Cooling plate and information processing device

A cooling plate includes a main body portion including a cooling surface; a first flow path formed inside the main body portion and configured to receive a refrigerant from a pump side; a second flow path formed inside the main body portion and configured to discharge the refrigerant to the pump side; a third flow path provided closer to a side of the cooling surface than the first flow path and the second flow path in the main body portion and configured to couple the first flow path and the second flow path; and a reduced diameter portion formed in the third flow path and configured to narrow a flow path diameter of the third flow path.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2018-40687, filed on Mar. 7, 2018, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a cooling plate and an information processing device.

BACKGROUND

A cooling device includes an aspirator incorporated in a liquid circulation path.

Related art is disclosed in Japanese Laid-open Patent Publication No. 2014-183107.

SUMMARY

According to an aspect of the embodiments, a cooling plate includes a main body portion including a cooling surface; a first flow path formed inside the main body portion and configured to receive a refrigerant from a pump side; a second flow path formed inside the main body portion and configured to discharge the refrigerant to the pump side; a third flow path provided closer to a side of the cooling surface than the first flow path and the second flow path in the main body portion and configured to couple the first flow path and the second flow path; and a reduced diameter portion formed in the third flow path and configured to narrow a flow path diameter of the third flow path.

DESCRIPTION OF EMBODIMENTS

For example, a cooling device in which a steam pipe extending from an evaporator that removes heat from a heat source is connected to an aspirator incorporated in a liquid circulation path. The evaporator that removes heat from a heat source is sometimes called a cooling plate or the like and demonstrates the cooling effect by latent heat when a liquid inside is heated by heat of the heat source to be nucleate boiling and the phase changes from a liquid to a gas.

For example, in an information processing devices, the size of a central processing unit (CPU) is reduced and a graphics processing unit (GPU) is mounted, which serve as heat sources; for this reason, the heat generation density is increasing. In order to cope with such a situation, improvement in cooling efficiency is also required for the cooling plate itself.

For example, the technology which improves cooling efficiency of a cooling plate may be provided.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that, in the drawings, the dimensions, ratios, and the like of respective portions are not illustrated so as to completely match the actual ones in some cases. In addition, in some drawings, there are cases where the actually existing constituent elements are omitted or the dimensions are drawn exaggeratedly than actually for the sake of convenience of the explanation.

First Embodiment

With reference toFIGS. 1, 2A and 2B, an information processing device100of an embodiment has a substrate102installed on a frame101. On the substrate102, a package substrate (PKG substrate)103is mounted. On the PKG substrate103, a CPU104that is a heat source and is to be cooled is mounted. The CPU104is an example of an object to be cooled. On the CPU104, a cooling plate1is installed. The cooling plate1is provided with an inflow pipe105and a discharge pipe106for a refrigerant. A refrigerant W having a low temperature (low temperature water) flows into the cooling plate1from the inflow pipe105. The refrigerant W after cooling the CPU104(high temperature water) is discharged from the discharge pipe106. The inflow pipe105and the discharge pipe106are connected to a circulation path108via a distribution unit107. The circulation path108is provided with a chiller109that cools the refrigerant W and a pump110that ejects the refrigerant W toward the cooling plate1. The refrigerant W cooled by the chiller109is ejected toward the cooling plate1by the pump110. Although the information processing device100of the present embodiment is a system board, the information processing device100may be another device. In addition, the CPU104is an example of an electronic component and any electronic component that generates heat can be regarded as an object to be cooled by the cooling plate1. Furthermore, in the present embodiment, water is used as the refrigerant W, but another refrigerant such as ethanol may be used.

Next, the cooling plate1will be described in detail with reference toFIGS. 3 to 6.FIG. 3is an explanatory view schematically illustrating the arrangement of flow paths in the cooling plate1of the embodiment.FIG. 4illustrates a state in which a top plate portion5is separated from a main body portion2and a cross section is taken at a position corresponding to line A-A inFIG. 3, in order to clearly illustrate the condition of the inside of the cooling plate1.FIG. 5is a cross-sectional view taken along line A-A inFIG. 3.FIG. 6is an explanatory view illustrating the inside of a third flow path8.

With reference toFIGS. 3 and 4, the metal cooling plate1includes the main body portion2and the top plate portion5integrated with the main body portion2. One surface of the main body portion2is prepared as a cooling surface2a. The cooling surface2ais a surface brought into contact with the CPU104to be cooled such that heat exchange with the CPU104is performed thereon. The cooling plate1of the present embodiment is made of copper, but the cooling plate1can be formed of another material. The top plate portion5can be bonded to the main body portion2by, for example, diffusion bonding.

