determining the pressure (ΔP) at which the pressure-flow curve when the porous elastomer is immersed intersects with the pressure-flow curve (half-dry curve) that is half the flow rate measured in a dry state, and then using the above formula (8).

[0065] (porosity) The higher the porosity of the porous elastic body used in the wick 6, the more advantageous it is for operating the loop heat pipe 1. Specifically, the porosity of the porous elastic body is preferably 20% or more. If the porosity is less than 20%, the fluid resistance of the wick to the working fluid increases, causing an increase in pressure loss in the wick and making it difficult to operate the loop heat pipe 1. More preferably, the porosity is 50% or more. The porosity can be calculated by the following formula. Porosity ([%]) = (specific gravity of solid - specific gravity of porous elastic body) / (specific gravity of solid) ×100 (9)

[0066] (Elasticity Modulus) The elastic modulus of Wick 6 was measured by a tensile test in accordance with JIS 7161. The elastic modulus can be calculated from the slope of the stress-strain curve obtained in the tensile test. Specifically, it is calculated using the following formula, using values ​​between 0.05% and 0.25% strain. E = (σ1-σ2) / (ε1-ε2) (10) Here, E is the elastic modulus, σ1 is the stress at 0.25% strain, σ2 is the stress at 0.05%, ε1 is the 0.25% strain, and ε2 is the 0.05% strain.

[0067] This material exhibits a fracture mode close to brittle fracture in tension, and there is also concern about chuck slippage, so a microscopic strain was used. However, when compressed, this material does not undergo plastic deformation until the strain reaches about 25%, and enters the elastic deformation region. The stress σ due to compressive deformation can be calculated from the elastic modulus E calculated using equation (10) and the strain ε, which corresponds to the amount of crushing when the wick is compressed.

[0068] The wick 6 is preferably made of a material having an elastic range with a compressive strain ε in the range of up to 20%. By setting the material in this range, the wick 6 can adhere to the inner surface of the heat receiving part 7 with a predetermined stress even if there is a dimensional fluctuation due to processing variations in the inner dimensions of the heat receiving part 7 or temperature changes. Furthermore, if the wick is in an elastic range with a compressive strain of 20%, it is better to have a high elastic modulus. Since the stress σ [Pa] due to compressive deformation is expressed as σ = ε / 100 × E depending on the compressive strain ε [%] and the elastic modulus E [Pa], even with the same compressive strain, the greater the elastic modulus E, the greater the stress σ due to compressive deformation can be, and a higher stress can be obtained.

[0069] FIG. 7 shows an example of an electronic device (projector) 20 equipped with the above-mentioned wick. The electronic device 20 shown in FIG. 7 is a projector equipped with an optical unit 21, and this projector is an example of an electronic device to which this embodiment is applied. Electronic devices to which the loop heat pipe 1 according to this embodiment can be applied are not limited to projectors. For example, the loop heat pipe 1 according to this embodiment can be applied to various electronic devices such as image forming devices such as printers, copiers, facsimiles, or multifunction machines thereof, personal computers, servers, electronic whiteboards, televisions, Blu-ray recorders, and game consoles.

[0070] The loop heat pipe 1 and cooling device according to the present embodiment can also be applied to devices other than electronic devices. For example, the loop heat pipe 1 and cooling device according to the present embodiment may be applied to a cooling device for cooling a chemical plant equipped with a reactor, or a container or building associated with electronic devices such as a server rack.

[0071] 1, the evaporator 2 (particularly the heat receiving part 7) of the loop heat pipe 1 is disposed so as to be in contact with the heat generating part of the optical unit 21. The evaporator 2 absorbs heat from the heat generating part and cools the object to be cooled (the heat generating part, the optical unit, or the projector).

[0072] The condenser 3 is disposed near an exhaust fan 22 provided on the side of the housing of the projector body. When the exhaust fan 22 exhausts air to the outside, an airflow is generated around the condenser 3, and the condenser 3 is cooled by the airflow, improving the heat dissipation effect of the condenser 3.

