JP2014022478A - Vapor cooling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the boiling heat transfer coefficient of a natural circulation type vapor cooling device having a heating element 20 dipped in a liquid-phase refrigerant while suppressing deterioration in discharging properties of air bubbles when the heating element 20 coming into contact with the liquid-phase refrigerant to transfer heat to the liquid-phase refrigerant is arranged having one surface 22a substantially in parallel with the gravity direction.SOLUTION: A thickness "x" of a liquid-phase refrigerant layer is so set as to satisfy the mathematical expression (1), where (y) represents a length of the one surface 22a of the heating element 20 in a direction along the gravity direction and "x" represents a thickness of the liquid-phase refrigerant layer present on the one surface 22a of the heating element 20 in the horizontal direction.

Description

  The present invention relates to a boiling cooling device that cools a heating element such as a semiconductor element by latent heat transfer caused by boiling and condensation of a refrigerant.

  Conventionally, a storage unit that stores liquid-phase refrigerant therein, a heating element that is immersed in the liquid-phase refrigerant inside the storage unit, and a gas-phase refrigerant that is boiled and vaporized by the heat of the heating element are cooled and condensed to form a liquid phase. A natural circulation boiling cooling device that circulates the refrigerant between the storage unit and the condensing unit using a rise of the gas-phase refrigerant and the self-weight of the liquid phase refrigerant, etc. (For example, refer to Patent Document 1).

Japanese Patent No. 3876593

  By the way, in the above-mentioned natural circulation type boiling cooling device, when the heating element is arranged in the liquid phase refrigerant so that one surface (heat transfer surface) of the heating element in contact with the liquid phase refrigerant is substantially parallel to the direction of gravity, In order to improve the boiling heat transfer coefficient, the horizontal thickness of the liquid-phase refrigerant layer existing on one surface of the heating element may be reduced.

  The horizontal thickness of the liquid-phase refrigerant layer existing on one surface of the heating element is, for example, when one surface of the heating element and the side wall of the storage unit are opposed to each other, and one surface of the heating element and the storage unit facing it. It is the horizontal direction length of the liquid-phase refrigerant which exists between the side walls (opposing surfaces) of the heat generating element, that is, the separation distance between one surface of the heating element and the opposing surface.

  However, in the natural circulation type boiling cooling device in which one surface of the heating element is arranged substantially parallel to the direction of gravity, if the separation distance between the one surface of the heating element and the opposing surface is too small, it occurs on one surface of the heating element. The air bubbles are in contact with both the one surface and the opposite surface of the heating element, and the air bubble discharge property deteriorates.

  The bubbles in this state are not limited to a single bubble but may be a plurality of continuous bubbles arranged between one surface of the heating element and the opposing surface. The bubbles in this state balance the buoyancy with gravity and the like so that the bubbles do not rise. Therefore, the bubbles in this state become a resistance, and the discharge of bubbles generated one after another from one surface of the heating element is delayed.

  As a result, it becomes difficult to supply the liquid phase refrigerant to one surface of the heating element, and the boiling heat transfer coefficient is not improved, but the boiling heat transfer coefficient is lowered.

  In view of the above points, the present invention is a natural circulation boiling cooling device in which a heating element is immersed in a liquid-phase refrigerant and at least one surface of the heating element is substantially parallel to the direction of gravity. An object of the present invention is to provide a boiling cooling device capable of improving the boiling heat transfer coefficient while suppressing the deterioration of the discharge property.

In order to achieve the above object, in the invention described in claim 1,
The heating element has one surface (22a, 23a) that contacts the liquid-phase refrigerant and transfers heat to the liquid-phase refrigerant, and is disposed so that the one surface is substantially parallel to the direction of gravity.
When the length of one surface in the direction along the direction of gravity is y and the thickness in the horizontal direction of the liquid refrigerant layer existing on the one surface is x, the one surface satisfies the following formula (1). The thickness of the liquid-phase refrigerant layer is set according to the length.

