Liquid immersion cooling method and liquid immersion cooling apparatus

Abstract

The preset invention can effectively cool an electronic device.　In this liquid immersion cooling method, an electronic device 9 is immersed in a liquid refrigerant R containing propylene glycol and cooled. According to this method, the electronic device 9 can be efficiently cooled. The liquid refrigerant R is composed of propylene glycol. The electronic device 9 is a GPU server device 90 having a graphic board 91 as a substrate and a GPU 92 as a processor mounted on the graphic board 91.

Description

Liquid immersion cooling method and liquid immersion cooling apparatus

[0001] The present invention relates to a liquid immersion cooling method and a liquid immersion cooling apparatus.

[0002] For example, Patent Document 1 describes an immersion cooling device for immersion cooling electronic equipment using an insulating liquid coolant.

[0003] Japanese Patent Publication No. 2024-073716

[0004] However, the immersion cooling device described in Patent Document 1 does not specify the material of the liquid refrigerant. Therefore, depending on the liquid refrigerant, it may not be possible to efficiently cool the electronic equipment.

[0005] The object of the present invention is to provide an immersion cooling method and an immersion cooling apparatus that can efficiently cool electronic devices.

[0006] These objectives are achieved by the present invention described below.

[0007] (1) A liquid immersion cooling method characterized by immersing electronic equipment in a liquid coolant containing propylene glycol to cool it.

[0008] (2) The liquid immersion cooling method according to (1) above, wherein the liquid refrigerant is composed of propylene glycol.

[0009] (3) The liquid immersion cooling method according to (1) above, wherein the liquid refrigerant is the aqueous solution of propylene glycol.

[0010] (4) The immersion cooling method described in (1) above, wherein a portion of the liquid refrigerant is frozen to form an ice slurry.

[0011] (5) The liquid immersion cooling method according to (1) above, wherein the electronic device comprises a substrate and a processor mounted on the substrate.

[0012] (6) The immersion cooling method described in (5) above, wherein the processor is a GPU (Graphics Processing Unit).

[0013] (7) A liquid immersion cooling device having a cooling tank in which a liquid refrigerant is stored, and which cools electronic equipment by immersing it in the liquid refrigerant, characterized in that the liquid refrigerant contains propylene glycol.

[0014] According to the immersion cooling method and apparatus of the present invention, electronic equipment is cooled using a liquid refrigerant containing propylene glycol. Therefore, electronic equipment can be cooled efficiently.

[0015] Figure 1 is an overall configuration diagram of the immersion cooling device according to the first embodiment. Figure 2 is a perspective view of the GPU server equipment. Figure 3 is a cross-sectional view showing a modified example of the GPU server equipment. Figure 4 is an overall configuration diagram showing a modified example of the immersion cooling device. Figure 5 is an overall configuration diagram of the immersion cooling device according to the second embodiment. Figure 6 is a graph showing the relationship between the concentration of the propylene glycol aqueous solution and the latent heat. Figure 7 is a graph showing the relationship between the concentration of the propylene glycol aqueous solution and the freezing point. Figure 8 is a cross-sectional view showing the state in which electronic equipment is housed in the housing. Figure 9 is a cross-sectional view showing the housing. Figure 10 is a cross-sectional view showing the processing of the intersection of the zipper and wiring. Figure 11 is a cross-sectional view showing a modified example of the housing. Figure 12 is a cross-sectional view showing a modified example of the housing. Figure 13 is a cross-sectional view showing a modified example of the housing. Figure 14 is a cross-sectional view showing a modified example of the housing. Figure 15 is an overall configuration diagram of the immersion cooling device according to the fourth embodiment. Figure 16 is a cross-sectional view showing the configuration of the cooling section.

[0016] The liquid immersion cooling apparatus and liquid immersion cooling method of the present invention will be described in detail below based on the embodiments shown in the attached drawings. Note that the upper side of the paper is the upper side in the vertical direction, and the lower side of the paper is the lower side in the vertical direction.

[0017] <First Embodiment> The liquid immersion cooling device 1 shown in Figure 1 is a device for cooling electronic equipment 9 by immersing it in a liquid coolant R. The electronic equipment 9 is not particularly limited, but examples include computer equipment equipped with a processor such as a CPU (Central Processing Unit), in particular server equipment, and among these, GPU (Graphics Processing Unit) server equipment which is indispensable for processing artificial intelligence. As shown in Figure 2, the electronic equipment 9 in this embodiment is a GPU server equipment 90 having a graphics board 91 as a substrate, a GPU 92 as a processor mounted on the graphics board 91, and an output interface 93 having at least one port. The demand for GPU server equipment 90 has been increasing with the recent spread of artificial intelligence, and it generates significantly more heat than conventional server equipment. The liquid immersion cooling device 1 can effectively cool even such a heat-generating GPU server equipment 90.

[0018] As shown in Figure 1, the immersion cooling system 1 is located, for example, within a data center (DC). However, the location of the immersion cooling system 1 is not particularly limited. A large number of GPU server devices 90 are installed within the data center (DC).

[0019] Furthermore, the immersion cooling device 1 includes a cooling unit 2 for cooling liquid refrigerant R, a storage tank 3 for storing liquid refrigerant R, a cooling tank 4 to which the cooled liquid refrigerant R stored in the storage tank 3 is supplied, a first circulation path 61 for circulating liquid refrigerant R between the cooling unit 2 and the storage tank 3, and a second circulation path 62 for circulating liquid refrigerant R between the storage tank 3 and the cooling tank 4.