[0073] An air inlet 23 is provided on the side of the housing opposite to the side on which the exhaust fan 22 is provided, and air taken in from the air inlet 23 passes through the inside of the projector and is exhausted from the exhaust fan 22. In the example shown in Fig. 3, the cooling device for cooling the projector includes a loop heat pipe 1 and an exhaust fan 22 for enhancing the heat dissipation effect of the loop heat pipe 1, but a blower fan for blowing air to the condenser 3 may be provided instead of the exhaust fan 22. Also, the cooling device may not include a fan and may include only the loop heat pipe 1.

[0074] (Example) Next, the cooling performance test performed by setting the main numerical ranges of the above-mentioned wick 6 and loop heat pipe conditions as examples and comparative examples outside the numerical ranges will be described with reference to appropriate figures. Figure 8 is an explanatory diagram of the specifications of the examples and comparative examples used in the cooling performance test, and the test results.

[0075] (Cooling performance test method) The cooling performance test method for each of Examples 1 to 3 and Comparative Examples 1 to 5 was performed under the same conditions. The wick used in the test had a thickness of 2 mm and was housed in the heat receiving part 7 of the evaporator 2. At that time, the inner dimension of the heat receiving part was adjusted so that the amount of crushing (distortion) ε [%] was a predetermined amount. For example, to achieve ε = 20%, the inner dimension of the wick in the thickness direction of the heat receiving part 7 can be adjusted to 1.6 mm.

[0076] The stress of compressive deformation σ [Pa] was calculated from the elastic modulus E [Pa] and the amount of compression (strain) ε [%] measured in advance by the method described above, using the relational formula σ = ε × E / 100. The maximum stress σmax that can be elastically deformed by compressive strain was calculated from the relationship shown in Figure 4, by measuring the amount of compression (strain) ε [%] and stress when compressing and deforming the wick.

[0077] The working fluid used in the test was pure water, which was filled in a vacuum inside a loop heat pipe.

[0078] The system pressure loss was calculated by measuring the pressure loss while the working fluid was flowing through each flow path constituting the loop heat pipe, and calculating the sum of the pressure losses.

[0079] The flow rate of the working fluid was calculated from the amount of heat processed by the loop heat pipe. The amount of heat processed by the loop heat pipe was set to 100 [W], and the mass flow rate Lm of the working fluid generated at that time was calculated based on equation (3). Furthermore, the flow rate of the liquid phase working fluid Ll [m 3 / s] and the flow rate of gas-phase working fluid Lg [m 3 / s] was calculated.

[0080] The pressure loss of the working fluid in each flow path is calculated by measuring the pressure at the inlet and outlet of the flow path when the working fluid is passed through the flow path at a calculated flow rate, and calculating the difference between the pressures. In the flow path where the working fluid in liquid phase flows, the liquid phase working fluid (water) is passed through the flow path at a flow rate of Ll [m 3 / s], and in the flow path where the gas phase working fluid flows, the gas phase working fluid (water vapor) is flowed at a flow rate of Lg [m 3 / s]. At this time, the height relationship between the inlet and outlet of the flow path was set to be the same as that of the layout during loop heat pipe operation. As a result, the measured pressure loss includes the pressure loss due to gravity.

[0081] The pressure losses of each configuration (ΔPgroove, ΔPVL, ΔPcond, ΔPLL, ΔPres, ΔPwick) thus determined can be integrated to determine the system pressure loss ΔPtotal.

