CN118804557A - Immersion liquid cooling system and control method thereof - Google Patents

Abstract

The present application relates to the field of liquid cooling, and specifically discloses an immersion liquid cooling system and a control method thereof, including a receiving chamber, wherein the receiving chamber provides a receiving cavity for installing electronic equipment, and the receiving cavity is filled with a single-phase heat-conducting liquid and a two-phase heat-conducting liquid, and the single-phase heat-conducting liquid and the two-phase heat-conducting liquid are miscible, so that the single-phase heat-conducting liquid and the two-phase heat-conducting liquid are mixed with each other to form a mixed heat-conducting liquid. Through the mutual cooperation of the single-phase heat-conducting liquid and the two-phase heat-conducting liquid in a miscible system, the heat transfer efficiency of the single-phase heat-conducting liquid is improved, the viscosity of the heat-conducting liquid system is reduced, the specific heat capacity is increased, and at the same time, the problem that the two-phase heat-conducting liquid is easy to leak when a phase change occurs is solved.

Description

Immersion liquid cooling system and control method thereof

Technical Field

The present application relates to the field of liquid cooling, and in particular to an immersion liquid cooling system.

Background Art

Immersion liquid cooling technology is one of the most efficient cooling solutions currently available. It has been widely used and developed in fields such as data centers, high-performance computers, and battery thermal management. Existing immersion liquid cooling systems are divided into single-phase immersion liquid cooling, two-phase immersion liquid cooling, and single/two-phase coexistence multi-layer immersion liquid cooling. Single-phase immersion liquid cooling uses a heat transfer fluid with a high boiling point, such as silicone-based oil and hydrocarbons, which remains in liquid form throughout the heat dissipation process. The design of the single-phase immersion liquid cooling system is relatively simple, easy to operate and maintain, the heat transfer fluid does not undergo phase change, and the pressure control and safety requirements for the system are lower. However, the heat transfer efficiency of the single-phase mode is lower than that of the two-phase mode, and the heat exchange effect is poorer than that of the two-phase mode.

The two-phase immersion liquid cooling uses the property of the heat transfer fluid to change from liquid to gas when heated, and effectively uses the phase change latent heat to dissipate heat through the conversion of gas-liquid state, such as fluorinated liquid. The two-phase immersion liquid cooling system has a high heat transfer efficiency and can quickly and effectively handle high-density heat, but the phase change of the heat transfer fluid also makes the system design more complicated, requiring more stringent pressure, temperature and other control systems to ensure its safe operation; at the same time, the requirements for the heat transfer fluid are greatly increased, resulting in an increase in the cost of the heat transfer fluid (phase change liquid is generally fluorinated liquid, and fluorinated liquid is considered to have a global warming potential value GWP. In order to prevent its gasification and leakage, higher requirements are placed on the sealing performance of the entire system).

In view of the above problems, the novel immersion cooling system disclosed in publication number CN115696850A contains a layer of two-phase coolant fluid and one or more layers of single-phase coolant fluid. The problem of gasification and leakage of two-phase heat transfer fluid is largely solved by gradually cooling multiple layers of single-phase heat transfer fluid.

With respect to the above-mentioned related technologies, the inventors believe that the following defects exist: the heat accumulation problem of the single-phase thermal fluid in the above-mentioned patents has not been well solved, and the temperature control of the upper single-phase thermal fluid has posed new challenges. Furthermore, the heat-generating electronic components are immersed in the two-phase layer. In order to prevent the bubbles of the two-phase thermal fluid from escaping, a certain liquid level height of the single-phase layer needs to be guaranteed, which increases the weight and cost of the entire system to a certain extent.

Summary of the invention

In order to improve the problem of heat conduction efficiency, the present application provides an immersion liquid cooling system.

The immersion liquid cooling system provided in the present application adopts the following technical solution: the immersion liquid cooling system includes a containing chamber, which provides a containing cavity for installing electronic equipment, and the containing cavity is filled with a mixed heat-conducting fluid, and the mixed heat-conducting fluid includes a single-phase heat-conducting fluid, a two-phase heat-conducting fluid, nanoparticles and a silane coupling agent, the boiling point of the single-phase heat-conducting fluid is higher than the boiling point of the two-phase heat-conducting fluid, and the boiling point of the two-phase heat-conducting fluid is lower than the working temperature of the mixed heat-conducting fluid.

