JP7126279B2 - Electronic device with bubble release device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electronic device capable of efficiently cooling an electronic component including a heating element such as a CPU.

Data centers containing supercomputers have rapidly increased in density in recent years. Conventionally, air-conditioning technology has mainly been used to cool server equipment in data centers, but it is difficult to efficiently remove the heat from such high-density servers that generate a large amount of heat with air-conditioning alone. Therefore, cooling techniques have been proposed that can solve the problem of high heat generation resulting from the application of high-density servers.

A typical example is the liquid wetting method. A system (forced convection system) is known in which a high heat generation board is directly wetted with a coolant, and the coolant is forcibly convected by a pump or fan to cool the high heat generation such as the CPU (non-patent document 1). However, the forced convection of the refrigerant requires a pump and a fan, which has the drawback of increasing the power consumption of the entire system.

As a method for solving this problem, a natural convection system that does not use fans or pumps has been proposed. In this method, the coolant is circulated by natural convection caused only by the heat generated by the CPU, so it has the advantage that the power consumption of the entire system is small, but has the disadvantage that the upper limit of the heat that can be cooled is limited.

On the other hand, there is also proposed a method of dripping a coolant only on a heat-generating part such as a CPU to cool it. However, this method requires a pump to lift the refrigerant from the drop point, which limits the power efficiency of the entire system.

On the other hand, a boiling cooling method using vaporization of a refrigerant has also been proposed (Patent Document 1). This is a method of selecting a coolant whose boiling point is lower than the heat generation temperature of a CPU or the like, and cooling the surface of the CPU or the like with the heat of vaporization. However, since this method utilizes the boiling phenomenon of the refrigerant, it is necessary to cool the vaporized refrigerant to return it to the liquid phase. Configuration required. Furthermore, there are many problems to be solved from a practical point of view, such as the generation of ultrasonic waves due to the boiling phenomenon, which adversely affects electronic devices, and the variation in cooling performance when a plurality of CPUs are arranged.

JP 2017-150715 A

Web magazine "FUJITSU JOURNAL" published by Fujitsu Ltd. August 15, 2016

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electronic device capable of efficiently cooling an electronic component including a heating element such as a CPU.

As a result of intensive research to solve the above problems, the present inventors have found a refrigerant, an electronic component immersed in the refrigerant, and a bubble discharge device immersed in the refrigerant, and the bubble discharge device The inventors have found that efficient cooling is possible with an electronic device in which air bubbles emitted from the device have an average length of 0.1 mm or more, and completed the present invention.

An electronic device equipped with the bubble ejection device of the present invention, which has achieved the above objects, has the following points.
[1] An electronic device in which a refrigerant, an electronic component immersed in the refrigerant, and a bubble discharge device immersed in the refrigerant are housed in a housing,
An electronic device, wherein an average major axis of air bubbles emitted from the air bubble ejection device measured by the following measuring method is 0.1 mm or more.
<Measurement method>
In the image obtained by photographing an area of 50 mm × 50 mm with a camera centered at a point 30 mm above the bubble discharge port of the bubble discharge device, 10 bubbles (long diameter of 0.05 mm) within the range of focus (excluding those less than 1) are measured, and the average value is taken as the average major diameter.
[2] The electronic device according to [1], wherein the refrigerant has a boiling point of 70°C or higher.
[3] The electronic device according to [1] or [2], wherein the refrigerant has a viscosity of 0.0008 kg/m·s or more and 0.05 kg/m·s or less at 25°C.
[4] Any one of [1] to [3], wherein the air bubbles released from the air bubble ejection device reach the liquid surface of the refrigerant, and the distance from the air bubble ejection device to the liquid surface of the refrigerant is 200 mm or more. The electronic device described in .
[5] A gas recovery port arranged in the upper part of the housing, a path for circulating the gas recovered from the gas recovery port to the bubble discharging device, and a pump for circulating the gas, wherein the refrigerant is supplied. The electronic device according to any one of [1] to [4], which does not have a circulating pump.
[6] The electronic device according to any one of [1] to [5], wherein the bottom of the housing has an installation area and a non-installation area for the bubble ejection device.
[7] The electronic device according to any one of [1] to [6], wherein the bubble ejection device includes a tubular body or porous body having holes.
[8] The electronic device according to any one of [1] to [7], wherein a cooling plate in which water is circulated is housed in the housing.
[9] The electronic device according to any one of [1] to [8], wherein the electronic device includes a board having a CPU package.