[0020] Liquid refrigerant R is propylene glycol (C ３ H ８ O ２ ) contains. In particular, the liquid refrigerant R of this embodiment is composed of propylene glycol. Note that "composed of propylene glycol" includes not only cases where it is 100% propylene glycol, but also cases where it contains small amounts of other substances, etc., which can be considered equivalent to 100% propylene glycol from a common technical standpoint.

[0021] By using propylene glycol as the liquid refrigerant R, the following effects can be achieved. First, propylene glycol is an insulating material. Therefore, the GPU server equipment 90 can be directly immersed in the liquid refrigerant R stored in the cooling tank 4 without any covering. As a result, the GPU server equipment 90 can be cooled efficiently. Also, propylene glycol is substantially colorless and transparent. Therefore, the GPU server equipment 90 in the liquid refrigerant R can be easily confirmed by visual inspection, etc. Furthermore, propylene glycol has a boiling point of 188°C, and for example, water (H ２ Its boiling point is higher than that of water (H). Therefore, compared to the case where water is used as the liquid refrigerant R, the natural decrease of liquid refrigerant R due to evaporation can be suppressed more effectively. On the other hand, propylene glycol has a freezing point of -59°C, and for example, water (H) ２ The freezing point of O) is lower than 0°C. Therefore, compared to the case where water is used as the liquid refrigerant R, the liquid refrigerant R can be cooled to a lower temperature while remaining in liquid. Consequently, a larger temperature difference can be achieved with the GPU server equipment 90, and the GPU server equipment 90 can be cooled more effectively.

[0022] Here, propylene glycol has a density of 1.04 [g / cm³]. ３ Its specific heat is 2430 [J / (kg°C)]. In contrast, water has a density of 1.00 [g / cm³]. ３] and has a specific heat of 4200 [J / (kg°C)]. Therefore, the amount of heat Qp contained in propylene glycol is V × 1.04 × 2430 × ΔTp [J / kg], where V is the volume and ΔTp is the temperature difference with the electronic device 9, and the amount of heat Qw contained in water is V × 1.00 × 4200 × ΔTw [J / kg], where V is the volume and ΔTw is the temperature difference with the electronic device 9. In other words, the heat ratio Qp / Qw = 0.6 × ΔTp / ΔTw. Therefore, in order to make propylene glycol exhibit the same cooling performance as water, ΔTp should be set to 1.67 times ΔTw. For example, assuming that water must be cooled to 5°C in order to maintain the GPU server device 90 at 15°C (i.e., when ΔTw = 10°C), propylene glycol should be cooled to -1.7°C so that ΔTp = 16.7°C.

[0023] Thus, propylene glycol has the advantage of being insulating, although its cooling performance (heat retention) is slightly inferior to that of water. If water were used as the liquid coolant R, since water is conductive, it would be necessary to take extra steps, such as placing the GPU server equipment 90 in a container, to avoid contact between the water and the GPU server equipment 90. This would make the preparation more complicated and increase costs. Furthermore, the heat exchange efficiency between the liquid coolant R and the GPU server equipment 90 would decrease due to the container and the air layer (insulating layer) that may form between the container and the GPU server equipment 90, preventing the water from exhibiting its full cooling performance. Therefore, considering all factors, using propylene glycol as the liquid coolant R allows for simpler and more efficient cooling of the GPU server equipment 90.

[0024] Here, one liquid coolant that has been conventionally used in immersion cooling methods is insulating dimethyl silicone oil. Dimethyl silicone oil has a density of 0.965 [g / cm³]. ３] and has a specific heat of 1500 [J / (kg°C)]. Therefore, the amount of heat Qs contained in dimethyl silicone oil is V × 0.965 × 1500 × ΔTs [J / kg], where V is the volume and ΔTs is the temperature difference with the electronic equipment 9. In other words, the heat ratio Qs / Qw = 0.345 × ΔTp / ΔTs. As mentioned above, for example, assuming that water must be cooled to 5°C to maintain the GPU server equipment 90 at 15°C, the dimethyl silicone oil must be cooled to -13.9°C so that ΔTs = 28.9°C. Thus, propylene glycol can exhibit the same cooling capacity as dimethyl silicone oil at a higher temperature than dimethyl silicone oil. In other words, at the same temperature, propylene glycol has higher cooling performance than dimethyl silicone oil. Therefore, propylene glycol can cool the GPU server equipment 90 more efficiently.

[0025] As shown in Figure 1, the cooling unit 2 includes a compressor 23, a condenser 24, an expansion valve 25, and a heat exchanger 21, and has a circuit for circulating the refrigerant N. In such a cooling unit 2, the refrigerant N is compressed in the compressor 23 to become a high-temperature, high-pressure gas. The refrigerant N, which has become a high-temperature, high-pressure gas in the compressor 23, flows into the condenser 24, where it condenses and liquefies to become a high-pressure liquid. The refrigerant N, which has become a high-pressure liquid in the condenser 24, is depressurized by the expansion valve 25 and flows into the heat exchanger 21. The low-pressure liquid refrigerant N that has flowed into the heat exchanger 21 evaporates and vaporizes while absorbing heat from the liquid refrigerant R, becoming a low-pressure gas. The refrigerant N, which has become a low-pressure gas in the heat exchanger 21, is returned to the compressor 23, compressed by the compressor 23, and discharged again as a high-temperature, high-pressure gas. Through this heat exchange cycle, the cooling unit 2 continuously cools the liquid refrigerant R circulating between the heat exchanger 21 and the storage tank 3.

