JP2016217684A - Cooler, cooling device using the same and method for cooling heater element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooler having a simple structure and showing a superior and stable cooling effect.SOLUTION: This invention relates to a boiling system cooler for cooling heater element comprising a container storing operation fluid and a cooling member arranged in the container. The cooling member is arranged to contact with operation fluid and oppositely face against the heater element and including a porous body having operation fluid supplying part for supplying operation fluid to a contact part contacted with the heater element under a capillary phenomenon and a steam discharging pipe for discharging steam generated at the contact part out of the operation fluid.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a cooler, a cooling device using the same, and a cooling method for a heating element, and more particularly to a boiling-type cooler, a cooling device using the same, and a cooling method for a heating element. is there.

  In recent years, in a pressure vessel of a light water reactor as shown in FIG. 1, there is a demand for a cooling mechanism that does not cause melt-through by cooling the bottom of the reactor pressure vessel with water from the outside even if a fuel rod causes a melting accident, As such a cooling mechanism, a boiling cooling system is known.

  The boiling cooling method includes a pool boiling method and a forced flow boiling method. Here, a general cooling mechanism of the heating element by the pool boiling method will be described. FIG. 2 shows a conventional pool boiling cooler. The cooler includes a container and a working fluid contained in the container, and the container has a contact portion with a heating element to be cooled. When heat is generated in the heating element and the heat is transmitted to the working fluid through the contact portion, the working fluid existing in the vicinity of the contact portion boils. When steam is generated by boiling, the working fluid is supplied to the contact portion due to the density difference between the gas and the liquid. In this way, the newly supplied working fluid is further evaporated, and heat is removed from the heating element. The pool boiling type cooler is advantageous in terms of compactness and energy saving because it does not require an external power source for circulating the liquid as in the forced flow boiling method.

JP 2009-139005 A

S. G. Kandlikar, M. Shoji, and V. K. Dhir, “Handbook of Phase Change: Boiling and Condensation,” Taylor & Francis, 1999

  However, when a large heat flux is applied to the contact portion, there is a problem in a conventional pool boiling type cooler. This is shown in FIG. As the heat flux increases, the amount of evaporation of the working fluid increases and the contact portion begins to be covered with steam. When the contact portion is completely covered with steam and becomes dry, and the working fluid is not supplied to the contact portion, the cooling capacity of the cooler is significantly reduced. The heat flux in this state is referred to as “limit heat flux”.

  In contrast to a conventional pool boiling type cooler (see Non-Patent Document 1), the present inventor disclosed in Japanese Patent Application Laid-Open No. 2009-139005 (Patent Document 1) that a porous body is made up of a heating element and water in a cooling container. By providing a structure in which water is supplied to the heating element by capillary action of the porous body and the generated steam is discharged into the water in the container, the conventional limit heat flux can be reduced with a simple structure. It has improved dramatically. However, a cooler that further enhances the cooling effect still has room for development.

  An object of the present invention is to provide a cooler having a simple structure and stably having a good cooling effect, a cooling device using the cooler, and a heating element cooling method.

  As a result of repeated research, the present inventors have described the details later, but a porous body provided with a working fluid supply unit that supplies a working fluid to a contact portion with the heating element by capillary action is opposed to the heating element. It was also found that it is possible to provide a cooler with a further improved cooling effect by providing a steam discharge pipe for discharging the steam generated at the contact portion to the outside of the working fluid.

  That is, one aspect of the present invention is a boiling-type cooler for cooling a heating element, which includes a container that contains a working fluid, and a cooling member provided in the container, and the cooling member Is a porous body provided with a working fluid supply part which is provided so as to be in contact with the working fluid and opposed to the heating element, and which supplies the working fluid to a contact part with the heating element by capillary action And a steam discharge pipe for discharging the steam generated at the contact portion to the outside of the working fluid.

  In the cooler according to an embodiment of the present invention, the steam discharge pipe is provided so that one end faces the heating element and the other end extends through the container and extends outside the container. ing.

  In the cooler according to another embodiment of the present invention, the steam discharge pipe is formed of a silicon tube.

  In the cooler according to another embodiment of the present invention, the porous body is formed of a porous layer having a mesh structure.