The present invention overcomes the drawbacks of the prior art and provides an electronic device that has a highly efficient cooling capacity against high heat generation. efficiency and efficiency.

The electronic device of the present invention efficiently cools a heat-generating CPU or the like by promoting the convection of the coolant by utilizing the rise of air bubbles of a predetermined size generated from the air bubble generator (bubble flow support). According to this bubble flow support method, in addition to natural convection, by simply adding a simple mechanism to send air to the bubble generator, it is possible to achieve the same level of cooling performance as the forced convection method. Since the electric power required for this mechanism is much smaller than that of a pump or fan for circulating the coolant, it is possible to provide an electronic device that is excellent in both cooling efficiency and electric power efficiency.

5 is a graph showing the relationship between the average major diameter of bubbles and the surface temperature of the CPU package; 1 is a top view of an electronic device according to an embodiment of the invention; FIG. 3 is an xx cross-sectional view of the electronic device shown in FIG. 2; FIG. 3 is a yy sectional view of the electronic device shown in FIG. 2; FIG. 3 is a cross-sectional view showing another example of the xx cross-sectional view of the electronic device shown in FIG. 2; FIG. 4 is a graph showing the relationship between the air bubble flow rate and the surface temperature of the CPU package; 7A to 7D are schematic diagrams of electronic devices according to different embodiments. 4 is a graph showing the relationship between coolant flow velocity and PUE on the surface of a CPU package; 4 is a graph showing the relationship between the surface temperature of a CPU package and PUE; 4 is a graph showing the relationship between cooling water temperature and CPU junction temperature; 4 is a graph showing the relationship between cooling water temperature and CPU junction temperature; 5 is a graph showing the relationship between CPU input power and CPU junction temperature; 4 is a graph showing the relationship between CPU input power and total system power; 5 is a graph showing the relationship between bubble flow rate and CPU junction temperature;

Hereinafter, the present invention will be described based on the embodiments, but the present invention is not limited by the following embodiments, and can be implemented by making appropriate changes within the scope that can conform to the gist of the preceding and following descriptions. are also possible, and all of them are included in the technical scope of the present invention. In each drawing, for the sake of convenience, hatching, member numbers, etc. may be omitted. In such cases, the specification and other drawings shall be referred to. In addition, the dimensions of various members in the drawings may differ from the actual dimensions, since priority is given to helping to understand the features of the present invention.

In an electronic device according to an embodiment of the present invention, an electronic component including a heating element that generates heat during operation and a bubble discharge device are immersed in a coolant and housed in a housing. The average length of the air bubbles released from the air bubble ejection device is 0.1 mm or more. The average length is measured by the method described below.

<Measurement method>
A 50 mm×50 mm area centered on a point 30 mm above the bubble ejection port of the bubble ejection device is photographed with an imaging device such as a high-speed camera. In the obtained image, the major diameters of 10 bubbles excluding those having a major diameter of less than 0.05 mm are measured, and the average value is taken as the average major diameter.

When bubbles are discharged from the bubble discharge device, an upward bubble flow is generated in the refrigerant, and the refrigerant itself also flows upward due to the bubble flow. When a heating element included in an electronic component generates heat, the heat causes natural convection of the coolant and upward convection of the coolant supported by bubbly flow. This bubble-assisted convection can efficiently cool electronic components.

FIG. 1 shows the relationship between the average major diameter of bubbles and the surface temperature of the CPU package, which is calculated by the inventor.

