JP2013024456A - Boiling cooler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiling cooler which can improve its cooling performance by suppressing the obstruction of heat conduction due to the occurrence of burnout or the production of a large quantity of bubbles.SOLUTION: The boiling cooler includes a cooler body 10, which has a contact part to an element 51 due to be cooled, and a liquid coolant 20, which is stored in the cooler body 10. The liquid coolant 20 is a liquid where a non-ionic fluorinated surfactant is added by 0.25 to 0.75 wt.%. The liquid coolant 20 enables suppression of the occurrence of burnout and further micronization of bubbles produced in boiling, so that heat can be conducted efficiently to improve its cooling performance.

Description

  The present invention relates to a boiling cooler that cools a heating element by latent heat transfer that occurs when a liquid refrigerant boils.

  A boiling cooler is a device that cools a heating element using a phase change of a liquid refrigerant from a liquid to a gas. The boiling cooler includes a liquid refrigerant that cools the heating element, a storage part that has a contact part that makes the heating element contact the liquid refrigerant, and a condensing part that is provided above the storage part and condenses the vaporized liquid refrigerant into a liquid. Prepare. Patent Document 1 discloses a vehicle-mounted boiling cooler that includes an accommodating portion that accommodates a liquid refrigerant therein. The liquid refrigerant used in the boiling cooler of Patent Document 1 is a mixed liquid of water and ethanol. Further, the ethanol concentration of the mixed liquid is 40 wt% or more.

  Patent Document 2 discloses a boiling cooler including a heat transfer circuit and a refrigerant circuit. The heat transfer circuit of Patent Document 2 is filled with a liquid refrigerant composed of water and HFC134a. The liquid refrigerant is a liquid to which 0.001 wt% to 30 wt% of an ionic fluorosurfactant is added.

JP 2010-121791 A JP 2002-243206 A

  In the boiling cooler disclosed in Patent Document 1, a liquid mixture of water and ethanol is used as the liquid refrigerant. For this reason, when compared with a mixed liquid of water and another alcohol, the critical heat flux can be increased, and accordingly, the occurrence of burnout can be suppressed. However, since the limit heat flux of ethanol is smaller than the limit heat flux of water, there is still concern about the occurrence of burnout.

  In this type of boiling cooler, liquid refrigerant is stored in a container or the like. At this time, if a large amount of bubbles are generated due to pool boiling, the heat transfer surface is covered with bubbles, and heat transfer may be hindered.

  In particular, the latent heat of ethanol is 855 kJ / kG and the latent heat of water is 2257 kJ / kG. Thus, the latent heat of ethanol is smaller than the latent heat of water. Therefore, when a mixed liquid of water and ethanol is used as the liquid refrigerant, the cooling performance is reduced due to the reduction of the latent heat. For this reason, it is required to compensate for the deterioration in cooling performance accompanying the decrease in latent heat.

  On the other hand, in the technique described in Patent Document 2, an ionic fluorosurfactant is added to the heat transfer medium. Therefore, the generation rate of the class rate can be improved. However, it has hardly contributed to the improvement of the cooling performance.

  Then, this invention makes it a subject to provide the boiling cooler which can aim at the improvement of cooling performance by suppressing generation | occurrence | production of a burnout and the inhibition of heat transfer by generation | occurrence | production of a large amount of bubbles.

  The boiling cooler according to the present invention includes a container having a contact portion with a heating element to be cooled and a liquid refrigerant accommodated in the container, and the liquid refrigerant is a nonionic fluorosurfactant having a value of 0. It is a liquid added with 25 to 0.75 wt%.

  According to this invention, the limit heat flux is greatly improved by adding a small amount of the fluorosurfactant to the liquid refrigerant. For this reason, occurrence of burnout can be prevented. And the refinement | miniaturization of a bubble is accelerated | stimulated by adding a trace amount of fluorine-type surfactant. Therefore, the problem that the heat transfer surface is covered with bubbles can be avoided, and the inhibition of heat transfer can be suppressed. Therefore, the cooling performance can be improved.