By adopting the above technical solution, the heat transfer efficiency of the single-phase heat-conducting liquid and the two-phase heat-conducting liquid are improved through the mutual cooperation of the single-phase heat-conducting liquid and the two-phase heat-conducting liquid in the miscible system, the viscosity of the heat-conducting liquid system is reduced, and the specific heat capacity is improved; the thermal conductivity efficiency is high. Miscibility means that the single-phase heat-conducting liquid and the two-phase heat-conducting liquid will mix together, and they may partially or completely merge, or they may just contact each other. Since when the working temperature of the mixed heat-conducting liquid should be higher than the boiling point of the two-phase heat-conducting liquid, the two-phase heat-conducting liquid in the mixed liquid will escape, reducing the heat exchange efficiency, so the working temperature needs to be controlled.

Optionally, the boiling point of the single-phase fluorinated liquid is 150-170°C, and the boiling point of the biphasic fluorinated liquid is 50-60°C.

Optionally, the mass ratio of the two-phase heat-conducting liquid: the single-phase heat-conducting liquid is 1-3:10.

By adopting the above technical solution, if the above mass ratio is too large, the heat transfer efficiency will be reduced (i.e., there is too much single-phase thermal fluid), and if it is too small, the cost will increase (i.e., there is too little single-phase thermal fluid). Therefore, after comprehensive testing, the ratio is set within the above range.

Optionally, the accommodation chamber is connected to a temperature control system, which includes a first temperature sensor for detecting the electronic device and a first refrigeration unit. The first refrigeration unit directly acts on the electronic device. When the temperature detected by the first temperature sensor exceeds a set value, the first refrigeration unit starts.

By adopting the above technical solution, the first temperature sensor is used to directly monitor the operating temperature of the electronic device, and when the operating temperature is too high, the first refrigeration unit is directly used to dissipate the heat of the electronic device.

Optionally, the temperature control system further includes a second temperature sensor and a second refrigeration unit located in the accommodation chamber. When the second temperature sensor detects that the temperature of the mixed thermal fluid is higher than a set value, the second refrigeration unit is started.

By adopting the above technical solution, the second temperature sensor is used to detect the temperature of the mixed heat transfer fluid. When the temperature is too high, the second refrigeration unit can be started.

Optionally, the first refrigeration unit and the second refrigeration unit both include at least one of a water cooling tower, a radiator, an evaporator, a condenser, a dry cooler, a heat exchanger, and a semiconductor refrigerator.

Optionally, a liquid level sensor is installed in the receiving chamber, the receiving chamber is an open structure, the receiving chamber is connected to a thermal liquid replenishing pipe, the thermal liquid replenishing pipe is connected to a thermal liquid replenishing tank, and the thermal liquid replenishing pipe controls the replenishment through a replenishment pump or a solenoid valve.

By adopting the above technical solution, since the two-phase thermal fluid will evaporate a small amount after long-term operation and will take away part of the single-phase thermal fluid, it is necessary to set up a thermal fluid replenishing tank to replenish the mixed thermal fluid, which can be replenished to the initial liquid level according to the prompt of the liquid level sensor.

Optionally, the containing chamber is connected to a liquid inlet pipe and a liquid outlet pipe, the liquid inlet pipe and the liquid outlet pipe are both connected to a heat exchanger, and a circulating pump is installed on the liquid inlet pipe and/or the liquid outlet pipe.

By adopting the above technical solution, the mixed heat transfer fluid can be cooled again after absorbing heat through the heat exchanger.

Another object of the present application is to provide a control method for an immersion liquid cooling system, comprising the following steps: installing an electronic device into a receiving chamber, then adding a mixed heat transfer liquid into the receiving chamber, and when the electronic device is working, starting a circulation pump so that the mixed heat transfer liquid exchanges heat with a heat exchanger and then flows back; when the immersion liquid cooling system is running, replenishing the liquid by judging the liquid level in the receiving chamber and replenishing the liquid by adding a mixed heat transfer liquid with a higher mass ratio.

