JP2011108685A - Natural circulation type boiling cooler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a natural circulation type boiling cooler capable of enhancing the condensing capability of a condenser unit. <P>SOLUTION: The natural circulation type boiling cooler includes a storage portion 2, which stores a liquid coolant for receiving the heat of a heating element Z; a partition portion 21 which partitions the space in the storage portion 2 into a boiling passage A and a circulation passage B; and the condensing unit 3, which communicates with the boiling passage A via an upper exit Aa of the boiling passage A, wherein the circulation passage B communicating with the boiling passage A at a lower portion of the boiling passage A. The opening area of the upper exit Aa of the boiling passage A is smaller than the area of the liquid surface of the liquid coolant inside the boiling passage A. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a natural circulation boiling cooling device that cools a heating element using a refrigerant.

  The boiling cooling device is a device that cools a heating element using latent heat when a liquid refrigerant boils. Some boiling cooling devices naturally circulate a liquid refrigerant depending on its structure. The natural circulation boiling cooling device transmits the heat generated by the heating element to the liquid refrigerant, causes the liquid refrigerant to boil and evaporate, condenses the vaporized refrigerant vapor, and returns it to the liquid refrigerant. The cycle of receiving heat is naturally performed by using the rise of the refrigerant vapor or the weight of the liquid refrigerant. A natural circulation boiling cooling device is described in, for example, Japanese Patent Laid-Open No. 10-173115 (Patent Document 1). Hereinafter, in the specification, the natural circulation boiling cooling device is simply referred to as “boiling cooling device”.

JP-A-10-173115

  By the way, the boiling cooling apparatus is provided with the accommodating part which accommodates a liquid refrigerant. The inside of the accommodating part is partitioned by a partition wall extending vertically, for example, into a boiling passage in which the liquid refrigerant that receives heat from the heating element is accommodated and a circulation passage that supplies the liquid refrigerant to the boiling passage. The boiling passage communicates with the reflux passage at the lower portion of the housing portion. Thereby, when the liquid refrigerant in the boiling passage decreases due to boiling, the liquid refrigerant in the circulation passage flows into the boiling passage by its own weight, and natural circulation is performed.

  The boiling passage communicates with a condensing unit disposed above the housing unit. The condensing unit cools and condenses the refrigerant vapor flowing from the boiling passage and returns it to the liquid refrigerant. The condensing unit includes a cooling unit (cooling pipe, fin, etc.) having a function of cooling the inside of the condensing unit. The liquid refrigerant condensed in the condensing part adheres to the surface of the cooling part in a film form and drops when it exceeds a certain amount. The condensing capacity of the condensing part is an ability largely related to the heat transfer coefficient in the boiling cooling device.

  The condensing capacity of the condensing part varies depending on the heat transfer coefficient of the cooling part. When a liquid refrigerant film (hereinafter referred to as a liquid film) adheres to the surface of the cooling unit, the heat transfer coefficient of the cooling unit is reduced by the amount of heat exchange between the condensing unit and the cooling unit. Therefore, it is required to improve the condensing capacity of the condensing part by removing the liquid film on the surface of the cooling part.

  This invention is made | formed in view of such a situation, and it aims at providing the boiling cooling device which can raise the condensing capability of a condensation part.

  The boiling cooling device of the present invention includes a housing part that houses a liquid refrigerant that receives heat from a heating element, a partition wall part that partitions a space in the housing part into a boiling passage and a circulation passage, and a boiling passage through an upper outlet of the boiling passage. A recirculation passage is a natural circulation boiling cooling device in communication with the boiling passage at a lower portion of the boiling passage, and an opening area of an upper outlet of the boiling passage is a liquid in the boiling passage. It is characterized by being smaller than the area of the liquid level of the refrigerant.

  The liquid refrigerant received from the heating element in the boiling passage is discharged as a vapor from the liquid surface of the boiling passage. The liquid level in the boiling passage serves as a vapor discharge port. In the present invention, since the opening area of the upper outlet of the boiling passage is smaller than the area of the liquid level in the boiling passage, the flow velocity of the steam discharged from the upper outlet of the boiling passage increases. Thereby, the vapor | steam which flowed up flows in into a condensation part. By increasing the steam inflow speed into the condensing unit, the effect of removing (dropping) the liquid film generated in the condensing unit by the wind pressure is increased. Furthermore, when the flow velocity of the steam is increased, a shearing force is applied to the liquid film in the condensing part, and the thickness of the liquid film is reduced. Thereby, the heat exchange through the liquid film becomes good. From the above, the condensing capacity of the condensing part is improved.