[0082] Here, the pressure loss of the wick may be calculated from the shape and dimensions of the wick and the physical properties of the working fluid. The pressure loss of the wick due to the flow of the working fluid can also be calculated by the following formula. ΔPwick=μ×L×Δx / (k×S) (11) Here, the symbols represent the following parameters: ΔPwick: Pressure loss in the wick due to the flow of the working fluid μ: Viscosity of the working fluid L: Flow rate of working fluid Δx: Wick thickness (thickness in the direction of working fluid flow) S: Cross-sectional area of ​​the wick (cross-sectional area perpendicular to the flow direction of the working fluid) k: penetration rate The permeability k can be calculated from the shape of the porous medium using the empirical formula of Blake Kozeny. k = (2 × rs) 2 ×εs 3 / (150×(1-εs)) 2 (12) Here, rs is the radius of the interconnected pores and εs is the porosity.

[0083] If there is a height difference between the inlet and outlet sides of the wick for the working fluid (for example, Δx due to the thickness of the wick), the pressure loss due to gravity can be included by adding the head difference corresponding to the height difference to the pressure loss.

[0084] The capillary pressure Pcap of the wick was calculated from the maximum pore size of each wick's communicating pores, the contact angle of the working fluid, and the surface tension of water (the working fluid) using equation (1).

[0085] The cooling performance test was performed by operating the electronic device (projector) 20 continuously for 10 minutes at a power of 210 W, and then measuring the temperature of the heat receiving part 7. The power of 210 W for the electronic device is a condition under which the heat generating part of the optical unit 21, for example a loop-type heat pipe installed in the light source, processes 100 W of heat. After the continuous operation, the temperature of the heat receiving part 7 of the evaporator was measured, and if it was below the upper operating temperature limit of the light source, the cooling performance test result was marked as "○", and if it exceeded the upper operating temperature limit, the cooling performance test result was marked as "×".

[0086] Next, the adhesion between the wick 6 and the inner surface of the heat receiving part 7 was evaluated. The adhesion was evaluated by observing the gap between the wick and the inner surface of the heat receiving part 7 using X-ray CT. When no gap was observed, the adhesion was judged to be good and was marked with "○", and when a gap was observed, the adhesion was judged to be poor and was marked with "×".

[0087] Furthermore, after the cooling test, the heat receiving part 7 was disassembled to check whether there was any deformation in the wick 6 and the heat receiving part 7. If there was no deformation in the wick 6 or the heat receiving part 7, the deformation evaluation result was marked as "○", and if deformation was observed, the deformation evaluation was marked as "×".

[0088] The conditions and test results of the loop heat pipe shown in Figure 8 are explained below.

[0089] Example 1 In Example 1 of this test, water-foamed silicone rubber was used as the material for the wick 6. The type of activator, the amount of activator, and the heating conditions during the synthesis of the silicone rubber were adjusted to obtain a silicone rubber formulation A having a porosity of 70% and a maximum pore size of the communicating holes of 5 μm.

[0090] The cross section of the completed wick was observed under an electron microscope and confirmed to be porous. Figure 6 is an image of the cross section of a wick made with silicone formulation A, observed under a scanning electron microscope. It can be seen that multiple pores are interconnected to form interconnected pores. It can also be seen that the diameter of the interconnected pores is 5μm or less.

[0091] The obtained wick was used to create a loop-type heat pipe with a strain (amount of crushing) of ε = 15%, and cooling performance tests, adhesion evaluations, and deformation evaluations were performed using the methods described above. All results were ``○'', indicating good results.

[0092] The stress and capillary pressure due to the compressive deformation in Example 1 are greater than the system pressure loss. Furthermore, the adhesion between the wick and the inner surface of the heat receiving part is good, and the wick does not deform. These conditions are believed to have prevented the gas phase working fluid from flowing back, maintaining good cooling performance.

[0093] Example 2 The wick used in Example 2 was made using the same base material as the wick used in Example 1. However, the type of activator, the amount of activator, and the heating conditions during synthesis were changed, and the maximum pore size of the communicating holes was adjusted to 20 μm, resulting in a silicone rubber formulation B. Since silicone rubber formulation B is made of the same base material as silicone rubber formulation A and has the same porosity, the elastic modulus of the wick in Example 2 was the same as that of silicone formulation A.