As shown in FIG. 1, if the average major diameter of the air bubbles released from the air bubble ejection device is 0.1 mm or more, the bubble flow generated in the coolant convects the coolant, and the CPU package can be cooled. The average length of the bubbles is preferably 0.3 mm or more, more preferably 0.6 mm or more. Furthermore, the average length of the air bubbles may be 0.8 mm or more, or may be 1.0 mm or more. If the bubbles are too small, they will not generate an upward flow, so the bubbly flow cannot convect the refrigerant. Also, the average length of the bubbles is preferably 20 mm or less, more preferably 15 mm or less, and particularly preferably 10 mm or less. If the bubbles are too large, not only is the convection assisting effect of the refrigerant reduced, but also the volume of air with low thermal conductivity increases, which is not preferable. Bubbles having an average major diameter within the above range are effective in cooling the surface of the CPU package because the bubbles generated in the coolant can convect the coolant.

A bubble ejection device included in an electronic device according to an embodiment of the present invention has a mechanism for ejecting gas into liquid. The structure is not particularly limited as long as it can release air bubbles, but for example, a structure in which a pump for sending a gas such as air is connected to a tubular body or porous body provided with small holes can be used.

The coolant contained in the electronic device according to the embodiment of the present invention is a liquid and has a structure including air bubbles. The type of coolant is not particularly limited as long as it is an inert liquid with excellent electrical insulation and thermal and chemical stability, but silicone oil, fluorine-based inert liquid, ethylene glycol aqueous solution and the like are preferably used. In general, Fluorinert FC3283, which is a fluorine-based inert liquid, has a high cooling effect, and silicone oil such as KF-96A-6cs has a relatively low cooling effect. According to this, by adjusting the bubble length, the bubble flow rate, and the like, even a refrigerant with a low cooling effect can be cooled in the same manner as a refrigerant with a high cooling effect.

The electronic component immersed in the coolant included in the electronic device according to the embodiment of the present invention is a general term for components that operate in a predetermined manner when energized, and has a size that allows it to be immersed in the coolant within the housing. Any part is applicable. For example, an example of an electronic component is a CPU chip. The CPU chip itself, a CPU chip molded with resin or the like, a CPU package in which the CPU chip is housed in a package, a motherboard on which the CPU package is mounted, a CPU, Any parts, such as memory chips and hard disks, can be applied as long as they can be immersed in the coolant inside the housing.

With such an electronic device according to the embodiment of the present invention, even high-density servers and supercomputers with high heat generation, whose power density has been increasing in recent years, can be efficiently operated in both cooling efficiency and energy efficiency. . In addition, since the electronic device according to the embodiment of the present invention has a simple structure in which a bubble discharge device is added, the space required for its installation can be extremely small compared to a system based on air conditioning. It is possible to save the space of the data center including the equipment.

An electronic device according to an embodiment of the present invention will now be described in detail with reference to FIGS. 2 to 5. FIG.

As shown in FIGS. 2 to 5, an electronic device 1 according to an embodiment of the present invention includes a coolant 20, an electronic component 30 immersed in the coolant 20, and a bubble discharge device 40 immersed in the coolant 20. are housed in the housing 10 . The bubble release device 40 may be placed below the electronic component 30 , which may be a board 31 with a CPU package 33 and a memory 32 . The electronic device 1 can have a plurality of boards 31 , and the plurality of boards 31 can be erected in parallel and housed in the housing 10 . In addition, the electronic device 1 may include a cooling plate 50 arranged so as not to interfere with the flow of bubbles generated by the rising air bubbles generated by the air bubble ejection device 40 .

The enclosure 10 may or may not be hermetically sealed. From the viewpoint of preventing the loss of the coolant 20 due to evaporation, it may be sealed. do not have. Therefore, when a plurality of boards 31 having, for example, a CPU package 33 as electronic components 30 are housed in the housing 10, when maintenance such as replacement of one board 31 or replacement of cables becomes necessary, the entire tank must be stopped. It is not necessary to release the strict sealing by means of a squeegee, and the boards 31 can be easily taken out one by one for maintenance.

Since the electronic device 1 suppresses the generation of ultrasonic waves due to the boiling phenomenon seen in the conventional boiling cooling method, there is no adverse effect on the electronic components 30, and for example, two CPU packages can be mounted on one board 31. 33 are arranged vertically, the operating state of the lower CPU does not affect the cooling performance of the upper CPU. Therefore, as shown in FIGS. 3 to 5, the CPU packages 33 can be arranged vertically, thus providing a high degree of freedom in arrangement.