  Here, the area ratio of the opening area of the upper outlet of the boiling passage to the area of the liquid level in the boiling passage is preferably 0.8 or less. In the range of 0.8 or less, the increase in the heat transfer coefficient appears remarkably, and the effect of removing the liquid film is increased. Therefore, the condensing capacity of the condensing part is further improved.

  Furthermore, the area ratio is preferably 0.5 or less. Thereby, a heat transfer rate rises to about 1.5 times, the heat exchange through a liquid film becomes still more favorable, and as a result, the condensation capability of a condensation part further improves.

  The area ratio is preferably 0.2 or more. When the area ratio is less than 0.2, the pressure in the boiling passage increases, the boiling point of the liquid refrigerant may increase, and the heat transfer surface is not covered with the liquid refrigerant due to a decrease in the liquid level. The possibility arises. Alternatively, it is conceivable that the heat transfer surface is covered with the liquid refrigerant even if the liquid level is lowered, but this is not preferable because it leads to an increase in the vertical dimension of the boiling cooling device. If the area ratio is 0.2 or more, these inconveniences can be avoided and a decrease in the heat transfer coefficient in the boiling passage can be suppressed.

  Here, in the case where the storage unit includes a container part that stores the liquid refrigerant therein and a widened part that is positioned above the container part and is wider than the container part, the liquid level in the boiling passage is in the container part. Preferably it is located. When the liquid level is located in the container portion, the area ratio is not significantly reduced, and a rapid rise in boiling point can be prevented.

  The partition wall portion includes a first wall portion disposed in the container portion and an inclined wall portion disposed in the widened portion, and the inclined wall portion extends from the upper end of the first wall portion in the widening direction of the widened portion. It is preferable that the upper surface of the inclined wall portion is inclined so as to be higher from the upper end of the first wall portion toward the widening direction. The inclined wall portion can reduce the opening area of the upper outlet, and the liquid refrigerant dropped on the inclined wall portion is guided to the circulation passage.

  According to the boiling cooling device of the present invention, the condensing capacity of the condensing part can be increased.

It is a longitudinal cross-sectional view which shows the boiling cooling device which concerns on 1st embodiment. It is a front view which shows the boiling cooling device which concerns on 1st embodiment. It is a graph which shows the prediction transition of the heat transfer rate ratio with respect to an area ratio. It is a longitudinal cross-sectional view which shows the boiling cooling device which concerns on 2nd embodiment. It is a graph which shows the prediction transition of the liquid level fall with respect to an area ratio. It is a longitudinal cross-sectional view which shows the boiling cooling device which concerns on other embodiment.

  Next, the present invention will be described in more detail with reference to embodiments.

<First embodiment>
A boiling cooling device 1 according to a first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a longitudinal sectional view showing a boiling cooling device 1. FIG. 2 is a front view showing the boiling cooling device 1.

  As shown in FIG. 1, the boiling cooling device 1 includes a storage unit 2 and a condensing unit 3. The accommodating part 2 is a metal container which accommodates a liquid refrigerant (for example, water, alcohol, chlorofluorocarbon, etc.) inside, and has a container part 2a and a widened part 2b. The container part 2a has a substantially rectangular parallelepiped shape and accommodates a liquid refrigerant therein. The widened portion 2b is located above the container portion 2a and has a substantially rectangular parallelepiped shape widened in one plane direction (to the right in FIG. 1) from the container portion 2a.

  The accommodating part 2 has the heat-transfer surface 21 and the partition wall part 22 inside. The heat transfer surface 21 is a part that extends in the vertical direction and transfers the heat of the heating element Z to the liquid refrigerant. The heat transfer surface 21 faces a boiling passage A, which will be described later, and is the inner side surface of the housing portion 2 corresponding to the position of the heating element Z. Here, considering that the heat of the heating element Z is transmitted through the side wall of the housing portion 2, a range widened at an angle of about 45 degrees from the heating element Z as the heat transfer surface 21 as shown by the dotted line in FIG. Yes. The heating element Z is a power module or the like that is attached to the housing portion 2 and includes, for example, a semiconductor element. As shown in FIG. 2, here, a plurality of heating elements Z are attached to the side wall of the housing portion 2. The liquid level of the liquid refrigerant is located in the container portion 2a when the boiling cooling device 1 is stopped.

