Patent Application
20140027100
The present invention relates to piping structures of cooling devices for semiconductor devices and electronic devices and the like, in particular, to a piping structure of a 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, a method for making the same, and a method for connecting pipes.
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 has been increasing. On the other hand, the miniaturization of semiconductor devices and electronic devices has been 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 referred to as an ebullient cooling device) is described in patent literature 1. The ebullient cooling device described in patent literature 1 includes an evaporator absorbing the heat from a heating element by the evaporation action of working fluids such as pure water and ethanol, and a condenser releasing heat by the condensation action of working fluids. The ebullient cooling device includes flow conduits circulating the working fluids between the evaporator and the condenser, and is configured so that the flow conduits can be bent at a number of points. It is said that the configuration enables the flow conduits to act as a spring and to absorb the force applied to the evaporator and the condenser.
In the ebullient cooling device described in patent literature 1, however, a metal pipe made of rigid metal with a spring function is used as the flow conduit, and consequently, there has been a problem that the degree of freedom to dispose the flow conduits with a bent form is limited. There has also been a problem that the mechanical strength cannot be maintained, for example, a buckling occurs in the process of bending, if the thickness of the metal pipe is reduced to a thickness in which it can be bent freely. Furthermore, there has been a problem that the corrosion (electrical corrosion) based on an electrochemical action occurs due to the electrical potential difference between the metal composing the flow conduit and the metal composing a connection of the evaporator or the condenser if an electrically-conductive refrigerant is used.
On the other hand, a low-boiling organic refrigerant is often used as the refrigerant in the ebullient cooling device in order to improve the cooling performance within a range of the operation temperature for a semiconductor device and an electronic device. It is possible to obtain a flexible pipe by using an organic material such as resin and rubber. If a pipe made of an organic material is used, however, there has been a problem that the internal pressure increases due to a chemical reaction with the organic refrigerant, and consequently, the cooling performance is degraded owing to the boiling point elevation of the refrigerant.
Patent literature 2 describes a technology to solve such problems. An ebullient cooling device described in patent literature 2 includes an evaporator container accommodating a refrigerant liquid, a condenser condensing the vaporized refrigerant, and a single pipe connecting the evaporator container to the condenser, through which a gas-liquid flows in a mixed phase. The pipe has a structure in which a thin film of a corrosion-resistant and permeation-resistant material such as aluminum and stainless steel is evaporated onto the inner wall of the pipe made of a resin. It is said that the structure enables the pipe to have enough rigidity to maintain its shape against the atmospheric pressure and thus the installation location of the evaporator container and the condenser can be freely decided.
Patent literature 1: Japanese Patent Application Laid-Open Publication No. 2006-125718 (paragraphs [0025] to [0044])
Patent literature 2: Japanese Patent Application Laid-Open Publication No. 1994-224337 (paragraphs [004] to [009])
As mentioned above, the pipe in the related ebullient cooling device has a structure in which a metal film is evaporated onto the inner surface of the pipe. The vapor of the refrigerant, however, is condensed again and liquefies in the middle of the pipe due to the surface roughness of the metal film evaporated on the resin. The related ebullient cooling device using such pipes, therefore, has a problem that the amount of heat transports by the refrigerant decreases.
Thus, in the piping structure of the related ebullient cooling device, there is a problem that the cooling performance of the cooling device is degraded if the pipe is provided with flexibility.
The objective of the present invention is to provide a piping structure of a cooling device, a method for making the same, and a method for connecting pipes which solve the problem mentioned above that in a piping structure of a cooling device using an ebullient cooling system, the cooling performance of the cooling device is degraded if the pipe is provided with flexibility.
A piping structure of a cooling device according to an exemplary aspect of the invention includes a first tubular part with a hollow portion through which a refrigerant used in the cooling device flows; wherein the first tubular part is made of metal materials; and the surface roughness of the inner surface of the first tubular part is less than or equal to the size of a condensation nucleus for the refrigerant.
A method for making a piping structure of cooling device according to an exemplary aspect of the invention includes the steps of: applying a rolling process to a metal material composing a hollow portion through which a refrigerant used in a cooling device flows; forming a plate-like metal plate material with a surface roughness less than or equal to the size of a condensation nucleus for the refrigerant by the rolling process; and bending the metal plate material into a tube and joining both ends.
A method for connecting pipes according to an exemplary aspect of the invention includes the steps of: fitting, in a connective projection, a pipe including a first tubular part, the first tubular part having a hollow portion through which a refrigerant used in a cooling device flowing, made of a metal material, and a surface roughness of its inner surface being less than or equal to the size of a condensation nucleus for the refrigerant; applying a pressure from the outer periphery of the pipe toward the center; and deforming the metal material composing the first tubular part by the pressure and attaching firmly the metal material to the connective projection.