Bubbles having an average major diameter of 0.1 mm or more measured by the above measuring method are discharged from the bubble discharging device 40, and the refrigerant 20 convects upward due to the bubble flow of the bubbles. As a result, in addition to the natural convection that occurs when the electronic components 30 generate heat, the coolant 20 also undergoes upward convection supported by the bubbly flow, removing heat from the surfaces of the electronic components 30 .

The electronic device 1 may include a cooling plate 50 arranged so as not to interfere with the bubble flow generated by rising bubbles generated from the bubble ejection device 40. For example, water is circulated in the cooling plate 50. good too. The electronic component 30 can be cooled by heat exchange between the coolant 20 and the cooling plate 50 . The cooling platen 50 may be arranged parallel to the board 31 as shown in FIGS. 2-5. Alternatively, although not shown, for example, the housing 10 has an outer wall and an inner wall, and water is circulated in a space formed between the outer wall and the inner wall. may also serve as the cooling plate 50 . The lower the temperature of the water circulating in the cooling plate 50, the higher the cooling effect. It becomes possible to achieve the same cooling effect even if the .DELTA.

Table 1 shows the surface temperature of the CPU package when using various refrigerants according to trial calculations by the present inventor, together with physical properties such as the boiling points and viscosities of the various refrigerants. Trial calculations were made assuming that the input power per CPU is 90 W (hereafter, the input power when described as CPU input power refers to the input power per CPU) and the temperature of the cooling water flowing through the cooling plate is 20°C.

The coolant 20 preferably has a boiling point higher than the surface temperature of the electronic component 30 so as not to boil on the surface of the electronic component 30 and to suppress loss due to evaporation. preferably has a boiling point of 70° C. or higher. It is more preferably 90° C. or higher, still more preferably 110° C. or higher.

The refrigerant 20 preferably has a viscosity at 25° C. of 0.0008 kg/m·s or more, more preferably 0.001 kg/m·s or more, and even more preferably 0.0012 kg/m·s or more. If the viscosity is too low, it will be less effective at removing heat from the CPU surface. Also, it is preferably 0.05 kg/m·s or less, more preferably 0.045 kg/m·s or less, and still more preferably 0.04 kg/m·s or less. If the viscosity is too high, it is not preferable because it is difficult to generate a bubbly flow and the heat conduction is deteriorated. If the upper and lower limits of the viscosity of the coolant 20 are within the above ranges, the coolant 20 convects due to the support of bubble flow by the bubbles released from the bubble ejection device 40, and the electronic component 30 can be cooled effectively.

The bubbles released from the bubble release device 40 rise as a bubble flow and reach the liquid surface of the coolant 20 . It is preferable that the distance from the bubble discharging device 40 to the liquid surface of the refrigerant 20 is 200 mm or more. If it is 200 mm or more, a bubble flow caused by rising bubbles can convect the refrigerant.

Only one type of refrigerant 20 may be used, or two or more types may be used. For example, as shown in FIG. 5, the first refrigerant 21 with high vapor pressure, high specific gravity, and high cooling efficiency is filled up to the part where the high heat generating part such as the CPU infiltrates, and the part without the high heat generating part is filled with the first refrigerant 21. can be filled with the second refrigerant 22 having a low vapor pressure and a low specific gravity. In that case, the first refrigerant 21 and the second refrigerant 22 preferably do not mix with each other like water and oil. When the first refrigerant 21 and the second refrigerant 22 are used in this way, the refrigerant with high cooling efficiency used as the first refrigerant 21 generally has a low boiling point, high evaporation loss, and high cost. Since the second refrigerant 22 having a low vapor pressure is filled on top of the first refrigerant 21, evaporation (loss) of the refrigerant is prevented, and a higher cooling capacity can be realized with less bubbles and at a lower cost. becomes possible. In the above example, Fluorinert such as FC-3283 can be selected as the first refrigerant 21, silicone oil such as KF-96A-6cs can be selected as the second refrigerant 22, and only Fluorinert such as FC-3283 can be used as the refrigerant 20. The cost of the refrigerant is 1/2 compared to the case of , and the bubble flow is 1/10 compared to the case where the refrigerant 20 is only silicone oil such as KF-96A-6cs, and the same cooling effect can be achieved. In addition, in the aspect using the first refrigerant 21 and the second refrigerant 22, even when a refrigerant with a high global warming potential is used as the first refrigerant 21, the rate of evaporation can be dramatically suppressed, which is preferable. .