  The partition wall portion 22 includes a first member 22a and a second member 22b. The first member 22a is a plate-like member, and is disposed in parallel to the side wall of the container portion 2a at a position facing the heat transfer surface 21. The second member 22b is a plate-like member and is continuously joined to the upper end of the first member 22a. The second member 22 b is inclined obliquely upward from the upper end of the first member 22 a toward the side surface of the container part 2 a including the heat transfer surface 21. The second member 22b is located above the liquid level of the liquid refrigerant.

  The partition wall portion 22 formed of the first member 22a and the second member 22b partitions the internal space of the housing portion 2 into a boiling passage A and a reflux passage B. The partition wall portion 22 is joined to the inner side surface of the housing portion 2, but is not joined to the inner bottom surface of the housing portion 2. For this reason, the boiling passage A and the circulation passage B communicate with each other on the lower side.

  The boiling passage A is a space surrounded by the inner side surface, the inner bottom surface, and the partition wall portion 22 of the accommodating portion 2, and is a region on the heat transfer surface 21 side (left side in FIG. 1). The boiling passage A extends in the vertical direction, communicates with the condensation chamber 31 of the condensing unit 3 through the upper outlet Aa, and communicates with the reflux passage B through the lower inlet. The boiling passage A causes the liquid refrigerant to boil by receiving heat from the heat transfer surface 21, and causes the refrigerant vapor to flow out to the condensation chamber 31. The flow passage cross-sectional area of the boiling passage A gradually decreases in the range defined by the second member 22b.

  Here, in the boiling passage A, the opening area of the upper outlet Aa is narrowed by the second member 22b. And the liquid level of the liquid refrigerant in the boiling channel | path A is located below rather than the 2nd member 22b. Therefore, the opening area of the upper outlet Aa of the boiling passage A is smaller than the area of the liquid surface in the boiling passage A (that is, the flow passage cross-sectional area of the boiling passage A partitioned by the first member 22a). Yes. The separation distance between the heat transfer surface 21 and the first member 22a is about 2 to 5 mm. The area ratio of the opening area of the upper outlet Aa to the liquid surface area in the boiling passage A (hereinafter referred to as area ratio) is about 0.8 or less.

  The circulation passage B is a space surrounded by the inner side surface, the inner bottom surface, and the partition wall portion 22 of the housing portion 2 and is a region on the side (the right side in FIG. 1) without the heat transfer surface 21. The reflux passage B extends in the vertical direction, communicates with the condensation chamber 31 via the upper inlet, and communicates with the boiling passage A via the lower outlet. In the circulation passage B, the liquid refrigerant condensed in the condensing unit 3 flows from the upper inlet, and supplies the liquid refrigerant to the boiling passage A through the lower outlet. The liquid refrigerant flows from the circulation passage B toward the boiling passage A by its own weight.

  The condensing part 3 is arrange | positioned above the accommodating part 2, and condenses the refrigerant | coolant vapor | steam which flowed in from the boiling channel | path A, and returns it to a liquid refrigerant. The condensing unit 3 includes a condensing chamber 31 that is an internal space and a plurality of cooling pipes 32. The condensation chamber 31 is a substantially rectangular parallelepiped space, and communicates with the boiling passage A and the circulation passage B, respectively. Refrigerant vapor flows from the boiling passage A into the condensing chamber 31.

  The cooling pipe 32 is a pipe through which the cooling fluid circulates, and is disposed through the condensing unit 3 as shown in FIG. The cooling fluid may be gas or liquid, and cold water is used here. The cooling pipe 32 is externally connected to a radiator, a circulation pump, or the like. The cooling pipe 32 cools the condensation chamber 31 and condenses the refrigerant vapor in the condensation chamber 31. The condensed liquid refrigerant adheres to the surface of the cooling pipe 32 in the form of a film, then drops and flows into the circulation passage B, and then circulates into the boiling passage A.

