JP2021162195A - Ebullient cooling working fluid, ebullient cooling device using the same, and ebullient cooling method - Google Patents

Abstract

To provide an ebullient cooling working fluid that can dramatically improve CHF while maintaining low heat resistance for a long term.SOLUTION: An ebullient cooling working fluid includes: a cooling medium; and calcium carbonate particles which are dispersed in the cooling medium with concentration of 1 wt.% or less and have an average particle size of less than 5 μm.SELECTED DRAWING: None

Description

The present invention relates to a boiling cooling hydraulic fluid, a boiling cooling device using the working fluid, and a boiling cooling method.

Boiling cooling technology is expected as a next-generation technology for efficiently cooling high-temperature objects with high heat generation density at low cost. In the boiling cooling technology, the latent heat when the heat transfer surface of the heating element (cooled portion) is brought into contact with the working fluid to change the phase from a liquid to a gas is used. Since more heat energy can be transported with a small temperature difference than the sensible heat that causes temperature changes, phase change type coolers using boiling cooling technology are being developed both in Japan and overseas. ..

ENHANCING THERMAL CONDUCTIVITYOF FLUIDS WITH NANOPARTICLES (Stephen U.S. Choi and J.A. Eastman) Effect of nanoparticles on critical heat flux of water in pool boiling heat transfer (S.M.You, J.H.Kim, and K.H.Kim APPLIED PHYSICS LETTERS VOLUME 83, NUMBER 16, 2003)

However, the boiling cooling technique has a problem of critical heat flux (CHF). This means that when a heat flux load larger than CHF is applied to the heat transfer surface, cooling by the boiling method becomes difficult. When the heat flux increases, the amount of evaporation of the working fluid increases and the boiling bubbles that have been isolated and generated on the heat transfer surface are united, and as shown in FIG. 1, one large united bubble 10 is the heat transfer of the heating element 16. Start covering surface 18. When the heat transfer surface 18 is completely covered with the coalesced bubbles 10, the heat transfer surface 18 and the working fluid 14 do not come into contact with each other, and heat transfer by latent heat becomes impossible. The transition to this state where the cooling capacity is significantly reduced is called dryout or burnout. The heat flux that transitions to this state is CHF.

If dryout occurs during boiling cooling, the temperature of the heat transfer surface rises sharply due to a decrease in cooling capacity, which leads to heat failure in semiconductor devices. Further, if it is a heat-generating object, it may exceed the melting point and melt, resulting in a dangerous state such as a fire. In order to cope with this, attempts have been made to increase the CHF of the boiling cooling device, and it has been proposed to add an additive to the hydraulic fluid. The method of adding nanoparticles to the hydraulic fluid causes less damage to mechanical elements such as pumps and allows forced convection during single-phase cooling (Non-Patent Document 1). It has been reported that CHF is improved by about 200% when nanoparticles are added to a refrigerant used for boiling cooling (Non-Patent Document 2).

Upon contact with the heat transfer surface, the working fluid boils, the nanoparticles are concentrated, and the nanoparticles are deposited on the surface of the heat transfer surface. It is considered that the effect of improving CHF can be obtained by making the wetting limit temperature of the nanoparticle deposition surface higher than the wetting limit temperature of the original heat transfer surface. The wetting limit temperature refers to the maximum temperature at which the hydraulic fluid can wet and spread with respect to an object. When the temperature exceeds the wetting limit temperature, the hydraulic fluid cannot wet the heat transfer surface that has been dried by boiling again, and the transition to dryout begins. The higher the wetting limit temperature, the more difficult it is to transition to dryout.

When a boiling cooling hydraulic solution containing nanoparticles is used for a long time, the nanoparticle layer that continues to accumulate on the heat transfer surface becomes a heat resistance layer, and the temperature of the heat transfer surface during boiling cooling rises, increasing the heat resistance. I will let you. Thermal resistance is one of the performance indexes of a cooling device for electronic devices, and is a value indicating a temperature difference (K) generated when heat (W) is transferred between two points, that is, heat transfer difficulty. Since thermal resistance is an important factor in the design of the cooling device, reduction is also required in the boiling cooling device. Especially in the case of a boiling cooling device for electronic devices, it is necessary to keep the thermal resistance and the heat transfer surface temperature low for a long time because the operating temperature is directly linked to the product life of the electronic device to be cooled.

