JPH03103488A - Low-temperature cooling medium, production thereof, method for cooling and cooler - Google Patents

Abstract

PURPOSE:To obtain a new low-temperature cooling medium for use in closed loop coolers by cooling a mixed gas of liquid nitrogen and a specific fluorocarbon under pressure and liquefying the mixed gas. CONSTITUTION:The objective cooling medium obtained by cooling a mixed gas of (A) liquid nitrogen and (B) a fluorocarbon expressed by the formula CnF2n+2 (n is an integer of 2-4) under pressure and liquefying the above- mentioned mixed gas. Furthermore, a closed loop cooler has a cryostat containing a fluorocarbon as a cooling medium placed therein and a heat exchange pipe, arranged in an upper internal space of the aforementioned cryostat and led from a liquefier. A liquefied gas as a heat exchange medium is circulating through the interior of the aforementioned heat exchange pipe. A substance to be cooled is dipped in the cooling medium to carry out cooling.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a low-temperature cooling medium, and provides a low-temperature cooling medium that can efficiently cool an object to be cooled with a high cooling capacity without causing unevenness in assembly or fluctuations in cooling capacity. For the purpose of this, liquid nitrogen and carbon fluoride represented by the following formula: CnF. ,,． 2 (in the formula, n is an integer of 2 to 4).

[Industrial application field]

The present invention relates to low temperature cooling media. More particularly, the present invention relates to cryogenic cooling media with high cooling capacity for use in cryogenic cooling devices.

The cooling medium (or "refrigerant") of the present invention is suitable for use in semiconductor devices at extremely low temperatures, e.g., less than about 123 K, e.g., 77.3 K (
That is, liquid nitrogen LN. (boiling point)) and other devices, such as devices and circuit boards using high Tc (critical temperature) phase oxide superconductors that exhibit superconductivity at liquid nitrogen temperatures. It is particularly suitable as a cooling medium or a heat exchange medium when cooling to the operating temperature. In addition, in the specification of this application, the following
The temperature at or near the boiling point of liquid nitrogen mentioned above will also be referred to as liquid nitrogen temperature, as is commonly used in this field. The invention also relates to a method of producing a low temperature cooling medium as described above, a method of cooling an object to a cryogenic temperature, and a closed loop cooling device using such a low temperature cooling medium.

[Conventional technology]

For example, as is well known, the carrier mobility of a semiconductor device increases as the temperature of the surroundings surrounding the device decreases due to a decrease in lattice scattering. Further, by utilizing this property, high-speed arithmetic elements such as HIEMT or CMOS have been developed with the aim of operating at liquid nitrogen temperature. Operating these devices requires a coolant to maintain them at liquid nitrogen temperatures while efficiently dissipating heat.

Conventionally, in order to maintain and cool electronic devices such as semiconductor devices in a low-temperature environment, there are two methods: one method is to bring the heat generating part of the device into contact with the heat exchange part of a refrigerator and radiate heat by conduction, and the other is to immerse the device in liquefied gas such as liquid nitrogen. There is a method of dissipating heat by boiling heat transfer. The method of immersing the device in liquefied gas is particularly advantageous for devices such as computer CPUs (Central Processing Units), which have a large heat generation density and are difficult to connect to a refrigerator. Furthermore, various types of liquefied gases can be considered as low-temperature refrigerants, but there are only a few stable refrigerants that are neither toxic nor reactive, such as liquid nitrogen and liquid helium.

Incidentally, the therapeutic properties of cryogenic liquids are shown in Table 1 below.

Table 1? O 81.7 215.9
140Ar 87. 3 16
3. 2 1200■ 90.2
213.1 148CH.
111.67 510,3
193Kr 119, 8 107.
7CF. 145.2 136.2
156C2F,l 195 N277,3 199' 1
40 Among the low-temperature liquids listed in Table 1 above, C○ is toxic, Cl4 is flammable, and 02 is oxidizing, so there are problems in its application as low-temperature refrigerants.
Liquid nitrogen obtained by liquefying and separating air is preferred as the low-temperature refrigerant.

Examples of using liquid nitrogen as a low-temperature refrigerant include, for example, F. H
, Gansslen et al., “Very Small M
OSFBT's forLow-Temperature
e Operation”, IEBεTRANSAC
TIONS ONE ELECTRON DEVICES,
Written in March 1977. In this literature,
It has been taught to immerse the FET directly in an open pool of liquid nitrogen. It is also known to use liquid fluorocarbon as a low temperature refrigerant. For example, “Cooling
a Superfast Computer”.ELE
CTRONIC PACKAG[NG & PROD[
ICTION. In July 1986, the entire supercomputer CRY-2 was taught to be immersed in recirculated liquid fluorocarbon.

Furthermore, as another useful low-temperature refrigerant, a refrigerant made by mixing liquid nitrogen with 8 mol% of liquid carbon tetrafluoride and having twice the cooling capacity of nitrogen is known [Amano, Nagao (Mitsubishi Electric, (Central Research Institute) May 1988, Society of Cryogenic Engineering, Spring Lecture C
I-41. According to this document, it is reported that an excellent cooling effect (approximately twice that of liquid nitrogen alone) can be obtained by directly immersing a high Tc superconductor in the described mixed refrigerant.

