Natural circulation evaporative cooling system

Abstract

The invention discloses a natural circulation evaporative cooling system which comprises a heating section, a condenser, a liquid return section and a pipeline connecting the heating section, the condenser and the liquid return section, the natural circulation evaporative cooling system further comprises a passive liquid injection device, and the liquid outlet end of the passive liquid injection device is connected with the liquid inlet end of the heating section. And a pressure transmission path is arranged between the passive liquid injection device and the condenser and is used for transmitting pressure to the passive liquid injection device when the pressure of the condenser is increased, so that the passive liquid injection device is forced to automatically inject a cooling working medium into the heating section to promote rapid establishment of a natural circulation process. Automatic regulation and control of the running state of the natural circulation evaporative cooling system can be achieved without an automatic element, the cooling efficiency of the cooling system can be improved, and the temperature peak value of a heating part in the whole work period is reduced.

Description

Technical Field

[0001] This invention relates to the field of heat exchange, and more specifically to a natural circulation evaporative cooling system. Background Technology

[0002] Evaporative cooling systems are closed-loop cooling systems that utilize the phase change process of the cooling medium to absorb heat from heat-generating components, achieving efficient cooling. They are typically classified into two types based on whether a drive unit is needed in the circulation loop to maintain the circulation of the cooling medium: forced circulation evaporative cooling and natural circulation evaporative cooling.

[0003] Combination Figure 1 As shown, the cooling medium circulation path of the natural circulation evaporative cooling system consists of a heating section, a condenser, a return section, and related connecting components. The circulation power of the cooling medium mainly comes from the density difference between the gas-liquid two-phase working medium in the heating section and the liquid working medium in the return section. When there is a sufficient amount of gas-liquid two-phase working medium in the heating section, the gravity head formed by the density difference overcomes the resistance in the circulation pipeline, driving the gas-liquid two-phase cooling medium in the heating section into the condenser. After heat exchange with the secondary cooling medium in the condenser, the gas-liquid two-phase cooling medium becomes liquid and naturally flows back to the return section. Then, under the action of gravity head, it re-enters the heating section to participate in the next circulation process.

[0004] However, in existing natural circulation cooling systems, the cooling medium in the heating section requires a certain amount of time to absorb heat, enabling sufficient amount of the cooling medium to complete its liquid-to-gas transition and thus drive it to overcome resistance and enter the condenser. The higher the heat flux density in the heating section, the shorter the time required to establish circulation. Before circulation is established, the pressure in the condenser will continuously increase. As the system pressure increases, the boiling point of the cooling medium in the lower half of the heating section also increases, potentially leading to a short period of relatively high temperature in the lower half of the heating section before circulation is established. For heat-generating objects that require strict temperature control throughout the entire operating process, this brief period of high temperature should be avoided, but existing natural circulation cooling systems cannot prevent this short-term high temperature phenomenon during the heating phase. Summary of the Invention

[0005] In view of this, the present invention provides a natural circulation evaporative cooling system to solve the problem that existing natural circulation cooling systems cannot avoid short-term high temperature phenomena during the heating phase. By passively injecting liquid into the circulation pipeline and temporarily increasing the system flow head, the natural circulation cooling process is quickly established, thus avoiding short-term high temperature phenomena during the heating phase.

[0006] This invention provides a natural circulation evaporative cooling system, including a heating section, a condenser, a return section, and pipelines connecting the heating section, condenser, and return section. The natural circulation evaporative cooling system also includes a passive liquid injection device, the outlet of which is connected to the inlet of the heating section. The passive liquid injection device has a pressure transmission path with the condenser, which is used to transmit pressure to the passive liquid injection device when the condenser pressure increases, thereby forcing the passive liquid injection device to automatically inject cooling medium into the heating section to promote the rapid establishment of the natural circulation process.