  In the cooler according to another embodiment of the present invention, the porous body is made of metal.

  In the cooler according to another embodiment of the present invention, the porous body is formed of an aggregate of porous nanoparticles.

  In a cooler according to still another embodiment of the present invention, a gap region is formed at a contact portion between the porous body and the heating element.

  Another aspect of the present invention is a cooling device including the cooler of the present invention and a condenser connected to a container of the cooler and configured to liquefy evaporated working fluid.

  According to still another aspect of the present invention, there is provided a cooling method using a boiling method in which a heating element is cooled by at least partially immersing the heating element in a working fluid of a container containing the working fluid. A working fluid supply that is provided on the surface of the portion immersed in the substrate so as to be in contact with the working fluid and to face the heating element, and supplies the working fluid to a contact portion with the heating element by capillary action The heating element cooling method includes mounting a cooling member including a porous body having a portion and a steam discharge pipe for discharging the steam generated at the contact portion to the outside of the working fluid.

According to the present invention, when vapor is generated in the working fluid supply section and the contact section of the porous body, the liquid is forcibly supplied to the contact section by capillary action. The container (water tank) for storing the working fluid does not need to be provided with a water flow path or a pump, can use a simple water reservoir, can have a simple structure, and is low in installation cost and running cost. . Further, since the steam discharge pipe directly discharges the steam generated at the contact portion to the outside of the working fluid, the steam can be quickly discharged at the contact portion, thereby improving the critical heat flux.
As described above, according to the present invention, it is possible to provide a cooler having a simple structure and stably having a good cooling effect, a cooling device using the cooler, and a heating element cooling method.

It is a schematic diagram of the pressure vessel of a light water reactor (an example is a boiling water reactor). It is a schematic diagram of the cooler by the conventional pool boiling system. It is a figure for demonstrating the limit heat flux of the cooler by the conventional pool boiling system. It is a schematic diagram of the cooler by the pool boiling system which concerns on Embodiment 1 of this invention. It is a top view of the porous body comprised by the porous layer of the mesh structure which has many rectangular holes (opening part). It is a schematic diagram of the cooler by the pool boiling system which concerns on Embodiment 2 of this invention. It is a schematic diagram of the cooler by the pool boiling system which concerns on Embodiment 3 of this invention. It is a cooling device concerning Embodiment 4 of the present invention. It is a modification of the cooling device concerning Embodiment 4. 1 is a schematic diagram of an experimental apparatus for pool boiling experiments used in Example 1. FIG. FIG. 2 is a schematic diagram of an experimental apparatus for capillary force extraction experiment used in Example 1; 1 is a diagram showing a honeycomb porous body used in Example 1 and its geometric dimensions. FIG. 1 is a schematic diagram of a measuring device for measuring effective pore radius and permeability coefficient of a honeycomb porous body used in Example 1. FIG. It is the schematic which showed the flow of the gas-liquid on the heat-transfer surface at the time of honeycomb porous body mounting | wearing. FIG. 4 is a graph showing the relationship between the plate thickness δh obtained in Example 1 and qCHF. It is an experimental apparatus schematic diagram of a liquid supply effect extraction experiment that flows directly into the vapor discharge flow path used in Example 1. 3 is an electric circuit used for detecting dryout inside a porous body in Example 2. FIG. It is a graph which shows the time-dependent change of resistance value RTS between the electrode rod inserted in the copper block before and after burnout in Example 2, and the pool liquid level, and temperature T1 in the copper block. (A) is a graph which shows the qCHF trial calculation result of the capillary limit model in Example 2. FIG. (B) is a photograph of the appearance of the porous body of the capillary limit model in Example 2 and the structure of the rectangular hole (opening portion) (wall thickness δs: 0.46 mm, plate thickness δh: 1 mm, cell width dg). FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 4 shows a cooler using a pool boiling method according to the first embodiment. The cooler is a boiling-type cooler for cooling a heating element, which includes a container for storing a working fluid and a cooling member provided in the container, and the cooling member is in contact with the working fluid. In addition, a porous body provided with a working fluid supply unit that is provided so as to face the heating element and supplies the working fluid to the contact part with the heating element by capillary action, and steam generated at the contact part are operated. And a steam discharge pipe for discharging out of the fluid.