[0026] The storage tank 3 stores the liquid refrigerant R. By arranging the storage tank 3, cooled liquid refrigerant R can be stockpiled, and the required amount of cooled liquid refrigerant R can be quickly supplied to the cooling tank 4 when needed. Furthermore, the storage tank 3 is covered with insulating material, etc., providing excellent insulation, which effectively suppresses the temperature rise of the liquid refrigerant R inside the storage tank 3. This enables efficient operation of the immersion cooling device 1.

[0027] While the cooling unit 2 is operating, the liquid refrigerant R in the storage tank 3 circulates between it and the heat exchanger 21 via the first circulation path 61. Therefore, the liquid refrigerant R is supplied from the storage tank 3 to the heat exchanger 21, cooled by heat exchange with the refrigerant N in the heat exchanger 21, and then returned to the storage tank 3. By continuously performing this circulation cycle, the liquid refrigerant R in the storage tank 3 is gradually cooled. When the temperature of the liquid refrigerant R in the storage tank 3 drops to a predetermined temperature, the operation of the cooling unit 2 is stopped.

[0028] Here, it is preferable to operate the cooling unit 2 during low-rate periods when electricity rates are low, such as at night, and to minimize the operation of the cooling unit 2 during high-rate periods when electricity rates are high, such as during the day. This makes it possible to cool the liquid refrigerant R at a lower cost.

[0029] The liquid refrigerant R stored in the storage tank 3 circulates between it and the cooling tank 4 via the second circulation path 62. The liquid refrigerant R may be continuously circulated between the storage tank 3 and the cooling tank 4 while the immersion cooling system 1 is in operation. Alternatively, the liquid refrigerant R may be circulated between the storage tank 3 and the cooling tank 4 intermittently. This method ensures that the liquid refrigerant R is continuously or continuously supplied to the cooling tank 4, allowing for continuous and stable cooling of the GPU server equipment 90. Furthermore, for example, a temperature sensor may be placed to detect the temperature of the liquid refrigerant R in the cooling tank 5. When the temperature of the liquid refrigerant R in the cooling tank 5 exceeds a predetermined temperature, the liquid refrigerant R may be circulated between the storage tank 3 and the cooling tank 4 until the temperature of the liquid refrigerant R in the cooling tank 5 falls below the predetermined temperature. This method reduces the operating time of the pump required for circulation, enabling power-saving operation of the immersion cooling system 1.

[0030] In the liquid immersion cooling system 1 described above, the GPU server equipment 90 is immersed in the liquid coolant R in the cooling tank 4. The GPU server equipment 90 (especially the GPU 92) is then cooled by heat exchange between the liquid coolant R and the GPU server equipment 90. As mentioned above, because propylene glycol, which is the liquid coolant R, is an insulator, the GPU server equipment 90 can be immersed in the liquid coolant R without any protection. Therefore, the GPU server equipment 90 can be cooled efficiently.

[0031] The liquid immersion cooling device 1 has been described above. In this liquid immersion cooling method using the liquid immersion cooling device 1, the electronic equipment 9 is cooled by immersing it in a liquid coolant R containing propylene glycol. This method allows for efficient cooling of the electronic equipment 9.

[0032] Furthermore, as mentioned above, the liquid refrigerant R is composed of propylene glycol. With this configuration, the liquid refrigerant R is insulating, allowing the electronic device 9 to be immersed in the liquid refrigerant R without any protection. Therefore, the electronic device 9 can be cooled efficiently.

[0033] Furthermore, as mentioned above, the electronic device 9 is a GPU server device 90 having a graphics board 91 as a circuit board and a GPU 92 as a processor mounted on the graphics board 91. With this configuration, the GPU 92 can be effectively cooled.

[0034] As mentioned earlier, the processor is a GPU92 (Graphics Processing Unit). Although the GPU92 generates more heat than other processors such as the CPU, it can still be adequately cooled.

[0035] Furthermore, as mentioned above, the immersion cooling device 1 has a cooling tank 4 in which liquid refrigerant R is stored, and is a immersion cooling device that cools electronic equipment 9 by immersing it in the liquid refrigerant R, the liquid refrigerant R containing propylene glycol. This allows for efficient cooling of the electronic equipment 9.

[0036] Although the first embodiment has been described above, the configuration of the immersion cooling device 1 is not particularly limited. For example, as shown in Figure 3, the GPU server device 90 may have a base 96, a graphics board 91 fixed to the base 96, a GPU 92 and output interface 93 mounted on the graphics board 91, a heatsink 94 positioned in contact with the GPU 92, and a metal fan cover 95 equipped with a plurality of fans 951 for cooling the heatsink 94. Currently, the GPU server device 90 is often distributed as a unit of a predetermined size with such a configuration. For this reason, it may be immersed in the liquid coolant R with the heatsink 94 and fan cover 95 attached. In this case, by driving the fans 951 in the liquid coolant R, convection of the liquid coolant R is generated, heat exchange between the liquid coolant R and the GPU server device 90 is promoted, and the cooling efficiency of the GPU server device 90 is further improved.