[0007] The beneficial effects of the aforementioned natural circulation evaporative cooling system are as follows: This invention does not rely on automated components; it achieves automatic control of the system's liquid injection state solely through a passive liquid injection device in response to condenser pressure changes. This significantly reduces system complexity and manufacturing costs, minimizes the use of automated components and complex drive mechanisms, and reduces potential failure points. By automatically injecting cooling medium into the heating section when the condenser pressure rises, natural circulation can be quickly established in the initial stage of system startup, avoiding short-term high-temperature phenomena before circulation establishment and improving system reliability and stability. The cooling medium injected by the passive liquid injection device creates a density difference with the gas-liquid two-phase working medium in the heating section, increasing the system flow head and accelerating the cooling medium circulation; simultaneously, it shortens the circulation start-up time, improves the cooling response speed, meets the rapid cooling requirements of the heating components, and improves the cooling efficiency of the cooling system. Through rapid circulation establishment and continuous efficient cooling, the peak temperature of the heating components throughout the entire working cycle is effectively reduced, avoiding the impact of high temperatures on component performance.

[0008] In one optional embodiment, the passive injection device includes:

[0009] A liquid storage tank is used to store the cooling working fluid; the pressure transmission path is located between the liquid storage tank and the condenser; The liquid injection pipeline is connected at one end to the liquid storage tank and at the other end to the inlet of the heating section; A pressure response mechanism is installed on the pressure transmission path between the liquid storage tank and the condenser. When the pressure in the condenser increases, the pressure response mechanism responds to the change in pressure difference between the liquid storage tank and the condenser, causing the cooling medium in the liquid storage tank to be injected into the heating section through the injection pipeline under the action of the pressure difference.

[0010] The beneficial effects of the above technical solution are as follows: the passive liquid injection device does not rely on automated components. It can automatically inject cooling working fluid into the heating section by passively responding to the pressure difference change between the condenser and the liquid storage tank through the pressure response mechanism. This simplifies the system structure and reduces manufacturing costs and failure risks. By increasing the system flow head for a short time, it can quickly establish a natural circulation cooling process, effectively eliminating the short-term relatively high temperature phenomenon in the heating section before the cycle starts in the prior art, and ensuring the temperature stability of the heating section.

[0011] In one optional embodiment, the liquid storage tank and the condenser are separately disposed, and the liquid storage tank and the condenser are connected by a connecting pipeline, and the pressure response mechanism is disposed on the connecting pipeline or the liquid injection pipeline.

[0012] In one optional embodiment, the pressure response mechanism is a one-way self-sealing valve, which has a closed position and an open position; when there is no external force interference, the one-way self-sealing valve is in the closed position that closes the connecting pipeline, and when the condenser pressure increases, the one-way self-sealing valve is in the open position that opens the connecting pipeline.

[0013] In one alternative embodiment, the liquid storage tank and the condenser are integrated, and the pressure response mechanism is disposed between the liquid storage tank and the condenser to separate the liquid storage tank from the condenser.

[0014] In one optional embodiment, the pressure response mechanism is a piston, which is slidably disposed between the liquid storage tank and the condenser; when the pressure in the condenser is greater than the pressure in the liquid storage tank, the piston moves toward the side closer to the liquid storage tank; when the pressure in the condenser is less than the pressure in the liquid storage tank, the piston moves toward the side closer to the condenser.

[0015] In one alternative implementation, the piston is maintained at a preset initial position by a spring or shape memory metal.

[0016] In one alternative embodiment, the storage tank is initially filled with cooling medium and closed at the top.

[0017] In one alternative embodiment, the liquid storage tank is at the same height as the condenser; or the liquid storage tank is higher than the condenser.

[0018] In one optional embodiment, the passive liquid injection device further includes a self-priming pump drive channel, which connects the lower part of the return section to the liquid storage tank for replenishing the liquid storage tank with cooling working fluid. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of an existing natural circulation cooling system; Figure 2 A schematic diagram of the passive liquid injection device for the natural circulation evaporative cooling system provided by the present invention; Figure 3 This is a schematic diagram of the natural circulation evaporative cooling system provided in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the natural circulation evaporative cooling system provided in Embodiment 2 of the present invention.

[0021] Explanation of reference numerals in the attached figures: 1. Heating section, 2. Condenser, 3. First connecting component, 4. Second connecting component, 5. Return section, 6. Liquid storage tank, 7. Liquid injection pipeline, 8. One-way self-sealing valve, 9. Connecting pipeline, 10. Piston. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The passive liquid injection device and natural circulation evaporative cooling system provided by this invention are based on the principle of passively injecting liquid into the system to increase the system flow head, thereby promoting the rapid establishment of the natural circulation cooling process and avoiding short-term high temperature phenomena during the heating phase.