The cooling method described in the literature by Amano et al. uses an open system as shown in FIG. That is, a mixed refrigerant 2 consisting of liquid nitrogen (LN2) and carbon tetrafluoride (CF4) is placed in an open vacuum container 3, and the object to be cooled 1 is poured into this mixed refrigerant (here, in order to evaluate the cooling capacity, A platinum wire is immersed in place of the superconductor. A thermocouple 4 as a temperature sensor is also immersed in the coolant 2, and the other end is connected to a recorder 8. This device also includes: A scale 5, a DC power source 6, and a resistor 7 are incorporated.

By the way, in low-temperature cooling, a closed-loop cooling system that is isolated from the outside air is used to avoid freezing and contamination of the atmosphere and moisture in the atmosphere, and to re-liquefy and circulate gas that has boiled and vaporized due to the heat of the heating element. Ru.

The above mixed refrigerants have high cooling capacity, but when a refrigerant with a high concentration of carbon tetrafluoride is used in a closed-loop cooling system, the vapor contains many low-boiling components, so the liquid phase and gas phase,
Or, an imbalance occurs in the refrigerant composition between the boiling section and the condensing section.
There was a drawback that the cooling capacity fluctuated. In addition, conventional mixed refrigerants require the addition of large amounts of carbon tetrafluoride to achieve high cooling capacity, making them difficult to use in closed-loop cooling systems that are essential for low-temperature cooling of electronic devices. I couldn't. Furthermore, the materials that can be expected to have a cooling effect when mixed with liquid nitrogen are limited to fluorocarbons, etc., which have a melting point higher than the boiling point of liquid nitrogen. However, in the conventional method of directly mixing liquid nitrogen and liquid carbon fluoride, most of the carbon fluorides, except carbon tetrafluoride, are assimilated and precipitated and do not dissolve.

The present inventors tried using liquid nitrogen and liquid argon, liquid nitrogen and liquid krypton, etc. as a mixed refrigerant, but no cooling effect could be obtained.

Therefore, in order to obtain a low-temperature refrigerant for closed-loop cooling that is free from non-uniform composition and fluctuations in cooling capacity within the circulation system, it is necessary that the amount of the other component is small and the cooling capacity is high.

On the other hand, a typical closed-loop cooling system is a device consisting of a cryostat (low-temperature cooling container) and a refrigerator. This device immerses the cooled body (heating element) in the refrigerant liquid in the cryostat, and circulates liquid nitrogen as a heat exchange refrigerant between the heat exchanger installed above the refrigerant liquid in the cryostat and the refrigerator. That's what I do. In this case, the refrigerator needs to be placed as far away from the cryostat as possible to prevent the vibrations of the refrigerator from being transmitted to the object to be cooled. The conventional method for connecting a cryostat and a refrigerator at a distance is to circulate helium gas through an insulated tube to a heat exchanger inside the cryostat, but because it uses gas for heat transfer, it requires a large amount of heat. It has the disadvantage that it cannot cope with cooling the amount of heat.

Therefore, it is desired to provide a low-temperature cooling device that has a large cooling capacity even if the distance between the cryostat and the refrigerator is increased.

[Problem to be solved by the invention]

It is an object of the present invention to provide a new low temperature cooling medium for use in closed loop cooling devices.

This cooling medium should exhibit a high cooling capacity and should not have the drawbacks of the prior art as mentioned above.

Another object of the invention is to provide a method for producing the above-mentioned novel cryogenic cooling medium in the form of a solution.

Another object of the present invention is to provide a cooling method using the above-mentioned novel low-temperature cooling medium.

Yet another object of the present invention is to provide a closed loop cooling device using the novel cryogenic cooling medium described above.

- [Means for Solving the Problems] As a result of intensive research to solve the above-mentioned problems, the present inventors found that if a specific fluorocarbon of the following formula: C. F2. , 2 (in the formula, n is an integer from 2 to 4) and liquid nitrogen can be used to achieve the desired purpose. Although this was completely unexpected, it was possible to significantly improve the cooling capacity simply by adding a small amount of fluorocarbon.

In one aspect of the invention, a low temperature cooling medium for use in a closed loop cooling system comprises liquid nitrogen and a fluorocarbon represented by the formula: ChF2n+2, where n is 2.
is an integer of ˜4).

In another aspect of the invention, liquid nitrogen and a fluorocarbon having the formula: ChF2n. 2 (n in the formula is 2
is an integer of ~4), nitrogen and fluorocarbon represented by the following formula: C-F2,,+2 (n in the formula is the same as defined above) A method for producing a low-temperature cooling medium is provided, which comprises cooling and liquefying a mixed gas under pressure.

In another aspect of the invention, liquid nitrogen and a fluorocarbon represented by the formula: C-F2-+2, where n is 2
In producing a low-temperature cooling medium consisting of a mixture of (an integer of ~4), a gaseous fluorocarbon represented by the following formula:
CnF2-+2 (n in the formula is the same as the above definition)
Provided is a method for producing a low-temperature cooling medium, which comprises blowing carbon fluoride into liquid nitrogen to obtain liquid nitrogen in which carbon fluoride is dissolved.