[0094] The obtained wick was used to create a loop-type heat pipe with a strain (amount of crushing) of ε = 15%, and cooling performance tests, adhesion evaluations, and deformation evaluations were performed using the methods described above. All results were ``○'', indicating good results.

[0095] The stress and capillary pressure due to the compressive deformation in Example 2 are larger than the system pressure loss. Furthermore, the adhesion between the wick and the inner surface of the heat receiving part is good, and the wick does not deform. It is believed that these conditions prevent the gas phase working fluid from flowing back, and good cooling performance is maintained.

[0096] Example 2 has a lower system pressure loss than Example 1. This is believed to be because the wick has a smaller hole diameter than Example 1, which reduces the fluid resistance of the wick. By configuring the loop heat pipe to have a lower system pressure loss, the components of the loop heat pipe, particularly the wick, can be reduced in pressure load. This can further improve the durability and long-term operational stability of the loop heat pipe.

[0097] The capillary pressure in the second embodiment is smaller than the stress caused by the compressive deformation of the wick. With this configuration, when the amount of heat processed by the loop heat pipe becomes excessive due to a malfunction of the electronic device 20, a backflow occurs in the wick itself before damage occurs due to deformation of the wick, and the pressure on the wick can be reduced. When the electronic device 20 returns to normal operation by a safety device or the like and the amount of heat processed becomes appropriate, the pressure on the wick becomes smaller than the capillary pressure, and the backflow stops, making it possible to return to normal operation. This makes it possible to prevent irreparable damage caused by deformation of the wick, and to increase the reliability of the loop heat pipe.

[0098] Example 3 The wick used in Example 3 was made with the same silicone rubber formula A as in Example 1. However, it differs from Example 1 in that the loop heat pipe was constructed with a wick distortion (amount of crushing) of ε = 20%. Using the created loop heat pipe, a cooling performance test, adhesion evaluation, and deformation evaluation were performed using the same method as in Example 1, and all results were "○", indicating good results.

[0099] The stress and capillary pressure due to the compressive deformation in Example 3 are larger than the system pressure loss. Furthermore, the adhesion between the wick and the inner surface of the heat receiving part is good, and the wick does not deform. It is believed that these conditions prevent the gas phase working fluid from flowing back, and good cooling performance is maintained.

[0100] In the loop heat pipe of Example 3, the stress due to compressive deformation of the wick is higher than that of Example 1. However, since the stress due to compressive deformation is set to be smaller than the maximum stress at which elastic deformation is possible, there is no plastic deformation of the wick and good cooling performance is maintained.

[0101] Comparative Example 1 The wick used in Comparative Example 1 was made with silicone rubber formula C, which was adjusted so that the wick material had a low elastic modulus. Silicone rubber formula C was made by adjusting the amount of silica filler and the crosslinking density of the base material of silicone rubber formula A. The porosity and maximum diameter of the interconnected pores were made the same as those of silicone rubber formula A in Example 1 by adjusting the type of activator, the amount of activator, and the heating conditions. The measurement results of the stress against the strain of the wick in Comparative Example 1 are shown in FIG. 9. Compared to formula A, the slope of FIG. 9 is smaller for silicone rubber formula C, indicating that the elastic modulus is smaller. The bulk modulus of silicone rubber formula C is 5000 [Pa], which is smaller than those of silicone rubber formulas A and B.