[0024] The basic working principle of a passive liquid injection device is as follows: Initially, the device is filled with working fluid, sealed at the top, and connected to the inlet of the heating section at the bottom. The working fluid is suspended in the storage tank and the replenishment pipeline. When the condenser pressure rises, the working fluid in the storage tank is injected into the evaporator under the short-term high pressure within the condenser.

[0025] Example 1 According to an embodiment of the present invention, a natural circulation evaporative cooling system is provided, combined with Figure 2 and Figure 3As shown, the system includes a heating section 1, a condenser 2, a return section 5, and piping connecting the heating section 1, condenser 2, and return section 5. The piping connecting the heating section 1, condenser 2, and return section 5 includes a first connecting component 3 and a second connecting component 4. The first connecting component 3 connects the heating section 1 to the condenser 2, and the second connecting component 4 connects the condenser 2 to the return section 5, forming a circulation loop. The natural circulation evaporative cooling system also includes a passive liquid injection device. The outlet of the passive liquid injection device is connected to the inlet of the heating section 1. A pressure transmission path exists between the passive liquid injection device and the condenser 2, used to transmit pressure to the passive liquid injection device when the pressure in the condenser 2 increases, thereby forcing the passive liquid injection device to automatically inject cooling fluid into the heating section 1 to promote the rapid establishment of the natural circulation process.

[0026] The aforementioned natural circulation evaporative cooling system does not rely on automated components. It automatically regulates the liquid injection state of the system solely through a passive liquid injection device in response to pressure changes in condenser 2, significantly reducing system complexity and manufacturing costs, minimizing the use of automated components and complex drive mechanisms, and reducing potential failure points. By automatically injecting coolant into the heating section 1 when the pressure in condenser 2 increases, a natural circulation process is quickly established, effectively solving the short-term relatively high temperature phenomenon in the lower half of the heating section 1 before circulation start-up in existing technologies, ensuring the temperature stability of the heating section 1. The coolant injected by the passive liquid injection device creates a density difference with the gas-liquid two-phase working fluid in the heating section 1, increasing the system flow head and accelerating the coolant circulation; simultaneously, it shortens the circulation start-up time, improves the cooling response speed, meets the rapid cooling requirements of the heating components, and improves the cooling efficiency of the cooling system. Through rapid establishment of circulation and continuous efficient cooling, the peak temperature of the heating components throughout the entire working cycle is effectively reduced, avoiding the impact of high temperatures on component performance.

[0027] In some embodiments, the passive liquid injection device includes a liquid storage tank 6, a liquid injection line 7, and a pressure response mechanism. The liquid storage tank 6 has an internal cavity structure for storing the cooling medium. A pressure transmission path is provided between the liquid storage tank 6 and the condenser 2. One end of the liquid injection line 7 is connected to the liquid storage tank 6, and the other end is connected to the inlet of the heating section 1. The pressure response mechanism is located on the pressure transmission path between the liquid storage tank 6 and the condenser 2. When the pressure inside the condenser 2 increases, the pressure response mechanism responds to the pressure difference change between the liquid storage tank 6 and the condenser 2, causing the cooling medium in the liquid storage tank 6 to be injected into the heating section 1 through the liquid injection line 7 under the action of the pressure difference.

[0028] In this embodiment, the passive liquid injection device does not rely on automated components such as sensors, controllers, and drive pumps. It can automatically inject cooling medium into the heating section 1 by passively responding to the pressure difference change between the condenser 2 and the liquid storage tank 6 through a pressure response mechanism. This simplifies the system structure and reduces manufacturing costs and failure risks. By briefly increasing the system flow head, it can quickly establish a natural circulation cooling process, effectively eliminating the short-term relatively high temperature phenomenon in the heating section 1 before the cycle starts in the prior art, and ensuring the temperature stability of the heating section 1.