In yet another aspect of the present invention, in cooling an object to be cooled (hereinafter referred to as a "cooled object") to an extremely low temperature of less than about 123 K, liquid nitrogen and Carbon fluoride: A cooling method characterized by immersing an object to be cooled in a low-temperature cooling medium of a closed-loop cooling system consisting of a mixture of C.F., (n in the formula is an integer from 2 to 4). provided.

In yet another aspect of the invention, a closed loop cooling system comprises liquid nitrogen and carbon fluoride: CnF2. +2 (in the formula, n is an integer from 2 to 4) has a cryostat containing a mixture as a cooling medium, and the object to be cooled is immersed in the cooling medium to perform cooling. A closed loop cooling device is also provided.

In yet another aspect of the present invention, there is provided a closed-loop cooling device comprising fluorocarbon represented by the following formula: c
．． F2n+. (m in the formula is an integer of 1 to 4v) is placed as a cooling medium, and the cryostat is arranged in an internal space above the cryostat, and a liquefied gas as a heat exchange medium is circulated inside the cryostat. There is also provided a closed loop cooling device characterized in that it has a heat exchange tube from a liquefier, and the object to be cooled is immersed in the cooling medium to perform cooling.

As detailed below, in accordance with the present invention, small amounts of fluorocarbon can be used in liquid nitrogen to provide unexpectedly enhanced cooling capacity.

Comparing this cooling capacity with the case of using liquid nitrogen alone, the cooling capacity of the present invention is approximately twice as high as that of the case of using liquid nitrogen alone. No shortcomings are recognized. These and other advantages of the invention will become more apparent from the description below.

[For production]

Although the details of the mechanism behind the improvement in cooling capacity when using the cooling medium of the present invention have not yet been clarified, based on the experience of the present inventors, it is assumed that there may be the following reasons. be done.

1> Decrease in the volume of the cooling medium due to a certain amount of mixing.

This volume reduction occurs in a manner similar to when mixing water and alcohol. That is, when the mean free path diameters of the molecules differ significantly, the volume of the molecular mixture decreases as a result of close packing of the molecules. Appropriate amount of fluorocarbon C. If F2n or (n=2, 3 or 4) is used in liquid nitrogen, the resulting reduction in the volume of the cooling medium will result in an additional increase in cooling capacity.

2) Decrease in the surface tension of the cooling medium. In other words, in the immersion cooling method of the present invention, the limit of the cooling capacity that can stably cool the object to be cooled (heating element) with a small temperature rise is the film boiling transition point of the cooling medium (cooling capacity when transitioning to the film boiling state). ), and the film boiling transition point, which is the limit for stable cooling, differs depending on the physical properties of the liquid fraction of the cooling medium, such as heat of vaporization and surface tension.

Carbon fluoride C. F2r++2 has a low surface tension and therefore dissolving fluorocarbon in liquid nitrogen significantly reduces the surface tension of the resulting mixture: cooling medium. Therefore, when a heating element is boiled and cooled in this mixed liquid, the vapor bubbles generated on the surface of the heating element will leave the heating element surface in the early stage of generation, delaying the transition to film boiling. It becomes like this. Furthermore, the generated bubbles destroy the boundary layer of the cooling medium that is in contact with the heating element.

As a result, the cooling capacity is improved. Note that with fluorinated carbon having a large molecular weight, the cooling ability can be improved at a lower concentration. However, if the carbon number n of carbon fluoride (CnF2n+2) exceeds 4, the boiling point will rise and it will become solid when mixed with liquid nitrogen, so in the present invention, n=2 to 4 was particularly selected.

In addition, various substances such as carbon chloride were investigated as substances to be mixed with liquid nitrogen, and the effect of carbon fluoride was remarkable.

One of the reasons for this is thought to be the decrease in surface tension described above.

3> Dissolution conditions for carbon fluoride. If liquid fluorocarbon is gradually frozen, it will thicken and become gelatinous. If carbon fluoride were to be dissolved in liquid nitrogen, a loose gelatinous liquid would form, and therefore the heat of vaporization and Therefore, it is considered that the cooling capacity is improved.

On the other hand, in order to cool and reliquefy the boiling and vaporized refrigerant in the cryostat using a heat exchanger, it is necessary to circulate a refrigerant with a lower boiling point than the refrigerant in the cryostat through the heat exchanger.

Therefore, the heat exchange refrigerant liquid nitrogen (boiling point 77.2K)
When CF4 (boiling point 145.2 K), which has a higher boiling point, is used as a refrigerant for cooling the immersion liquid and circulated inside the cryostat, boiling heat transfer occurs in the heat exchanger section, so it is more efficient than convective heat transfer using helium gas. Highly efficient heat transfer is possible.

In addition, the heat of vaporization of CF is as large as 136 J/g.
Since the heat of vaporization of liquid nitrogen is close to 198 J/g, C
F. Even if the circulation speed is slow, sufficient cooling can be achieved within the cryostat.

In one aspect, the present invention utilizes these results to improve cooling capacity.