According to the piping structure of the cooling device of the present invention, it is possible to obtain a piping structure of a cooling device which does not cause deterioration in the cooling performance of the cooling device even if the pipe is provided with flexibility.
The exemplary embodiments of the present invention will be described with reference to drawings below.
The first tubular part 11 is made of metal materials, and the surface roughness of the inner surface of the first tubular part 11 is less than or equal to the size of a condensation nucleus for the refrigerant. Here, the condensation nucleus means a spot which acts as a base point when a vapor liquefies. If the vapor touches the base points, the liquefaction is accelerated there. It is possible to use aluminum materials and the like as the first tubular part 11, for example. By setting the center line average roughness of a surface equal to or more than 0.1 micrometers and less than or equal to 10 micrometers, preferably less than or equal to 1 micrometer, it is possible to prevent the inner surface of the first tubular part 11 from acting as a condensation nucleus of the refrigerant.
It is possible to use a material formed through an annealing process for the first tubular part. By means of the annealing process, it is possible to adjust a strain arising at a processing treatment, and it becomes possible to maintain the strength of the first tubular part with maintenance of its flexibility.
Next, the method for making the piping structure of cooling device 10 according to the present exemplary embodiment will be described. In the method for making according to the present exemplary embodiment, first, a plate-like metal plate material made of a metal material such as aluminum is prepared. The metal plate material can be produced by a conventional rolling process. The metal plate material is bent into a tube by using a cylindrical jig such as a roll, for example, and both ends are joined by means of a weld process and the like. By this process, the first tubular part 11 made of a metal material is completed. It is also acceptable to perform the annealing process subsequently. The annealing process can be performed under conditions normally used for the metal material to be used. It is desirable to set the thickness of the first tubular part, which is determined by the plate thickness of the metal plate material, equal to or more than 0.4 mm and less than or equal to 1 mm. This is because it becomes difficult to weld the ends and to maintain the bending strength and the internal pressure capacity of the first tubular part if the plate thickness of the metal plate material becomes thinner than 0.4 mm. On the other hand, it is also because the flexibility of the piping structure of cooling device 10 decreases if the thickness of the first tubular part is more than 1 mm.
As mentioned above, according to the present exemplary embodiment, it is possible to obtain a piping structure of a cooling device which does not cause deterioration in the cooling performance of the cooling device even if the pipe is provided with flexibility.
Next, the second exemplary embodiment of the present invention will be described.
The first tubular part 110 is made of metal materials, and the surface roughness of the inner surface of the first tubular part 110 is less than or equal to the size of a condensation nucleus for the refrigerant. Here, the condensation nucleus means a spot which acts as a base point when a vapor liquefies. If the vapor touches the base points, the liquefaction is accelerated there. It is possible to use aluminum materials and the like as the first tubular part 110, for example. By setting the center line average roughness of a surface equal to or more than 0.1 micrometers and less than or equal to 10 micrometers, preferably less than or equal to 1 micrometer, it is possible to prevent the inner surface of the first tubular part 110 from acting as a condensation nucleus of the refrigerant.
The second tubular part is made of organic materials such as resin and rubber, and it is possible to use polyethylene materials and butyl rubber materials, for example.
As mentioned above, the piping structure of cooling device 100 according to the present exemplary embodiment is configured in which the first tubular part 110 touching the refrigerant is made of metal materials and the surface roughness of the inner surface is less than or equal to the size of a condensation nucleus for the refrigerant. Accordingly, it is possible to prevent the piping structure of cooling device 100 from reacting chemically with the refrigerant, and prevent the vapor of the refrigerant from condensing again. Additionally, since the piping structure of cooling device 100 includes a multi-layered structure in which the first tubular part 110 is covered with the second tubular part 120 made of organic materials, it is possible to maintain the mechanical strength of the piping structure of cooling device 100 with maintenance of its flexibility. As a result, according to the present exemplary embodiment, it is possible to obtain a piping structure of a cooling device which does not cause deterioration in the cooling performance of the cooling device even if the pipe is provided with flexibility.
Next, the method for making the piping structure of cooling device 100 according to the present exemplary embodiment will be described.