Therefore, the present invention presents the above two problems that are problematic during boiling cooling, that is, a boiling cooling hydraulic solution, a boiling cooling device, and a boiling cooling device that can significantly improve CHF while maintaining low thermal resistance for a long period of time. It is an object of the present invention to provide a boiling cooling method.

The boiling cooling hydraulic solution according to the present invention is characterized by containing a refrigerant and calcium carbonate particles having an average particle diameter of less than 5 μm dispersed in the refrigerant at a concentration of 1% by weight or less.

The boiling cooling device according to the present invention includes a portion to be cooled and a working fluid that can come into contact with the portion to be cooled, and the portion to be cooled is cooled by boiling evaporation of the working fluid due to the heat of the portion to be cooled. The boiling cooling device is characterized in that the above-mentioned working fluid for boiling cooling is used as the working fluid.

The boiling cooling method according to the present invention is a boiling cooling method for cooling the cooled portion by contacting the working fluid with the cooled portion and boiling and evaporating the working fluid by the heat of the cooled portion. It is characterized in that the above-mentioned hydraulic fluid for boiling and cooling is used as the hydraulic fluid.

According to the present invention, it is possible to provide a boiling cooling hydraulic fluid, a boiling cooling device, and a boiling cooling method capable of significantly improving CHF while maintaining low thermal resistance for a long period of time.

It is a figure for demonstrating the critical heat flux. It is a schematic diagram which shows an example of the boiling cooling apparatus of this invention. It is a schematic diagram which shows another example of the boiling cooling apparatus of this invention. It is the schematic which shows the heat transfer experiment system used for the evaluation of the hydraulic fluid for boiling cooling. It is a graph which shows the relationship between the distance from a heat transfer surface and a temperature. It is a schematic diagram which shows the other structural example of the boiling cooling apparatus of this invention. It is a schematic diagram which shows the other structural example of the boiling cooling apparatus of this invention. It is a schematic diagram which shows the other structural example of the boiling cooling apparatus of this invention. It is a schematic diagram which shows the other structural example of the boiling cooling apparatus of this invention. It is a schematic diagram which shows the other structural example of the boiling cooling apparatus of this invention. It is a schematic diagram which shows the other structural example of the boiling cooling apparatus of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
The boiling cooling hydraulic solution of the present invention (hereinafter, also simply referred to as a hydraulic solution) is a dispersion in which calcium carbonate particles having an average particle diameter of less than 5 μm are dispersed in a refrigerant. As the refrigerant, water is preferable, and pure water having less impurity elements, ion-exchanged water, and the like are more preferable. Ammonia, alcohols, hydrocarbons, fluorocarbons and the like may be used as the refrigerant. Examples of alcohols include ethanol and the like, examples of hydrocarbons include, for example, heptane, and examples of fluorocarbons include Freon-11 and the like.

Such a refrigerant may be used alone or in combination of two or more. When mixing, it is desirable to use a type and mixing ratio that uniformly dissolve each other. As the refrigerant, it is preferable that calcium carbonate can be dissolved. Further, the refrigerant preferably has a negative temperature characteristic in the solubility of calcium carbonate. The dissolved calcium carbonate is selectively reprecipitated in the vicinity of the heat transfer surface having a high temperature. This is because the contact thermal resistance between the particles in the calcium carbonate deposit layer on the heat transfer surface and the contact thermal resistance between the heat transfer surface and the particles are reduced, and the overall thermal resistance is reduced.

Calcium carbonate dissolves in the hydraulic fluid located in a region away from the heat transfer surface and having a relatively low temperature, and in the hydraulic fluid when the heat load is low or the device is stopped. As a result, long-term stable thermal resistance can be obtained by promoting the exfoliation of the calcium carbonate deposit layer. Alcohols compatible with water (ethanol, methanol, etc.) are preferable because calcium carbonate dissolves in the same manner as water.

Calcium carbonate particles are defined to have an average particle size of less than 5 μm. The average particle size in the present specification refers to the average particle size obtained by microscopic observation such as an electron microscope. The average particle size of the calcium carbonate particles is preferably 1 μm or less, more preferably 0.5 μm or less. The shape of the calcium carbonate particles is not particularly limited and may be any shape.