[0037] Furthermore, as shown in Figure 4, the storage tank 3 may be omitted, and the liquid refrigerant R may circulate between the cooling unit 2 (heat exchanger 21) and the cooling tank 4. With such a configuration, the device can be made smaller and less expensive by omitting the storage tank 3.

[0038] <Second Embodiment> The immersion cooling device 1 of this embodiment is the same as that of the first embodiment described above, except that a portion of the liquid refrigerant R is frozen to form an ice slurry Rs. In the following description, this embodiment will be described mainly for the differences from the first embodiment described above, and similar matters will not be described. Also, in the figures of this embodiment, the same reference numerals are used for components that are the same as those in the previously described embodiment.

[0039] As shown in Figure 5, in the immersion cooling device 1 of this embodiment, the cooling unit 2 cools the liquid refrigerant R and generates ice slurry Rs by freezing a portion of the liquid refrigerant R. The ice slurry Rs is a sherbet-like ice in which fine ice particles are mixed into the liquid refrigerant R, and is sometimes referred to as slurry ice, ice slurry, or slurry ice. By using ice slurry Rs instead of liquid refrigerant R in this way, it is possible to achieve high cooling efficiency by utilizing latent heat while maintaining fluidity within the device.

[0040] The storage tank 3 stores the liquid refrigerant R and the ice slurry Rs. By arranging the storage tank 3, a fixed amount of the ice slurry Rs can be stocked, and a required amount of the ice slurry Rs can be rapidly supplied to the cooling tank 4 when necessary. The storage tank 3 is provided with excellent heat insulation properties, for example, by being covered with a heat insulating material, and melting of the ice slurry Rs in the storage tank 3 is effectively suppressed. Thereby, the ice slurry Rs can be stored in the storage tank 3 for a long time, and the immersion cooling device 1 can be operated efficiently. In addition, in order to suppress aggregation of the ice slurry Rs in the storage tank 3, a stirring device that stirs the ice slurry Rs in the storage tank 3 may be disposed.

[0041] The ice slurry Rs stored in the storage tank 3 circulates between the storage tank 3 and the cooling tank 4 via the second circulation path 62. Note that the ice slurry Rs may be constantly circulated between the storage tank 3 and the cooling tank 4 during operation of the immersion cooling device 1. Alternatively, the ice slurry Rs may be intermittently circulated between the storage tank 3 and the cooling tank 4. According to such a method, fresh ice slurry Rs is continuously or successively supplied to the cooling tank 4, so that the GPU server device 90 can be continuously and stably cooled. Further, for example, a temperature sensor that detects the temperature of the ice slurry Rs in the cooling tank 5 is disposed, and the ice slurry Rs is circulated between the storage tank 3 and the cooling tank 4 at the timing when the temperature of the ice slurry Rs starts to rise, that is, at the timing when all the ice contained in the ice slurry Rs has melted, so that the inside of the cooling tank 4 is filled with fresh ice slurry Rs, and thereafter, the circulation may be stopped until the temperature of the ice slurry Rs starts to rise again. According to such a method, the driving time and the like of the pump required for circulation are suppressed, and power-saving operation of the immersion cooling device 1 is enabled.

[0042] In the immersion cooling apparatus 1 as described above, the GPU server device 90 is immersed in the ice slurry Rs in the cooling tank 4. Then, heat exchange is performed between the ice slurry Rs and the GPU server device 90, and the GPU server device 90 is cooled. Note that the temperature of the ice slurry Rs is maintained near the freezing point, that is, near -59°C, until the ice (solid component) melts due to the action of latent heat. Therefore, according to the ice slurry Rs, the GPU server device 90 can be continuously cooled for a longer period of time. Therefore, according to the immersion cooling apparatus 1, the GPU server device 90 can be effectively cooled. In particular, since the ice slurry Rs has fluidity, it adheres closely to the surface of the GPU server device 90. Therefore, the GPU server device 90 can be cooled more effectively.

[0043] As described above, in the present embodiment, a part of the liquid refrigerant R is frozen to form the ice slurry Rs. According to such a method, the electronic device 9 can be effectively cooled.

[0044] Also by the second embodiment as described above, the same effects as those of the first embodiment described above can be exhibited.

[0045] <Third Embodiment> The immersion cooling apparatus 1 of the present embodiment is the same as the second embodiment described above, except that the configuration of the liquid refrigerant R is different. In the following description, the present embodiment will be described focusing on the differences from the first embodiment described above, and descriptions of the same matters will be omitted. In addition, in each drawing of the present embodiment, the same reference numerals are assigned to the same configurations as those of the previously described embodiments.

[0046] In the immersion cooling apparatus 1 of the present embodiment, as the liquid refrigerant R, propylene glycol is mixed with water (H ２ O) to use a diluted propylene glycol aqueous solution. According to such a configuration, the freezing point of the liquid refrigerant R can be easily adjusted.

[0047] Figure 6 shows the relationship between the concentration [wt%] of a propylene glycol aqueous solution and its latent heat [kJ / kg]. The figure also shows an example of an ethanol aqueous solution as a comparative example. As can be seen from the figure, for example, if the latent heat is 300 [kJ / kg], the concentration of the propylene glycol aqueous solution should be 25 [wt%], and the concentration of the ethanol aqueous solution should be 20 [wt%].