Although not shown, bubbles that have reached the liquid surface of the coolant 20 may be recovered from a gas recovery port arranged at the top of the closed housing 10 . The recovered gas may be circulated through the path from the gas recovery port to the bubble release device 40 by a pump. By closing the housing 10, the coolant 20 can be prevented from disappearing due to vaporization, and the recovered gas can be supplied to the gas release device. As described above, the electronic device according to the embodiment of the present invention may have a pump for circulating the collected gas, but may not have a pump for circulating the coolant 20 . Compared to a pump that circulates the refrigerant, a pump that circulates the gas consumes less power. High energy efficiency can be achieved compared to the convection method. A small motor such as a micro DC motor can be used for the pump for sending air into the air bubble releasing device 40 and the pump for circulating the collected gas when the air bubbles reach the liquid surface of the coolant 20.

One or more bubble ejection devices 40 may be arranged, and may be arranged at the bottom of the housing 10 as shown in FIGS. 3-5. In this case, as shown in FIGS. 3 and 5, it is preferable that the bottom of the housing 10 has an installation area and a non-installation area for the bubble ejection device 40 . A bubbly flow is generated above the installation area, causing the coolant 20 to convect upward, and the coolant 20 convects downward above the non-installation area, thereby circulating the coolant and efficiently cooling the electronic component 30. can.

The bubble releasing device 40 may include a tubular body having holes or a porous body. When the bubble releasing device 40 is a tubular body having holes, the hole may be single or plural. good. The long diameter of each hole is sufficient as long as it can release air bubbles having an average long diameter of 0.1 mm or more, for example, 0.05 mm or more is preferable, and 0.07 mm or more is more preferable. Moreover, the long diameter of each hole may be 0.3 mm or more, or may be 0.5 mm or more. Further, in order to set the upper limit of the average long diameter of bubbles to 20 mm or less, more preferably 15 mm or less, and particularly preferably 10 mm or less, the long diameter of each hole of the bubble release device is preferably 15 mm or less, more preferably 10 mm or less, and 8 mm or less. is particularly preferred. The long diameter of the air bubbles released from the air bubble ejection device 40 depends on the flow rate of the air sent into the air bubble ejection device 40, but generally it is larger than the long diameter of the hole of the air bubble ejection device 40. Therefore, since there is a tendency for the air bubbles to coalesce and become larger, the long diameter of the holes of the air bubble discharge device 40 is preferably smaller than the desired long diameter of the air bubbles.

The type of gas that constitutes the bubbles is not particularly limited, and it may be a gas other than air, but air that normally exists in the environment is preferable. min or more, 0.09 L/min or more, 0.1 L/min or more, 0.5 L/min or more, 1 L/min or more, and 1.2 L/min or more. If the bubble flow rate is too low, sufficient bubble flow cannot be obtained. On the other hand, if the air bubble flow rate is too large, the number of air bubbles with low thermal conductivity in the refrigerant will increase and the cooling efficiency will decrease. More preferably, 8 L/min is particularly preferred. Also, the air bubble flow rate can be selected according to the cooling effect of the refrigerant itself. For example, when using a refrigerant with a high cooling effect such as Fluorinert FC3283, the bubble flow rate is set to 0.1 L / min, and when using a refrigerant with a relatively low cooling effect such as silicone oil KF-96A-6cs, the bubble flow rate is set to 0.1 L / min. The bubble flow rate can be adjusted by the refrigerant, such as 1 L/min, 2 L/min, 4 L/min, or 7 L/min.

