Patent Application
20130206368
The present invention relates to cooling devices for semiconductor devices and electronic devices and the like, in particular, to a cooling device and a method for producing the same using an ebullient cooling system in which the heat transportation and heat radiation are performed by a cycle of vaporization and condensation of a refrigerant.
In recent years, with the progress of high performance and high functionality in semiconductor devices and electronic devices, the amount of heat generation from them is increasing. On the other hand, the miniaturization of semiconductor devices and electronic devices is advancing due to the popularization of portable devices. Because of such background, a cooling device with high efficiency and a small size is highly required. The cooling device using an ebullient cooling system in which the heat transportation and heat radiation are performed by a cycle of vaporization and condensation of a refrigerant, is expected as a cooling device for the semiconductor devices and the electronic devices because it does not require any driving unit such as a pump.
An example of the cooling device using an ebullient cooling system (hereinafter, also denoted as the ebullient cooling device) is described in the patent literature 1. The ebullient cooling device described in the patent literature 1 includes an evaporator which stores a liquid phase refrigerant, and a condenser which condenses and liquefies the refrigerant steam evaporated by the heat received from a body to be cooled in the evaporator and radiates the heat. The evaporator includes cuboids convex parts made of the same material as a boiling surface on the boiling surface at the side of the inner wall in contact with the liquid phase refrigerant. And a blasting treatment is processed using an abrasive material for all over the surface of the top surface and lateral surface of the convex parts and the flat surface other than the convex parts.
As shown in
Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2003-139476 (paragraphs [0023] to [0049]).
As mentioned above, in the related ebullient cooling device, the bubble nuclei 315 are formed on the boiling surface 313 and all surface of the convex parts (projections) 314 in the evaporator 310. However, because the bubbles generated on the side surfaces of the convex parts (projections) 314 prevent the bubbles generated on the boiling surface 313 from moving, the cooling performance adversely decreases.
As mentioned above, the related ebullient cooling device has a problem that the cooling performance adversely decreases if the evaporator includes projections activating the convection heat transfer and the bubble nuclei are formed on the inner wall surface.
The object of the present invention is to provide a cooling device and a method for producing the same which solve the problem mentioned above that in a cooling device using an ebullient cooling system, the cooling performance adversely decreases if the evaporator includes projections activating the convection heat transfer and the bubble nuclei are formed on the inner wall surface.
A cooling device according to an exemplary aspect of the invention includes an evaporator storing a refrigerant; a condenser condensing and liquefying a vapor-state refrigerant vaporized in the evaporator and radiating heat; and a connection connecting the evaporator and the condenser; wherein the evaporator includes a base thermally contacting with an object to be cooled, and a container; the base includes a plurality of projections on a boiling surface of a surface at an inner wall side contacting with the refrigerant; and a bubble nucleus forming surface is included only on a part of a refrigerant contacting surface including the boiling surface and the surface of the projections.
A method for producing a cooling device according to an exemplary aspect of the invention includes the steps of: forming a plurality of projections on a boiling surface of a surface at an inner wall side contacting with a refrigerant in a base included by an evaporator storing the refrigerant; forming a bubble nucleus forming surface only on a part of a refrigerant contacting surface including the boiling surface and the surface of the projections; forming the evaporator by joining the base to a container; and connecting the evaporator to a condenser condensing and liquefying a vapor-state refrigerant vaporized in the evaporator and radiating heat.
A method for producing a cooling device according to an exemplary aspect of the invention includes the steps of: performing a roughening process on a boiling surface of a surface at an inner wall side contacting with a refrigerant in a base included by an evaporator storing the refrigerant; forming a bubble nucleus including a concavo-convex shape with a size determined by properties of the refrigerant; forming a projection by carving and raising a part of the base from the boiling surface side; forming the evaporator by joining the base to a container; and connecting the evaporator to a condenser condensing and liquefying a vapor-state refrigerant vaporized in the evaporator and radiating heat.
According to the cooling device of the present invention, it is possible to obtain a cooling device with an ebullient cooling system whose cooling performance is improved.
The exemplary embodiments of the present invention will be described with reference to drawings below.
The evaporator 110 includes a base 111 thermally contacting with an object to be cooled 140, and a container 112. The base 111 and the container 112 are joined by welding or brazing and the like to form a sealed structure, which stores the refrigerant inside it. The connection 130 is connected to the container 112, and the refrigerant circulates in a vapor-state or liquid-state between the evaporator 110 and the condenser 120 through the connection 130.