For reference, the thermal properties of cryogenic liquids are shown in the table below. Here, the boiling point is K1, the heat of vaporization is J/g, and the thermal conductivity is mW/mK.
It is expressed as

Low temperature liquid boiling point 81.7 87.3 90.2 111.7 1
19.8 145.2 Heat of vaporization 215, 9 163.
2 213.1 510.3 107.7 1
36.2 Thermal conductivity 140 120 148
193 [Preferred Aspects and Examples of the Invention] As described in the "Means for Solving the Problems" section, the low-temperature cooling medium according to the present invention comprises liquid nitrogen and fluorocarbon CnF2n+a (n in the formula (same as in the definition). This low-temperature cooling medium is preferably used in the form of carbon fluoride dissolved in liquid nitrogen.

The carbon fluoride used in the present invention is C, F6, C3
Fll, C4FIO or a mixture thereof. C.F. It is also possible to use CF. It is necessary to add a large amount of CF. There may also be disadvantages caused by the use of More specifically, carbon fluoride, C2Fg, CsFe, etc., which have large molecular weights, have a high melting point and are difficult to dissolve in liquid nitrogen, but can lower the surface tension at a lower concentration than carbon tetrafluoride.

Therefore, in the present invention, instead of the conventional carbon tetrafluoride, attention was paid to carbon fluoride having a larger molecular weight as a mixture. As detailed below, a mixed refrigerant of carbon fluoride with a large molecular weight can be produced by cooling a mixed gas of nitrogen and carbon fluoride under pressure, or by blowing carbon fluoride gas into liquid nitrogen. This made it possible to obtain a mixed refrigerant with a small amount of other components and a high cooling capacity.

On the other hand, fluorocarbon C. n in the formula of F2ゎ+2 is 5
or more, the boiling point is high due to its large molecular weight, and it dissolves only in trace amounts in liquid nitrogen, or hardly dissolves at all, but rather can solidify when mixed with liquid nitrogen, and therefore when cooled Its use as a medium is not possible.

According to the present invention, about 8 to 20 mole % or more of fluorocarbon CF. Compared to conventional cooling media that added C to liquid nitrogen, a smaller amount of fluorocarbon C,
, F2, , +2 (n=2n3 or 4) to liquid nitrogen is sufficient. That is: In order to obtain the cooling medium of the present invention, fluorocarbon C total 2-+2 (Tl = 2.3 or 4) is preferably added to liquid nitrogen in an amount of 0.1 to 3 mol%. In C2FG, 0
．． The cooling capacity can be improved with an addition amount of 1 mol% or more, and 3
．． The maximum improvement in cooling capacity can be obtained at 5mo1%. Even if the amount added is higher than that, the cooling effect will not change much.

Due to the solubility of C2F6 in liquid nitrogen, if 3 mol % or more of C2F6 is mixed, the resulting cooling medium becomes cloudy and its effectiveness decreases. Therefore, the mixing ratio of C and F6 to liquid nitrogen is:
Preferably it is 0.1 to 3 mol%. C3F8, like the above-mentioned C2F6, dissolves up to approximately 3 mol%, and when it exceeds this, the resulting cooling medium becomes cloudy, and the effect of adding it to liquid nitrogen is almost the same as in the case of C2F6. The mixing ratio of C3F8 is more preferably 0.1 to 0.
It is 5 mol%.

The same applies to C4FIO. In C4FIO, the amount dissolved in liquid nitrogen is 0.5 mol% or less, and although the solubility becomes low, the cooling capacity can be improved at 0.1 to 0.5 mol%. The mixing ratio of C4FIO is more preferably 0.1 to 0.3 mol%.

The low temperature cooling medium according to the invention can be advantageously manufactured according to the procedure as described below.

The first manufacturing method uses nitrogen and fluorocarbon represented by the following formula: Cr+F2n. This method includes the step of cooling and liquefying a mixed gas of 2 (n in the formula is the same as defined above) under pressure. In the case of this manufacturing method, the ratio of nitrogen to fluorocarbon in the gas mixture is preferably substantially the same as that of the resulting cooling medium, and during the cooling step, the ratio of nitrogen to fluorocarbon is preferably 1-2.
Preferably, elevated pressure is applied to the gas mixture, and the gas mixture in a high-pressure container, such as a cylinder, is also introduced into a liquefier where it is cooled with compressed, adiabatic cooling gas onboard. It is preferable to do so.

The second manufacturing method uses gaseous fluorocarbon represented by the following formula: C,,F2,,. 2 (in the formula, n is the same as defined above) is blown into liquid nitrogen to obtain liquid nitrogen in which carbon fluoride is dissolved.In the case of this production method, a high-pressure vessel Blowing the gaseous fluorocarbon therein into liquid nitrogen in a container such as a Dewar bottle, and also pre-cooling the gaseous fluorocarbon before blowing it into the liquid nitrogen, specifically Specifically, the gaseous fluorocarbon can be cooled to a temperature near its boiling point (just before the fluorocarbon is liquefied) by passing it through liquid nitrogen in a separate Dewar-like container. preferable.

In the cooling method and cooling apparatus according to the present invention, that is, in the method for cooling an object to be cooled to a cryogenic temperature of less than about 123 K, and in the apparatus for carrying out such a method, a mixture of liquid nitrogen and fluorocarbon as described above is used. A low-temperature cooling medium is used in a closed loop system, and the object to be cooled is immersed in the cooling medium.

According to a preferred embodiment of the invention, a cooling medium is introduced into the closed talioskut of the cooling device as a medium for cooling the object to be cooled. In this embodiment, it is preferable that the cooling medium boiled and vaporized in the cryostat is transferred to another liquefier and liquefied there, and the obtained liquid cooling medium is returned to the cryostat again.