In a data center using the electronic equipment according to the embodiment of the present invention, the ratio of the power used by the ICT equipment among the electronic equipment (the power of the ICT equipment) to the power used by the entire data center (total power) PUE (Power Usage Effectiveness) is preferably less than 1.1 (total power/ICT device power <1.1). PUE is an index representing the operating efficiency of ICT equipment in a data center. Since the cooling power is included in the total power, not the power of the ICT equipment, it means that the closer the PUE is to 1.0, the lower the proportion of the cooling power in the total power. The electronic device according to the embodiment of the present invention can achieve a PUE of less than 1.1, which has been regarded as an index of high efficiency, because the refrigerant convects with the help of bubble flow that uses less power. Also, a low PUE of 1.05 or less, or even 1.02 or less can be realized.

If the electronic component 30 includes, for example, a CPU package 33, it will not operate normally as a device if the temperature rises above the limit of movement of the CPU. For example, in a CPU, the CPU junction temperature T _j needs to be below a certain temperature. As described above, the power that can be supplied to the electronic component 30 is limited by the movable limit temperature, but the electronic device according to the embodiment of the present invention efficiently cools the heat generating element such as the CPU package 33 included in the electronic component 30. Therefore, the temperature of the heating element can be kept low even with the same input power. Therefore, the electronic device according to the embodiment of the present invention can raise the upper limit of input power as compared with the natural convection system, and can realize an electronic device with high power density. Further, when the electronic device according to the embodiment of the present invention and the forced convection system are compared, the maximum input power to the electronic component 30 is the same, but the PUE value at that time is Smaller and more energy efficient. Table 2 shows the maximum power that can be input to the CPU and the best PUE values for the input power in the electronic device (bubble flow support method) according to the embodiment of the present invention and the electronic device of the forced convection method and the natural convection method. The forced convection method can apply the same maximum CPU power as the present invention, but the PUE is higher. On the other hand, the natural convection system can achieve a PUE equivalent to that of the present invention, but the maximum input power that can be input to the CPU is smaller.

Furthermore, according to the bubble flow support system of the present invention, even if the cooling effect of the refrigerant 20 is different, the same cooling effect can be expected by adjusting the bubble length, the bubble flow rate, etc. Therefore, for example, the cooling effect is relatively low. Even if a silicone oil such as KF-96A-6cs is used as the coolant 20, the CPU junction temperature T _j will be kept below a certain temperature in substantially the same way as when Fluorinert FC3283 or the like, which has a high cooling effect, is used as the coolant 20. can do. As a result, the power input to the CPU can be increased regardless of the type of refrigerant 20, and the total system power can be increased while maintaining a low PUE value.

This application claims the benefit of priority based on Japanese Patent Application No. 2018-213141 filed on November 13, 2018. The entire contents of the specification of Japanese Patent Application No. 2018-213141 filed on November 13, 2018 are incorporated herein by reference.

EXAMPLES The present invention will be specifically described below with reference to Examples.

<Example 1: Air bubble flow rate and CPU package surface temperature>
In the electronic device according to the embodiment of the present invention, an electronic device including a fluorine-based inert liquid Fluorinert FC-3283 as a coolant and a CPU package is used, and the relationship between the bubble flow rate and the CPU package surface temperature when the CPU input power is 145 W. examined. FIG. 6 shows the results of measuring the temperatures of the water flowing through the cooling plate at 10° C. and 25° C. FIG. In FIG. 6, a bubble flow rate of 0 L/min means that there is no bubble flow support, that is, a natural convection system. With bubble flow support, the surface temperature of the CPU package is lower than without bubble flow support, and when the bubble flow rate increases in the range of 0.1 L/min to 7 L/min, the surface temperature of the CPU package becomes monotonic. found to decrease.