Here, the relationship between the area ratio and the steam flow rate will be described. The area of the liquid surface in the boiling passage A is S ₁ , the opening area of the upper outlet Aa of the boiling passage A is S ₂ , the flow velocity of the steam discharged from the liquid surface is u ₁ , and the flow velocity of the steam flowing out from the upper outlet Aa Is u ₂ . By making the following two assumptions, u ₁ × S ₁ = u ₂ × S ₂ holds from the flow rate conservation law. From this, u ₂ = (S ₁ / S ₂ ) × u ₁ . Since the area ratio is S ₂ / S ₁ , if this is X, u ₂ = u ₁ / X. From this, it can be seen that if the area ratio is smaller than 1, the flow velocity of the steam flowing out from the upper outlet Aa increases.

Next, the relationship between the area ratio and the heat transfer coefficient of the condensing unit 3 will be described with reference to FIG. FIG. 3 is a graph showing a predicted transition of the heat transfer coefficient ratio with respect to the area ratio. The horizontal axis is the area ratio (S ₂ / S ₁ ), and the vertical axis is the degree of increase in the heat transfer coefficient. The heat transfer coefficient when the area ratio S ₂ / S ₁ is Divided by heat transfer coefficient (heat transfer coefficient ratio).

  The graph shown in FIG. 3 is based on the following formula (1). Formula (1) is a formula according to “Water film theory for Nusselt's flowing saturated steam”.

α is the heat transfer coefficient, C is a constant due to the flow direction and condition, C _f is the friction coefficient, lambda is the thermal transfer coefficient, [rho is the density, u is the mean velocity, mu is viscosity coefficient, t _s is the saturation temperature, theta wall The temperature, l is the height of the vertical wall, and h _lat is the latent heat of evaporation. The subscript L means the value for the liquid, and the subscript V means the value for the vapor.

Here, two assumptions are introduced. The first is to use boiling gas as an ideal fluid (u _V S is constant: S is a channel area). Second, the condensation unit blow port (i.e., top outlet Aa) a fixed value of pressure _{P 2} of the _{(P 2} is a constant). From this assumption, the following equations (2) and (3) hold.

Then, u ₂ in Expression (2) is substituted for u _V in Expression (1). Further, by regarding the P ₂ and the pressure in the condenser unit, and assigned to the following formula (4) is an expression of Antoine regarding vapor pressure and boiling point.

A, B, and C in the formula are constants determined by the gaseous substances. Thus, the condensation point temperature of the condensing unit can be defined (saturation temperature) t _s. By substituting the _{t s} in the formula (1), the equation (1) can be written in _S 2 / _{S 1,} they tend to 3 appearing. As shown in FIG. 3, according to the predicted transition based on Nusert's equation, it can be seen that the heat transfer coefficient increases as the area ratio decreases. In particular, it can be seen that when the area ratio is 0.5 or less, the increase in heat transfer coefficient increases.

  In the boiling cooling device 1, the opening area of the upper outlet Aa of the boiling passage A is smaller than the area of the liquid level in the boiling passage A. As a result, the flow velocity of the steam at the upper outlet Aa increases, and the liquid film on the surface of the cooling pipe 32 is easily removed as the increased speed of the steam flows into the condensation chamber 31. Furthermore, as shown in FIG. 3, when the area ratio is small, the heat transfer coefficient of the condensing unit 3 is improved. By these two actions, the condensing capacity of the condensing part 3 is improved.

  In 1st embodiment, since an area ratio is 0.8 or less, the heat transfer rate of the condensation part 3 improves. Moreover, since the upper part of the accommodating part 2 is the widening part 2b, the condensation space by the condensation part 3 can be expanded, and a condensation capability can be improved.

<Second embodiment>
The boiling cooling apparatus 10 of 2nd embodiment is demonstrated with reference to FIG. FIG. 4 is a longitudinal sectional view showing the boiling cooling device 10. In the second embodiment, parts having the same names as those in the first embodiment have the same functions, and therefore, the portions having different arrangements and shapes will be mainly described.