Subsequently, as shown in
Here, it is desirable to set the surface roughness of the inner surface of the first tubular part 110 made of the metal plate material 140 equal to or more than 0.1 micrometers and less than or equal to 10 micrometers, preferably less than or equal to 1 micrometer. This can be achieved by producing the metal plate material 140 by means of a conventional rolling process. By setting the surface roughness within the range, it is possible to prevent the inner surface of the first tubular part 110 from acting as a condensation nucleus of the refrigerant. It is desirable to set the thickness of the first tubular part, which is determined by the plate thickness of the metal plate material 140, equal to or more than 0.4 mm and less than or equal to 1 mm. This is because it becomes difficult to weld the ends 160 and to maintain the bending strength and the internal pressure capacity of the first tubular part if the plate thickness of the metal plate material 140 becomes thinner than 0.4 mm. On the other hand, it is also because the flexibility of the piping structure of cooling device 100 decreases if the thickness of the first tubular part is more than 1 mm.
Next, the third exemplary embodiment of the present invention will be described. In the present exemplary embodiment, a cooling device will be described which uses the piping structure of cooling device 100 according to the second exemplary embodiment, but it is also acceptable to use the piping structure of cooling device 10 according to the first exemplary embodiment. A case will be described below in which the piping structure is applied to a cooling device using an ebullient cooling system (hereinafter, referred to as an ebullient cooling device).
The evaporator 220 is connected to the condenser 230 by using the piping structure of cooling device 100 according to the second exemplary embodiment. As shown in
As mentioned above, the ebullient cooling device 200 of the present exemplary embodiment is configured in which the evaporator 220 is connected to the condenser 230 by using the pipe 250 including the first tubular part 110 made of metal materials as the inner layer and the second tubular part 120 made of organic materials having the flexibility as the outer layer. By adopting this configuration, it is possible to change the layout of the ebullient cooling device 200 easily even if the layout or the specifications of a device to be cooled are changed. Accordingly, it becomes unnecessary to design and produce the evaporator 220 and the condenser 230 with respect to each device to be cooled, and it becomes possible to standardize them. As a result, it is possible to reduce the costs of the evaporator 220 and the condenser 230.
It is also possible that the evaporator 220 is configured to include a first connective projection 221 connected to the first connection 131 of the piping structure of cooling device 100 and the condenser 230 is configured to include a second connective projection 231 connected to the second connection 132. It is also acceptable that at least one of the first connective projection 221 and the second connective projection 231 is made of the same material as the metal material of which the first tubular part 131 is made. In this case, since the electrical potential difference does not arise between the same type of metals, it is possible to prevent the corrosion based on the electrochemical action (electrical corrosion) even though a conductive refrigerant such as water is used.
In general, a semiconductor device, an electronic device and the like are designed so as to operate at temperature in the range from several tens of degrees Celsius to about 100 degrees Celsius. By using a material with small surface tension and a low boiling point as the refrigerant used in the ebullient cooling device, therefore, it is possible to activate the generation of bubbles in the evaporator and improve the cooling performance. For this reason, organic refrigerants such as hydrofluorocarbon and hydrofluoroether are used as the refrigerant. These organic refrigerants, however, react chemically with organic materials such as resin and rubber. Since the chemical reaction generates a reaction gas and the internal pressure in the related ebullient cooling device increases, the boiling point of the refrigerant rises. As a result, the cooling performance in the related ebullient cooling device is degraded by the prolonged use.
In contrast, the ebullient cooling device 200 of the present exemplary embodiment uses the piping structure of cooling device 100 including the first tubular part 110 made of metal materials as the vapor-phase pipe 251 and the liquid-phase pipe 252. As a result, the reaction between the refrigerant and the pipe is suppressed, and accordingly, it is possible to prevent the cooling performance from degrading and ensure long-term reliability of the ebullient cooling device.
Next, the method for connecting pipes will be described in more detail using
In the method for connecting pipes according to the present exemplary embodiment, first, as shown in
Next, a pressure is applied from the outer periphery of the second tubular part 120 toward the center. As shown in
Here, the connective projection 260 can be configured to be a nipple shape, as shown in
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. 2011-089347, filed on Apr. 13, 2011, the disclosure of which is incorporated herein in its entirety by reference.
10, 100 piping structure of cooling device
11, 110 first tubular part
120 second tubular part
140 metal plate material
150 cylindrical jig
160 end section
170 nozzle
200 ebullient cooling device
210 refrigerant
220 evaporator
221 first connective projection
230 condenser
231 second connective projection
240 heat generating unit
250 piping
251 vapor-phase pipe
252 liquid-phase pipe
260 connective projection
270 clamp
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-089347 | Apr 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/060197 | 4/10/2012 | WO | 00 | 10/8/2013 |