  The structure of the porous body is not particularly limited as long as it has at least a working fluid supply section. For example, the porous body may be formed of a porous layer having a mesh structure. As a specific example, FIG. 5 shows a plan view of a porous body composed of a porous layer having a mesh structure having a large number of rectangular holes (opening portions). The shape of the pores of the porous body can be various shapes such as a polygonal shape, a circular shape, and an elliptical shape.

  Further, the porous body may be formed of ceramics such as cordierite, may be formed of metal, or may be formed of an aggregate of porous nanoparticles. In particular, when the porous body is composed of an aggregate of metals or porous nanoparticles, the wettability of the heat transfer surface is improved, and the supply of the working fluid to the heat transfer surface is improved. Thereby, it becomes difficult to produce the dry area | region of a heat-transfer surface, and it can prevent that a limit heat flux becomes small. The average particle size of the porous nanoparticles is preferably 10 to 50 nm. Moreover, as a material of the said porous nanoparticle, a metal, an alloy, an oxide, nitride, a carbide | carbonized_material, carbon etc. can be used, for example. As a method of forming a porous body with an aggregate of porous nanoparticles, for example, an aqueous solution in which nanoparticles are diffused is provided by a predetermined means on a heat transfer surface where a porous body is to be formed, While maintaining this state, the heat transfer surface is boiled by heating. In this way, the porous nanoparticles precipitate on the boiling heat transfer surface to form an aggregate, which becomes the porous body. When the porous body is composed of an aggregate of nanoparticles, a large number of pores between or within the particles form a working fluid supply unit. The particle part around the pores functions as a working fluid supply part that supplies the working fluid to the contact part by capillary action.

  The steam discharge pipe discharges the steam generated at the contact portion between the heating element and the porous body to the outside of the working fluid. In the case where the vapor discharge pipe is formed of a porous layer having a mesh structure having a large number of rectangular holes (openings) as shown in FIG. It can be provided so as to be plugged in. Moreover, when the porous body is formed of an aggregate of porous nanoparticles, a vapor discharge pipe can be provided so as to penetrate the porous body. It is preferable to provide a plurality of steam discharge pipes in order to discharge the steam generated at the contact portion between the heating element and the porous body to the outside of the working fluid more efficiently. Although the constituent material of a vapor | steam exhaust pipe is not specifically limited, For example, you may be formed with the silicon tube.

  The working fluid can be a liquid having a surface tension such as water, a low-temperature fluid, a refrigerant, an organic solvent, or the like.

  A working fluid supply part supplies a working fluid to a contact part with a heat generating body by a capillary phenomenon. The steam discharge pipe discharges the steam generated at the contact portion between the heating element and the porous body due to the heat from the heating element to the outside of the working fluid. As described above with reference to FIG. 3, the supply of the working fluid and the discharge of the steam are performed using separate paths in this manner, so that the steam covers the contact portion and the limit heat flux is limited. Can be suppressed. In addition, when vapor is generated at the working fluid supply part and the contact part of the porous body, liquid is forcibly supplied to the contact part by capillary action. Therefore, when using the pool boiling cooling method, the working fluid such as water is accommodated. The container (water tank) to be used does not need to be provided with a water flow path, a pump, or the like, can use a simple water reservoir, can have a simple structure, and has low installation costs and running costs. Further, since the steam discharge pipe directly discharges the steam generated at the contact portion to the outside of the working fluid, the steam can be quickly discharged at the contact portion, thereby improving the critical heat flux.