According to another preferred embodiment of the invention, the cooling medium boiled and vaporized in the cryostat is not transferred to a separate liquefier and liquefied there, but is liquefied in the same cryostat. In other words, the vapor of the cooling medium produced within the cryostat and its appropriate position within the cryostat (
Heat exchange is performed with a heat exchange medium in a heat exchange tube disposed in the heat exchange section, and as a result, the vapor of the cooling medium is liquefied. In this embodiment, the heat exchange medium circulated within the heat exchange tubes is preferably liquid nitrogen. However, other heat exchange media may be used if desired.

In the cooling device of the present invention, openings for charging and discharging are provided on the wall surface of the cryostat, and these openings are
It communicates with another liquefier via a conduit. With such a structure, the cooling medium that boils and vaporizes in the cryostat due to the heat generated by the object to be cooled can be guided to the liquefier and liquefied there, and the obtained liquid cooling medium can be returned to the cryostat.

Otherwise, a heat exchange tube is placed at a suitable location in the internal space above the cryostat and communicated with another liquefier. Assuming such ta, the cooling medium that boils and vaporizes in the cryostat due to the heat generated by the object to be cooled is transferred in the same cryostat as a result of heat exchange between the vapor of the cooling medium and the heat exchange medium in the heat exchange tube. , can be liquefied. The coolant thus liquefied falls into the coolant remaining in the cryostat.

The liquefier used in the practice of this invention can have any conventional construction, but preferably has a Stirling cycle refrigerator and compressor combination.

As previously mentioned, any heat exchange medium may be used in practicing the present invention. However, a satisfactory heat exchange effect can be obtained. At the same time, it is necessary to use a heat exchange medium that has a lower boiling point than the cooling medium for the object to be cooled used in the cryostat, and to circulate this heat exchange medium through the heat exchange tubes of the liquefier. If this requirement is met, boiling heat transfer will occur in the heat exchange tube section, and therefore more efficient heat transfer than convective heat transfer obtained by using helium gas in the heat exchange tubes. It becomes possible. This is why, as mentioned above, the cooling medium of the present invention is preferably used as a cooling medium for the object to be cooled in a cryostat, while liquid nitrogen is used as a heat exchange medium in a heat exchanger tube. .

The present invention can be applied to cooling an object to be cooled to a cryogenic temperature of less than about 123K. Examples of suitable cooled objects include, but are not limited to, HEMT. These include semiconductor devices such as CMOS, devices using high Tc superconductors that exhibit superconductivity at extremely low temperatures, electronic devices designed to be used at extremely low temperatures, circuit boards, and others. Surprisingly,
According to the present invention, even a large-sized computer can be cooled with high efficiency within a cooling device with a simple structure.

Next, the present invention will be described in detail with reference to the accompanying drawings, in which FIG. 1 and FIG. 2 each illustrate an apparatus for producing a low-temperature cooling medium according to the present invention.

In the apparatus shown in Fig. 1, the Stirling cycle refrigerator l
A cooling medium was produced using a liquefier 13 having a high-pressure compressor 15 and a high-pressure compressor 15. A gas cylinder 11 was charged with a mixed gas of nitrogen and carbon fluoride (C2F6 was used here), and the mixed gas was supplied to the refrigerator 14 via a conduit l2. Freezer 1
The gas in the container 17 of No. 4 is cooled under pressure of about 1.3 to 1.5 atmospheres, and is liquefied to form a cooling medium, that is, liquid nitrogen (L
A mixture of N2) and C2F6, 18, was formed. To cool the mixed gas, the bottom of the container 17 was cooled by a cold head (not shown) of a refrigerator l4. To explain in more detail now, a suitable cooling gas having a temperature of about 70K, for example helium at 11-13 kg/cd, is supplied to the compressor 1.
5, this compressed gas was adiabatically cooled by a piston 16, and the thus cooled gas was transferred to a cold head so that the cooling gas and the mixed gas from the gas cylinder 11 came into indirect contact. The liquefied mixed gas l8 accumulated in the container 17.

In the case of manufacturing the low-temperature refrigerant shown in the figure, the mixing ratio of carbon fluoride (C2Fg) in the resulting mixed refrigerant is determined by the concentration of the nitrogen monofluoride (C2FG) mixed gas filled in the gas cylinder. A mixed refrigerant ratio can be obtained with good controllability and reproducibility.

In the apparatus shown in FIG.
The cooling medium was produced by blowing 2FB gas). The C2FG gas in the gas cylinder 21 was pre-cooled to a temperature before the C2F6 gas was liquefied before being blown into the liquid nitrogen 28 in the Dewar bottle 27. That is, the C. F. Precooling was performed by passing the gas via conduit 22 to a cooling tube 23 immersed in liquid nitrogen 26 of a Dewar bottle 25 and circulating it inside the tube. After precooling, the cooled fluorocarbon gas from cooling pipe 23 was sent through conduit 24 to Dewar bottle 27 and bubbled in liquid nitrogen 28 within the bottle. As a result of this bubbling, the cooling medium, i.e.
Liquid nitrogen and C. F. A mixture of 27 was obtained in a Dewar bottle. Here, C2F. The mixing ratio of C. F. Gas pressure; C. By appropriately changing the flow rate of F6 gas, etc., it was possible to freely control the flow rate.

