A low-temperature boiling mixed working medium for a low-pressure two-phase liquid cooling system and an application and maintenance method thereof

Abstract

The application provides a low-temperature boiling mixed working medium for a low-pressure two-phase liquid cooling system and an application and maintenance method thereof, and relates to the technical field of liquid cooling heat dissipation of data centers. The working medium is mixed by at least one low-boiling-point polar solvent and water in proportion, and a corrosion inhibition component can be added. In a closed low-pressure circulation pipeline, the physical principle of the reduction of the boiling point of liquid under low pressure is used, so that the working medium is boiled and phase-changed in the safe temperature range of the chip, and the latent heat of vaporization is used to efficiently take away heat. The application also discloses an online monitoring and maintenance method of the working medium. The working medium has extremely low cost, is safe and environmentally friendly, the base fluid is water and a large amount of organic solvent, does not contain fluoride, and has an ozone depletion potential of zero. When the working medium is used in combination with a low-pressure two-phase liquid cooling system, extremely low pump power consumption and extremely small circulation flow can be realized, the heat dissipation demand of high-density IT equipment can be met, and the energy consumption and working medium cost of the cooling system of the data center are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of liquid cooling technology for data centers, and in particular to a low-temperature boiling mixed working fluid for low-pressure two-phase liquid cooling systems, and its application and maintenance methods. Background Technology

[0002] With the explosive growth of artificial intelligence and high-performance computing, the heat flux density of server chips has exceeded 100W / cm², and the power of a single server rack is rapidly increasing to 80kW or even 150kW and above. Traditional single-phase liquid cooling systems rely on the sensible heat of the working fluid to raise the temperature and remove heat, which requires large flow rates, high pump power consumption, and large pipe sizes, making it difficult to economically meet the ultra-high density heat dissipation requirements.

[0003] Two-phase latent heat liquid cooling technology utilizes the latent heat of vaporization of the working fluid to absorb heat. The heat that a unit mass of working fluid can remove is tens of times that of single-phase sensible heat. Therefore, the required circulation flow rate and pump power consumption can be significantly reduced, making it an inevitable technical path for solving ultra-high density heat dissipation. However, the performance of two-phase liquid cooling systems is highly dependent on the thermophysical properties of the working fluid, and existing working fluids generally suffer from the following problems: First, fluorinated liquid working fluids, such as FC-72 and Novec series, although they have good insulation and stable chemical properties, are extremely expensive (hundreds of yuan per liter) and have high global warming potential (GWP), facing increasingly stringent environmental regulations.

[0004] Second, pure water. Water is one of the most ideal heat transfer media, with high specific heat, high latent heat, extremely low cost, and is completely environmentally friendly. However, water only boils at 100°C under normal pressure, which is far above the safe operating temperature of chips (usually not exceeding 85°C). If it were forcibly used in a two-phase system, the chip would have already overheated and been damaged.

[0005] Third, low-boiling-point organic solvents. Pure ethanol has a boiling point of approximately 78°C (at normal pressure), close to the maximum allowable temperature for chips, but its boiling point is still relatively high at normal pressure, resulting in insufficient safety margin. Furthermore, pure ethanol has a flash point of only 13°C, making it highly volatile and flammable, posing a serious fire hazard in data centers. Other solvents such as methanol and acetone are even more toxic or flammable, rendering them impractical for engineering applications.

[0006] Fourth, existing working fluids lack online monitoring and maintenance methods. During long-term operation, the concentration of the working fluid may drift, and its boiling point may change, affecting heat dissipation stability. Currently, there is no systematic method in the industry for online monitoring, boiling point drift compensation, and lifespan assessment of two-phase liquid-cooled working fluids.

[0007] Fifth, there is a lack of coordinated optimization between the working fluid and system operating parameters. Existing systems typically have fixed working fluid ratios and operating pressures, which cannot be dynamically adjusted according to load changes and environmental conditions, resulting in suboptimal energy efficiency under certain operating conditions.

[0008] In summary, existing two-phase liquid cooling media suffer from significant drawbacks, including high cost, poor environmental performance, mismatched boiling temperatures, high safety risks, and a lack of online maintenance methods and collaborative optimization strategies. There is an urgent need for a novel two-phase cooling media system that is extremely low-cost, has a boiling temperature adapted to the chip's safety range, is safe and environmentally friendly, and possesses online maintenance and collaborative optimization capabilities. To this end, a low-temperature boiling mixture for low-pressure two-phase liquid cooling systems, along with its application and maintenance methods, are proposed. Summary of the Invention

[0009] In view of this, the present invention provides a cryogenic boiling mixed working fluid for a low-pressure two-phase liquid cooling system and its application and maintenance method, so as to solve or alleviate one of the technical problems existing in the prior art, and at least provide a beneficial option.