  In the boiling cooler according to the present invention, the liquid refrigerant is preferably a liquid obtained by adding 0.25 to 0.75 wt% of a fluorosurfactant to an ethanol aqueous solution.

  According to this invention, since ethanol is contained as the liquid refrigerant, the freezing point of the liquid refrigerant can be lowered. Therefore, freezing of the liquid refrigerant can be suppressed.

  According to the present invention, when a mixed liquid is used as a liquid refrigerant, a boiling cooler capable of improving the cooling performance by suppressing the occurrence of burnout and the inhibition of heat transfer due to the generation of a large amount of bubbles. Can be provided.

It is a schematic block diagram of the boiling cooler which concerns on embodiment of this invention. It is the graph which showed the relationship between the heat transfer rate of a liquid refrigerant | coolant, and a superheat degree for every density | concentration of surfactant. It is a graph which shows the relationship between surfactant concentration and a cooling performance index.

  Hereinafter, preferred embodiments of the boiling cooler of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted.

  FIG. 1 is a schematic configuration diagram of a boiling cooler 1 according to an embodiment of the present invention.

  The boiling cooler 1 according to the present embodiment is a so-called pool-type boiling cooler that performs air-cooling condensation. As shown in FIG. 1, the boiling cooler 1 includes a cooler body 10 and a liquid refrigerant 20 accommodated in the cooler body 10.

  The cooler body 10 is a hollow container having a substantially rectangular parallelepiped shape. The cooler body 10 includes a condensing unit 11, an evaporating unit 12, and a base plate 13. The condensing unit 11 is provided above the evaporation unit 12. The condensing unit 11 includes a plurality of heat radiation fins 11a. The evaporation unit 12 is a container that stores the liquid refrigerant 20. The evaporation part 12 is formed with an opening for fitting the base plate 13 therein. The base plate 13 has a function as a contact portion between the heating element to be cooled and the liquid refrigerant 20. The base plate 13 is fitted into the opening of the evaporation unit 12. The base plate 13 has a heat transfer surface 13a. The heat transfer surface 13 a is exposed inside the evaporation unit 12. For this reason, the heat transfer surface 13 a is in direct contact with the liquid refrigerant 20. Note that the base plate 13 is formed of a material having high thermal conductivity.

  The liquid refrigerant 20 is accommodated inside the evaporation unit 12. The liquid refrigerant 20 is a liquid obtained by adding 0.25 wt% to 0.75 wt% of a nonionic fluorosurfactant to an ethanol aqueous solution.

  Examples of the heating element to be cooled include a heating element 50 including an element 51 that is a power semiconductor element and a power module 52 on which a plurality of elements 51 are mounted. The element 51 is fastened to the evaporation unit 12 by a bolt (not shown) via the base plate 13.

  The operation of the boiling cooler 1 configured as described above will be described. First, the temperature of the element 51 increases in a state where the element 51 is performing its function. The heat of the element 51 is transmitted from the base plate 13 to the liquid refrigerant 20 through the heat transfer surface 13a. And the liquid refrigerant | coolant 20 boils on the heat-transfer surface 13a with this heat, becomes a refrigerant | coolant vapor | steam, and cools the heat-transfer surface 13a by the phase change from this liquid to gas.

  The evaporated refrigerant vapor rises in the liquid refrigerant 20 from the heat transfer surface 13a by buoyancy. Then, after reaching the liquid level of the liquid refrigerant 20, the inside of the cooler body 10 is further raised and reaches the condensing unit 11 installed above the cooler body 10. Thereafter, the refrigerant vapor exchanges heat with a secondary cooling medium such as air or water through the heat radiation fins 11 a of the condensing unit 11, and is condensed again to become the liquid refrigerant 20. The condensed liquid refrigerant 20 descends due to gravity and merges with the liquid refrigerant 20 in the evaporation unit 12.