  When the liquid evaporates in the working fluid supply section, the porous body supplies the working fluid to the contact section by capillary action, but considering the limit mechanism of liquid supply by capillary force, the length of the capillary (ie As the thickness of the porous body is smaller, the limit, that is, the “limit heat flux” can be increased. On the other hand, FIG. 3 shows a state in which the vapor mass is formed on the contact portion under the high heat flux condition, but the volume of the vapor mass increases with time and eventually cuts off from the contact portion. If the vapor mass and the vicinity of the contact portion are described in more detail, a liquid film having a finite thickness (generally called a macro liquid film) exists between the vapor mass and the contact portion (that is, the bottom of the vapor mass). . Under such a high heat flux condition, burnout occurs when the macro liquid film at the bottom of the vapor mass is exhausted and exhausted while the vapor mass remains on the macro liquid film. The heat flux at this time is called “limit heat flux”. As described above, the thickness of the porous body should be thinner than the limit mechanism (capillary limit mechanism) of the liquid supply by capillary force, but if it is too thin and the same as the thickness of the macro liquid film, the contact of the porous body Liquid drainage tends to occur in the vicinity of the part, and the critical heat flux becomes small. For this reason, it is preferable that the thickness of a porous body shall be 200-300 micrometers. Here, as in the first embodiment of the present invention, the supply of the working fluid and the discharge of the steam are made separate paths, so that the stay of the steam mass above the working fluid supply unit does not occur in FIG. As a result, it is possible to ensure that the working fluid supply unit and the working fluid are always in contact with each other, and even when the porous body has the same thickness as the macro liquid film, liquid drainage in the vicinity of the contact portion of the porous body is prevented. Is possible.

  It is preferable that a gap region is formed at a contact portion between the porous body of the cooling member and the heating element. Vapor generated at the bottom surface of the working fluid supply unit of the porous body travels along the bottom surface of the working fluid supply unit, travels to the steam discharge pipe, and is discharged through the steam discharge pipe. Here, when a gap region is formed at the contact portion between the porous body of the cooling member and the heating element, the gap region becomes a passage for the vapor generated at the bottom surface of the porous body, and the discharge of the vapor is promoted. The critical heat flux is improved. The gap area may be processed to be rough on the surface of the contact part, but since the gap area necessary for the discharge of the vapor is very small, simply contacting the porous body with the contact part from the beginning. A sufficient gap region is formed by the roughness of the surface of the contact portion. In addition, since the gap | emission area | region disappears, the vapor | steam discharge | emission property falls, but the porous body may be fixed to the contact part with the adhesive agent.

  Further, as another aspect of the present invention, cooling can be performed by immersing the entire heating element in the working fluid, or by partially immersing a part of the heating element from the liquid level of the working fluid. In this case, the heating element takes various forms depending on cases such as a floating state, a state where it is placed on the bottom surface of the container, etc. In short, by attaching a cooling member to a portion immersed in the working fluid, Cooling can be performed in the same manner as described above.

(Embodiment 2)
FIG. 6 shows a cooler using a pool boiling system according to Embodiment 2 of the present invention. Embodiment 2 is that the cooler according to Embodiment 2 is provided such that one end of the steam discharger faces the heating element and the other end extends through the container and extends outside the container. 1 is different from the cooler according to 1.

(Embodiment 3)
FIG. 7 shows a cooler using a pool boiling system according to Embodiment 3 of the present invention. The cooler according to the third embodiment is different from the cooler according to the second embodiment in that the cooling member and the container are provided below the heating element. That is, in the cooler according to the third embodiment, a container including a working fluid is installed below the heating element, and a porous body is provided in the container so as to face the heating element. . The steam discharge pipe is provided so that one end thereof faces the heating element and the other end extends through the container and extends out of the container.

(Embodiment 4)
FIG. 8 shows a cooling device according to Embodiment 4 of the present invention. The cooling device includes the cooler according to the first embodiment and a capacitor connected to the container. In the condenser, the evaporated working fluid is liquefied and returned to the container. The cooling device does not require an external power source such as a pump, and is excellent in compactness and energy saving as the entire device. FIG. 9 shows a modification of the cooling device according to the fourth embodiment. 8 and 9 can be used together with the cooler of the second or third embodiment.