[0029] In this embodiment, during operation, the heating section 1 begins to release heat due to the input of the heat source. The small amount of residual working fluid inside vaporizes, causing the steam pressure in the condenser 2 to gradually increase. When this pressure exceeds the initial pressure in the storage tank 6, the pressure difference between the two drives the pressure response mechanism. The cooling working fluid in the storage tank 6 is then forced into the inlet of the heating section 1 along the injection pipe 7. The injected working fluid quickly absorbs heat from the heating section 1 and vaporizes. The resulting high-temperature steam enters the condenser 2, exchanges heat with the external environment, and condenses into liquid working fluid. The liquid working fluid then returns to the heating section 1 through the return path, thus quickly establishing a stable natural circulation cooling loop. As the loop stabilizes, the steam pressure in the condenser 2 gradually stabilizes, and the pressure difference between the storage tank 6 and the condenser 2 decreases below the threshold. The pressure response mechanism returns to its initial state, and the storage tank 6 stops injecting liquid into the heating section 1. At this time, the system relies on the continuous vaporization-condensation cycle of the working fluid to maintain the temperature of the heating section 1 within the set range, effectively avoiding the short-term high-temperature phenomenon at the beginning of the cycle and ensuring the operational reliability of the heat source equipment.

[0030] In some embodiments, the liquid storage tank 6 is separately disposed from the condenser 2, and the liquid storage tank 6 and the condenser 2 are connected by a connecting pipe 9. The pressure response mechanism is disposed on the connecting pipe 9 or the liquid injection pipe 7. This separate layout not only improves the spatial adaptability of the system in different installation scenarios, but also facilitates the individual inspection and maintenance of the liquid storage tank 6 or the condenser 2.

[0031] The pressure response mechanism is a one-way self-sealing valve 8, which has a closed position and an open position.

[0032] Under normal conditions (without external interference), the one-way self-sealing valve 8 can achieve a tight seal from the liquid storage tank 6 side to the condenser 2 side under the action of its own pressing structure. That is, the one-way self-sealing valve 8 is in the closed position that closes the connecting pipeline 9, and the working fluid in the liquid storage tank 6 will not flow downward.

[0033] When the pressure in condenser 2 increases, the pressure balance on both sides of the one-way self-sealing valve 8 is broken, and the one-way self-sealing valve 8 is in the open position that opens the connecting pipe 9. Under the combined action of the pressure in condenser 2 and its own gravity, the liquid working medium begins to flow downward and is injected into the heating section 1. At the same time, the passive liquid injection device is connected to the heating section 1. The liquid cooling medium in the liquid injection pipe 7 and the liquid storage tank 6 forms a density difference with the gas-liquid two-phase cooling medium in the heating section 1, increasing the flow head in the natural circulation system, thereby driving the establishment of the self-circulation process.

[0034] The specific structure of the one-way self-sealing valve 8 may include a valve body, a valve core, an elastic clamping element, and a sealing assembly; the valve body is fixed at the corresponding position of the connecting pipe 9, and an internal chamber is formed to accommodate the valve core; one end of the valve core is connected to the elastic clamping element, and the other end is equipped with a sealing assembly; the elastic clamping element is in a pre-compressed state, and under normal conditions, it pushes the valve core to make the sealing assembly tightly fit against the sealing port of the connecting pipe 9 near the liquid storage tank 6, thereby sealing the pipe; when the pressure on the condenser 2 side increases, the pressure difference on the valve core overcomes the pre-tightening force of the elastic clamping element, causing the sealing assembly to leave the sealing port, thus opening the connecting pipe 9.

[0035] In some embodiments, the volume of the storage tank 6 should be designed according to system requirements to ensure that sufficient working fluid can be provided for injection. The response pressure threshold of the one-way self-sealing valve 8 should be set according to the system operating characteristics to ensure that it opens at an appropriate pressure to achieve the best injection effect.

[0036] In some embodiments, the liquid storage tank 6 is initially filled with cooling medium and closed at the top. This is to maintain a stable initial pressure inside the chamber and prevent outside air from entering and affecting the phase change characteristics and circulation efficiency of the cooling medium. At the same time, the closed structure at the top can effectively prevent the cooling medium from evaporating and being lost in the non-operating state, ensuring that the system has sufficient circulating medium every time it starts up.

[0037] In some embodiments, the liquid storage tank 6 is at the same height as the condenser 2, or the liquid storage tank 6 is higher than the condenser 2, so that the liquid working fluid in the liquid storage tank 6 can flow into the condenser 2 more smoothly by means of gravitational potential energy, thereby reducing the flow resistance during the circulation process.