<Example 2: Shape of Bubble Ejecting Device and Surface Temperature of CPU Package>
In the electronic device according to the embodiment of the present invention, the surface temperature of the CPU package was examined when the diameter of the hole and the number of holes of the bubble ejection device were changed under the following conditions.
CPU input power: 90W
Refrigerant: Fluorinert FC-3283
Air bubble flow rate: 0.1 L/min Cooling water temperature: 25°C
Schematic diagrams of the electronic device are shown in FIGS. 7(a) to 7(d), and the results are shown in Table 3. It can be seen that the CPU package is cooled in the same way when the hole diameter is 1 mm, when there are one hole (bubble discharging device a), when there are four holes (bubble discharging device c), and when there are multiple holes (bubble discharging device d). rice field. It was also found that the CPU package was cooled in the case of the hole diameter of 7 mm (bubble discharge device b) as well as in the case of the hole diameter of 1 mm.

<Example 3: Coolant flow velocity on the surface of the CPU package and PUE>
In addition to the natural convection, the relationship between the coolant flow velocity on the surface of the CPU package and the PUE was investigated in the case of the bubble flow support system using the electronic device according to the embodiment of the present invention and the convection in the case of the forced convection system. . The power applied to the CPU was 90 W, and the refrigerant used was fluorine-based inert liquid Fluorinert FC-3283. The results are shown in FIG. It was found that the bubble flow support system of the present invention achieves a low PUE equivalent to that of the natural convection system even at the same coolant flow velocity on the surface of the CPU package as that of the forced convection system.

<Example 4: CPU package surface temperature and PUE>
The relationship between the surface temperature of the CPU package and the PUE was investigated in the bubble flow support method using the electronic device according to the embodiment of the present invention, the forced convection method, and the natural convection method. The power applied to the CPU was 90 W, and the refrigerant used was fluorine-based inert liquid Fluorinert FC-3283. The results are shown in FIG. It was found that the bubble flow support system of the present invention can reduce the surface temperature of the CPU package to the same level as the forced convection system, and also realizes a low PUE equivalent to that of the natural convection system.

<Example 5: Cooling water temperature and CPU junction temperature depending on the type of refrigerant>
Using Fluorinert FC3283 as a refrigerant with a high cooling effect and silicone oil KF-96A-6cs as a refrigerant with a low cooling effect, a bubble flow support system (with bubble flow support) using the electronic device according to the embodiment of the present invention and The relationship between the cooling water temperature and the CPU junction temperature T _j in the natural convection system (without bubble flow support) was investigated. The CPU input power was 125 W, and the cooling water flow rate was 39 L/min. The results are shown in FIGS. 10 and 11. FIG. From FIG. 10, it can be seen that in the case of Fluorinert FC3283, which has a high cooling effect, the cooling water temperature is 46° C. without bubble flow support, and 51° C. with bubble flow support, and the CPU junction temperature T _j can be less than 93° C. rice field. That is, with the help of bubble flow, the cooling water temperature was able to be reduced from 46°C to 51°C to keep the CPU junction temperature T _j below 93°C. On the other hand, from FIG. 11, in the case of silicone oil KF-96A-6cs, which has a low cooling effect, the CPU junction temperature T _j cannot be set to less than 93° C. unless the cooling water temperature is as low as 34° C. without bubble flow support. In contrast, it was found that the CPU junction temperature T _j can be made less than 93° C. even if the cooling water temperature is 49° C. with bubble flow support. That is, with the aid of bubbly flow, the cooling water temperature was able to be reduced from 34°C to 49°C to keep the CPU junction temperature T _j below 93°C. This shows that the bubble flow support can keep the CPU junction temperature below a certain level even if the cooling water temperature is high. Even if there is, it means that the permissible range of the cooling water temperature can be increased to the same level as that of Fluorinert FC3283, which has a high cooling effect, if bubble flow support is performed.

<Example 6: CPU input power and CPU junction temperature depending on the type of refrigerant>
Fluorinert FC3283 is used as a coolant with a high cooling effect, silicone oil KF-96A-6cs is used as a coolant with a low cooling effect, and CPU input when the bubble flow support system using the electronic device according to the embodiment of the present invention is used. The relationship between power and CPU junction temperature was investigated. The cooling water temperature was set to 20° C., and the cooling water flow rate was set to 39 L/min. The results are shown in FIG. From FIG. 12, it was found that with the Fluorinert FC3283, which has a high cooling effect, the CPU junction temperature T _j can be kept below 93° C. even if the CPU input power is increased to 257 W by using the bubbly flow support method. Furthermore, it was found that even with silicone oil KF-96A-6cs, which has a low cooling effect, the power supplied to the CPU can be increased to 238 W by using the bubbly flow support method.