ここで、数式（１）は、気泡の排出性が良好となるときの一面の長さｙと液相冷媒層の厚さｘとの関係を、本発明者が実験から求めたものである。

Here, in the formula (1), the inventor obtained from the experiment the relationship between the length y of one surface when the bubble discharge property is good and the thickness x of the liquid phase refrigerant layer.

  For this reason, when setting the thickness of the liquid-phase refrigerant layer to be small in order to improve the boiling heat transfer coefficient, by setting the thickness of the liquid-phase refrigerant layer so as to satisfy Equation 1, one surface of the heating element It can suppress that the bubble which generate | occur | produced from will be in the state which contacted both the one surface and opposing surface of a heat generating body.

  Therefore, according to the present invention, it is possible to improve the boiling heat transfer rate while suppressing the deterioration of the bubble discharge performance.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

It is a figure which shows the cross-sectional structure of the boiling cooling device in 1st Embodiment. It is a graph which shows the relationship between the separation distance x of the outer surface 22a of the 1st heat sink 22 in FIG. 1, and its opposing surface, and superheat degree (DELTA) _Tsat . It is a graph which shows the area | region which satisfy | fills Numerical formula (1). It is a figure which shows the cross-sectional structure of the boiling cooling device in 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
The boiling cooling device 1 of the present embodiment includes a storage unit 10, a heating element 20, and a condensing unit 30, and natural circulation in which refrigerant circulates between the storage unit 10 and the condensing unit 30 by gravity or buoyancy. Of the formula.

  The storage part 10 stores the liquid-phase refrigerant 12 inside, and is comprised by the housing 11 made from copper or aluminum in this embodiment. The housing 11 has an upper wall 11a, a bottom wall 11b, and side walls 11c and 11d, and the inner wall surfaces of the side walls 11c and 11d are parallel to the direction of gravity. As the refrigerant, for example, an insulating fluorine-based refrigerant such as a hydrofluoroether, hydrofluorocarbon, or hydrofluoroketone is used. Further, the refrigerant is sealed in a decompressed state.

  The condensing unit 30 cools and condenses the vapor-phase refrigerant boiled and vaporized in the storage unit 10, and returns the liquid-phase refrigerant 12 to the storage unit 10. In this embodiment, the condensing part 30 is arrange | positioned above the storage part 10, is provided between the several tubes 31 which form the flow path of a refrigerant | coolant inside, and the adjacent tubes 31, and expands a thermal radiation area. It is comprised as a heat exchanger provided with the fin 32 to do. The tube 31 and the fin 32 are made of copper or aluminum. By heat exchange between the gas-phase refrigerant in the tube 31 and the cooling air as an external fluid flowing between the adjacent tubes 31, the heat of the gas-phase refrigerant is released and the gas-phase refrigerant is condensed (liquefied).

  The condensing unit 30 and the storage unit 10 are connected by a gas phase refrigerant pipe 41 through which the gas phase refrigerant flows and a liquid phase refrigerant pipe 42 through which the liquid phase refrigerant 12 flows. Specifically, one end 41 a of the gas-phase refrigerant pipe 41 communicates with the upper portion of the housing 11, the other end 41 b of the gas-phase refrigerant pipe 41 communicates with the upper end side of the tube 31, and one end of the liquid-phase refrigerant pipe 42 42 a communicates with the lower part of the housing 11, and the other end 42 b of the liquid-phase refrigerant pipe 42 communicates with the lower end side of the tube 31.

  The heating element 20 is arranged inside the storage unit 10 and is immersed in the liquid phase refrigerant 12 inside the storage unit 10. The heating element 20 of the present embodiment includes a semiconductor element as the heating part 21, a first heat radiating plate 22 bonded to one surface 21 a of the heating part 21, and the other surface 21 b opposite to the one surface 21 a of the heating part 21. The heat generating portion 21, the first and second heat radiating plates 22, 23 are sealed while exposing the joined second heat radiating plate 23 and the outer surfaces 22a, 23a of the first and second heat radiating plates 22, 23. And a mold resin 24. The first and second heat radiating plates 22 and 23 are made of copper.