Specifically, the shape of the calcium carbonate particles may be spherical, granular, plate-shaped, rectangular parallelepiped, cubic or needle-shaped. In the case of spherical calcium carbonate particles, the diameter is defined as less than 5 μm, and in the case of non-spherical calcium carbonate particles, the major axis is defined as less than 5 μm. In the case of granular, plate-shaped and rectangular parallelepiped-shaped calcium particles, the length in the longitudinal direction is specified to be less than 5 μm, and in the case of cubic-shaped calcium particles, the length of one side is specified to be less than 5 μm. In the case of needle-shaped calcium carbonate particles, the length in the longitudinal direction is defined as less than 5 μm.

Calcium carbonate particles can be synthesized, for example, by blowing carbon dioxide gas into a calcium hydroxide suspension. The calcium hydroxide suspension is obtained by reacting calcium oxide with a sufficient amount of water. The average particle size of the calcium carbonate particles can be controlled, for example, by the reaction time. In the case of calcium carbonate particles having an average particle size of 5 μm or more, the average particle size may be adjusted to less than 5 μm by, for example, sieving.
Alternatively, the working fluid of the present invention can be prepared using commercially available calcium carbonate particles having an average particle diameter of less than 5 μm. Examples of the calcium carbonate particles that can be used include ultra-high purity calcium carbonate (CS) manufactured by Ube Material Industries Ltd.

The purity of calcium carbonate is not particularly limited, but high purity is preferable in consideration of its small amount of dissolution in the refrigerant. When low-purity calcium carbonate is dissolved in the refrigerant, impurity elements in calcium carbonate may elute into the working fluid, causing problems such as corrosion in the boiling cooling device.

The calcium carbonate particles are dispersed in the refrigerant at a concentration of 1% by weight or less to obtain the hydraulic fluid of the present invention. The concentration of calcium carbonate particles in the working fluid is preferably 0.5% by weight or less, more preferably 0.1% by weight or less. In order for the effects of the present invention to be exhibited, the concentration of calcium carbonate particles is desired to be 0.001% by weight or more.

The calcium carbonate particles can be dispersed in the refrigerant by, for example, shaking, stirring, or applying ultrasonic waves with a low-power ultrasonic bath. The method of dispersion is not particularly limited, but a method in which calcium carbonate particles are uniform and agglutination is reduced is preferable, and a method having high industrial practicality is preferable.

A dispersant may be used to disperse the calcium carbonate particles as long as the effects of the present invention are not impaired. Examples of the dispersant include a polycarboxylic acid-based dispersant containing a polymer composed of a polycarboxylic acid or an anhydride thereof or a salt thereof. As the polycarboxylic acid-based dispersant, Na-free polycarboxylic acid ammonium salts and acidic types that are not neutralized with cations are preferable. The amount of the dispersant is not particularly limited, but is generally about 0.1 to 10 parts by mass with respect to 100 parts by mass of calcium carbonate. The dispersant may be attached to the surface of the calcium carbonate particles.

Since the hydraulic fluid of the present invention contains calcium carbonate particles having an average particle diameter of less than 5 μm at a concentration of 1% by weight or less, the hydraulic fluid of the present invention has low thermal resistance and excellent heat transfer characteristics. Boil cooling can be performed. Specifically, it is possible to achieve a large CHF of about 200 to 500% in the conventional case where only water is used as the hydraulic fluid. Further, by using the hydraulic fluid of the present invention, it is possible to obtain the effect of suppressing the time-dependent change in the heat transfer efficiency on the heat transfer surface.

An example of the boiling cooling device of the present invention is shown in FIG. The boiling cooling device 20 includes a container 22 that houses the working fluid 24. Since the cooled portion 26 is in contact with a part of the bottom of the container 22, the working fluid 24 can be in contact with the cooled portion 26 via the container 22. Examples of the cooled portion 26 include a heat generating member such as a semiconductor device (IC chip). Depending on the type of the part to be cooled 26, it may be in direct contact with the working fluid 24.

The container 22 and the cooled portion 26 can have any shape. Further, the size and aspect ratio of the container 22 and the capacity of the working fluid 24 are not particularly limited and can be appropriately selected. The object of the present invention can be achieved if the working fluid 24 contained in the container 22 can be condensed after boiling and evaporating. The pressure in the container 22 may be atmospheric pressure, a pressurized environment, or a reduced pressure environment.