<CPU input power and total system power depending on the type of refrigerant>
FIG. 13 shows the relationship between the CPU input power and the total system power in the sixth embodiment. With the Fluorinert FC3283, which has a high cooling effect, the total system power could be reduced to 16.6 kW because the CPU input power could be increased to 257 W if the bubbling support system was used. In addition, even with silicone oil KF-96A-6cs, which has a low cooling effect, if the bubble flow support system is used, the power input to the CPU can be increased to 238 W, so the total system power can be reduced to 16 kW. We were able to almost cancel out the differences due to From this, it was found that the choice of refrigerant can be expanded by using the bubble flow support method.

<Example 7: Bubble flow rate and CPU junction temperature depending on the type of refrigerant>
Using Fluorinert FC3283 as a coolant with a high cooling effect and silicone oil KF-96A-6cs as a coolant with a low cooling effect, the relationship between the bubble flow rate and the CPU junction temperature T _j was investigated. The CPU input power was 125 W, the cooling water temperature was 20° C., and the cooling water flow rate was 39 L/min. The results are shown in FIG. Here, the bubble flow rate of 0/min means that there is no bubble flow support, that is, the natural convection system is used. means. From FIG. 14, with Fluorinert FC3283, which has a high cooling effect, the CPU junction temperature monotonically decreased when the air bubble flow rate ranged from 0.1 L/min to 8 L/min. On the other hand, with silicone oil KF-96A-6cs, which has a low cooling effect, when the air bubble flow rate is 1 L/min or more, the CPU junction temperature is kept lower than when there is no bubble flow support and when the air bubble flow rate is less than 1 L/min. From this, it was found that the CPU junction temperature can be lowered by using the bubbly flow support method and setting the bubble flow rate to 1 L/min or more, even if silicone oil KF-96A-6cs, which has a low cooling effect, is used as the coolant.

1: Electronic Device 10: Housing 20: Refrigerant 21: First Refrigerant 22: Second Refrigerant 30: Electronic Component 31: Board 32: Memory 33: CPU Package 40: Bubble Ejector 50: Cooling Panel

Claims (8)

An electronic device in which a refrigerant, an electronic component immersed in the refrigerant, and a bubble discharge device immersed in the refrigerant are housed in a housing, wherein the boiling point of the refrigerant is 70° C. or higher, and the 1. An electronic device characterized in that the average major axis of air bubbles released from a bubble ejection device measured by the following measuring method is 0.1 mm or more.
<Measurement method>
In the image obtained by photographing an area of 50 mm × 50 mm with a camera centered at a point 30 mm above the bubble discharge port of the bubble discharge device, 10 bubbles (long diameter of 0.05 mm) within the range of focus (excluding those less than 1) are measured, and the average value is taken as the average major diameter. The electronic device according to claim 1, wherein the refrigerant has a viscosity of 0.0008 kg/m·s or more and 0.05 kg/m·s or less at 25°C. 3. The electronic device according to claim 1, wherein the air bubbles released from the air bubble ejection device reach the liquid surface of the coolant, and the distance from the air bubble ejection device to the liquid surface of the coolant is 200 mm or more. A pump for circulating the refrigerant, having a gas recovery port arranged in the upper part of the housing, a path for circulating the gas recovered from the gas recovery port to the bubble discharging device, and a pump for circulating the gas. The electronic device according to any one of claims 1 to 3 , which does not have The electronic device according to any one of claims 1 to 4 , wherein the bottom of the housing has an installation area and a non-installation area for the bubble ejection device. The electronic device according to any one of claims 1 to 5 , wherein the bubble ejection device includes a tubular body or porous body having holes. The electronic device according to any one of claims 1 to 6 , wherein a cooling plate in which water is circulated is housed in the housing. The electronic device according to any one of claims 1 to 7 , wherein the electronic device includes a board having a CPU package.

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