  In the present embodiment, the entire outer surfaces 22a, 23a of the first and second radiator plates 22, 23 are immersed in the liquid refrigerant 12, and the outer surfaces 22a, 23a of the first and second radiator plates 22, 23 are Each of them forms one surface (heat transfer surface) of the heating element 20 that is in contact with the liquid phase refrigerant 12 and transfers heat to the liquid phase refrigerant 12. The outer surface 22a of the first heat radiating plate 22 constitutes one surface of the heat generating body 20, the outer surface 23a of the second heat radiating plate 23 forms the other surface of the heat generating body 20, or the outer surface 23a of the second heat radiating plate 23 is formed. It can be said that one surface of the heating element 20 is configured, and the outer surface 22 a of the first heat radiating plate 22 configures the other surface of the heating element 20.

  The heating element 20 is arranged so that the outer surfaces 22a and 23a of the first and second heat radiating plates 22 and 23 are substantially parallel to the direction of gravity, and the mold resin 24 is placed on the top wall 11a and the bottom wall 11b of the housing 11. One end 24a and the other end 24b are inserted and fixed. At one end 24 a of the mold resin 24, a connection terminal 25 extending from the first heat dissipation plate 22 is exposed from the mold resin 24, and at the other end 24 b of the mold resin 24, a lead frame electrically connected to the semiconductor element 21. 26 is exposed from the mold resin 24, and the connection terminal 25 and the lead frame 26 are electrically connected to the external electrode outside the housing 11.

  In the storage unit 10, the horizontal thickness x of the liquid phase refrigerant layer existing on one surface of the heating element 20 is set small in order to improve the boiling heat transfer coefficient. Furthermore, when the length of one surface of the heating element 20 in the direction along the gravity direction is y and the thickness of the liquid phase refrigerant layer existing on the one surface of the heating element 20 in the horizontal direction is x, the following The thickness x of the liquid-phase refrigerant layer is set according to the length y of one surface of the heating element 20 so as to satisfy Equation (1).

発熱体２０の一面上に存在する液相冷媒層とは、発熱体２０の一面に接する液相冷媒１２であって、発生した気泡１３が上昇する流路となる部分のことである。本実施形態において、重力方向に沿った方向での発熱体２０の一面の長さｙは、第１、第２放熱板２２、２３の外面２２ａ、２３ａの重力方向長さであり、発熱体２０の一面上に存在する液相冷媒層の水平方向での厚さｘは、第１、第２放熱板２２、２３の外面２２ａ、２３ａとそれに対向するハウジング１１の内壁面（対向面）との水平方向での離間距離である。例えば、第１、第２放熱板２２、２３の外面２２ａ、２３ａの重力方向長さが４７ｍｍのとき、第１、第２放熱板２２、２３の外面２２ａ、２３ａ上に存在する液相冷媒層の厚さが６ｍｍ以上に設定されている。

The liquid-phase refrigerant layer existing on one surface of the heating element 20 is the liquid-phase refrigerant 12 in contact with one surface of the heating element 20 and is a portion that becomes a flow path in which the generated bubbles 13 rise. In the present embodiment, the length y of the one surface of the heating element 20 in the direction along the gravity direction is the length of the outer surfaces 22a and 23a of the first and second radiator plates 22 and 23 in the direction of gravity. The horizontal thickness x of the liquid refrigerant layer existing on one surface is determined by the outer surfaces 22a and 23a of the first and second heat radiating plates 22 and 23 and the inner wall surface (facing surface) of the housing 11 facing the outer surfaces 22a and 23a. The separation distance in the horizontal direction. For example, when the gravity direction length of the outer surfaces 22a and 23a of the first and second heat radiating plates 22 and 23 is 47 mm, the liquid refrigerant layer existing on the outer surfaces 22a and 23a of the first and second heat radiating plates 22 and 23. Is set to 6 mm or more.

  Here, Formula (1) will be described.