  As described above, in the boiling cooler 1 of the present embodiment, the element 51 mounted on the power module 52 is cooled via the heat transfer surface 13a by the phase change of the liquid refrigerant 20 in the vicinity of the heat transfer surface 13a. it can.

  By the way, the liquid refrigerant 20 in the present embodiment is a liquid obtained by adding 0.25 wt% to 0.75 wt% of a nonionic fluorosurfactant (hereinafter simply referred to as “surfactant”) to an ethanol aqueous solution. is there. Thus, in this embodiment, since a trace amount of surfactant is added to the ethanol aqueous solution, the foaming of the liquid refrigerant 20 and the miniaturization of the bubbles are promoted. Therefore, the problem that the heat transfer surface 13a is covered with bubbles can be avoided, and drying on the heat transfer surface 13a can be suppressed. Further, by adding the surfactant, the critical heat flux is greatly improved as compared with the case where the surfactant is not added, so that the occurrence of burnout can be prevented. Therefore, the heat transfer inhibition due to the generation of a large amount of bubbles and the occurrence of burnout are suppressed, so that the cooling performance can be improved.

  Furthermore, according to the liquid refrigerant 20 to which a small amount of surfactant is added, the surface tension of the liquid refrigerant 20 is reduced, so that the bubbles formed on the heat transfer surface 13a are easily decomposed. Is made finer. Therefore, the problem that the entire heat transfer surface 13a is covered with bubbles can be avoided, and the occurrence of dryness on the heat transfer surface 13a can be suppressed. And the contact property of the element 51 and the liquid refrigerant | coolant 20 can be maintained favorable, and cooling performance can be improved.

Below, the effect which the boiling cooler 1 show | plays is demonstrated using FIG. FIG. 2 is a graph showing the relationship between the heat transfer coefficient (W / m ² K) and the degree of superheat (° C.) between the liquid refrigerant 20 containing a surfactant and the liquid refrigerant containing no surfactant. In the graph shown in FIG. 2, the vertical axis represents the heat transfer coefficient and the horizontal axis represents the degree of superheat. The degree of superheat is the difference between the temperature of the heat transfer surface 13a and the boiling point of the liquid refrigerant, and the higher the degree of superheat, the more difficult the liquid refrigerant boils. In FIG. 2, black dots indicate the case where the surfactant concentration is 0.0 wt% and no surfactant is added. A white square point indicates a case where the concentration of the surfactant is 0.25 wt%. The white diamond points indicate the case where the surfactant concentration is 0.5 wt%. The white triangle points indicate the case where the surfactant concentration is 0.75 wt%.

  In FIG. 2, the line connecting the white figure to which 0.25 wt% to 0.75 wt% of the surfactant is added is located on the left side as compared to the line connecting the black circle to which the surfactant is not added. I can see that That is, when a small amount of surfactant is added, the degree of superheat is suppressed and the heat transfer coefficient is high.

Therefore, for example, when the ethanol concentration in the liquid refrigerant 20 is 50 wt%, the surface tension is about 60% smaller than that of water having 72 dyn / cm ² . Thus, when the surface tension is small, an event called a deaeration state occurs in which bubble nuclei decrease when the boiling cooler 1 is stopped. When the boiling cooler 1 is restarted in a state where this deaeration state has occurred, the boiling start temperature rises and the degree of superheat tends to be higher than when the deaeration state has not occurred. However, as described above, when 0.25 wt% to 0.75 wt% of the surfactant is added, the degree of superheat is suppressed and the heat transfer coefficient is increased, so that the temperature of the heat transfer surface 13a is increased. It is possible to promote boiling. Therefore, it is possible to improve the cooling performance.