[0038] If the volume of the storage tank 6 cannot be significantly larger than the amount of liquid replenished in a single operation, then the storage tank 6 needs to be replenished after multiple injections. To maintain the total amount of working fluid in the system, a self-priming pump-driven channel can be established between the lower part of the return section 5 and the storage tank 6. When the heat-generating components stop working, the self-priming pump-driven channel draws cooling working fluid from the return section 5 and replenishes the storage tank 6. Through the self-priming pump-driven channel, cooling working fluid can be automatically replenished from the return section 5 to the storage tank 6 without the need for an external replenishment system, thus maintaining a stable total amount of working fluid in the system.

[0039] The specific working process of the above-mentioned natural circulation evaporative cooling system is as follows: In the initial state, the one-way self-sealing valve 8 is in the closed position, and the connecting pipe 9 between the liquid storage tank 6 and the condenser 2 remains isolated.

[0040] When the heat source equipment in heating section 1 starts operating, the cooling medium in heating section 1 absorbs the heat released by the heat source and gradually vaporizes. The generated steam rises into condenser 2 under the driving force of natural circulation. As the amount of steam in condenser 2 increases, its internal pressure gradually rises. When the pressure reaches the opening set value of one-way self-sealing valve 8, the one-way self-sealing valve 8 switches from the closed position to the open position. At this time, the liquid working medium condensed in condenser 2 flows smoothly into storage tank 6 through connecting pipe 9. Under the combined action of the pressure of condenser 2 and its own gravity, the liquid working medium in storage tank 6 begins to flow downward and inject into heating section 1.

[0041] When the pressure inside the condenser 2 drops below the opening threshold, the one-way self-sealing valve 8 automatically resets to the closed state to prevent the working fluid in the storage tank 6 from flowing back through the connecting pipe 9.

[0042] During this process, the system continuously controls the temperature of heating section 1 within the set range through the continuous vaporization-condensation cycle of the working fluid, effectively avoiding the problem of short-term high temperature at the beginning of the cycle.

[0043] Example 2 Based on Example 1, this example provides a natural circulation evaporative cooling system, combined with Figure 2 and Figure 4 As shown, the difference between this embodiment and embodiment 1 is that the liquid storage tank 6 and the condenser 2 are set up differently, and the pressure response mechanism is different.

[0044] In this embodiment, the liquid storage tank 6 and the condenser 2 are integrated. A pressure response mechanism is disposed between the liquid storage tank 6 and the condenser 2 to separate them. The pressure response mechanism is a piston 10, which is slidably disposed between the liquid storage tank 6 and the condenser 2. When the pressure inside the condenser 2 is greater than the pressure inside the liquid storage tank 6, the piston 10 moves towards the side closer to the liquid storage tank 6; when the pressure inside the condenser 2 is less than the pressure inside the liquid storage tank 6, the piston 10 moves towards the side closer to the condenser 2.

[0045] Piston 10 is maintained in a preset initial position by means of a spring or shape memory metal. When the system is in an initial state with no pressure difference, the piston can be stably maintained in the preset position, avoiding unexpected flow of the working fluid between the reservoir and the condenser.

[0046] The specific working process of the above-mentioned natural circulation evaporative cooling system is as follows: Initially, the passive liquid injection device is filled with working fluid. Because the upper end of the passive liquid injection device is closed, although the passive liquid injection device is full of liquid, the liquid levels in condenser 2 and heating section 1 can be set arbitrarily.

[0047] When piston 10 moves, it acts like a syringe, driving the flow of working fluid in the injection line to draw or inject working fluid into heating section 1.

[0048] Under normal conditions, piston 10 remains stationary, and the cooling medium in the evaporative cooling system circulates naturally.

[0049] When the pressure in condenser 2 rises, piston 10 moves from the condenser 2 side to the liquid storage tank 6 side, thereby replenishing liquid to heating section 1. The working fluid in heating section 1 begins to flow, promoting the establishment of a natural circulation process for the cooling working fluid.