In the boiling cooling apparatus 1 having the configuration shown in FIG. 1, the inventor of the present invention has a horizontal thickness of the liquid-phase refrigerant layer existing on the outer surface 22 a of the first heat radiating plate 22, that is, the outer surface of the first heat radiating plate 22. The degree of superheat ΔT _sat was measured by setting the separation distance x between 22a and the facing surface to each value. The degree of superheat ΔT _sat is expressed by the following formula and is calculated from the measurement results of T _r and T _w .
ΔT _sat = T _r −T _w
T _r : refrigerant temperature when bubbles are generated (saturation temperature of liquid), T _w : surface temperature of heating element The measurement conditions at this time are as follows. As for the size of the outer surface (heat transfer surface) 22a of the first heat radiating plate 22 of the heating element, the gravity direction (vertical direction) length y is 47 mm, and the lateral length is 21 mm. The refrigerant used is a hydrofluoroether type. The refrigerant is sealed inside the boiling cooling device 1 in a depressurized state. Specifically, when the outside air temperature is 20 ° C., the refrigerant is sealed so that the internal pressure (saturated vapor pressure) of the boiling cooling device 1 is about 20 kPa. Has been. When the inside of the boiling cooling device 1 is in a reduced pressure state, the generated bubbles become enormous compared to the case of atmospheric pressure, so that it is likely to be in contact with both the one surface and the opposite surface of the heating element, and the bubble discharge property The deterioration becomes remarkable.

As shown in FIG. 2, when the heat flux q of the heating element 20 (heating element 21) is 30 W / cm ² or less, the value of the superheat degree ΔT _sat is constant when x ≧ 6, and when x = ∞. It was the same as ΔT _sat of. From this result, when the length in the gravity direction of the outer surface 22a of the first heat radiating plate 22 is 47 mm, the separation distance x between the outer surface 22a of the first heat radiating plate 22 and the opposing surface is set to 6 mm or more, thereby It is possible to improve the boiling heat transfer coefficient while suppressing the deterioration of the discharge performance.

  And even if the gravity direction length of one surface of the heating element 20 is other than 47 mm, it is assumed that the same relationship as this time is established, and the general formula when the gravity direction length of one surface of the heating element 20 is y is Equation (1).

  Here, as shown in FIG. 3, the vertical axis is the gravity direction length y of one surface of the heating element, and the horizontal axis is the horizontal thickness x of the liquid-phase refrigerant layer existing on one surface of the heating element. , A hatched area below the straight line of x = (6/47) y is an area that satisfies Expression (1). Note that the straight line in FIG. 3 is a straight line that passes through the origin and two points (x, y) = (6, 47).

Further, FIG. 3 shows the result of measuring ΔT _sat as in the case of the measurement in FIG. 2 when the length y in the gravity direction of one surface of the heating element is other than 47 mm. Compared with ΔT _sat when x = ∞, the case where the difference in ΔT _sat was 1K or more was evaluated as x, and the case where the difference in ΔT _sat was less than 1K was evaluated as ○. Note that when x = ∞ is assumed, the distance is sufficiently large so that it is clear that the bubbles do not contact both the one surface and the opposite surface of the heating element. As shown in FIG. 3, ◯ is shown in the hatched area that satisfies the formula (1), and x is shown outside the hatched area that does not satisfy the formula (1), so the formula (1) is appropriate. I understand that.

  The experimental results shown in FIG. 2 and FIG. 3 are for the case where a hydrofluoroether refrigerant is used, but in other fluorine refrigerants whose physical property values are similar to those of the hydrofluoroether refrigerant. It is speculated that similar results can be obtained.

  Next, the effect of the boiling cooling device 1 of this embodiment is demonstrated.

  When the heat generating part 21 of the heat generating element 20 is activated and generates heat in the storage part 10, the heat of the heat generating part 21 is transmitted to the liquid phase refrigerant 12 from the outer surfaces 22 a and 23 a of the first and second heat radiating plates 22 and 23. As a result, the liquid-phase refrigerant 12 is boiled and evaporated (evaporated). At this time, the outer surfaces 22a and 23a of the first and second radiator plates 22 and 23 are cooled by the latent heat of vaporization caused by the evaporation of the liquid-phase refrigerant 12.