In addition, in the production of the above-mentioned low-temperature cooling medium with reference to FIGS. 1 and 2, ChF2 where n in the formula is 2 is used as fluorocarbon.
n+2, that is, C. F. As mentioned above, this example uses C3F8, C4P r with n=3.4.
o or a mixture thereof.

Also, in the example of FIG. 2, C2F. Although gas was used, nitrogen gas may also be mixed therein.

In the present invention, the low-temperature cooling medium of the present invention is introduced into a closed-loop cooling device, particularly its cryostat, in order to cool the object to be cooled to extremely low temperatures. Cooling using this cryostat will be explained below with reference to the attached FIGS. 3 and 4. Note that in FIG. 3, the heat exchange section is omitted in order to facilitate understanding of the invention.

In FIG. 3, a closed cryostat 33 was loaded with a cooling medium 34 of the present invention. Cooling medium 34 used here
was a mixture of liquid nitrogen and fluorocarbon CF4 at 3.41 mole percent of the total media. 10mm square LSI chip 3
100+n+n square circuit board 32 with 4x4 1 mounted
was immersed in the cooling medium 34 in the cryostat 33.

Here, when electric power is applied to the element (LSI chip 31) via a supply cable (not shown), the cooling medium 34 starts boiling, and fine vapor bubbles 3 form the surface of the element.
5 occurred. The element was thus removed from the heat of vaporization and cooled.

The cooling capacity of the used cooling medium was evaluated by defining it by the heat flow east when the cooling medium transitions from nucleate boiling to film boiling. The film boiling transition point was determined by measuring the relationship between device temperature and power loss. Measurement of the temperature of the device was performed at a diode formed on the surface of the device.

From the results of this evaluation, when the cooling medium was pure liquid nitrogen, the cooling capacity per unit area of the element when transitioning to the film boiling state was 15 to 20 W/crl, but in the above example, it was 30 to 50 W/crl. /crl, which was clearly improved by 2 to 3 times.

Furthermore, the above method can be applied to CF. By changing the mixing amount of (
0 to 20.7 mol%> Repeatedly, the CF. of the cooling capacity of the cooling medium. A graph showing the concentration dependence was plotted. The results obtained are shown in FIG.

Above, the cooling of the present invention has been described with reference to FIG.

To explain this cooling in more detail, the cooling of the present invention is as follows:
For example, it can be carried out advantageously using the cooling device shown in FIG. 5 or FIG. 6.

As is clear from the figure, the cooling device shown in FIG. 5 was a closed loop cooling system having a cryostat 33 and a liquefier 13. The liquefier 13 was isolated from the refrigerator 14 and the high-pressure compressor 15, as described above with reference to FIG. The cooling medium 34 filled in the cryostat 33 was a mixture of liquid nitrogen and 0.5 mol % carbon fluoride (C2F, used here), that is, a mixed refrigerant.

4x4 10mm square LSI chips 3L are mounted on a 100mm square circuit board 32, and these are mounted on a cryostat 33.
It was directly immersed in the mixed refrigerant 34 inside. When power was applied to the element (LSI chip 31) from a power source (not shown) via a power supply cable (not shown), the mixed refrigerant 34 started boiling, and fine bubbles 35 were generated from the surface of the element 31.Element 31 was therefore deprived of the heat of vaporization and cooled.

The vapor of the vaporized mixed refrigerant was sent to the container 17 of the refrigerator 14 via the supply conduit 36, and then liquefied in the container. To perform this liquefaction, the bottom of the container 17 was cooled with a cold head (not shown) of the refrigerator 14. Also, this cooling, as described earlier with reference to FIG.
The test was carried out using the compressor 15 and the piston 16 attached to it. That is, the function of the liquefier R13 shown in FIG. 5 is substantially the same as that shown in FIG. The coolant liquid collected in vessel 17 was circulated to cryostat 33 via supply conduit 37 .

The cooling capacity of the used cooling medium was evaluated as described above, and the evaluation results are plotted in FIG. 7 as a relationship between the temperature of the LSI chip immersed in the cooling medium. For comparison, liquid nitrogen alone was used as the cooling medium, and the evaluation results of the cooling capacity were plotted in FIG. 7 as well. From the results plotted in FIG. 7, it is clear that the mixture of the present invention had a cooling capacity per unit area of about 15 to 20 W/cal when the device transitioned to the film boiling state when immersed in pure liquid nitrogen. By applying the refrigerant, the amount of CJs mixed with only 0.5 mol% can be almost doubled to about 49
It can be seen that it is now possible to cool down to W/cn. It should be noted that since the mixed amount of 0.5 mol% C2Fll is extremely small, problems such as coagulation or separation of the refrigerant in a closed system liquefaction machine do not occur at all.