[0050] When the heating section 1 stops generating heat, the gaseous cooling medium in the natural circulation evaporative cooling system is condensed into a liquid state by the condenser 2. The pressure in the condenser 2 decreases, and the piston 10 moves from the liquid storage tank 6 side to the condenser 2 side. Since the liquid injection line is connected to the heating section 1, the cooling medium flows from the natural circulation evaporative cooling system to the liquid storage tank 6 side as the piston 10 moves.

[0051] The aforementioned passive liquid injection device can maintain the total amount of working fluid in the system on its own, without the need for an additional pump drive channel to replenish the liquid in the storage tank 6.

[0052] This invention can be applied to various systems that require natural circulation evaporative cooling, especially those systems with strict temperature control requirements and where short-term high temperatures during startup are undesirable. For example, it can be applied to electronic equipment cooling, industrial equipment cooling, and other fields.

[0053] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A natural circulation evaporative cooling system, comprising a heating section (1), a condenser (2), a liquid return section (5), and piping connecting the heating section (1), the condenser (2), and the liquid return section (5), characterized in that, The natural circulation evaporative cooling system also includes a passive liquid injection device. The liquid outlet of the passive liquid injection device is connected to the liquid inlet of the heating section (1). There is a pressure transmission path between the passive liquid injection device and the condenser (2). When the pressure of the condenser (2) increases, the pressure is transmitted to the passive liquid injection device, thereby forcing the passive liquid injection device to automatically inject cooling medium into the heating section (1) to promote the rapid establishment of the natural circulation process.

2. The natural circulation evaporative cooling system according to claim 1, characterized in that, The passive injection device includes: A liquid storage tank (6) is used to store the cooling working fluid; the pressure transmission path is set between the liquid storage tank (6) and the condenser (2); The liquid injection pipeline (7) is connected at one end to the liquid storage tank (6) and at the other end to the inlet of the heating section (1); A pressure response mechanism is installed on the pressure transmission path between the liquid storage tank (6) and the condenser (2). When the pressure in the condenser (2) increases, the pressure response mechanism responds to the change in pressure difference between the liquid storage tank (6) and the condenser (2), causing the cooling medium in the liquid storage tank (6) to be injected into the heating section (1) through the injection pipe (7) under the action of the pressure difference.

3. The natural circulation evaporative cooling system according to claim 2, characterized in that, The liquid storage tank (6) is separated from the condenser (2), and the liquid storage tank (6) and the condenser (2) are connected by a connecting pipe (9). The pressure response mechanism is installed on the connecting pipe (9) or the liquid injection pipe (7).

4. The natural circulation evaporative cooling system according to claim 3, characterized in that, The pressure response mechanism is a one-way self-sealing valve (8), which has a closed position and an open position. When there is no external force interference, the one-way self-sealing valve (8) is in the closed position that closes the connecting pipe (9), and when the pressure of the condenser (2) increases, the one-way self-sealing valve (8) is in the open position that opens the connecting pipe (9).

5. The natural circulation evaporative cooling system according to claim 2, characterized in that, The liquid storage tank (6) is integrated with the condenser (2), and the pressure response mechanism is located between the liquid storage tank (6) and the condenser (2) to separate the liquid storage tank (6) from the condenser (2).

6. The natural circulation evaporative cooling system according to claim 5, characterized in that, The pressure response mechanism is a piston, which is slidably disposed between the liquid storage tank (6) and the condenser (2); when the pressure in the condenser (2) is greater than the pressure in the liquid storage tank (6), the piston moves toward the side closer to the liquid storage tank (6); when the pressure in the condenser (2) is less than the pressure in the liquid storage tank (6), the piston moves toward the side closer to the condenser (2).

7. The natural circulation evaporative cooling system according to claim 6, characterized in that, The piston is maintained in a preset initial position by a spring or shape memory metal.

8. The natural circulation evaporative cooling system according to claim 2, characterized in that, The storage tank (6) is initially filled with cooling medium and closed at the top.

9. The natural circulation evaporative cooling system according to claim 2, characterized in that, The liquid storage tank (6) is at the same height as the condenser (2); or the liquid storage tank (6) is higher than the condenser (2).

10. The natural circulation evaporative cooling system according to any one of claims 1-9, characterized in that, The passive liquid injection device also includes a self-priming pump drive channel, which connects the lower part of the return liquid section (5) to the liquid storage tank (6) for replenishing the cooling working fluid to the liquid storage tank (6).

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