  FIG. 3 is a graph showing the relationship between the surfactant concentration and the cooling performance index based on the case where the liquid refrigerant is ethanol containing no surfactant. As shown in the graph of FIG. 3, as the surfactant concentration increases from 0, the cooling performance index increases from the reference value of 100, and when the surfactant concentration is 0.25 wt%, the cooling performance index increases. The maximum value is about 115. The cooling performance index maintains the maximum value of about 115 from the surfactant concentration of 0.25 wt% to 0.75 wt%. Furthermore, when the surfactant concentration is higher than 0.75 wt%, the cooling performance index gradually decreases. Thus, it can be seen that the highest cooling performance is exhibited when the surfactant concentration is about 0.25 to 0.75 wt%.

  As described above, the boiling cooler 1 according to the present embodiment includes the cooler body 10 having a contact portion with the element 51 to be cooled and the liquid refrigerant 20 accommodated in the evaporation portion 12, and the liquid The refrigerant 20 is a liquid to which 0.25 to 0.75 wt% of a nonionic fluorine-based surfactant is added. Therefore, an event such as a decrease in the latent heat of the liquid refrigerant, an increase in boiling start temperature, or an inhibition of heat transfer can be avoided, and the cooling performance can be improved. In addition, nonionic fluorosurfactants do not dissolve in water and thus have good compatibility when mixed.

  The liquid refrigerant 20 is a liquid in which a surfactant is added to an aqueous ethanol solution. Therefore, since ethanol having a lower freezing point than water is used as a reference liquid, an effect of lowering the freezing point of the liquid refrigerant 20 and preventing the liquid refrigerant 20 from freezing can be obtained.

  In addition, embodiment mentioned above demonstrates embodiment of the boiling cooler which concerns on this invention, and the boiling cooler which concerns on this invention is not limited to what was described in this embodiment. The boiling cooler according to the present invention may be a modification of the boiling cooler according to the present embodiment, or may be applied to another.

  For example, in the above-described embodiment, the boiling cooler 1 that is a pool boiling cooler has been described. However, the boiling cooler 1 does not necessarily have to be a pool boiling cooler. That is, even if the boiling cooler is a water-cooled condenser, a fluid boiling type or a heat pipe, it is possible to prevent the cooling performance from being lowered as in the case of the boiling cooler 1 which is a pool-type boiling cooler.

  In the above-described embodiment, an example in which a liquid obtained by adding a surfactant to an ethanol aqueous solution is used as the liquid refrigerant 20. However, the liquid refrigerant 20 may not be an ethanol aqueous solution. For example, a methanol aqueous solution or pure water may be used as the liquid refrigerant 20. However, since methanol has a lower freezing point than other alcohols such as methanol, the freezing point can be lowered more significantly even with a small amount. Therefore, it is possible to prevent the liquid refrigerant from freezing.

  Moreover, although embodiment mentioned above demonstrated the example which the heat-transfer surface 13a contacted the liquid refrigerant 20 directly, the heat-transfer surface 13a may contact the liquid refrigerant 20 indirectly. For example, by providing a plate member made of a material having high thermal conductivity between the heat transfer surface 13 a and the liquid refrigerant 20, heat may be indirectly transferred from the heat transfer surface 13 a to the liquid refrigerant 20.

  DESCRIPTION OF SYMBOLS 1 ... Boiling cooler, 10 ... Cooler main body, 11 ... Condensing part, 11a ... Radiation fin, 12 ... Evaporating part, 13 ... Base plate, 13a ... Heat-transfer surface, 20 ... Liquid refrigerant, 50 ... Heat generating body, 51 ... Element 52 ... Power module.

Claims (2)

A container having a contact portion with a heating element to be cooled;
A liquid refrigerant contained in the container,
The above-mentioned liquid refrigerant is a liquid to which a nonionic fluorosurfactant is added in an amount of 0.25 wt% to 0.75 wt%.   2. The boiling cooler according to claim 1, wherein the liquid refrigerant is a liquid obtained by adding 0.25 wt% to 0.75 wt% of the fluorosurfactant to an ethanol aqueous solution.

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