Optionally, the temperature of the electronic device is detected by a first temperature sensor, and the first refrigeration unit is started after the temperature of the first temperature sensor exceeds a set value; the temperature of the mixed thermal fluid is detected by a second temperature sensor, and the second refrigeration unit is started after the temperature of the second temperature sensor exceeds a set value.

In summary, the present application includes at least one of the following beneficial technical effects: 1) Through the mutual cooperation of single-phase heat-conducting liquid and two-phase heat-conducting liquid in a miscible system, the heat transfer efficiency of the single-phase heat-conducting liquid is improved, the viscosity of the heat-conducting liquid system is reduced, and the specific heat capacity is improved; the thermal conductivity efficiency is high.

2) Due to the mutual cooperation of the single-phase heat-conducting fluid and the two-phase heat-conducting fluid in the miscible system, the problem of easy leakage of the two-phase heat-conducting fluid during phase change is solved;

3) Through the combination of single-phase thermal conductive fluid and two-phase thermal conductive fluid, the cost is effectively reduced while ensuring the heat dissipation efficiency.

4) Ensure the normal operation of the system by setting up a heat exchanger;

5) By setting up the first refrigeration unit and the second refrigeration unit, accidents can be avoided and safety is high.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of Example 1 of the present application;

FIG2 is a schematic diagram of Example 2 of the present application;

FIG3 is a schematic diagram of Example 3 of the present application;

FIG4 is a schematic diagram of Examples 4 and 5 of the present application;

FIG5 is a schematic diagram of another refrigeration unit of Example 4.

Figure numerals: 1. Accommodation chamber; 2. Electronic equipment; 3. Heat exchanger; 4. Circulation pump; 5. Liquid level sensor; 6. Thermal liquid replenishing tank; 7. Liquid replenishing pump; 8. First temperature sensor; 9. Semiconductor refrigeration chip; 10. Second temperature sensor; 11. Fan.

DETAILED DESCRIPTION

The present application is further described in detail below in conjunction with Figures 1-5.

Embodiment 1: An immersion liquid cooling system, as shown in FIG1 , includes a receiving chamber 1, which is preferably an open-top structure for convenient installation of electronic equipment 2. The receiving chamber 1 provides a receiving cavity for installing electronic equipment 2. The receiving cavity is filled with a mixed thermal conductive liquid, which includes a single-phase thermal conductive liquid, a two-phase thermal conductive liquid, nanoparticles and a silane coupling agent. The boiling point of the single-phase thermal conductive liquid is higher than the boiling point of the two-phase thermal conductive liquid, and the boiling point of the two-phase thermal conductive liquid is lower than the working temperature of the mixed thermal conductive liquid. The mass ratio of single-phase thermal conductive liquid: two-phase thermal conductive liquid = 10:1-3.

Specifically, the single-phase thermal fluid can be Novec7100/7100DL or Novec71IPA produced by 3M, wherein the boiling point of Novec7100/7100DL is 61° C., and the boiling point of Novec71IPA is 55° C. The single-phase thermal fluid can be the Novec7700 series products produced by 3M, and the boiling point of Novec7700 is 167° C.

The single-phase fluorinated liquid, the two-phase fluorinated liquid, the nanoparticles and the silane coupling agent are uniformly mixed at room temperature to obtain the mixed thermal conductive liquid. The silane coupling agent is selected from KH550. The amount of nanoparticles added is 1 to 1.5% of the total amount of the single-phase fluorinated liquid and the two-phase fluorinated liquid. The nanoparticles are boron nitride, and the particle size of the nanoparticles is 50-100nm. By limiting the amount of nanoparticles added within a reasonable range, they can play a better synergistic role with the mixed fluorinated liquid and the silane coupling agent, better improve the heat transfer efficiency and specific heat capacity of the composite thermal conductive liquid, reduce the viscosity of the system, and at the same time will not affect the stability of the composite thermal conductive liquid.