[0102] The wick of Comparative Example 1 was placed in the heat receiving part 7 of the evaporator 2 with the same strain (squeezing amount) ε = 15% as in Example 1, and a cooling performance test, an adhesion evaluation, and a deformation evaluation were performed. As a result, the cooling performance was evaluated as "x", and sufficient performance was not obtained. This is considered to be caused by the fact that the bulk modulus of the wick of Comparative Example 1 is low, so that even with a squeezing amount of 15%, the stress due to the compressive deformation is smaller than those of Examples 1 to 3, and is smaller than the system pressure loss. The system pressure loss, which is the pressure difference applied to the boundary between the liquid phase and the gas phase of the wick 6, became larger than the stress due to the compressive deformation of the wick, so the wick 6 was deformed, and a gap was generated between the wick and the heat receiving part, causing the gas phase working fluid to flow back. This is considered to have reduced the amount of heat that the loop heat pipe can process, and increased the temperature of the heat receiving part.

[0103] (Comparative Examples 2 and 3) In Comparative Example 2 and Comparative Example 3, the wick of silicone rubber formulation A used in Example 1 was used, but the crushing amount was adjusted to 5% and 30%, respectively. When the loop heat pipes of Comparative Example 2 and Comparative Example 3 were used to carry out the same cooling performance test as in Example 1, the evaluation results were both "X".

[0104] The result of the adhesion evaluation of the loop heat pipe of Comparative Example 2 was "x", and it was confirmed that there was a gap between the wick and the inner surface of the heat receiving part. This is because the amount of compression was small at 5%, and the stress of the compressive deformation was also smaller than that of Example 1. Therefore, it is considered that the dimensional variation in the thickness of the wick and the dimensional variation in the inner dimensions of the heat receiving part could not be absorbed by the elastic deformation of the wick, and the gap remained. Therefore, it is considered that the gas phase working fluid flowed back through the gap between the wick and the inner surface of the heat receiving part, and sufficient cooling performance was not obtained.

[0105] The deformation evaluation of the loop heat pipe of Comparative Example 3 is "x", and the wick itself has been plastically deformed. Therefore, there is no data on the value of the stress due to the compressive deformation of Comparative Example 2 in FIG. 8. This is because the wick was plastically deformed by being crushed to 30%, which exceeds the maximum elastically deformable amount of 25% of the silicone rubber formulation A. Therefore, even if the adhesion evaluation is "○", it is considered that the stress of the compressive deformation of the wick is insufficient, the wick is deformed by the pressure of the gas phase working fluid, and the gas phase working fluid flows back, so that cooling performance was not obtained. Similarly, it is considered that the dimensional change due to the temperature change of the wick and the heat receiving part during operation could not be absorbed by elastic deformation, a gap was generated between the wick and the inner surface of the heat receiving part, and the gas phase working fluid flowed back, so that cooling performance was not obtained.

[0106] Comparative Example 4 Comparative Example 4 is different in that polyethylene is used as the base material of the wick. The porosity, maximum diameter of the communicating holes, and contact angle of the completed wick were all within the appropriate range. The completed wick was placed in the heat receiving part of the evaporator in a compressed and deformed state with a crush amount of 15% as in Example 1, and a cooling performance test, adhesion evaluation, and deformation evaluation were performed. As a result, the cooling performance evaluation result was "X".

[0107] The stress due to the compressive deformation in Comparative Example 4 is smaller than the system pressure loss. This is because the bulk modulus of the polyethylene, which is the base material of the wick, is low, so even with a strain of 15%, sufficient stress for the compressive deformation can be obtained. This is thought to be because the pressure of the gas phase working fluid reduces the adhesion between the inner surface of the wick and the heat receiving part, causing the gas phase working fluid to leak and flow back, resulting in a decrease in cooling performance.

[0108] In Comparative Example 5, a wick material is a metal sintered body formed by sintering metal particles. Such a metal sintered body is porous and can be permeated with a liquid-phase working fluid, and is therefore used in conventional loop-type heat pipes. The metal sintered body wick was compressed and deformed by 5% and housed in the heat receiving part of the evaporator, and the cooling performance, adhesion, and deformation evaluations were performed in the same manner as in Example 1. All evaluation results were "x".