The working fluid 24 that has boiled and evaporated due to the heat of the portion 26 to be cooled rises in the direction of arrow a and is liquefied in the condenser 32 as a cooler. At this time, heat is released as shown by the arrow b, and the liquefied working fluid 24 returns to the container 22 as shown by the arrow c. As the capacitor 32, any shape and type can be used.

The boiling cooling device having the configuration shown in the figure does not require an external power source such as a pump, and the device as a whole is compact and excellent in energy saving. Since the boiling cooling device 20 of the present invention uses the boiling cooling hydraulic fluid as described above as the working fluid 24, high CHF can be repeatedly obtained with good reproducibility. Moreover, it is possible to suppress the time-dependent change in heat transfer efficiency on the heat transfer surface. Moreover, since no special treatment such as coating on the heat transfer surface is required, it can be produced at low cost.

FIG. 3 shows another example of the boiling cooling device of the present invention. The boiling cooling device 30 includes a container 22 that houses the working fluid 24 and is in contact with the cooled portion 26. In the boiling cooling device 30, two systems of piping are provided between the container 22 and the condenser 42. The working liquid that has boiled and evaporated due to the heat of the part to be cooled 26 rises in the direction of arrow a in one of the pipes and is liquefied in the condenser 42.

Similar to the case of the boiling cooling device 20 shown in FIG. 2, in the boiling cooling device 30, heat is released as shown by the arrow b due to the liquefaction in the condenser 42. The liquefied working fluid 24 passes through the other pipe as indicated by an arrow c and returns to the container 22. Since the piping is separately provided in this way, the boiling cooling device 30 is cooled more efficiently than the boiling cooling device 20 shown in FIG.

As described above, in the boiling cooling method of the present invention, the working fluid comes into contact with the cooled portion that requires boiling cooling, and the working fluid boils and evaporates due to the heat of the cooled portion, so that the cooled portion is cooled. Will be done. Any method in which the cooled portion is cooled by such a mechanism is within the scope of the present invention.

Specific examples of the present invention will be shown below, but these are not limited to the present invention.

Pure water was used as the refrigerant, and the hydraulic fluids for boiling and cooling of Examples 1 to 5 and Comparative Examples 1 to 5 were prepared according to the formulations shown in Table 1 below.

Specifically, the boiling cooling hydraulic fluids of Examples and Comparative Examples were prepared by the following methods.

[Example 1]
Calcium oxide and pure water were put into a reaction vessel equipped with a cooling device to prepare 2 L of a calcium hydroxide suspension having a concentration of 7.5 wt%. This suspension was cooled to 16 ° C., and carbon dioxide gas was introduced while stirring to carry out a carbonation reaction. Carbon dioxide gas was introduced so that the introduction rate was 5 L / min with respect to 1 kg of calcium hydroxide. Thus, a suspension containing calcium carbonate particles was obtained.

To the suspension containing calcium carbonate particles, 8 g of ammonium acrylate copolymer was added as a dispersant. This suspension was diluted with pure water so that the calcium carbonate concentration was 0.001 wt%, and ultrasonic waves were applied by an ultrasonic bath to carry out dispersion treatment to obtain a working solution of Example 1. The average particle size obtained by observing the calcium carbonate particles with an electron microscope was 0.07 μm.

[Examples 2 and 3]
The hydraulic fluids of Examples 2 and 3 were obtained by the same method as in Example 1 except that the calcium carbonate concentrations of the hydraulic fluids were changed to 0.01 wt% and 0.1 wt%, respectively.

[Example 4]
Calcium carbonate particles (ultra-high purity calcium carbonate CS3N-A manufactured by Ube Material Industries Ltd., average particle diameter <0.5 μm, purity 99.9%) are added to pure water and shaken in a polyethylene container. A suspension having a concentration of 10 wt% was prepared. This suspension was diluted with pure water so that the calcium carbonate concentration was 0.1 wt%, and ultrasonic waves were applied by an ultrasonic bath to carry out dispersion treatment to obtain a working solution of Example 4.

[Example 5]
The working fluid of Example 5 was obtained by the same method as in Example 4 except that the calcium carbonate concentration of the working fluid was changed to 1 wt%.

[Comparative Example 2]
Calcium carbonate particles (manufactured by Fuji Film Wako Co., Ltd., purity 99.9%, average particle diameter 5 μm) were added to pure water and shaken in a polyethylene container to prepare a suspension having a concentration of 10 wt%. This suspension was diluted with pure water so that the calcium carbonate concentration was 0.001 wt%, and ultrasonic waves were applied by an ultrasonic bath to carry out dispersion treatment to obtain a working solution of Comparative Example 2.