On the basis of the above, the receiving chamber 1 is connected with a liquid inlet pipe and a liquid outlet pipe, and the liquid inlet pipe and the liquid outlet pipe are both connected with a heat exchanger 3 (generally a plate heat exchanger 3 or a tube heat exchanger 3), and a circulation pump 4 is installed on the liquid inlet pipe and/or the liquid outlet pipe, and the mixed heat transfer fluid absorbs heat and then recovers and cools through the heat exchanger 3. The circulation pump 4 is provided as required, and at least one is provided. If accelerated circulation is considered, one can be provided on each of the liquid inlet pipe and the liquid outlet pipe.

When in use, the electronic device 2 should be completely immersed in the mixed thermal fluid, and the main heating end of the electronic device 2 should be located at the bottom of the accommodation chamber 1. Under the operation of the above-mentioned product, the main heating components in the electronic device 2 are the GPU and the CPU, and the maximum heating temperature range is about 70-75°C. Taking the mass ratio of single-phase thermal fluid: two-phase thermal fluid as an example of 10:3, the operating temperature of the thermal fluid is maintained at about 50°C when the system is running stably.

A control method for an immersion liquid cooling system comprises the following steps: installing an electronic device 2 into a receiving chamber 1, then adding a mixed heat transfer fluid into the receiving chamber 1, and when the electronic device 2 is working, starting a circulation pump 4 so that the mixed heat transfer fluid exchanges heat with a heat exchanger 3 and then flows back.

Embodiment 2: As shown in FIG2 , a liquid level sensor 5 is added to Embodiment 1. The liquid level sensor 5 is located in the receiving chamber 1 and is used to detect the liquid level of the mixed thermal liquid. The liquid level sensor 5 can specifically be a float type liquid level sensor 5. Due to the problem of the mixed thermal liquid level dropping caused by long-term operation (mainly the evaporation of the two-phase thermal liquid and part of the single-phase thermal liquid carried away by evaporation), the receiving chamber 1 is connected to a thermal liquid replenishing pipe, the thermal liquid replenishing pipe is connected to a thermal liquid replenishing tank 6, and the thermal liquid replenishing pipe controls the replenishment of liquid through a replenishing pump 7 or a solenoid valve. If the thermal liquid replenishing tank 6 is arranged above the receiving chamber 1, a solenoid valve can be directly arranged and the liquid can be replenished by gravity. If it is arranged on the side of the receiving chamber 1, the solenoid valve can be cancelled and the liquid can be replenished directly through the liquid replenishing pump 7. Of course, if the liquid is replenished only by the liquid replenishing pump 7, when the pump stops working, the liquid in the pipeline will fall into the receiving chamber 1 due to gravity, so that it exceeds the initial liquid level (that is, the position of the standard liquid level line in the figure). Of course, it does not affect the normal operation. If more precise control is required, when the thermal liquid replenishing tank 6 is arranged on the side of the receiving chamber 1, it is best to set the solenoid valve and the liquid replenishing pump 7 at the same time.

And considering that the two-phase heat-conducting liquid evaporates more, when the mixed heat-conducting liquid is added, its mass ratio is higher than the mass ratio of the two-phase heat-conducting liquid to the single-phase heat-conducting liquid in the mixed heat-conducting liquid in the original containing chamber 1. At present, this scheme adopts the method of selecting to add supplementary liquid with a mass ratio of 4:10 between the two-phase heat-conducting liquid and the single-phase heat-conducting liquid, and adding it to the normal working liquid level.

A control method for an immersion liquid cooling system comprises the following steps: installing an electronic device 2 into a receiving chamber 1, then adding a mixed heat transfer liquid into the receiving chamber 1, and when the electronic device 2 is working, starting a circulation pump 4 so that the mixed heat transfer liquid exchanges heat with a heat exchanger 3 and then flows back; when the immersion liquid cooling system is running, replenishing the liquid by judging the liquid level in the receiving chamber 1 and replenishing the liquid by adding a mixed heat transfer liquid with a higher mass ratio.