[0048] Furthermore, Figure 7 shows the relationship between the concentration [wt%] of the propylene glycol aqueous solution and its freezing point [°C]. The figure also includes an example of an ethanol aqueous solution as a comparative example. As can be seen from the figure, the freezing point of a 25 [wt%] propylene glycol aqueous solution is approximately -5°C, while the freezing point of a 20 [wt%] propylene glycol aqueous solution is approximately -11°C. Thus, for the same latent heat, the propylene glycol aqueous solution has a higher freezing point than the ethanol aqueous solution, allowing for the generation of ice slurry Rs with less energy. Therefore, the GPU server equipment 90 can be cooled efficiently.

[0049] Here, since the aqueous propylene glycol solution is conductive, if the GPU server equipment 90 is immersed in the liquid coolant R in an unprotected state, there is a risk of malfunctions or failures of the GPU server equipment 90 due to short circuits, etc. Therefore, in this embodiment, as shown in Figure 8, the GPU server equipment 90 is immersed in the ice slurry Rs while housed in the housing 8, and heat exchange between the GPU server equipment 90 and the ice slurry Rs is performed via the housing 8. As a result, the GPU server equipment 90 and the ice slurry Rs are not in contact, and the above problem is resolved.

[0050] Next, the container 8 will be described. The container 8 is flexible, insulating, and airtight. Furthermore, the container 8 is light-transmitting, allowing the inside of the container 8 to be seen from the outside. The constituent material of the container 8 is not particularly limited, but various resin materials such as polypropylene can be used, for example.

[0051] As shown in Figure 9, the housing 8 is a bag-shaped structure made of a thin film or the like, with an opening 80 at its upper end. Therefore, the GPU server equipment 90 can be easily inserted into and housed in the housing 8 through the opening 80. The housing 8 is also provided with a zipper 81 for closing the opening 80 and creating an airtight seal inside. Furthermore, the housing 8 is provided with a valve 82 for removing (degassing) the air inside the housing 8 while it is airtightly sealed. The valve 82 is a check valve, which can remove the air from inside the housing 8 but prevents air from entering from the outside.

[0052] In this type of housing 8, the GPU server equipment 90 is placed inside the housing 8, and then the zipper 81 is closed to hermetically seal the housing 8. Furthermore, the air inside the housing 8 is removed via the valve 82, reducing the pressure (degassing) inside the housing 8. As a result, as shown in Figure 8, the housing 8 is in close contact with the main surface 921 of the GPU server equipment 90, particularly the GPU 92. In this state, it is immersed in ice slurry Rs. Therefore, the GPU 92 can be efficiently cooled by the ice slurry Rs. However, since the wiring 99 connected to the GPU server equipment 90 crosses the zipper 81, gaps are likely to form at their intersections. Therefore, in this embodiment, as shown in Figure 10, adhesive 83 is applied to the intersections to seal the gaps and more reliably ensure the hermetically sealed housing 8.

[0053] The containment body 8 has been described above. However, the containment body 8 is not particularly limited as long as it can reduce the pressure inside. For example, the containment body 8 may be both flexible and stretchable. In this way, the stretchable nature of the containment body 8 makes it less likely for wrinkles to form in the containment body 8 under reduced pressure, and when the containment body 8 is in close contact with the GPU 92, it becomes less likely for an air layer to form between them. Therefore, the GPU 92 can be efficiently cooled by the ice slurry Rs. In this case, the constituent material of the containment body 8 can be, for example, various resin rubber materials such as silicone rubber or various elastomers.

[0054] Furthermore, the housing 8 may be conductive in at least a portion thereof, provided that it prevents short circuits in the GPU server equipment 90. Conductive materials generally have excellent thermal conductivity, allowing the GPU 92 to be cooled more efficiently by the ice slurry Rs. In this case, the constituent material of the housing 8 can be, for example, various resin materials containing conductive fillers, various rubber materials, various elastomers, etc.

[0055] Alternatively, as shown in Figure 11, for example, a heat conductive member 84 may be placed between the housing 8 and the GPU 92, and the housing 8 and the GPU 92 may be brought into close contact via the heat conductive member 84. The heat conductive member 84 has a thermal conductivity at least higher than that of air. The heat conductive member 84 is, for example, a sheet-like member (heat conductive sheet) made of various resin materials such as acrylic resin or silicone resin containing a highly thermally conductive filler such as a metal filler, and has sufficient flexibility and thermal conductivity. With such a configuration, the heat conductive member 84 elastically deforms in a reduced pressure state, making it difficult for an air layer to form between the housing 8 and the GPU 92. Therefore, the GPU 92 can be efficiently cooled by the ice slurry Rs. The heat conductive member 84 may be placed in advance at a predetermined location on the housing 8, or it may be placed in advance on the main surface 921 of the GPU 92. Furthermore, the heat conductive member 84 is not limited to a sheet-like form, but may be, for example, a grease-like form.

[0056] Furthermore, the zipper 81 may be omitted from the container 8. In this case, the container 8 can be airtightly sealed using, for example, adhesive, double-sided tape, clips, welding, etc. Also, the valve 82 may be omitted from the container 8. In this case, for example, air can be released through the opening 80.