After enclosing the refrigerant in the evaporator 110, the evaporator 110 is evacuated. Thereby, the inside of the evaporator 110 is always kept in the saturated vapor pressure of the refrigerant, and the boiling point of the refrigerant becomes equal to room temperature. Therefore, when the object to be cooled 140 produces heat and the heat quantity is transferred to the refrigerant through the base 111, the refrigerant is vaporized and bubbles arise. At that time, since the heat quantity from the object to be cooled 140 is taken away as vaporization heat by the refrigerant, it is possible to avoid rise in temperature of the object to be cooled 140. The vaporized refrigerant flows through the connection 130, is cooled and condensed in the condenser 120, and the refrigerant in liquid-state flows again into the evaporator 110 through the connection 130. It is possible for the cooling device 100 to cool the object to be cooled 140 by the foregoing circulation of the refrigerant without using a driving unit such as a pump.
The base 111 is provided with a plurality of projections 114 on a boiling surface 113 of a surface at an inner wall side contacting with the refrigerant. The projection 114 can be formed in the fin geometry, for example, and it has the effect that the convection heat transfer is enhanced when the bubbles of the refrigerant generated on the boiling surface 113 pass thorough. It is desirable to arrange these projections 114 in an interval in which the convection heat transfer by the bubbles becomes maximized. As the material of the base 111 and the projections 114, it is possible to use the metal having an excellent thermal conductive property such as aluminum, for example.
The evaporator 110 according to the present exemplary embodiment includes a bubble nucleus forming surface 115 only on a part of a refrigerant contacting surface composed of the boiling surface 113 and the surface of the projections 114. A plurality of bubble nuclei, each of which becomes a source nucleus for the bubbles of the refrigerant, are formed on the bubble nucleus forming surface 115, and each of the bubble nuclei has a concavo-convex shape with a projection and a hollow. The optimum value of the size of the concavo-convex shape is determined by considering physical properties such as surface tension of the refrigerant. For example, if hydrofluorocarbon, hydrofluoroether, and the like, which are insulating and inactive materials, are used as the refrigerant, the optimum size of the bubble nucleus is in the range of sub-micron to tens of micrometers in center line average roughness. Therefore, it is possible to form the bubble nuclei by a mechanical processing using abrasive grains, a sandblast, and the like, or by a chemical processing such as a plating.
Thus, the cooling device 100 according to the present exemplary embodiment includes the bubble nucleus forming surface 115 on the boiling surface 113 of the base 111 composing the evaporator 110. Therefore, the generation of the bubbles on the boiling surface 113 is activated and the cooling effect is enhanced.
In addition, in the evaporator 110 according to the present exemplary embodiment, the bubble nucleus forming surface 115 is disposed only on a part of the surface of the projections 114. Therefore, the bubbles generated on the surface of the projections 114 decrease. Consequently, it is possible to suppress the phenomenon that the bubbles generated on the projection 114 prevent the bubbles generated on the boiling surface 113 from moving.
Here, the case is considered that the bubble nucleus forming surface is formed on entire surface of the projections 114 in order to increase the number of bubble nuclei, as the related ebullient cooling device described in the background art. Since the temperature of the projections 114 drastically decreases toward the upper part away from the boiling surface 113, the bubble nucleus forming surface disposed at the upper part of the projections 114 hardly contributes to generating the bubbles. That is to say, the contribution to the cooling performance due to the increase in the number of the bubble nuclei is small. Accordingly, the decrease in the total number of the bubble nuclei has a small effect even though the bubble nucleus forming surface 115 is disposed on only a part of the surface of the projections 114.
As described above, according to the cooling device 100 of the present exemplary embodiment, it is possible to obtain a cooling device with an ebullient cooling system whose cooling performance is improved.
As mentioned above, the projection 114 hardly contributes to generating the bubbles, and the effect on the convection of the bubbles generated on the boiling surface 113 becomes dominant in the effects of cooling due to disposing the projection 114. Accordingly, it is possible to determine the interval of the projections 114 so that the convection heat transfer by the bubbles can be maximized taking into account the amount of generation and the rate of generation of the bubbles depending on the amount of heat generation of the object to be cooled 140. For example, if the amount of heat generation is in the range of about 100 W, it is possible to obtain excellent cooling performance on the condition that the interval of the projections 114 is in the range of about 0.1 mm to about 2 mm.