[0010] The technical solution of this invention is implemented as follows: a low-temperature boiling mixed working fluid for a low-pressure two-phase liquid cooling system, characterized in that it is composed of at least one low-boiling-point polar solvent and water in a certain proportion. By adjusting the type and ratio of the low-boiling-point polar solvent, the boiling initiation temperature of the working fluid under a preset low-pressure environment falls into the safe operating temperature range of the chip. In a closed low-pressure circulation pipeline, the working fluid undergoes a boiling phase change within the temperature range by utilizing the physical principle of the decrease in the boiling point of liquids under low pressure, thereby carrying away heat in the form of latent heat of vaporization.

[0011] I. Composition Ratio of Working Fluid

[0012] The working fluid is primarily a mixture of at least one low-boiling-point polar solvent and water. The low-boiling-point polar solvent is one or more of alcohols, ketones, or other low-boiling-point polar organic compounds miscible with water. By adjusting the type and volume concentration of the solvent, the boiling initiation temperature of the working fluid under the target low-pressure environment is brought to the range of 45-70°C.

[0013] Alcohol solvents are preferably selected from one or more of ethanol, isopropanol, n-propanol, propylene glycol, and ethylene glycol. Ketone solvents are preferably selected from one or more of acetone and butanone. Different solvents have different boiling points, latent heats of vaporization, and azeotropic properties with water, and can be selected comprehensively based on chip junction temperature requirements, system pressure settings, and safety specifications.

[0014] In one preferred embodiment, the low-boiling-point polar solvent is ethanol with a volume concentration of 20%-40%, and a boiling onset temperature of approximately 60-62°C at an absolute pressure of approximately 0.4 bar. In another preferred embodiment, the low-boiling-point polar solvent is isopropanol with a volume concentration of 15%-35%, and a boiling onset temperature of approximately 58-63°C at the same pressure. In yet another embodiment, the low-boiling-point polar solvent is a mixture of ethanol and propylene glycol; by adjusting the ratio of the two, the boiling temperature can be precisely controlled and the low-temperature antifreeze performance can be improved.

[0015] Water provides a high latent heat of vaporization (approximately 2260 kJ / kg) in the working fluid, while significantly increasing the flash point of the mixed solution, making it much higher than that of pure organic solvents, and greatly reducing its flammability. The working fluid contains no fluorides, has an ozone depletion potential (ODP) of zero, and a global warming potential (GWP) of less than 10.

[0016] In a preferred embodiment, the ratio of solvent to water causes the mixed working fluid to form an azeotropic or near-azeotropic mixture, in which the gas phase and liquid phase compositions are substantially the same during boiling, thus avoiding concentration drift caused by preferential evaporation.

[0017] II. Addition of corrosion inhibitor components

[0018] As needed, an appropriate amount of corrosion inhibitor can be added to the working fluid. The corrosion inhibitor can be one or more of the following: azoles (such as benzotriazole), molybdates (such as sodium molybdate), and silicates (such as sodium silicate). The amount added is 0.01%-1% of the total mass of the working fluid. The corrosion inhibitor is used to protect metal components such as circulation pipelines, cold plate microchannels, and condenser plates, extending the system's service life.

[0019] III. Low-voltage working environment

[0020] This working fluid is specifically designed for low-pressure two-phase liquid cooling systems. The coolant distribution unit in the system establishes and maintains a low-pressure environment within the pipeline via a pressure-maintaining device. The pressure value of this low-pressure environment is determined based on the working fluid ratio and the target boiling temperature, and is set using a temperature-pressure equivalence curve to ensure that the working fluid's boiling initiation temperature falls within the range of 45-70°C. In a preferred embodiment, the absolute pressure of the low-pressure environment is 0.2-0.6 bar.

[0021] IV. Phase Change Heat Dissipation Process

[0022] The working fluid, in liquid form, enters the microchannels of the chip cold plate driven by a circulating pump. The chip heats up, raising the temperature of the cold plate wall above the working fluid's boiling initiation temperature. The working fluid in contact with the wall undergoes nucleation boiling, generating numerous microbubbles that rapidly detach from the wall, absorbing a large amount of latent heat of vaporization. The generated vapor and unboiled liquid form a vapor-liquid two-phase mixture, which enters the CDU condenser via the return vapor line. In the condenser, the vapor is condensed into liquid by the primary-side cooling water, merges with the unboiled condensate, and flows back to the storage tank, completing the cycle.