  The boiling cooling device 10 includes a storage unit 20 and a condensing unit 30. The accommodating part 20 is substantially T-shaped with the upper part widened. The accommodating part 20 includes a container part 20a that accommodates the liquid refrigerant, and a widened part 20b that is wider than the container part 20a at the upper part of the container part 20a. The liquid level of the liquid refrigerant is located in the container portion 20a when the boiling cooling device 10 is stopped. Furthermore, the accommodating part 20 is equipped with the heat-transfer surfaces 211 and 212 and the partition wall parts 221 and 222 inside.

  The heat transfer surface 211 (212) corresponds to the heating element Z1 (Z2), and is disposed on each of the inner side surfaces (left and right in FIG. 3) that are opposed to each other in the storage unit 20. A plurality of heating elements Z1 and Z2 are attached to the side wall of the accommodating portion 20 as in the first embodiment.

  The partition wall portion 221 is disposed in the accommodating portion 20 so as to be separated from the inner side surface, and the first member 221a (corresponding to the “first wall portion” in the present invention) and the second member 221b (in the present invention “ It is a plate-like member consisting of “an inclined wall portion”. The first member 221a is disposed in the container portion 20a so as to face and be parallel to the heat transfer surface 211. The distance between the first member 221a and the heat transfer surface 211 is about 2 to 5 mm. The 2nd member 221b is joined to the upper end of the 1st member 221a, and inclines in the said widening direction (left diagonally upward of FIG. 4) with respect to the 1st member 221a in the wide part 20b. In other words, the second member 221b extends so as to be inclined upwardly toward the widening direction from the upper end of the first member 221a. The separation distance between the tip of the second member 221b and the inner side surface of the opposing widened portion 20b is 0.5 times the separation distance between the first member 221a and the heat transfer surface 211.

  The partition wall part 222 is composed of a first member 222a and a second member 22bb, like the partition wall part 221. The partition wall 222 has a mirror image structure with the partition wall 221, and a description thereof is omitted. The partition wall part 221 (222) partitions the inner space of the housing part 20 into a boiling passage A1 (A2) and a circulation passage B.

  The boiling passage A <b> 1 faces the heat transfer surface 211 and is a space surrounded by the inner side surface, the inner bottom surface, and the partition wall portion 221 of the housing portion 2. The boiling passage A <b> 2 faces the heat transfer surface 212 and is a space surrounded by the inner side surface, the inner bottom surface, and the partition wall portion 222 of the housing portion 2. The boiling passage A1 (A2) has a channel cross-sectional area smaller than that in the container 20a at the upper outlet A1a (A2a) (area ratio 0.5). The circulation passage B is a space surrounded by the inner side surface, the inner bottom surface, and the partition wall portions 221 and 222 of the housing portion 2. The upper part of the circulation path B is widened by the inclination of the second members 221b and 222b. The boiling passages A <b> 1 and A <b> 2 and the circulation passage B are in communication with each other at the lower part of the housing portion 20.

  The condensing part 30 is disposed above the accommodating part 20 (the widened part 20b) and has a condensing chamber 31 and a plurality of cooling pipes 32. The condensation chamber 31 communicates with the boiling passages A1 and A2 and the reflux passage B. The liquid refrigerant condensed in the condensing unit 30 drops and flows into the widened circulation passage B.

  Here, in the second embodiment, the opening area of the upper outlet A1a (A2a) of the boiling passage A1 (A2) is smaller than the area of the liquid surface in the boiling passage A1 (A2) (that is, the flow passage cross-sectional area). ing. Thereby, the effect similar to 1st embodiment is exhibited. Furthermore, in the second embodiment, the area ratio is 0.5, and the condensing capacity of the condensing unit 30 is further improved by increasing the effect of removing the liquid film by increasing the flow velocity and improving the heat transfer coefficient shown in FIG. Can be made.

  Further, since the area ratio is 0.2 or more, the boiling point of the liquid refrigerant is hardly increased, and good heat transfer can be realized. When the area ratio is less than 0.2, the boiling point may increase by about 10 to 20 ° C. depending on the type of the liquid refrigerant, and in this case, it is difficult to cool the IC chip. Further, in this case, since the refrigerant liquid level is lowered by the pressure, the heat transfer surface may not be covered with the liquid refrigerant, and boiling cooling may not be performed. As shown in FIG. 5, when the area ratio is less than 0.2, the liquid level reduction amount increases rapidly. The graph of FIG. 5 is derived based on the formula (1), where the horizontal axis represents the area ratio and the vertical axis represents the liquid level drop (mm). Thus, the area ratio is preferably 0.2 or more.