Embodiment 3: As shown in Figure 3, on the basis of the above-mentioned embodiment 2, a temperature control system is further added. The temperature control system includes a first temperature sensor 8 for detecting the electronic device 2, and a first refrigeration unit. The first refrigeration unit directly acts on the electronic device 2. When the temperature detected by the first temperature sensor 8 exceeds the set value, the first refrigeration unit starts. The function of the first refrigeration unit is mainly for emergency cooling. When the electronic device 2 has an abnormal situation and generates high temperature, causing the mixed thermal fluid to be unable to quickly drop to the set working temperature, the first refrigeration unit can be selected to directly use the electronic device 2 for emergency cooling. The first refrigeration unit and the second refrigeration unit both include at least one of a water cooling tower, a radiator, an evaporator, a condenser, a dry cooler, a heat exchanger 3, and a semiconductor refrigerator. The semiconductor refrigerator is used in this solution. Specifically, a semiconductor refrigeration sheet 9 is installed at the bottom of the electronic device 2, and its cold end is in contact with the electronic device 2.

A control method for an immersion liquid cooling system comprises the following steps: installing an electronic device 2 into a receiving chamber 1, then adding a mixed heat transfer liquid into the receiving chamber 1, and when the electronic device 2 is working, starting a circulation pump 4 so that the mixed heat transfer liquid exchanges heat with a heat exchanger 3 and then flows back; when the immersion liquid cooling system is running, replenishing the liquid by judging the liquid level in the receiving chamber 1 and replenishing the liquid by adding a mixed heat transfer liquid with a higher mass ratio; detecting the temperature of the electronic device 2 by a first temperature sensor 8, and starting a first refrigeration unit after the temperature of the first temperature sensor 8 exceeds a set value;

Embodiment 4, as shown in FIG4, is based on Embodiment 2, and a temperature control system is further added. The temperature control system includes a second temperature sensor 10 for detecting the temperature of the mixed thermal fluid, and a second refrigeration unit. The first refrigeration unit and the second refrigeration unit both include at least one of a water cooling tower, a radiator, an evaporator, a condenser, a dry cooler, a heat exchanger 3, and a semiconductor refrigerator. The second refrigeration unit is mainly used to assist the heat exchanger 3 in controlling the temperature of the mixed thermal fluid when the efficiency of the heat exchanger 3 is not high. In this scheme, a radiator is used, specifically, heat is dissipated by a fan 11, and a plurality of fans 11 are arranged in an array on the top of the receiving chamber 1, and the liquid surface of the mixed thermal fluid is blown by the fan 11. It can also be achieved by directly connecting the heat exchanger 3 to a dry cooler or a water cooling tower (as shown in FIG5).

A control method for an immersion liquid cooling system includes the following steps: installing an electronic device 2 into a receiving chamber 1, then adding a mixed heat transfer liquid into the receiving chamber 1, and when the electronic device 2 is working, starting a circulation pump 4 so that the mixed heat transfer liquid exchanges heat with a heat exchanger 3 and then flows back; when the immersion liquid cooling system is running, replenishing the liquid by judging the liquid level in the receiving chamber 1 and replenishing the liquid by adding a mixed heat transfer liquid with a higher mass ratio. The temperature of the mixed heat transfer liquid is detected by a second temperature sensor 10, and the second refrigeration unit is started after the temperature of the second temperature sensor 10 exceeds a set value.

Embodiment 5, as shown in FIG4 , is based on Embodiment 2, and a first temperature sensor 8, a second temperature sensor 10, a first refrigeration unit and a second refrigeration unit are combined. If cost is not considered, its safety and reliability are the best.

A control method for an immersion liquid cooling system comprises the following steps: installing an electronic device 2 into a receiving chamber 1, then adding a mixed heat transfer liquid into the receiving chamber 1, and when the electronic device 2 is working, starting a circulation pump 4 so that the mixed heat transfer liquid exchanges heat with a heat exchanger 3 and then flows back; when the immersion liquid cooling system is running, replenishing the liquid by judging the liquid level in the receiving chamber 1 and replenishing the liquid by adding a mixed heat transfer liquid with a higher mass ratio; detecting the temperature of the electronic device 2 by a first temperature sensor 8, and starting a first refrigeration unit after the temperature of the first temperature sensor 8 exceeds a set value; detecting the temperature of the mixed heat transfer liquid by a second temperature sensor 10, and starting a second refrigeration unit after the temperature of the second temperature sensor 10 exceeds a set value.