A first flow path3into which the refrigerant W ejected by the pump110flows and a second flow path4that discharges the refrigerant W to the side of the pump110are provided inside the main body portion2. The first flow path3and the second flow path4are provided in parallel and extend in the same direction. The first flow path3and the second flow path4are provided such that the refrigerant W flows in the same direction as indicated by arrows inFIG. 3. The first flow paths3and the second flow paths4are alternately arrayed in a direction orthogonal to a flow direction indicated by the arrows inFIG. 3.

A refrigerant inflow hole6is provided in an upstream portion of the top plate portion5for each first flow path3. The refrigerant W flows into each first flow path3from a refrigerant distribution pipe7coupled to the inflow pipe105of the refrigerant W through the refrigerant inflow hole6. The refrigerant W having a low temperature (low temperature water) flows in the first flow path3, while the refrigerant W after cooling the CPU104(high temperature water) flows in the second flow path4.

The adjacent first flow path3and second flow path4are connected by the third flow path8. The third flow path8is a microchannel and is provided on a side closer to the cooling surface2athan the first flow path3and the second flow path4in the main body portion2. When the cooling plate1is installed on the CPU, the third flow path8is provided under the first flow path3and the second flow path4. A first end portion8aof the third flow path8is located within the first flow path3. A second end portion8bof the third flow path8is located within the second flow path4. The first end portion8aopens into the first flow path3and serves as an entrance of the third flow path8. The second end portion8bopens into the second flow path4and serves as an exit of the third flow path8. The second end portion8bcorresponds to a flow path end portion where the third flow path8merges with the second flow path4.

A plurality of the third flow paths8are provided along the flow direction of the refrigerant W in the first flow path3and the second flow path4. Therefore, a row of the first end portions8ais formed within the first flow path3along the flow direction of the refrigerant W. In addition, a row of the second end portions8bis formed within the second flow path4along the flow direction of the refrigerant W.

With reference toFIG. 5, a reduced diameter portion9that narrows a flow path diameter of the third flow path8is provided in each third flow path8. The reduced diameter portion9of the present embodiment is formed by projecting portions9aeach obtained by projecting an inner peripheral wall of the third flow path8toward a center portion of the third flow path8.

When the reduced diameter portion9is provided within the third flow path8, bubbles Wb are produced in the refrigerant W as the refrigerant W passes through the reduced diameter portion9, as illustrated inFIG. 6. This may mean that the refrigerant W is brought into a boiling state. Since the refrigerant W removes heat from the surroundings by latent heat when the refrigerant W is brought into a boiling state, the temperature of the refrigerant W decreases and the cooling efficiency is enhanced.

Here, the operation of the reduced diameter portion9will be described with reference toFIGS. 7A to 10B.FIG. 7Aschematically represents the condition of the refrigerant W moving through a flow path80of a comparative example. Since the flow path diameter of the flow path80is fixed, when the condition for moving the refrigerant W is fixed, for example, when the ejection amount of the pump110is fixed, the flow velocity of the refrigerant W moving through the flow path80is fixed and the pressure of the refrigerant within the flow path80is also fixed.

In contrast, if the reduced diameter portion9is provided as in the third flow path8illustrated inFIG. 7B, the flow velocity of the refrigerant W at point b on the reduced diameter portion9is high, as compared with the flow velocity at point a on the upstream side of the reduced diameter portion9. Point b is a point having the narrowest flow path diameter in the reduced diameter portion9and the flow velocity immediately after passing through point b is the highest.

When the flow velocity of the refrigerant W becomes higher, the pressure of the refrigerant W decreases according to the Bernoulli's theorem indicated by Formula 1 and the law of constant flow rate indicated by Formula 2.
ρUa/2+ρgh+Pa=ρUb/2+ρgh+PbFormula 1
Aa×Ua=Ab×UbFormula 2

Ua: refrigerant flow velocity at point a, Ub: refrigerant flow velocity at point b

Pa: refrigerant pressure at point a, Pb: refrigerant pressure at point b

Aa: flow path area at point a, Ab: flow path area at point b

h: potential head

Here, since the relationship of Aa>Ab is satisfied because the reduced diameter portion9is provided, the relationship of Pa>Pb holds.

FIG. 8Aillustrates the condition of the refrigerant W before decompression andFIG. 8Billustrates the condition of the refrigerant W after decompression.FIG. 8Cis an explanatory view illustrating the condition of the refrigerant W after further decompression. As illustrated inFIG. 8B, when the refrigerant W is decompressed, bubbles Wb are produced in the refrigerant W to demonstrate a cooling effect; when the refrigerant W is further decompressed as illustrated inFIG. 8C, the bubbles Wb grows to further enhance the cooling efficiency.