  The present invention can be applied to various electronic equipment and other thermal equipment having a high heat generation density in addition to cooling of the reactor pressure vessel. For example, divertor cooling in fusion reactors, high performance of capillary pump loops, semiconductor lasers, data center server cooling, CFC-cooled chopper control devices, power electronics, and the like are conceivable. Alternatively, it can be applied to a water-cooled jacket that improves the high-temperature work environment by reducing the heat dissipated from the side or bottom of a glass or aluminum melting furnace to the surrounding environment. Furthermore, the present invention can be applied to a water-cooled jacket installed on the side of the fire wall or the bottom of the fire wall to reduce damage by cooling the fire wall such as a large garbage incinerator from the outside.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

Example 1
FIG. 10 shows an outline of an experimental apparatus for the pool boiling experiment used in Example 1. The heat transfer surface is the same height as the pool bottom, and the diameter of the heat transfer surface in contact with the liquid is 30 mm. Heating was performed with a cartridge heater embedded in the bottom of the copper block. The honeycomb porous body was fixed on the heat transfer surface with a stainless steel wire. A φ1mm K-type sheathed thermocouple is installed on the copper block center axis at positions of 10mm (TC1), 15mm (TC2), 20mm (TC3), and 25mm (TC4) downward from the heat transfer surface. The heat transfer surface temperature was extrapolated from the value, and the heat transfer surface heat flux was calculated from the indicated temperature difference, the installation distance, and the thermal conductivity of copper from the Fourier equation. The pool is made of Pyrex (registered trademark) glass having an inner diameter of 87 mm, and an internal boiling mode can be observed. The test liquid was distilled water, the water depth was 60 mm, the system pressure was 0.1 MPa, and the liquid around the heat transfer surface was heated with a preliminary heater to maintain the saturation temperature. The generated steam was condensed in a cooler and returned to the container. In the experiment, heating was performed by applying a predetermined voltage to the cartridge heater, and when each temperature change from TC1 to TC4 became 0.25K or less in 10 minutes, it was considered that the steady state was reached and measurement was performed. It was. The above operation was repeated until the steady state could not be maintained, the wall temperature started to rise rapidly, and burnout occurred. When burnout occurred, heating was stopped immediately and the heat flux immediately before that was defined as q _CHF .

FIG. 11 shows an apparatus outline of the capillary force extraction experiment used in Example 1. In order to extract the liquid supply effect due to the capillary force, it is necessary to exclude the liquid supply directly flowing into the vapor discharge flow path due to gravity. For this purpose, as shown in the detailed view of the heat transfer surface in FIG. 11, the heat transfer surface is turned downward, and the test liquid is circulated by a pump so that the pool liquid surface always coincides with the end face of the honeycomb porous body. The steam generated on the heat transfer surface was discharged to the outside by passing through a silicon tube (steam discharge pipe) penetrating the bottom of the pool container. Here, one end of the silicon tube (steam discharge pipe) is provided so as to be inserted into the hole of the honeycomb porous body. In this way, liquid supply to the heat transfer surface can be performed only by capillary force. The heat transfer surface was an end surface of a copper cylinder having a diameter of 10 mm, and was heated by a cartridge heater inserted in the copper block. The honeycomb porous body was fixed on the heat transfer surface with a wire. A φ1mm K-type sheath thermocouple is installed at the position of 10mm (TC1), 15mm (TC2), 20mm (TC3), 25mm (TC4) from the heat transfer surface to the upper end. The hot surface temperature and heat flux were calculated. The test liquid was distilled water, heated by a preliminary heater, and the water temperature in the vicinity of the pool liquid surface was measured to confirm that it was always saturated. The system pressure is 0.1 MPa. In the experiment, after a predetermined heating amount was applied, the temperature change of TC1 to TC4 was regarded as a steady state when the temperature change was 0.25 K or less per 10 minutes, and the measurement was performed. The above operation was repeated until the steady state could not be maintained, the heat transfer surface temperature started to rise rapidly, and burnout occurred. q The _CHF value is measured in the steady state just before burnout.

FIG. 12 shows the honeycomb porous body used in Example 1, the wall thickness δs between the cells, the cell width dg, and the plate thickness δh. This honeycomb porous body is a cylindrical honeycomb porous body (hereinafter abbreviated as NA honeycomb porous body), which is manufactured by Nagamine Manufacturing Co., Ltd. Its components are calcium aluminate (CaO · Al ₂ O ₃ ): 30-50 wt%, fused silica (Fused SiO ₂ ): 40-60 wt%, and titanium dioxide (TiO ₂ ): 5-20 wt%. Pore radius: 1.8 μm, porosity: 24.8%, permeability coefficient: 2.4 × 10 ⁻¹⁴ [m ² ]. A method for measuring the effective pore radius reff and the permeability coefficient K will be described later. The NA honeycomb porous body was manufactured in the same lot for the purpose of minimizing individual differences in manufacturing.