  The gas-phase refrigerant boiled and vaporized in the storage unit 10 rises from the upper part of the storage unit 10, flows into the condensation unit 30 through the inside of the gas-phase refrigerant pipe 41, is cooled and condensed, and the liquid-phase refrigerant 12 Become. The liquid phase refrigerant 12 descends from the lower part of the condensing unit 30 due to its own weight, returns to the storage unit 10 through the liquid phase refrigerant pipe 42. In this way, the heating element 20 is cooled by the latent heat transfer caused by the boiling and condensation of the refrigerant.

  In the present embodiment, as described above, the horizontal separation distance x between the outer surfaces 22a and 23a of the first and second heat radiating plates 22 and 23 and the opposing surfaces thereof is as small as possible in order to improve the boiling heat transfer coefficient. And is set so as to satisfy the formula (1). For this reason, when bubbles 13 are generated from the outer surfaces 22a and 23a of the first and second heat radiating plates 22 and 23, both the outer surfaces 22a and 23a of the first and second heat radiating plates 22 and 23 and the opposing surfaces thereof. The generated bubbles 13 can be raised without being in contact with the bubbles 13.

  Therefore, according to the present embodiment, it is possible to improve the boiling heat transfer rate while suppressing the deterioration of the dischargeability of the bubbles 13.

(Second Embodiment)
As shown in FIG. 4, the boiling cooling device 1 of the present embodiment is different from the first embodiment in that a plurality of heating elements 20 are arranged inside the storage unit 10. It is the same as the form. In FIG. 4, the condensing unit 30, the gas-phase refrigerant pipe 41, and the liquid-phase refrigerant pipe 42 are omitted.

  The plurality of heating elements 20 are immersed in the liquid refrigerant 12 inside the storage unit 10, the surfaces of the adjacent heating elements 20 are opposed to each other, and the liquid phase refrigerant 12 is interposed between the opposing surfaces. Are arranged as follows. Specifically, three heating elements 20 having the same structure are arranged inside the housing 11. For example, the outer surface 23 a of the second heat radiation plate 23 of the first heating element 20 from the left in FIG. The outer surface 22a of the 1st heat sink 22 of the 2nd heat generating body 20 opposes, and the liquid phase refrigerant | coolant is interposing between both the outer surfaces 23a and 22a.

  Also in the present embodiment, as in the first embodiment, the horizontal surface between the outer surface 22a of the first heat radiating plate 22 of the first heating element 20 from the left in FIG. The separation distance x in the direction is set so as to satisfy Expression (1). The same applies to the third heating element 20 from the left in FIG.

  Further, in the present embodiment, as shown in FIG. 4, the liquid refrigerant layer existing between the surfaces of the adjacent heating elements 20 is divided into two regions in the horizontal direction, and one surface of one heating element 20 (for example, 4, the thickness x of the liquid-phase refrigerant layer present on the outer surface 23 a of the second heat radiating plate 23 of the first heating element 20 from the left in FIG. 4, and one surface of the other heating element 20 (for example, in FIG. 4). The thickness x of the liquid-phase refrigerant layer existing on the outer surface 22a of the first heat radiating plate 22 of the second heating element 20 from the left is set so as to satisfy the formula (1).

  That is, the horizontal thickness of the liquid refrigerant layer existing between the surfaces of the opposing heating elements 20 is set to 2x, and the horizontal thickness of the liquid refrigerant layer satisfies the formula (1). Has been. Specifically, the separation distance 2x between the outer surface 23a of the second heat radiating plate 23 of the first heat generating element 20 from the left in FIG. 4 and the outer surface 22a of the first heat radiating plate 22 of the second heat generating element 20 from the left in FIG. , So as to satisfy the formula (1).

  Also in the present embodiment, in all of the plurality of heating elements 20, the horizontal thickness x of the liquid refrigerant layer existing on the outer surfaces 22a and 23a of the first and second heat radiating plates 22 of the heating elements 20 is expressed by the formula ( Since it is set so as to satisfy 1), the same effects as in the first embodiment can be obtained.