[0057] Alternatively, as shown in Figure 12, for example, after depressurizing the housing 8, an insulating liquid 85 may be injected into the housing 8 via a valve 82 or the like. This allows the liquid 85 to enter any gap (air layer) formed between the housing 8 and the main surface 921 of the GPU 92, thereby eliminating the air layer. As a result, the GPU 92 can be cooled more efficiently by the ice slurry Rs. The liquid 85 is not particularly limited as long as it has a higher thermal conductivity than air; for example, a polyimide-based oil can be effectively used.

[0058] Furthermore, the housing 8 may be a rigid body, that is, a rigid body with sufficient stiffness to not deform substantially under forces received during use. In this case, the housing 8 can be made of a metallic material such as Fe (iron), copper (Cu), aluminum (Al), brass (copper / zinc alloy), or stainless steel (iron / chromium alloy). By making the housing 8 out of a metallic material in this way, the housing 8 will have high thermal conductivity. Therefore, the GPU server equipment 90 can be effectively cooled. If necessary, the inner surface of the housing 8 may be insulated to prevent short circuits of the GPU server equipment 90 through the housing 8.

[0059] For example, as shown in Figure 13, the housing 8 is box-shaped and has a housing section 86 for housing the GPU server equipment 90 and an opening 87 for inserting and removing the GPU server equipment 90 from the housing section 86. With this configuration, the electronic equipment 9 can be inserted into and removed from the housing section 86 without damaging the housing 8. Therefore, the housing 8 can be reused, and the running costs of the immersion cooling device 1 can be effectively reduced. In addition, the shape of the housing section 86 is determined to match the shape of the GPU server equipment 90, and when the GPU server equipment 90 is housed in the housing section 86, the inner surface 861 of the housing section 86 and the main surface 921 of the GPU 92 are in contact. By bringing the GPU 92 into contact with the inner surface 861 in this way, the heat exchange efficiency between the ice slurry Rs and the GPU 92 is further increased, and the GPU server equipment 90 can be cooled more effectively.

[0060] The housing 8 is submerged in the ice slurry Rs such that its opening 87 is located vertically above the liquid level F of the ice slurry Rs. This prevents the ice slurry Rs from entering the housing 86. Furthermore, since there is no risk of the ice slurry Rs entering the housing 86, there is no need to seal the opening 87. This makes it easy to insert and remove the GPU server equipment 90 from the housing 86. Moreover, heat from the GPU server equipment 90 is less likely to accumulate inside the housing 86, allowing the GPU server equipment 90 to be cooled more effectively. In particular, in this embodiment, when the housing 8 is placed in the ice slurry Rs, the GPU 92 is located within the ice slurry Rs. With this configuration, the GPU 92 can be cooled more effectively.

[0061] Furthermore, as shown in Figure 14, for example, the housing 8 may also have a biasing part 88 that biases the GPU 92 toward the inner surface 861 of the housing 86. With this configuration, the main surface 921 of the GPU 92 is pressed against the inner surface 861 of the housing 86 by the biasing part 88, and they come into close contact. As a result, the GPU 92 can be effectively cooled through the housing 8. The biasing part 88 has an intermediate plate 881 placed inside the housing 86 and a leaf spring 882 inserted into the housing 86 in a compressed state, and is configured to bias the GPU server equipment 90 with the intermediate plate 881 by utilizing the elastic force of the leaf spring 882.

[0062] <Fourth Embodiment> The immersion cooling device 1 of this embodiment is the same as the first embodiment described above, except that the configuration of the cooling unit 2 is different. In the following description, this embodiment will be described mainly for the differences from the first embodiment described above, and similar matters will not be described. Also, in the figures of this embodiment, the same reference numerals are used for components that are the same as in the previously described embodiments.

[0063] The cooling unit 2 of this embodiment cools the liquid refrigerant R by heat exchange with liquefied natural gas (LNG) as the liquefied gas, and generates natural gas (NG) by evaporating and vaporizing at least a portion of the liquefied natural gas (LNG). Note that the liquefied gas is not limited to liquefied natural gas (LNG), but may also be liquefied petroleum gas (LPG), liquefied ammonia gas, etc.

[0064] Here, for example, some countries and regions rely almost entirely on imports for their natural gas (NG). Furthermore, to improve transportation efficiency, natural gas (NG) is converted into liquefied natural gas (LNG) at approximately -162°C by liquefaction plants installed in natural gas fields, and then transported (by sea) to receiving terminals (7) using LNG tankers.

[0065] As shown in Figure 15, the receiving base 7 is equipped with an LNG tank 71 for temporarily storing the transported liquefied natural gas (LNG), a vaporizer 72 for vaporizing the LNG stored in the LNG tank 71 to produce the required amount of natural gas (NG), and an odorizer 73 for adding an odor to the natural gas (NG) produced by the vaporizer 72. The natural gas (NG) that has been odorized by the odorizer 73 is then temporarily stored in gas holders 74 installed in various locations in urban areas, and is typically sent from there through gas pipes to each of the client's buildings 75.

[0066] Furthermore, a configuration using a seawater shower as the vaporizer 72 is commonly used, that is, a configuration that exchanges heat between seawater pumped from the sea and liquefied natural gas (LNG). However, this means that the cold energy of the liquefied natural gas (LNG) is not utilized and is instead dumped into the sea, and there is a risk of it leading to an increase in seawater temperature, resulting in a significant environmental burden.