It should be noted that the above embodiments all have a controller and a power supply. The power supply supplies power to various electrical components, and the controller is used to control various actuators to work. For example, when the first temperature sensor 8 is higher than the set value, the controller controls the first refrigeration unit to work.

In the description of the present invention, it should be understood that the terms "upper", "lower", "left", "right", etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, and a specific direction structure and operation, and therefore, cannot be understood as a limitation on the present invention. In addition, "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", etc. should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims (10)

1. An immersion liquid cooling system, comprising a receiving chamber, wherein the receiving chamber provides a receiving cavity for installing an electronic device, characterized in that: the receiving cavity is filled with a mixed thermal conductive fluid, wherein the mixed thermal conductive fluid comprises a single-phase thermal conductive fluid, a two-phase thermal conductive fluid, nanoparticles and a silane coupling agent, wherein the boiling point of the single-phase thermal conductive fluid is higher than the boiling point of the two-phase thermal conductive fluid, and the boiling point of the two-phase thermal conductive fluid is lower than the working temperature of the mixed thermal conductive fluid. 2. The immersion liquid cooling system according to claim 1, characterized in that the boiling point of the single-phase fluorinated liquid is 150-170°C, and the boiling point of the two-phase fluorinated liquid is 50-60°C. 3. The immersion liquid cooling system according to claim 1 is characterized in that the mass ratio of the two-phase heat transfer liquid to the single-phase heat transfer liquid is 1-3:10. 4. The immersion liquid cooling system according to claim 1 is characterized in that: the accommodation chamber is connected to a temperature control system, and the temperature control system includes a first temperature sensor for detecting the electronic device, and a first refrigeration unit, the first refrigeration unit directly acts on the electronic device, and the first refrigeration unit is started when the temperature detected by the first temperature sensor exceeds a set value. 5. The immersion liquid cooling system according to claim 4 is characterized in that: the temperature control system also includes a second temperature sensor and a second refrigeration unit located in the accommodation chamber, and when the second temperature sensor detects that the temperature of the mixed thermal liquid is higher than the set value, the second refrigeration unit is started. 6. The immersion liquid cooling system according to claim 5 is characterized in that the first refrigeration unit and the second refrigeration unit both include at least one of a water cooling tower, a radiator, an evaporator, a condenser, a dry cooler, a heat exchanger, and a semiconductor refrigerator. 7. The immersion liquid cooling system according to claim 6 is characterized in that: a liquid level sensor is installed in the receiving chamber, the receiving chamber is an open structure, the receiving chamber is connected to a thermal liquid replenishing pipe, the thermal liquid replenishing pipe is connected to a thermal liquid replenishing tank, and the thermal liquid replenishing pipe controls the replenishment of liquid through a replenishing pump or a solenoid valve. 8. The immersion liquid cooling system according to claim 1 is characterized in that: the containing chamber is connected with a liquid inlet pipe and a liquid outlet pipe, the liquid inlet pipe and the liquid outlet pipe are both connected with a heat exchanger, and a circulating pump is installed on the liquid inlet pipe and/or the liquid outlet pipe. 9. A control method for an immersion liquid cooling system, using the immersion liquid cooling system as described in any one of claims 1 to 8, characterized in that it includes the following steps: installing the electronic equipment into a receiving chamber, then adding a mixed heat transfer liquid into the receiving chamber, and when the electronic equipment is working, starting a circulation pump so that the mixed heat transfer liquid exchanges heat with a heat exchanger and then flows back; when the immersion liquid cooling system is running, replenishing the liquid by judging the liquid level in the receiving chamber and replenishing the liquid by adding a mixed heat transfer liquid with a higher mass ratio. 10. The control method of the immersion liquid cooling system according to claim 9 is characterized in that: the temperature of the electronic device is detected by a first temperature sensor, and the first refrigeration unit is started after the temperature of the first temperature sensor exceeds a set value; the temperature of the mixed thermal fluid is detected by a second temperature sensor, and the second refrigeration unit is started after the temperature of the second temperature sensor exceeds a set value.