When calculating the predicted value of q _CHF using a capillary limit model described later, the effective pore radius reff and permeability coefficient K of the porous body are required. Therefore, each measurement was performed using the measurement apparatus shown in FIG. The effective pore radius was calculated from the equations (1) and (2) by measuring the capillary suction height h as shown in FIG. Further, the transmission coefficient K was calculated from the equations (1) and (3) from Darcy's law as shown in FIG.

  In measuring the effective pore radius reff, the test part is slowly lifted up, and the weight of the liquid column and the capillary force of the porous body are balanced at a certain height. Eventually, bubbles are generated and separated between the porous body and the liquid column. To do. The height was taken as the capillary suction height. In measuring the permeability coefficient K, a liquid column having a height exceeding the capillary suction height was prepared, the height was measured, and the flow rate per unit time was measured.

FIG. 14 is an enlarged sectional view of a part of the honeycomb porous body. When the honeycomb porous body is mounted, the flow of gas-liquid when the liquid is supplied to the heat transfer surface by capillary force and the generated vapor is discharged from the vapor discharge flow path is indicated by arrows. q The mechanical balance when _CHF is reached, as shown in equation (4), is the pressure loss Δp _l when the liquid flow passes through the porous body and the flow of the vapor flow through the discharge channel pressure loss Delta] p _g of the sum is the maximum capillary pressure Delta] PC, is considered a case where equal to max.

Also, in equation (4), the left side is determined by Laplace's equation, the right side first term is determined by Darcy's equation, and the right side second term is determined by Hagen-Poiseuille rule, and q _CHF can be calculated from the following equation (5).

  Where qCHF: critical heat flux, A: heat transfer surface area, K: permeability coefficient, ρ: density, hfg: latent heat of vaporization, Aw: contact area between porous material and heat transfer surface, reff: effective pore radius, μ: viscosity coefficient, δh: plate thickness of the porous body, and subscripts l and g indicate liquid and gas, respectively. From Equation (5), the validity of the model can be examined by comparing the measured value when the plate thickness δh of the honeycomb porous body is changed with the calculated value of the model.

FIG. 15 shows the relationship between the plate thickness δh and qCHF. The honeycomb porous body was tested by changing the cell width dg = 1.33 mm, the wall thickness Δs = 0.46 mm, and the plate thickness Δh to 2, 5, and 10 mm. In the figure, “◯” indicates the result of pool boiling experiment, “Δ” indicates the result of extraction of the liquid supply effect of capillary force, and the solid line indicates the calculation result of the capillary limit model. From FIG. 15, it can be seen that the liquid supply extraction experiment by capillary force is in good agreement with the capillary limit model. The pool boiling qCHF shows a tendency to increase as δh decreases, similar to the experimental value based only on liquid supply by capillary force and the predicted value based on the capillary limit model. It can be seen that at δh = 10 mm, the difference between the two experimental results is larger than the other cases. This can be attributed to the fact that the liquid supply effect directly flowing into the vapor discharge flow channel cannot be ignored with respect to the liquid supply effect due to the capillary force. Therefore, using the experimental apparatus shown in FIG. 16, extraction of the effect of supplying the liquid directly flowing into the vapor discharge flow path was performed. The steam passing through the inside of the steam discharge channel was simulated by flowing nitrogen gas from below the honeycomb porous body, and the steam generation flow rate from the heat transfer surface where the liquid just did not flow into the steam discharge channel was estimated. The experiment was conducted in an unheated system. A honeycomb porous body with dg = 1.33mm, δs = 0.46mm, δh = 5mm was installed, and when the nitrogen gas flow rate was measured when the liquid just did not flow into the vapor discharge flow path, the heat transfer surface heat flux was It was found that the gas flow rate was about 1.5 MW / m ^{2 in} terms of conversion. Here, from FIG. 15, in the experiment of extracting the liquid supply effect by the capillary force, when δh = 10 mm, qCHF is about 0.75 MW / m ² , but under this heating condition, It is considered that there is a liquid supply that flows directly into the channel. From the above, in the case of δh = 10mm, in the pool boiling experiment, the liquid supply effect extraction due to the capillary force is combined with the liquid supply effect due to the capillary force and the liquid supply effect that flows directly into the vapor discharge channel. It is thought that qCHF improved compared to the previous experiment. In addition, since the qCHF in the pool boiling experiment in the case of Δh = 5 mm is about 1.5 MW / m ^2, it is considered that there is almost no effect of supplying liquid directly flowing into the cell. Therefore, in the case of Δh = 5 mm, it is considered that the qCHF of the liquid supply effect extraction experiment by the capillary force and the pool boiling experiment are approximately the same.
From the above results, it was found that qCHF in pool boiling can be well explained by a one-dimensional capillary limit model under high heat flux conditions where there is no liquid supply directly flowing into the steam discharge channel.