With reference toFIG. 9, a saturated water vapor curve of water that is the refrigerant W is indicated. Water boils at 100° C. under the atmospheric pressure (1 atm, 101.325 kPa) environment, but the boiling temperature can be lowered by decreasing the pressure. Thus, in the present embodiment, the pressure Pb is decreased by providing the reduced diameter portion9such that the boiling temperature is decreased. The extent to which Pb is decreased is determined in consideration of the working temperature of the CPU104to be cooled. Assuming that the working temperature of the CPU104is around 60° C., the flow path diameters at points a and b are determined such that the pressure Pb becomes approximately 20 kPa or less. When a substance other than water is adopted as the refrigerant W, the flow path diameters at points a and b are appropriately set on the basis of the saturated water vapor curve of that refrigerant W such that the pressure Pb becomes lower than the saturated water vapor pressure.

In the cooling plate1of the present embodiment, the reduced diameter portion9is provided within the third flow path8provided at a position close to the cooling surface2aand, by generating the bubbles Wb in the third flow path8, the temperature of the refrigerant W is lowered in the third flow path8to improve the cooling efficiency.

Modifications

Here, a reduced diameter portion90which is a modification of the reduced diameter portion9will be described with reference toFIG. 10A. In the reduced diameter portion9of the example illustrated inFIG. 6and other drawings, when the third flow path8is taken as a cross section, the projecting portion9ais projected from a side close to the cooling surface2atoward a center side of the third flow path8and additionally another projecting portion9ais also projected from a side opposing the aforementioned side. In contrast, in the reduced diameter portion90illustrated inFIG. 10A, a projecting portion90ais projected from a side away from the cooling surface2atoward the center portion of the third flow path8. When the flow path diameter of the reduced diameter portion90is made to match the flow path diameter of the reduced diameter portion9, the projecting amount of the projecting portion90ais larger than the projecting amount of the projecting portion9a. In such a form, the wall thickness on the side of the cooling surface2abecomes thinner and the thermal resistance becomes smaller, such that the cooling efficiency improves.

Next, a reduced diameter portion91which is another modification of the reduced diameter portion9will be described with reference toFIG. 10B. In the reduced diameter portion91illustrated inFIG. 10B, a projecting portion91ais projected from the side close to the cooling surface2atoward the center portion of the third flow path8. When the flow path diameter of the reduced diameter portion91is made to match the flow path diameter of the reduced diameter portion9, the projecting amount of the projecting portion91ais larger than the projecting amount of the projecting portion9a. In such a form, the generated bubbles Wb are likely to gather on the side away from the cooling surface2a. Since the bubbles Wb decrease the efficiency of heat exchange, if the bubbles Wb gather on the side close to the cooling surface2a, it is conceivable that the cooling efficiency decreases. Accordingly, by providing the projecting portion91aon the side close to the cooling surface2a, the bubbles Wb are collected on the side away from the cooling surface2aand the cooling efficiency may be improved.

It is possible to appropriately select which form to adopt from the reduced diameter portions9,90, and91according to the installation environment of the cooling plate1, and the like.

Second Embodiment

Next, a second embodiment will be described with reference toFIGS. 11 to 14. Constituent elements common to the first embodiment are denoted by the same reference numerals in the drawings and detailed description thereof will be omitted.

First, the behavior of the bubbles Wb in a third flow path8will be described with reference toFIG. 11. Upon passing through a reduced diameter portion9, the refrigerant W generates bubbles Wb immediately thereafter. For this reason, it is supposed that the cooling effect owing to the generation of the bubbles Wb is enjoyed from an area immediately ahead of the reduced diameter portion9to a predetermined range downstream of the reduced diameter portion9. However, on the downstream side of the reduced diameter portion9, the flow path diameter is restored. For this reason, the pressure is restored and becomes higher on the downstream side of the reduced diameter portion9. As a result, the bubbles Wb are crushed by pressure and become burst bubbles Wbb. The phenomenon that the bubble Wb is crushed by pressure and becomes the burst bubble Wbb is condensation and raises the temperature of the refrigerant W. The bubble Wb generated by passing through the reduced diameter portion9is crushed by pressure at a position away from the reduced diameter portion9on the flow of the refrigerant W; depending on the flow velocity of the refrigerant W, however, it is presumed that the bubble Wb is crushed by pressure in the downstream vicinity of the reduced diameter portion9, where the cooling effect is desired. For example, when the flow velocity of the refrigerant W is low, it is presumed that it takes time for the bubble Wb to proceed away from the downstream vicinity of the reduced diameter portion9, where the cooling effect is desired; as a consequence, the bubble Wb is crushed by pressure in the downstream vicinity of the reduced diameter portion9and the temperature of the refrigerant W is raised.