[Comparative Examples 3 and 4]
The hydraulic fluids of Comparative Examples 3 and 4 were obtained in the same manner as in Comparative Example 2 except that the calcium carbonate concentrations of the working fluids were changed to 0.01 wt% and 0.1 wt%, respectively.

[Comparative Example 5]
Aluminum oxide dispersion (ALW 10 wt% manufactured by CIK Nanotech Co., Ltd., average particle size 0.02 μm) is diluted with pure water so that the aluminum oxide concentration becomes 0.001 wt%, and ultrasonic waves are applied by an ultrasonic bath. The dispersion treatment was carried out to obtain the working fluid of Comparative Example 5.

The hydraulic fluids of Examples and Comparative Examples were evaluated using a heat transfer experimental system imitating a vapor chamber boiling cooling device. The outline of the heat transfer experiment system is shown in FIG. The system 50 includes a container 51 that houses the working fluid 54. The container 51 has a frame 52 made of SUS304, an oxygen-free copper upper plate 56 provided on the frame 52 via a gasket 53, and a bottom plate made of SUS304 provided under the frame 52 via a gasket 55. Includes 57 and.

The upper plate 56, the gasket 53, the frame 52, the gasket 55, and the bottom plate 57 are integrally crimped and fixed with bolts (not shown), whereby the space 59 accommodating the working fluid 54 is kept airtight. It is formed. A silicon rubber sheet is used as the gasket. In this embodiment, the volume of the space 59 is 60 mm × 60 mm × 22 mm.

A water-cooled heat sink 58 as a cooling unit is provided on the upper surface of the upper plate 56. The water-cooled heat sink 58 can circulate cooling water (for example, water at 25 ° C.). The pressure in the space 59 is adjusted by a vacuum pump (not shown) connected via the valve 64 and can be confirmed by the pressure gauge 66. The end face of the test piece block 60 that can be heated by the heater 62 is exposed on a part of the bottom plate 57. The test piece block 60 is a cylinder made of oxygen-free copper (diameter 9 mm), and the exposed upper end surface serves as a heat transfer surface 68.

A K-shaped sheath thermocouple 63 (Class 1, diameter 0.5 mm) is inserted radially from the side surface to the center of the test piece block 60 at a predetermined distance (3 mm, 6 mm, 9 mm) from the heat transfer surface 68. With these thermocouples 63 and a data logger (not shown), the temperature at a predetermined position of the test piece block 60 can be measured. By changing the applied voltage of the heater 62 with a transformer (not shown), the heat flux passing through the heat transfer surface 68 of the test piece block 60 can be controlled.

Prior to the evaluation test of the hydraulic fluid, the state of the heat transfer surface 68 of the test piece block 60 is adjusted. Specifically, after the heat transfer surface 68 is polished in one direction with polishing paper, dirt such as polishing powder generated is cleaned. The working fluids of Examples and Comparative Examples were filled into the space 59 of the heat transfer experimental system as the working fluid 54 so as to be 30% of the volume, and the amount of heat was applied under a vacuum atmosphere (pressure at the start of the test-95 kPa or less). The test was conducted.

The heat transfer surface temperature, heat flux, and thermal resistance at that time were determined. Each method is as follows.
After adjusting the applied voltage of the heater 62 to a steady state, the temperature at a predetermined distance (3 mm, 6 mm, 9 mm) from the heat transfer surface 68 of the test piece block 60 was measured with a thermocouple 63 for 1 minute, and each of them was measured. An average value was obtained for the distance. This was plotted in the graph of FIG. 5 as a measured value at each position at a predetermined distance from the heat transfer surface 68. The regression line of the temperature distribution at the three points shown in FIG. 5 was extrapolated to obtain the heat transfer surface temperature Tw (° C.).