[0109] In the adhesion evaluation of Comparative Example 5, a gap was observed between the wick and the inner surface of the heat receiving part. The gas phase working fluid flowed back into the reservoir from this gap, causing a decrease in cooling performance. This is thought to be because the elastic deformation range of the metal sintered compact is narrow, and the wick cannot absorb the flatness and dimensional variation between the wick and the inner surface of the heat receiving part through elastic deformation.

[0110] In the deformation evaluation of Comparative Example 5, it was found that the heat receiving part of the evaporator was deformed. In order to increase the adhesion between the wick and the inner surface of the heat receiving object, the wick was housed in the heat receiving part with a 5% crushing amount, but the rigidity of the wick was too high when assembling the housing, so the housing of the heat receiving part was deformed. It is believed that this deformation caused a gap between the wick and the inner surface of the heat receiving part, and the gas phase working fluid flowed back through this gap, resulting in a decrease in cooling performance.

[0111] When constructing a loop heat pipe using the wick of Comparative Example 5, it is considered necessary to significantly improve the dimensional accuracy of the wick, such as the flatness and thickness variation, and the dimensional accuracy of the inner surface of the heat receiving part, such as the flatness, etc. Such processing is undesirable because it increases the manufacturing cost of the loop heat pipe.

[0112] From the results of the cooling performance tests using the samples of the above-mentioned Examples 1 to 3, the above-mentioned Examples 1 to 3, and Comparative Examples 1 to 5, it was confirmed that the following effects are achieved with respect to the compressive deformation stress of the wick 6 of the loop heat pipe of this embodiment, system pressure loss, etc.

[0113] (Configurations of Examples 1 to 3) Examples 1 to 3 have a configuration in which the stress due to compressive deformation of the wick is greater than the system pressure loss (first configuration). With the first configuration, the wick 6 is in close contact with the inner surface of the heat receiving portion 7, thereby preventing backflow of the working fluid. This makes it possible to stably maintain the cooling performance.

[0114] Examples 1 to 3 have a configuration (second configuration) in which the stress due to compressive deformation of the wick is smaller than the maximum stress at which elastic deformation is possible. With the second configuration, even if dimensional fluctuation occurs due to temperature changes in the wick or the heat receiving part, the wick 6 can be stably attached to the inner surface of the heat receiving part 7, stabilizing thermal contact and preventing backflow of the working fluid. This makes it possible to stably maintain cooling performance. Furthermore, good thermal contact between the wick 6 and the inner surface of the heat receiving part 7 can be achieved, improving cooling efficiency.

[0115] In Examples 1 to 3, the capillary pressure of the working fluid in the wick is greater than the system pressure loss (third configuration). The third configuration can prevent the working fluid in the gas phase from flowing back through the boundary portion 62 between the liquid phase and the gas phase formed in the wick 6. This makes it possible to stably maintain the cooling performance in the above-mentioned cooling performance test.

[0116] Here, Comparative Examples 1, 2, and 4 are different from the first configuration in that the stress due to the compressive deformation of the wick is smaller than the system pressure loss. Comparative Examples 3 and 4 are different from the second configuration in that the wick is plastically deformed and therefore a stress equal to or greater than the maximum stress at which elastic deformation is possible is applied.

[0117] These comparisons show that cooling performance can be maintained stably by making the stress due to compressive deformation of the wick greater than the system pressure loss and less than the maximum stress at which the wick can elastically deform.

[0118] The fourth feature is that the wick 6 in Examples 1 to 3 is made of foamed silicone rubber. When the wick 6 is a porous elastic body such as foamed silicone rubber, it is possible to apply an appropriate stress to the wick and thereby ensure adhesion with the heat receiving part 7. Furthermore, when the wick is made of foamed silicone rubber, it is possible to impart heat resistance.