(Example 2)
In the capillary limit model described above, the porous body is completely filled with liquid before reaching qCHF, and when qCHF is reached, the dry region expands and burnout occurs. The results of a comparison between the qCHF generation model and actual phenomena are described below.

  An experimental apparatus similar to the experimental apparatus for extracting the liquid supply effect of the capillary force used in Example 1 was used. FIG. 17 shows an electric circuit used to detect dryout inside the porous body. By applying a constant current (I = 0.5mA) to the circuit simultaneously with heating the heat transfer surface, the resistance value between the electrode rod inserted in the copper block and the pool liquid surface is measured. Dry-out inside the body was detected.

FIG. 18 shows changes over time in the resistance value RTS between the electrode rod inserted in the copper block and the pool liquid level before and after the burnout and the temperature T1 in the copper block. The sudden change region of T1 in the figure indicates that burnout has occurred. It can also be seen that the RTS has risen sharply just before that. Further, the RTS before burnout is approximately the same as the resistance value (70 kΩ) when not heated, that is, when the porous body is completely hydrated. From the above results, as in the capillary limit model, it is considered that a dry region is not formed inside the porous body before burnout, and the dry region is widened when qCHF is reached and burnout occurs.
From the results up to this point, the qCHF generation mechanism can be well explained by the capillary limit model. Therefore, the optimum geometric shape of the honeycomb porous body was examined. FIG. 19 shows a trial calculation result by a model when the wall thickness δs is 0.46 mm, the plate thickness δh is 1 mm, and the cell width dg is changed. FIG. 19 suggests that when dg = 0.2 mm, qCHF can be improved up to 11 MW / m ^{2 at the} maximum.

Claims (9)

A boiling-type cooler for cooling a heating element, comprising a container for containing a working fluid, and a cooling member provided in the container;
The cooling member is
A porous body provided with a working fluid supply section provided in contact with the working fluid and facing the heating element, and supplying the working fluid to a contact portion with the heating element by capillary action;
A steam discharge pipe for discharging the steam generated at the contact portion out of the working fluid;
With cooler.   The cooler according to claim 1, wherein the vapor discharge pipe is provided so that one end faces the heating element and the other end extends through the container and extends outside the container.   The cooler according to claim 1 or 2, wherein the steam discharge pipe is formed of a silicon tube.   The cooler according to any one of claims 1 to 3, wherein the porous body is formed of a porous layer having a mesh structure.   The cooler according to any one of claims 1 to 4, wherein the porous body is made of metal.   The cooler according to any one of claims 1 to 3, wherein the porous body is formed of an aggregate of porous nanoparticles.   The cooler as described in any one of Claims 1-6 in which the clearance gap area is formed in the contact part of the said porous body and the said heat generating body. The cooler according to any one of claims 1 to 7,
A cooling device comprising a condenser connected to the container of the cooler and liquefying the evaporated working fluid. In the cooling method by the boiling method in which the heating element is cooled at least partially by immersing the heating element in the working fluid of the container containing the working fluid,
On the surface of the part immersed in the working liquid of the heating element,
A porous body provided with a working fluid supply section provided in contact with the working fluid and facing the heating element, and supplying the working fluid to a contact portion with the heating element by capillary action; A method for cooling a heating element, comprising a cooling member provided with a steam discharge pipe for discharging the steam generated at the contact portion to the outside of the working fluid.