  In the second embodiment, in the upright state as shown in FIG. 4, the liquid refrigerant level is located in the container portion 20 a both when the boiling cooling device 10 is operating and when it is stopped. Therefore, the liquid level is not located in the widened portion 20b, and an increase in boiling point due to a significant decrease in the area ratio can be prevented. Moreover, since the upper part of the accommodating part 20 is the wide part 20b, the condensation space by the condensation part 30 can be expanded, and the condensation capability by the condensation part 30 can be improved. In addition, the opening area of the upper outlet of the boiling passage A1 (A2) can be reduced by the second member 221b (222b), and the liquid refrigerant dripped from the condensing unit 30 is guided to the circulation passage B to cause natural circulation. Become smooth.

<Other embodiments>
As shown in FIG. 6, the width (flow path cross-sectional area) of the boiling passage A <b> 1 may be a structure that changes in the vertical direction when a part of the side wall of the container portion 20 a is inclined. When the liquid level is always located in the container part 20a, any channel cross-sectional area in the boiling channel A1 in the container part 20a is larger than the opening area of the upper outlet A1a. This also exhibits the same effect as in the above embodiment.

  The condensing unit may be an air-cooled condenser that has fins or the like and condenses the refrigerant vapor by air cooling. In the case of the air-cooled type, the cooling performance is lowered as compared with the case where the cooling pipe 32 is used. However, the configuration of the present invention is effective because the condensing capacity can be increased without increasing the size and cost. It is. In addition, the heat generating body may be disposed inside the housing portion, and in this case, the heat transfer surface is a surface in contact with the liquid refrigerant of the heat generating body.

1, 10: Boiling cooling device,
2, 20: accommodating portion, 2a, 20a: container portion, 2b, 20b: widened portion,
21, 211, 212: heat transfer surface, 22, 221, 222: partition wall,
22a, 221a, 222a: second member 22b, 221b, 222b: second member,
3, 30: condensing part, 31: condensing chamber, 32: cooling pipe,
A, A1, A2: Boiling passage, B: Circulation passage, Z, Z1, Z2: Heating element

Claims (6)

An accommodating portion for accommodating a liquid refrigerant that receives heat from the heating element;
A partition wall portion for partitioning the space in the housing portion into a boiling passage and a reflux passage;
A condensing part communicating with the boiling passage through an upper outlet of the boiling passage;
The natural circulation boil cooling device, wherein the circulating passage is in communication with the boiling passage at a lower portion of the boiling passage,
The natural circulation boiling cooling device, wherein an opening area of an upper outlet of the boiling passage is smaller than an area of a liquid surface of the liquid refrigerant in the boiling passage.   2. The natural circulation boiling cooling device according to claim 1, wherein an area ratio of an opening area of an upper outlet of the boiling passage to an area of a liquid surface in the boiling passage is 0.8 or less.   The natural circulation boiling cooling device according to claim 2, wherein an area ratio of an opening area of an upper outlet of the boiling passage to an area of the liquid surface in the boiling passage is 0.5 or less.   The natural circulation boiling cooling device according to claim 2 or 3, wherein an area ratio of an opening area of an upper outlet of the boiling passage to an area of the liquid surface in the boiling passage is 0.2 or more. The accommodating portion includes a container portion that contains a liquid refrigerant therein, and a widened portion that is located above the container portion and is wider than the container portion,
The liquid level in the boiling passage is the boiling cooling device according to any one of claims 1 to 4, which is located in the container portion. The accommodating portion includes a container portion that contains a liquid refrigerant therein, and a widened portion that is located above the container portion and is wider than the container portion,
The partition wall portion includes a first wall portion disposed in the container portion, and an inclined wall portion disposed in the widened portion,
The inclined wall portion extends from the upper end of the first wall portion in the widening direction of the widened portion,
The boiling cooling device according to any one of claims 1 to 5, wherein an upper surface of the inclined wall portion is inclined so as to be higher from the upper end of the first wall portion toward the widening direction.

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