[0023] V. Methods for Online Monitoring and Maintenance of Working Fluids

[0024] This invention also discloses an online monitoring and maintenance method for the aforementioned low-temperature boiling working fluid, comprising one or more of the following steps: (a) Online detection of working fluid concentration: The ratio of organic solvent to water in the working fluid is detected online by one or more of the following: densitometer, refractometer, sound velocity sensor or conductivity sensor, to determine whether the concentration deviates from the set range; (b) Boiling point drift monitoring and compensation: By monitoring the relationship between the system operating pressure and the boiling temperature of the working fluid, it is determined whether the boiling point drifts due to changes in the concentration of the working fluid or the accumulation of impurities; when the drift exceeds the preset threshold, an alarm is issued and the concentration is adjusted automatically or manually or the working fluid is replaced. (c) Working fluid life assessment: The cumulative operating time and number of high-temperature cycles of the working fluid are assessed to evaluate the degree of consumption of corrosion inhibitors and the overall performance degradation of the working fluid, and to provide a prediction of the remaining effective life of the working fluid and replacement recommendations.

[0025] VI. Collaborative Optimization Methods for Working Fluid and System

[0026] This invention also discloses a synergistic optimization method for a working fluid and a low-pressure two-phase liquid cooling system, comprising: Based on real-time IT load, ambient temperature and humidity, and chip junction temperature feedback, dynamically adjust one or more of the following operating parameters: (a) By adjusting the set value of the system pressure maintaining device, the absolute pressure in the pipeline is changed, thereby dynamically adjusting the boiling start temperature of the working fluid to adapt to the changing heat load. (b) When the system is equipped with a variable concentration working fluid charging device, the working fluid concentration is dynamically adjusted by adding deionized water or organic solvent to the circulation pipeline to optimize the boiling temperature and heat transfer coefficient. (c) Coordinate the adjustment of the circulating pump speed and the primary side cooling water flow rate to minimize the total power consumption of the system while meeting the heat dissipation requirements.

[0027] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: 1. Precise boiling temperature matching: By utilizing the principle of lowering the boiling point through low pressure, the boiling temperature of the working fluid is precisely matched to the safe operating temperature range of the chip, so that it will not boil too early and affect the stability of the system, nor will it boil too late and cause the chip to overheat.

[0028] 2. Extremely low cost: The main raw materials of the working fluid are bulk organic solvents and water, and the cost is only one-tenth of that of fluorinated liquid working fluids, which greatly reduces the initial charging and subsequent replenishment costs of data center cooling systems.

[0029] 3. Safe and environmentally friendly: The flash point of the water-based mixed solution is much higher than that of pure organic solvents, and the risk of use in data centers is controllable; the working fluid does not contain fluoride, the ozone depletion potential (ODP) is zero, and the global warming potential (GWP) is extremely low.

[0030] 4. High heat exchange efficiency: Water-based working fluid retains the high latent heat of vaporization of water and has a high boiling heat transfer coefficient, enabling ultra-high density heat dissipation with extremely small flow rate and extremely low pump power consumption.

[0031] 5. Flexible formulation and strong adaptability: Multiple solvents and ratios are available, and formulations can be flexibly prepared according to chip requirements, environmental conditions and safety regulations.

[0032] 6. Online monitoring ensures long-term stability: Concentration detection, boiling point drift compensation, and life assessment technologies ensure the working fluid's performance remains stable throughout its entire life cycle, reducing operational and maintenance risks.

[0033] 7. Collaborative optimization to improve energy efficiency under all operating conditions: The working fluid and system are adjusted in tandem, and the boiling temperature and heat exchange efficiency are dynamically optimized according to the load to maximize system energy efficiency.

[0034] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 The phase diagram of the binary system of the working fluid of this invention (comparison of boiling point curves under normal pressure and low pressure conditions). Figure 2 This is a graph showing the boiling temperature curves of mixed solutions of different solvents (ethanol, isopropanol, propylene glycol) and water under low pressure. Figure 3 This is a schematic diagram of the circulation principle of the low-pressure two-phase liquid cooling system of the working fluid of the present invention. Figure 4 This is a block diagram of the working fluid and system collaborative optimization control logic of the present invention. Detailed Implementation

[0037] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0038] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0039] Example 1 (Ethanol-water mixture)

[0040] Preparation of the working medium: Mix anhydrous ethanol (purity ≥99.5%) and deionized water (conductivity ≤1μS / cm) thoroughly in a clean container at a volume concentration of 20%-40%. Add 0.1% benzotriazole and 0.05% sodium molybdate as corrosion inhibitors, and stir thoroughly to dissolve. The resulting working medium is a colorless, transparent liquid with a slight ethanol odor and a pH of approximately 6.5-7.5.