As mentioned above, once the bubbles arise at the projections 114, the flow of the bubbles arising on the boiling surface 113 is prevented. If the flow of the bubbles is prevented, the internal pressure of the evaporator 110 increases and the boiling temperature of the refrigerant which maintains the saturated vapor pressure also increases, therefore the cooling performance deteriorates. However, since the bubble nucleus forming surface 115 is disposed on only a part of the surface of the projection 114 in the evaporator 110 according to the present exemplary embodiment, the generation of the bubbles at the projection 114 is suppressed. Therefore, according to the present exemplary embodiment, it is possible to avoid the above-mentioned deterioration of the cooling performance.
Next, the method for producing the cooling device 100 according to the present exemplary embodiment will be described.
According to the method for producing the cooling device of the present exemplary embodiment, it is possible to form the projections 114 and the bubble nucleus forming surface in one process including a sequence of steps, as described below. First, the base 111 with the fin-shaped projections 114 is formed by means of the extrusion processing using die and mold.
Then, as shown in
At that time, as shown in
After that, the base 111 and the container 112 are joined by welding or brazing and the like to form the evaporator 110. Finally the cooling device 100 according to the present exemplary embodiment is completed by connecting the evaporator 110 to the condenser 120 through the connection 130.
In the above-mentioned method for producing the cooling device, the case has been described that the bubble nucleus forming surface 115 is formed by using the rotary forming unit 160 on which the abrasive grain 162 is formed. However, it is not limited to this, as shown in
In the related ebullient cooling device described in the background art, the roughening process by the blasting treatment is performed all over the surface of the inner wall side in the evaporator. However, if the roughening process such as etching, plating, and sandblasting is performed with a masking process after forming the convex parts (projections), the production cost increases due to an increase in producing step.
In contrast, according to the method for producing the cooling device of the present exemplary embodiment, since it is possible to perform the roughening process, that is, to form the bubble nucleus forming surface 115 in one process continuous with the process for forming the projections or in the same process as that, it is possible to suppress the increase in the production cost.
Next, the second exemplary embodiment according to the present invention will be described.
The cooling device 200 according to the present exemplary embodiment is different from the cooling device 100 of the first exemplary embodiment in the configuration of a bubble nucleus forming surface 215 which is disposed in the evaporator 210. That is to say, as shown in
As mentioned above, in the cooling device 200 according to the present exemplary embodiment, the bubble nucleus forming surface 215 is provided on the boiling surface 113 of a base 211 composing the evaporator 210. Therefore, the generation of the bubbles on the boiling surface 113 is activated and the cooling effect is enhanced.
Furthermore, in the evaporator 210 according to the present exemplary embodiment, the bubble nucleus forming surface 215 is disposed on one of the lateral surfaces of the projections 214. Therefore, the bubbles arising from the surface of the projections 214 decrease. As a result, it is possible to suppress the phenomenon that the bubbles generated on the projection 214 prevent the bubbles generated on the boiling surface 113 from moving. As described above, according to the cooling device 200 of the present exemplary embodiment, it is possible to obtain a cooling device with an ebullient cooling system whose cooling performance is improved.
Next, the method for producing the cooling device 200 according to the present exemplary embodiment will be described.
Next, as shown in
After that, as is the case with the first exemplary embodiment, the base 211 and the container 112 are joined by welding or brazing and the like to form the evaporator 210. Finally the cooling device 200 according to the present exemplary embodiment is completed by connecting the evaporator 210 to the condenser 120 through the connection 130.
According to the method for producing the cooling device of the present exemplary embodiment, since the masking process becomes unnecessary in the roughening process, and additionally it is possible to form the bubble nucleus forming surface 215 without adding any particular equipment, it is possible to suppress the increase in the production cost.
The present invention is not limited to the above-mentioned exemplary embodiments and can be variously modified within the scope of the invention described in the claims. It goes without saying that these modifications are also included in the scope of the present invention.
This application is based upon and claims the benefit of priority from Japanese patent application No. 2010-234359, filed on Oct. 19, 2010, the disclosure of which is incorporated herein in its entirety by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-234359 | Oct 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/074236 | 10/14/2011 | WO | 00 | 4/18/2013 |