[0119] Here, the wick of Comparative Example 5 is made of metal (aluminum) and is different from the fourth configuration. Therefore, although the wick of Comparative Example 5 has heat resistance, it has poor elasticity and cannot adhere to the inner surface of the heat receiving part. In order to adhere the wick of Comparative Example 5 to the inner surface of the heat receiving part, high-precision processing is required for the wick and the inner surface of the heat receiving part.

[0120] The maximum stress at which the wick of the second embodiment can be elastically deformed is configured to be greater than the capillary pressure of the working fluid in the wick (fifth configuration). By having the fifth configuration, even if a larger amount of heat than expected is applied to the loop heat pipe, causing a larger pressure than expected, damage such as plastic deformation of the wick can be prevented. As a result, a more reliable loop heat pipe can be obtained.

[0121] The present embodiment has been described above with reference to the drawings, but the specific configuration is not limited to the configuration of the loop heat pipe 1 of the present embodiment described above, and design changes may be made within the scope of the present invention.

[0122] For example, the loop heat pipe 1 of the present embodiment described with reference to Figures 1 and 2 has one evaporator 2 and one condenser 3, but the configuration of the loop heat pipe of the present embodiment is not limited to this configuration. The present invention can also be applied to a loop heat pipe having two or more of at least one of the evaporators 2 and the condensers 3.

[0123] The loop heat pipe 1 of this embodiment described with reference to Figures 1 and 2 has been described as having one wick 6 inside the evaporator 2, but it can also be applied to a configuration having multiple wicks in parallel. In the configurations of Figures 1 and 2, a groove is provided in the wick, but a configuration in which a groove is provided in the housing is also possible. In the configurations of Figures 1 and 2, the heat receiving part 7 of the evaporator 2 and the wick 6 are described as having a flat plate shape, but they can also be any shape such as a cylindrical shape or a wedge shape.

[0124] The above description is merely an example, and each of the following aspects provides unique effects.

[0125] (Aspect 1) In a loop heat pipe comprising an evaporator which changes the state of a liquid phase working fluid to a gas phase working fluid, a condenser which changes the state of the gas phase working fluid to a liquid phase working fluid, a vapor pipe connected to the evaporator and condenser and through which the gas phase working fluid flows, a liquid pipe through which the liquid phase working fluid flows, and an elastomer wick which is contained in a compressed and deformed state inside the evaporator and through which the liquid phase working fluid permeates to form a boundary between the liquid phase working fluid and the gas phase working fluid, the stress due to the compressive deformation of the elastomer wick is made larger than the pressure loss which occurs when the working fluid circulates from the gas phase side of the boundary through the condenser to the liquid phase side of the boundary.

[0126] As explained in the cooling test above, the stress caused by the compressive deformation of the wick is greater than the pressure loss caused by the circulation of the working fluid, so that the adhesion between the wick and the inner surface of the evaporator can be stably increased and the cooling performance can be stably maintained. Furthermore, the thermal contact between the wick and the inner surface of the heat receiving part is improved, so the cooling efficiency can be improved.

[0127] (Aspect 2) In the first aspect, the stress due to the compressive deformation is set to be smaller than the maximum stress at which the elastic wick can be elastically deformed. As a result, as described in the above embodiment, the wick is accommodated inside the evaporator with the amount of strain in the elastic range, so that even if the temperature of the evaporator and the wick change and the dimensions fluctuate, the adhesion can be maintained due to the elastic deformation of the wick.

[0128] (Aspect 3) In the first or second embodiment, the elastic wick is made porous, and the capillary pressure of the liquid-phase working fluid in the elastic wick is made greater than the pressure loss.

[0129] According to this, since the pressure at the boundary between the liquid phase and the gas phase of the wick is higher than the pressure of the above-mentioned gas phase working fluid, it is possible to prevent the gas phase working fluid from flowing back inside the wick.

[0130] (Aspect 4) In the third embodiment, the stress due to the compressive deformation of the elastic wick is set to be greater than the capillary pressure in the wick of the liquid phase working fluid.