[0041] The working fluid is introduced into the two-phase liquid cooling system. The system establishes and maintains a low-pressure environment of approximately 0.4 bar within the pipeline using a pressure maintaining device. At this pressure, the boiling point of the working fluid is approximately 60-62°C.

[0042] System operation test: Simulating a 100kW heat load, the chip cold plate wall temperature was approximately 65℃, and the working fluid underwent stable nucleus boiling within the microchannels. The circulation pump outlet flow rate was approximately 1.2 m³ / h, and the pump power consumption was approximately 90W. The vapor was condensed in the CDU condenser by primary-side 35℃ cooling water, and the supply liquid temperature remained stable at approximately 58℃. The system ran continuously for 24 hours, demonstrating stable heat dissipation performance and no abnormal pressure fluctuations.

[0043] Example 2 (Isopropanol-water mixture)

[0044] Isopropanol was mixed with deionized water at a volume concentration of 15%-35%, with 0.08% benzotriazole and 0.02% sodium silicate added as corrosion inhibitors. The system operated at an absolute pressure of approximately 0.35 bar, with a working fluid boiling point of approximately 57-60°C. The isopropanol-water mixture, within the stated concentration range, also exhibited a significantly higher flash point than pure isopropanol, meeting the safety requirements for data center use. Other operating parameters were similar to those in Example 1.

[0045] Example 3 (Ethanol-Propylene Glycol-Water Ternary Working Fluid)

[0046] The ethanol and propylene glycol were mixed at a volume concentration of 15%-25% and 5%-15% respectively, with deionized water. The addition of propylene glycol further improved the low-temperature antifreeze performance of the working fluid, preventing it from freezing above -20°C, making it particularly suitable for cold regions or scenarios where the system is shut down without venting during winter. The system operates at an absolute pressure of approximately 0.45 bar, with the working fluid's boiling point at approximately 62-65°C. This embodiment utilizes the synergistic effect of the two solvents to balance boiling temperature control and low-temperature protection requirements.

[0047] Example 4 (Azeotropic working fluid)

[0048] With an ethanol volume concentration of approximately 95% (forming an azeotropic mixture with water, azeotropic point 78.2℃ at atmospheric pressure), under an absolute pressure of approximately 0.3 bar, the boiling temperature of the azeotrope drops to approximately 52-55℃. The working fluid in this azeotropic formulation exhibits essentially identical gas and liquid phase compositions during boiling, avoiding concentration drift caused by preferential evaporation during long-term operation, reducing the frequency of online concentration correction, and making it suitable for scenarios with extremely high requirements for ease of maintenance.

[0049] Example 5 (Online Monitoring and Maintenance of Working Fluid)

[0050] An online densitometer and refractometer are installed in the CDU storage tank or circulation pipeline to monitor the concentration of organic solvents in the working fluid in real time. When the concentration deviates from the set value by ±3%, the control system issues an early warning; when it deviates by ±5%, it automatically replenishes deionized water or organic solvent through the replenishment device to restore the set concentration. Simultaneously, by comparing the correlation between system pressure and boiling temperature, it determines whether the boiling point has drifted. If the drift exceeds 2°C and concentration adjustment cannot restore the concentration, the system prompts for replacement of the working fluid. After the working fluid has accumulated more than 8000 hours of operation or undergone more than 5000 high-temperature cycles, the system automatically prompts for sampling and testing to assess its remaining lifespan.