(Other embodiments)
(1) In each of the above-described embodiments, the first and second heat radiating plates 22 and 23 are provided and both surfaces of the heating element 20 are cooled. However, only one of the first and second heat radiating plates 22 and 23 is provided. The present invention can also be applied to the case where one side of the heating element 20 is cooled.

  (2) In each of the embodiments described above, the first and second heat radiating plates 22 and 23 of the heating element 20 may be omitted, and the one surface 21a and the other surface 21b of the heat generating portion 21 may be in contact with the liquid phase refrigerant 12. . In this case, one surface 21a of the heat generating portion 21 corresponds to one surface of the heat generator.

  (3) In each above-mentioned embodiment, you may provide a porous layer in the outer surfaces 22a and 23a of the 1st, 2nd heat sinks 22 and 23 of the heat generating body 20. FIG. In this case, since the outer surface of the porous layer (the surface opposite to the heat receiving surface) corresponds to one surface of the heating element 20, the liquid phase present on the outer surface of the porous layer so as to satisfy Equation (1). What is necessary is just to set the thickness in the horizontal direction of a refrigerant | coolant layer.

  (4) In each of the above-described embodiments, pin fins including a plurality of columnar pins may be provided on the outer surfaces 22a and 23a of the first and second heat radiating plates 22 and 23 of the heating element 20. In this case, the thickness of the liquid refrigerant layer from the position of the tip of the pin fin is set to x, and x is set so as to satisfy the formula (1). When the liquid phase refrigerant layer has a plurality of thicknesses as described above, the thickness of the liquid phase refrigerant layer at the position where the thickness of the liquid phase refrigerant layer is minimized is set to x. That is, at any position on one surface of the heating element, the horizontal thickness of the liquid-phase refrigerant layer existing on one surface of the heating element is set so as to satisfy Equation (1).

  (5) In each of the above-described embodiments, one surface of the heating element and its opposite surface are parallel to each other, but the present invention can be applied even when it is not completely parallel. For example, when the side walls 11c and 11d of the housing 11 are inclined so that the distance from the one surface of the heating element 20 increases toward the upper side, the horizontal thickness of the liquid refrigerant layer at the lower end of the one surface of the heating element 20 The horizontal thickness of the liquid-phase refrigerant layer is maximized at the upper end. In this case, what is necessary is just to set so that the minimum thickness of a liquid phase coolant layer may satisfy | fill Numerical formula (1).

  (6) You may combine each above-mentioned embodiment in the range which can be implemented.

DESCRIPTION OF SYMBOLS 1 Boiling cooler 10 Reservoir part 12 Liquid phase refrigerant 20 Heat generating body 22a The outer surface (one surface of a heat generating body) of a 1st heat sink
23a Outer surface of second heat sink (one surface of heating element)
30 Condensing section

Claims (3)

A reservoir (10) for storing the liquid-phase refrigerant (12) therein;
A heating element (20) immersed in a liquid refrigerant inside the reservoir;
In the natural circulation boiling cooling device, comprising a condensing unit (30) that cools and condenses the vapor-phase refrigerant boiled and vaporized in the storage unit and returns the liquid-phase refrigerant to the storage unit.
The heating element has one surface (22a, 23a) that is in contact with the liquid phase refrigerant and transmits heat to the liquid phase refrigerant, and the one surface is arranged so as to be substantially parallel to the direction of gravity.
When the length of the one surface in the direction along the direction of gravity is y and the thickness in the horizontal direction of the liquid phase refrigerant layer existing on the one surface is x, the following formula (1) is satisfied. The boiling cooling device is characterized in that the thickness of the liquid-phase refrigerant layer is set according to the length of the one surface.

A plurality of the heating elements are arranged so that one surface of the adjacent heating elements faces each other, and a liquid refrigerant is interposed between the facing surfaces.
The horizontal thickness of the liquid refrigerant layer existing between the opposing surfaces is 2x, and the horizontal thickness of the liquid refrigerant layer existing between the opposing surfaces is expressed by the equation (1). The boiling cooling device according to claim 1, wherein the boiling cooling device is set so as to satisfy. The boiling cooling device according to claim 1 or 2, wherein the heat flux of the heating element is 30 W / cm ² or less.

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