Accordingly, as a countermeasure for rise in temperature due to such burst bubbles Wbb, it is conceivable to provide a bubble discharge flow path10as illustrated inFIG. 12. The bubble discharge flow path10is provided in the downstream vicinity of the reduced diameter portion9and promptly discharges the generated bubbles Wb from the third flow path8. The bubble discharge flow path10uses the buoyancy of the bubble Wb to discharge the bubble Wb from the third flow path8. Although the bubble discharge flow path10illustrated inFIG. 12extends in a vertical direction from the third flow path8, as long as a flow path through which the bubble Wb can be raised by its buoyancy is implemented, the bubble discharge flow path10does not have to extend in the vertical direction but, for example, may extend obliquely upward.

Next, an embodiment incorporating such a bubble discharge flow path10will be described with reference toFIG. 13. With reference toFIG. 13, the bubble discharge flow path10is provided between the reduced diameter portion9provided within the third flow path8and a second end portion8bwhich is a flow path end portion where the third flow path8merges with a second flow path4. By arranging the bubble discharge flow path10in this manner, the bubble Wb generated as the refrigerant W passes through the reduced diameter portion9is instantly discharged to the second flow path4through the bubble discharge flow path10. Since the refrigerant W having a high temperature after contributing to the cooling of the CPU104is moving in the second flow path4, the cooling effect on the cooling surface2awill not be decreased even if the bubble Wb discharged to the second flow path4becomes the burst bubble Wbb within the second flow path4.

As illustrated inFIG. 14, when the third flow path8is placed longitudinally, the generated bubble Wb proceeds away from the reduced diameter portion9by its buoyancy and is not crushed by pressure in the downstream vicinity of the reduced diameter portion9; therefore, no special measures are required.

Third Embodiment

Next, a reduced diameter portion19of a third embodiment will be described with reference toFIG. 15. The reduced diameter portion19of the third embodiment is formed by a reduced diameter maintaining portion19athat maintains a reduced diameter state of the flow path diameter toward the downstream side of a third flow path8after the flow path diameter is reduced. The bubble Wb is produced due to a decrease in pressure caused by the flow velocity of the refrigerant W becoming higher because of the reduction of the flow path diameter; however, when the flow path diameter is expanded thereafter, the pressure is restored and the bubble Wb is crushed by pressure. In view of this action, in the third embodiment, by maintaining the flow path diameter such that the pressure of the refrigerant W is not restored, crush of the bubble Wb by pressure is suppressed as a countermeasure for rise in temperature of the refrigerant W.

Fourth Embodiment

Next, a fourth embodiment will be described with reference toFIG. 16. In the fourth embodiment, a first flow path3includes a reduced diameter portion20that narrows the flow path diameter of the first flow path3. By generating the bubbles Wb in the refrigerant W passing through the reduced diameter portion20in the first flow path3, the temperature of the refrigerant W in the first flow path3is supposed to be decreased. The refrigerant W whose temperature has decreased flows into a third flow path8. Since the temperature of the refrigerant W further decreases in the third flow path8in which a reduced diameter portion9is formed, the cooling efficiency is improved.

For example, as illustrated inFIG. 16, the reduced diameter portion20can be arranged in the upstream vicinity of a region R desired to be further cooled. This makes it easier to meet the requirement of locally enhancing the cooling effect.

Fifth Embodiment

Next, a fifth embodiment will be described with reference toFIG. 17. The fifth embodiment includes a plurality of reduced diameter portions9and29provided along the flow direction of a third flow path8. Every time the refrigerant W passes through the reduced diameter portions9and29, the refrigerant W generates the bubbles Wb to decrease the temperature. Consequently, the cooling efficiency may be improved.

Sixth Embodiment

Next, a sixth embodiment will be described with reference toFIG. 18. The sixth embodiment includes a reduced diameter portion39having a tapered portion39athat narrows the flow path diameter of a third flow path gradually toward the downstream side of the third flow path8. The reduced diameter portion39includes the tapered portion39a, such that the nearer the downstream side, the smaller the flow path diameter. Along with this tapered portion39a, the velocity of the refrigerant W is made higher and the pressure is decreased; consequently, the bubbles Wb are likely to be generated. As a result, the cooling efficiency may be improved.

Although the preferred embodiments of the present invention have been described in detail thus far, the present invention is not limited to such specific embodiments and various modifications and alterations may be made within the scope of the present invention described in the claims.