[0051] Example 6 (Working medium and system synergistic optimization)

[0052] During low-load periods at night, the IT load drops to 50% of its rated capacity, and the ambient wet-bulb temperature decreases from 28°C to 24°C. The collaborative optimization control system automatically reduces the cooling tower fan speed by 15%, while simultaneously fine-tuning the system absolute pressure from 0.4 bar to 0.45 bar via the pressure maintenance device, raising the working fluid boiling point from 60°C to 63°C. This further reduces pump and fan power consumption while meeting cooling requirements, resulting in a decrease of approximately 12% in total system cooling power consumption. When the load resumes during the day, the parameters automatically revert to their normal values.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A cryogenic boiling working fluid for a low-pressure two-phase liquid cooling system, characterized in that, It is made by mixing at least one low-boiling-point polar solvent with water in a certain proportion. By adjusting the type and ratio of the low-boiling-point polar solvent, the boiling initiation temperature of the working fluid in a preset low-pressure environment is made to fall into the range of 45-70℃. In a closed low-pressure circulation pipeline, the principle of the liquid boiling point decreases under low pressure is used to make the working fluid undergo boiling phase change within the safe operating temperature range of the chip, and remove heat in the form of latent heat of vaporization.

2. The low-temperature boiling mixed working fluid according to claim 1, characterized in that, The low-boiling-point polar solvent is one or more of alcohols and ketones that are miscible with water; the alcohol is selected from one or more of ethanol, isopropanol, n-propanol, propylene glycol, and ethylene glycol; the ketone is selected from one or more of acetone and butanone.

3. The low-temperature boiling working fluid according to claim 2, characterized in that, The low-boiling-point polar solvent is ethanol, with a volume concentration of 20%-40%; the preset low-pressure environment has an absolute pressure of 0.2-0.6 bar, and the working fluid boiling start temperature is 55-65℃.

4. The low-temperature boiling working fluid according to claim 2, characterized in that, The low-boiling-point polar solvent is isopropanol with a volume concentration of 15%-35%; or a mixture of ethanol and propylene glycol with a volume concentration of 15%-25% for ethanol and 5%-15% for propylene glycol.

5. The low-temperature boiling mixed working fluid according to claim 1, characterized in that, The ratio of solvent to water enables the mixed working fluid to form an azeotropic or near-azeotropic mixture, in which the gas phase and liquid phase composition are basically the same during boiling, avoiding concentration drift caused by preferential evaporation.

6. The low-temperature boiling mixed working fluid according to claim 1, characterized in that, The working fluid also contains a corrosion inhibitor, which is selected from one or more of azole, molybdate, and silicate corrosion inhibitors, and the amount added is 0.01%-1% of the total mass of the working fluid.

7. The low-temperature boiling mixed working fluid according to claim 1, characterized in that, The water content of the working fluid makes its flash point significantly higher than that of pure organic solvents, meeting fire safety requirements in data center environments; the working fluid contains no fluorides, has an ozone depletion potential of zero, and a global warming potential of less than 10.

8. A method for applying and maintaining a low-temperature boiling mixed working fluid as described in any one of claims 1 to 7, characterized in that, Includes the following steps: The working fluid is filled into the closed circulation pipeline of the two-phase liquid cooling system. A low-pressure environment is established and maintained in the pipeline by a pressure maintaining device. The absolute pressure of the low-pressure environment is determined by the working fluid ratio and the target boiling temperature through the temperature-pressure equivalence relationship, so that the boiling start temperature of the working fluid falls into the range of 45-70℃. The working fluid is heated and boiled in the chip cold plate. The vapor-liquid two-phase mixture enters the condenser through the return vapor pipeline, is condensed by the primary side cooling medium, and is then recycled.

9. The application and maintenance method according to claim 8, characterized in that, It also includes online monitoring and maintenance procedures for the working fluid, including one or more of the following: The ratio of organic solvent to water in the working fluid is detected online using one or more of the following: a densitometer, a refractometer, a sound velocity sensor, or a conductivity sensor. The system monitors the relationship between operating pressure and boiling temperature of the working fluid to determine whether boiling point drift has occurred. When the drift exceeds a preset threshold, the concentration is adjusted or the working fluid is replaced. The cumulative operating time and number of high-temperature cycles of the working fluid are used to assess the consumption of corrosion inhibitor components and the degradation of working fluid performance, and to predict the remaining effective lifespan.

10. The application and maintenance method according to claim 8, characterized in that, It also includes the steps of co-optimization of the working fluid and the system: Based on real-time IT load, ambient temperature and humidity, and chip junction temperature feedback, dynamically adjust one or more of the following operating parameters: Adjusting the set value of the system pressure maintaining device changes the absolute pressure in the pipeline, thereby dynamically adjusting the boiling start temperature of the working fluid. When the system is equipped with a variable concentration working fluid filling device, deionized water or organic solvent is added to the circulation pipeline to dynamically adjust the working fluid concentration. The circulating pump speed and primary side cooling water flow rate are adjusted in a coordinated manner to minimize the total power consumption of the system.

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