The closed loop cooling device of FIG. 6 is a variation of the cooling device previously described with reference to FIGS. 3 or 5. As shown in the figure, the cryostat 33 is placed apart from the liquefier 13, but in order to cool and liquefy the cooling medium (mixed refrigerant) vaporized in the cryostat 33, a heat exchanger extending from the liquefier 13 is installed. The tube 38 is the cryostat 33
It is located in the internal space above the. Cryostat 3
3. The mixed refrigerant 34 in the cryostat 33, the circuit board 32 on which the LSI chip 31 is mounted, and the liquefier 13 correspond to those in FIG. 5, and therefore have already been explained, so they will not be explained repeatedly here. omitted.

In addition, in this example, the heat exchange medium 39 circulated within the heat exchange tube 38 was liquid nitrogen.

10mII 1 square LSI on 100mm square circuit board 32
4×4 chips 31 were mounted, and these were directly immersed in the mixed refrigerant 34 in the cryostat 33. When power was applied to the element (LSI chip 31) from a power supply (not shown) via a power supply cable (not shown), the mixed refrigerant 34 started boiling, and fine bubbles 35 were generated from the surface of the element 31. The element 31 was thus deprived of the heat of vaporization and cooled. Next, the vaporized mixed refrigerant was subjected to indirect heat exchange with liquid nitrogen 39 in the heat exchange tube 38, and as a result, the vapor of the mixed refrigerant was liquefied and dripped into the unvaporized mixed refrigerant 34.

When the cooling capacity of the used cooling medium was evaluated as described above, the evaluation results obtained were satisfactory.
It was comparable to that obtained using the cooling device shown in FIG. In the case of the illustrated device, the heat exchange medium used was not gas but a liquid such as liquid nitrogen, so it was possible to reduce the diameter of the heat exchange tubes used without reducing the cooling capacity. did it. For example, lk! In case of IJ cooling, heat transfer can be increased up to 10'W/m''K, and when using helium gas, it is possible to increase the heat transfer to 10'W/m''K.
n”K), and the diameter of the heat exchange tube can be reduced to 25 mm, and when using helium gas, the diameter is 50 mm.
Seal〉.

In carrying out the present invention, in addition to the closed-loop cooling device shown in FIGS. 5 and 6, the device shown in FIG. 1 used for producing the low-temperature cooling medium of the present invention may be used as necessary. You can. That is, the circuit board on which the LSI described above is mounted can be immersed in the mixed refrigerant l8 collected in the container 17 having a vacuum double insulation layer. Although not shown in the apparatuses of FIGS. 1, 5, and 6,
A heater for temperature control is provided at the bottom of the container, and the temperature of the mixed refrigerant can be controlled to a temperature near the boiling point, and the speed of the heat exchange reaction can be controlled.

FIG. 8 is a graph plotting data obtained through experiments by the present inventors, so that the present invention can be understood in more detail from this graph.

Three lines and one point are plotted in the graph of FIG. That is, the first solid line is LN2 +C. F2n
．． ．． (n = 2 or 3), and the second
The solid line is the cooling capacity curve of LN2 + C4FIO,
The third dotted line is the cooling capacity curve of LN2 + CF4,
And one point is LN. Indicates the cooling capacity of In the case of the cooling medium of the present invention (a mixture of LN. and C.F2n+2, where n is 2n3 or 4), a small amount of CnF2n+
A significantly improved cooling effect was obtained by simply adding 2 to LN2. In addition, CoF 2ゎ+2 (n=2
The range of 0.5 to 1 mol % of Cr+F2n+2 is indicated by a dotted line, which means that Cr+F2n+2 could not be dissolved in LN2. Conventional cooling medium (LN2
alone or LN2 and CF. (a mixture of LN2 and CSF+2), a satisfactory cooling effect could not be obtained;
In the case of a mixture of (not shown), no improvement in cooling capacity was obtained; on the contrary, this mixture had a tendency to agglomerate.

Furthermore, although the above describes the use of a mixture of LN and C2F6 as a cooling medium in a cryostat with reference to the cooling device of FIG. It has been found that satisfactory results can be obtained using only carbon fluoride. That is, CF. Any fluorocarbon can be used as a cooling medium in the cryostat, and any liquefied gas can be used as a heat exchange medium in the heat exchange tubes of the liquefier. The type of liquefied gas used here will depend primarily on the properties of the fluorocarbon chosen as the cooling medium. It is common for the liquefied gas in the heat exchange tubes to have a lower boiling point than the fluorocarbon in the cryostat.

Using the closed-loop cooling device of FIG. was added as a cooling medium, and the LSI chip was cooled by the following procedure.

1 equipped with 3 x 3 lQ+nm square cut-out Sl chips 31
A 00 mm square circuit board 32 is placed in a liquid CF. It was immersed in a cooling medium 34 consisting of.

Here, when power was applied to the element (LSI chip 31), the cooling medium 34 started boiling, and fine vapor bubbles 35 were generated from the surface of the element. The element was thus removed from the heat of vaporization and cooled.

C.F. The vapor was cooled to about 90 K in a heat exchange tube 38 in which liquid nitrogen 39 was circulated, and was re-liquefied. In addition, the liquid nitrogen 39 removes heat from the CF4 vapor and boils, causing the gas and liquid to 2
It became a phase flow and returned to the refrigerator 14, where it was reliquefied.

Although not shown, a pump for circulating liquid nitrogen 39 is disposed in the middle of the heat exchange tube 38.