[0067] Therefore, in the immersion cooling device 1 of this embodiment, the cold energy of liquefied natural gas (LNG), which has not been utilized until now, is used to cool the liquid refrigerant R, and at least a portion of the used liquefied natural gas (LNG) is vaporized to become natural gas (NG). With this configuration, the cold energy of liquefied natural gas (LNG) can be effectively utilized, and the amount of liquefied natural gas (LNG) vaporized in the vaporizer 72 can be reduced. As a result, the immersion cooling device 1 can reduce the environmental burden. In particular, since liquefied natural gas (LNG) is at an extremely low temperature of about -162°C, a lot of heat is exchanged with the liquid refrigerant R, and the cooling of the liquid refrigerant R and the vaporization of the liquefied natural gas (LNG) are carried out efficiently.

[0068] As shown in Figure 16, the cooling unit 2 includes a heat exchanger 21 in which heat exchange takes place between liquefied natural gas (LNG) and liquid refrigerant (R), and a liquid level measuring unit 22 for measuring the amount of liquefied natural gas (LNG) in the heat exchanger 21. The cooling unit 2 also includes piping 261 connecting the LNG tank 71 and the heat exchanger 21, piping 262 connecting the heat exchanger 21 and the odorizer 73, and a liquid level adjustment valve 263 located in the middle of piping 261. In other words, the cooling unit 2 bypasses the space between the LNG tank 71 and the vaporizer 72, and the space between the vaporizer 72 and the odorizer 73, and is arranged in parallel with the vaporizer 72.

[0069] Therefore, liquefied natural gas (LNG) in the LNG tank 71 is supplied to the heat exchanger 21 via piping 261, where it evaporates and vaporizes through heat exchange with the liquid refrigerant R to become natural gas (NG), which is then supplied to the odorizer 73 via piping 262. The amount of liquefied natural gas (LNG) supplied to the heat exchanger 21 is adjusted by a liquid level adjustment valve 263 installed upstream of the heat exchanger 21. While the cooling unit 2 is in operation, the amount of liquefied natural gas (LNG) supplied to the heat exchanger 21 is adjusted by the liquid level adjustment valve 263, and the amount of liquefied natural gas (LNG) in the heat exchanger 21, i.e., the liquid level of the liquefied natural gas (LNG), is maintained at the target liquid level. This allows for stable and continuous cooling of the liquid refrigerant R.

[0070] Furthermore, as shown in Figure 16, the heat exchanger 21 includes a main heat exchanger 211 and a sub-heat exchanger 215. The main heat exchanger 211 includes an outer tube 212 and an inner tube 213 coaxially arranged inside the outer tube 212. The outer tube 212 and inner tube 213 are installed vertically, with their axes oriented vertically. In other words, the main heat exchanger 211 is a vertical double-tube evaporator.

[0071] The main heat exchanger 211 is a liquid-filled type, and almost the entire space between the outer tube 212 and the inner tube 213 is filled with liquefied natural gas (LNG). Hereafter, this space will also be referred to as the "liquefied natural gas storage section 214". Meanwhile, the liquid refrigerant R flows through the inner tube 213. Therefore, heat exchange between the liquid refrigerant R and the liquefied natural gas (LNG) takes place via the wall surface of the inner tube 213. In a liquid-filled main heat exchanger 211, the liquefied natural gas (LNG) is in direct contact with the outer surface of the inner tube 213, which allows for high work efficiency and improves the heat exchange efficiency between the liquefied natural gas (LNG) and the liquid refrigerant R.

[0072] Here, because liquefied natural gas (LNG) is at an extremely low temperature of about -162°C, the amount of work done by the LNG is large, and the liquid refrigerant R can be cooled in a short time. On the other hand, this makes the liquid refrigerant R more likely to freeze in the main heat exchanger 211, and there is a high risk that ice will adhere to and grow on the inner wall of the inner tube 213. If ice continues to adhere to and grow on the inner wall of the inner tube 213, the volume inside the inner tube 213 will gradually decrease, and accordingly the cooling efficiency of the liquid refrigerant R will gradually decrease, and eventually the inner tube 213 may become blocked, making it impossible to circulate the liquid refrigerant R.

[0073] Therefore, although not shown in the diagram, a rotating blade for scraping off ice adhering to the inner wall may be installed inside the inner tube 213. By rotating the rotating blade around the central axis of the inner tube 213, the ice adhering to the inner wall can be scraped off, suppressing ice growth inside the inner tube 213 and preventing a decrease in the cooling efficiency of the liquid refrigerant R. In addition, the rotation of the rotating blade creates a swirling convection in the liquid refrigerant R flowing inside the inner tube 213. As a result, the heat exchange efficiency between liquefied natural gas (LNG) and the liquid refrigerant R is increased, and the liquid refrigerant R can be cooled efficiently and evenly. The blades of the rotating blade may or may not be in contact with the inner wall of the inner tube 213. In the former case, the ice removal effect is improved, but on the other hand, high precision is required in the dimensions and mounting of the rotating blade. In the latter case, the ice removal effect is slightly inferior to the former, but there is more leeway in the dimensional and mounting precision, making the device configuration simpler.