Further, the slope of the regression line ΔT / Δx is regarded as the slope of the temperature change dT / dx, and the thermal conductivity k (W / m · K) is used to obtain the heat flux q (from the Fourier law of the following equation (1)). W / cm ² ) was calculated.
q = -k (dT / dx) ... Formula (1)

Here, the heat flux in the steady state at the applied voltage immediately before the transition to the dryout was defined as CHF while increasing the applied voltage in steps of 2 V or less. The definition of dryout is a state in which the temperatures of the three points measured by the thermocouple 63 have risen sharply compared to the previous states and have reached almost the same temperature.
Further, the thermal resistance R (K / W) was calculated by the following mathematical formula (2), where the center temperature of the water-cooled heat sink 58 and the upper plate 56 was Tc (° C.). The smaller the thermal resistance R, the better the heat transfer performance.
R = (Tw-Tc) / (q × heat transfer surface area) ... Formula (2)

Each of the working fluids of Examples and Comparative Examples was evaluated by performing three tests, and the thermal resistance and CHF were averaged. Table 2 below summarizes the measured values and averages of thermal resistance during CHF when the hydraulic fluids of Examples and Comparative Examples were used.

The thermal resistance of the working fluid containing no particles (Comparative Example 1) is 1.41 (K / W), whereas the thermal resistance of the working fluid of the examples is 1.30 (K / W) or less at the maximum. Therefore, it can be seen that the hydraulic fluid of the example is excellent in heat transfer performance.
When calcium carbonate particles having an average particle size of 5 μm are contained, the thermal resistance reaches 2.32 (K / W) at the maximum (Comparative Example 3). Its thermal resistance is as large as three times or more that of Example 2 containing calcium carbonate particles having an average particle diameter of 0.07 μm at the same concentration (0.01 wt%).

Table 3 below shows the measured values and averages of the critical heat flux (CHF) when the hydraulic fluids of Examples and Comparative Examples were used. Further, the relative CHF was obtained with the average CHF as 100% when only water was used as the hydraulic fluid (Comparative Example 1), and the results are shown in Table 3 below.

When the hydraulic fluid of the example was used, a relative CHF of 200% or more was obtained, and it was confirmed that a high CHF could be repeatedly obtained with good reproducibility by the hydraulic fluid of the example.
When calcium carbonate particles having an average particle size of 5 μm are contained, CHF is lowered (Comparative Examples 2 to 4). Even if the particles have an average particle size of 0.02 μm, in the case of aluminum oxide, the relative CHF is at most 157% (Comparative Example 5), which is not as good as that of the examples containing calcium carbonate particles.
The boiling cooling device of the present invention is not limited to the above configuration. The boiling cooling hydraulic fluid of the present invention can be used in boiling cooling devices having various configurations as shown in FIGS. 6 to 11.

In the boiling cooling device 70 shown in FIG. 6, a container 72 in which the wick 73 is arranged on the inner surface is used. The container 72 containing the working fluid 78 is in contact with the heating element 74 on the bottom surface and in contact with the cooling unit 76 on the top surface. The working fluid 78 that has boiled and evaporated due to the heat of the heating element 74 rises in the direction of arrow e and is liquefied by the cooling unit 76. The liquefied working fluid 78 moves in the wick 73 by the capillary phenomenon as indicated by the arrow r. By using calcium carbonate particles having a small average particle size, cooling is possible without clogging the wick. The shape of the container 72, the installation position and shape of the heating element 74 and the cooling unit 76, and the like are not particularly limited and can be appropriately selected.

The boiling cooling device can also be a flow type as shown in FIG. In the flow boiling cooling type boiling cooling device 80 shown in FIG. 7, the working fluid 88 is housed in the piping flow path 82. A pump 83 for transporting the working fluid 88 and a radiator 86 for cooling are provided in the middle of the piping flow path 82. The pressure in the pipe flow path 82 is not particularly limited, and may be any of atmospheric pressure, pressurized environment, and reduced pressure environment.
The working fluid 88 in the pipe flow path 82 is moved in the direction of the arrow by the pump 83. Although the heating element 84 is in contact with a part of the piping flow path 82, it can also be provided in direct contact with the working fluid 88. Since the particles contained in the boiling cooling hydraulic fluid of the present invention are fine particles having an average particle diameter of less than 5 μm, the influence on the bearings and the like in the pump 83 is minimized. The smaller the average particle size, the smaller the effect on moving parts such as pump bearings.

The cooling unit can also be housed in the container together with the working fluid. FIG. 8 shows the configuration of the pool boiling cooling type boiling cooling device 90. In the illustrated device 90, a condensing unit 96 as a cooling unit is provided inside the container 92 that houses the working fluid 98. The pressure in the container 92 is not particularly limited, and may be any of atmospheric pressure, pressurized environment, and reduced pressure environment. Although the heating element 94 is in contact with the bottom surface of the container 92, it can also be provided in direct contact with the working fluid 98. The shapes of the container 92, the heating element 94, and the condensing portion 96 are not particularly limited and can be appropriately selected.