As a result of actual measurements of the cooling capacity, in the case of a conventional device using helium gas as a heat exchange medium, the cooling capacity was 100W, but in the case of the above-mentioned device of the present invention, the cooling capacity was 500W, which is about five times as much. It increased to Although liquid CF4 was used in the above example, other fluorocarbons such as C2Fg, C3F8, . C,F+o
or mixtures thereof can be used, and also suitable heat exchange media can be used depending on the fluorocarbon selected.

〔Effect of the invention〕

As explained above, according to the present invention, a cooling medium with a high heat flux value when transitioning to film boiling can be obtained, and low-temperature cooling with a simple mechanism and high cooling capacity is possible.

Furthermore, in a cooling system using a heat exchanger, by selecting a refrigerant for immersing the object to be cooled and a refrigerant for heat exchange, it is possible to provide a cooling device with high cooling capacity.

Furthermore, according to the present invention, closed-loop cooling is advantageous for immersing in liquid a device with a complex shape that has a large heat generation density and is difficult to connect to a refrigerator, such as a CPU of a computer, and is essential for low-temperature cooling of electronic equipment. It can be used in a wide range of systems, and there is no unevenness in the composition or fluctuations in cooling capacity within the circulation system.
Furthermore, it is possible to provide a low-temperature cooling medium that requires only a small amount of carbon fluoride to be mixed into liquid nitrogen and has a high cooling capacity, a method for producing the same, and a cooling method and device using the same. A device for electronic equipment (HE
MT, CMOS, etc., devices using high Tc phase oxide superconductors that exhibit superconductivity at liquid nitrogen temperature, circuit boards, etc.
can greatly contribute to the cooling of

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views showing an example of an apparatus used to produce a low-temperature cooling medium according to the present invention, and FIG. 3 is an example of a cryostat used in carrying out the present invention. FIG. 4 is a graph plotting the relationship between the concentration of CF4 in the cooling medium and the obtained cooling capacity, and FIGS. 5 and 6 are
FIG. 7 is a schematic cross-sectional view showing a preferred example of the closed-loop cooling device according to the present invention, FIG. 7 is a graph plotting changes in cooling capacity with and without the addition of C2FG with respect to the temperature of the LSI chip, and FIG. FIG. 9 is a graph plotting the relationship between the concentration of carbon fluoride in the medium and the cooling capacity obtained, and FIG. 9 is a schematic cross-sectional view showing an example of a conventional open type cooling device. In the figure, 11 is a gas cylinder, 12 is a conduit, 13 is a liquefier,
14 is a refrigerator, 15 is a compressor, 16 is a piston, 17 is a container, and 18 is a cooling medium. Low-temperature refrigerant manufacturing device 13...Liquifier 14...Freezer 15...Compressor 16...Piston 17...Cryostat for container closed-loop cooling snow storage Fig. 3 25 23 24 27 Low-temperature refrigerant Figure 2 CF4 concentration (mol%) Dependence of cooling capacity on CF4 concentration Figure 4 32 31 Closed loop cooling device Closed loop cooling device Figure 6 LSI chip temperature (K) Dependence of cooling capacity on LSI chip temperature Figure 7: Cooling capacity depends on fluoride carbon concentration Figure 8

Claims (1)

[Claims] 1. A low-temperature cooling medium for use in a closed-loop cooling device, comprising liquid nitrogen and fluorocarbon represented by the following formula: C
A low-temperature cooling medium comprising a mixture of _nF_2_n_+_2 (n in the formula is an integer from 2 to 4). 2. Liquid nitrogen and carbon fluoride represented by the following formula: C_n
F_2_n_+_2 (n in the formula is an integer from 2 to 4)
In producing a low-temperature cooling medium consisting of a mixture of nitrogen and carbon fluoride represented by the following formula: C_nF_2_n
A method for producing a low-temperature cooling medium, characterized in that a mixed gas of _+_2 (n in the formula is the same as defined above) is cooled under pressure and liquefied. 3. Liquid nitrogen and carbon fluoride represented by the following formula: C_n
F_2_n_+_2 (n in the formula is an integer from 2 to 4)
In producing a low-temperature cooling medium consisting of a mixture of, gaseous fluorocarbon represented by the following formula: C_nF_2_n_
+_2 (n in the formula is the same as defined above) into liquid nitrogen to obtain liquid nitrogen in which carbon fluoride is dissolved. 4. In cooling the object to be cooled to an extremely low temperature of less than about 123K, liquid nitrogen and fluorocarbon expressed by the following formula: C_
A cooling method characterized in that the object to be cooled is immersed in a low-temperature cooling medium of a closed loop cooling system consisting of a mixture of nF_2_n_+_2 (n in the formula is an integer from 2 to 4). 5. A closed-loop cooling device, comprising a cryostat in which a mixture of liquid nitrogen and carbon fluoride represented by the following formula: C_nF_2_n_+_2 (in the formula, n is an integer from 2 to 4) is placed as a cooling medium. 1. A closed-loop cooling device, characterized in that the object to be cooled is immersed in the cooling medium to perform cooling. 6. A closed-loop cooling device, which is carbon fluoride represented by the following formula: C_mF_2_m_+_2 (m in the formula is 1 to 4
is an integer of has,
A closed loop cooling device characterized in that cooling is performed by immersing an object to be cooled in the cooling medium.