[0074] The sub-heat exchanger 215 is installed horizontally alongside the main heat exchanger 211. The sub-heat exchanger 215 is a pipe with its lower end closed. The sub-heat exchanger 215 is also installed vertically, with its axis oriented vertically. This sub-heat exchanger 215 is connected to the liquefied natural gas storage unit 214 via a pair of pipes 216. Therefore, the liquefied natural gas LNG supplied to the liquefied natural gas storage unit 214 is also supplied to the sub-heat exchanger 215 through these pipes 216. The natural gas NG produced by evaporation and vaporization through heat exchange with the liquid refrigerant R in the main heat exchanger 211 is supplied from the upper end of the sub-heat exchanger 215 through pipe 262 to the odorizer 73.

[0075] The liquid level measuring unit 22 is installed in the sub-heat exchanger 215 and measures the liquid level of liquefied natural gas (LNG) in the sub-heat exchanger 215. Since the liquid level of the liquefied natural gas (LNG) in the sub-heat exchanger 215 is equal to the liquid level of the liquefied natural gas (LNG) in the main heat exchanger 211, the liquid level of the liquefied natural gas (LNG) in the main heat exchanger 211 can be measured by measuring the liquid level of the liquefied natural gas (LNG) in the sub-heat exchanger 215. In this way, by installing the liquid level measuring unit 22 in a location different from the liquefied natural gas (LNG) storage unit 214, the liquid level of the liquefied natural gas (LNG) in the liquefied natural gas (LNG) storage unit 214 can be detected without hindering heat exchange between the liquefied natural gas (LNG) and the liquid refrigerant (LNG) R.

[0076] While the cooling unit 2 is operating, the liquid refrigerant R in the storage tank 3 circulates between it and the heat exchanger 21 via the first circulation path 61. Therefore, the liquid refrigerant R is supplied from the storage tank 3 to the heat exchanger 21, cooled by heat exchange with liquefied natural gas (LNG) in the heat exchanger 21, and then returned to the storage tank 3. By continuously performing this circulation cycle, the liquid refrigerant R in the storage tank 3 is gradually cooled. The cooled liquid refrigerant R is then supplied to the cooling tank 4.

[0077] This fourth embodiment can also achieve the same effects as the first embodiment described above.

[0078] Although the immersion cooling device and method of the present invention have been described above based on the illustrated embodiments, the present invention is not limited thereto. The configuration of each part can be replaced with any configuration having a similar function. Furthermore, other arbitrary configurations may be added to the present invention. In addition, each embodiment may be combined as appropriate.

[0079] Furthermore, in the embodiment described above, the cooling unit 2 directly cools the liquid refrigerant R, but this is not limited to this. For example, the cooling unit 2 may cool another refrigerant (primary refrigerant), and the liquid refrigerant R (secondary refrigerant) may be cooled by heat exchange between that refrigerant and the liquid refrigerant R (secondary refrigerant).

[0080] The present invention's immersion cooling method involves immersing electronic equipment in a liquid coolant containing propylene glycol to cool it.

[0081] Furthermore, the immersion cooling device of the present invention has a cooling tank in which a liquid coolant is stored, and cools electronic equipment by immersing it in the liquid coolant, wherein the liquid coolant contains propylene glycol.

[0082] According to this invention, electronic devices can be cooled efficiently. Therefore, the immersion cooling method and immersion cooling apparatus of the present invention have industrial applicability.

[0083] 1...Immersion cooling system, 2...Cooling section, 21...Heat exchanger, 211...Main heat exchanger, 212...Outer pipe, 213...Inner pipe, 214...Liquefied natural gas storage section, 215...Sub heat exchanger, 216...Piping, 22...Liquid level measurement section, 23...Compressor, 24...Condenser, 25...Expansion valve, 261...Piping, 262...Piping, 263...Liquid level adjustment valve, 3...Storage tank, 4...Cooling tank, 5...Cooling tank, 61...First circulation path, 62...Second circulation path, 7...Receiving base, 71...LNG tank, 72...Vaporizer, 73...Odorizer, 74...Gas holder, 75...Building, 8...Container, 80 ...Opening, 81...Zipper, 82...Valve, 83...Adhesive, 84...Heat conductive material, 85...Liquid, 86...Housing section, 861...Inner surface, 87...Opening, 88...Biasing section, 881...Middle plate, 882...Leaf spring, 9...Electronic equipment, 90...GPU server equipment, 91...Graphics board, 92...GPU, 921...Main surface, 93...Output interface, 94...Heat sink, 95...Fan cover, 951...Fan, 96...Base, 99...Wiring, DC...Data center, F...Liquid level, LNG...Liquefied natural gas, N...Refrigerant, R...Liquid refrigerant, Rs...Ice slurry

Claims

1. A liquid immersion cooling method characterized by immersing electronic equipment in a liquid coolant containing propylene glycol to cool it.

2. The liquid immersion cooling method according to claim 1, wherein the liquid refrigerant is composed of propylene glycol.

3. The immersion cooling method according to claim 1, wherein the liquid refrigerant is an aqueous solution of propylene glycol.

4. The immersion cooling method according to claim 1, wherein a portion of the liquid refrigerant is frozen to form an ice slurry.

5. The liquid immersion cooling method according to claim 1, wherein the electronic device comprises a substrate and a processor mounted on the substrate.

6. The immersion cooling method according to claim 5, wherein the processor is a GPU (Graphics Processing Unit).

7. An immersion cooling device having a cooling tank for storing a liquid refrigerant, and for cooling electronic equipment by immersing it in the liquid refrigerant, wherein the liquid refrigerant contains propylene glycol.

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