The working fluid does not necessarily have to be contained in the container and can be brought into contact with the heating element by spraying it toward the heating element. FIG. 9 shows the configuration of the mist cooling type boiling cooling device 100. In the illustrated device 100, a plate 102 in contact with the heating element 104 on the bottom surface is used, and the working fluid 108 is sprayed toward the plate 102 by the spray nozzle 106. In this case, the working fluid 108 comes into contact with the heating element 104 via the plate 102, but the working fluid 108 may be sprayed directly onto the heating element 104.

Parameters such as the spray rate of droplets from the spray nozzle 106 and the distance between the spray nozzle 106 and the heat transfer surface are not particularly limited and can be appropriately selected. Since the particles contained in the boiling cooling hydraulic solution of the present invention are fine particles having an average particle diameter of less than 5 μm, there is little possibility that the spray nozzle 106 will be clogged, and the particles will be dispersed even in the scattered mist. Can exist. The smaller the average particle size, the less adverse effects on the spray nozzle.

FIG. 10 shows the configuration of the collision jet boiling cooling type boiling cooling device 110. The device 110 shown has the same configuration as the mist cooling type device 100 except that the nozzle spray is changed to the jet nozzle 112. The working fluid 118 collides with the plate 102 by the jet nozzle 112, but may directly collide with the heating element 104. Parameters such as the jet of droplets from the jet nozzle 112 and the distance between the jet nozzle 112 and the heat transfer surface are not particularly limited and can be appropriately selected. Since the particles contained in the boiling cooling hydraulic fluid of the present invention are fine particles having an average particle diameter of less than 5 μm, the influence on the pump bearing, the nozzle, and the like is minimized.

FIG. 11 shows the configuration of the liquid immersion cooling type boiling cooling device 120. In the illustrated device 120, a heating element 124 is provided in a container 122 that houses the working fluid 128. The shapes of the container 122 and the heating element 124, the water level of the working fluid 128 in the container 122, and the like are not particularly limited and can be appropriately selected. Since there is no condenser, the evaporated refrigerant flows out, but cooling can be continued simply by replacing or adding the hydraulic fluid. Therefore, it is advantageous for reducing the size and weight of the entire cooling system.

In any of the above, a boiling cooling device including a portion to be cooled and a working fluid that can come into contact with the portion to be cooled, and the portion to be cooled is cooled by boiling evaporation of the working fluid due to the heat of the portion to be cooled. Therefore, a desired effect can be obtained by using the boiling cooling hydraulic fluid of the present invention as a working fluid.

10 ... Combined air bubbles 14 ... Working fluid 16 ... Heat transfer part (heat generator) 18 ... Heat transfer surface 30 ... Boiling cooling device 32 ... Condenser 40 ... Boiling cooling device 42 ... Condenser 50 ... Heat transfer experiment system 51 ... Container 52 ... Frame 53 ... Gasket 54 ... Working fluid 55 ... Gasket 56 ... Top plate 57 ... Bottom plate 58 ... Water-cooled heat sink 59 ... Space 60 ... Test piece block 62 ... Heater 64 ... Valve 66 ... Pressure gauge

Claims (4)

A working liquid for boiling cooling, which contains a refrigerant and calcium carbonate particles having an average particle diameter of less than 5 μm dispersed in the refrigerant at a concentration of 1% by weight or less. The working fluid for boiling and cooling according to claim 1, wherein the calcium carbonate particles have an average particle diameter of 1 μm or less. A boiling-cooling device that includes a portion to be cooled and a working fluid that can come into contact with the portion to be cooled, and the portion to be cooled is cooled by boiling evaporation of the working fluid due to the heat of the portion to be cooled.
A boiling cooling device according to claim 1 or 2, wherein the boiling cooling hydraulic fluid is used as the working fluid. A boiling cooling method in which a working fluid comes into contact with a cooled portion and the working fluid boils and evaporates due to the heat of the cooled portion to cool the cooled portion.
A boiling cooling method comprising using the boiling cooling hydraulic fluid according to claim 1 or 2 as the working fluid.

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