[0131] According to this, as described in the embodiment, the increase in pressure of the gas phase working fluid causes the gas phase working fluid to flow back through the inside of the wick before the wick is deformed, thereby preventing irreparable damage due to deformation of the wick.

[0132] (Aspect 5) In any one of the first to fourth embodiments, the elastic wick is made of foam rubber.

[0133] According to this, as described in the above embodiment, the elastic deformation of the wick can improve the adhesion between the wick and the inner surface of the evaporator.

[0134] (Aspect 6) In the fifth embodiment, the foamed rubber was water-foamed silicone rubber.

[0135] As a result, as explained in the above embodiment, the operating temperature range can be widened due to the high heat resistance.

[0136] (Aspect 7) The loop heat pipe according to any one of the embodiments 1 to 6 was used in a cooling device.

[0137] This makes it possible to obtain good cooling performance.

[0138] (Aspect 8) The cooling device of embodiment 7 was used in electronic equipment such as a projector.

[0139] This allows the heat-generating parts of the electronic device to be cooled effectively.

[0140] (Aspect 9) In the wick used in the loop heat pipe, the wick is made of a porous elastic body that is permeated with a working fluid and elastically deforms under stress, and the maximum stress at which the porous elastic body can be elastically deformed by compressive deformation is set to be greater than the capillary pressure of the working fluid in the porous elastic body. As a result, as explained in the above embodiment, when the wick is applied to the loop heat pipe, damage due to irreversible deformation of the wick can be prevented, and the reliability of the loop heat pipe can be improved.

[0141] (Aspect 10) In the ninth aspect, the porous elastic body is foamed rubber. As a result, as described above, when used in a loop heat pipe, the adhesion between the wick and the inner surface of the evaporator can be improved.

[0142] (Aspect 11) In an eleventh aspect, the foamed rubber is water-foamed silicone rubber, which can improve the heat resistance and chemical resistance of the wick. [Explanation of symbols]

[0143] 1 Loop type heat pipe 2. Evaporator 3. Condenser 4 Steam Pipe 5 Liquid Pipe 6. Wick 7 Heat receiving part 62 Boundary 20 Electronic equipment (projectors) [Prior art documents] [Patent documents]

[0144] [Patent Document 1] JP 2020-20495 A

Claims

1. A wick for use in a loop heat pipe, comprising: The wick is a porous elastic body that allows the working fluid to permeate therein and elastically deforms due to stress, The maximum stress by which the porous elastic body can be elastically deformed due to compressive deformation is A wick, the capillary pressure of the working fluid being greater than the capillary pressure in the poroelastic body.

2. The wick according to claim 1 , wherein the porous elastic body is foamed rubber.

3. The wick of claim 2 , wherein the foamed rubber is a water-foamed silicone rubber.

4. The stress due to the compressive deformation of the wick is less than the maximum stress that can cause elastic deformation. The wick of claim 1.

5. The water-foamed silicone rubber is configured so that bubbles, which are spherical voids present in a cross section obtained by cutting a foam formed from the composition, have a size in the range of 0.1 μm to 50 μm, with the majority of bubbles having a size of 5 μm to 20 μm. The wick of claim 3.

6. The porous elastic body is mixed with liquid silicone rubber, and the liquid silicone rubber has a specific gravity of 1.00 to 1.05 [g / cm3]. The wick of claim 1.

7. The pores of the porous elastic body are 50 μm or less. The wick of claim 1.

8. The porous elastic body has communicating pores, and the diameter of the communicating pores is 20 μm or less. The wick of claim 1.

9. The average pore size of the communicating holes is 3 μm or less. The wick of claim 8.

10. The lower limit of the maximum diameter of the communicating holes is 0.1 μm or more. The wick of claim 8.

11. The diameter of the communicating holes is measured by a bubble point method, and the maximum diameter obtained is the maximum diameter of the communicating holes. The wick of claim 8.

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