Aqueous solution for enhancing latent heat of liquid water and application thereof

Abstract

The application relates to a water solution for improving latent heat of liquid water and application thereof, and relates to a water solution and application thereof. The application is used for solving the problems of the existing water-based sweating cooling working medium in high heat flux density heat protection application. The liquid additive is a water component effective vaporization enthalpy enhanced liquid additive, can form a uniform solution with water, and changes a local solvation environment, a liquid phase network constraint or a gas-liquid interface escape behavior of the water component through hydrogen bond action, ion-dipole action, dipole-dipole action or other non-covalent interaction, so that the water component shows higher effective vaporization enthalpy in the evaporation process, thereby improving the phase change heat absorption capacity of the water-based working medium. The application belongs to the technical field of sweating cooling and phase change heat management.

Description

Technical Field

[0001] This invention relates to a liquid additive and its application, as well as a method for preparing a water-based sweating cooling working fluid, belonging to the technical fields of sweating cooling and phase change heat management. Background Technology

[0002] Sweating cooling is an active thermal protection method. Its basic process involves a cooling medium flowing under pressure through a porous medium or porous wall, absorbing heat within the heated area, and further undergoing phase change to absorb heat and release gas, thereby reducing the temperature of the heated structure and creating a cooling effect on the outer surface. This method can be used in aerospace thermal protection, engine thermal protection, high heat flux density porous media cooling, and other phase change thermal management scenarios.

[0003] Water possesses high specific heat capacity, significant latent heat of vaporization, low cost, and environmental friendliness, making it a commonly used working fluid in water-based evaporative cooling and phase change cooling. However, in applications where mass, volume, and available temperature windows are limited, the total heat absorption provided by water-based working fluids is constrained by their own thermal properties. Especially in scenarios such as aircraft thermal protection, compact thermal management, and porous media cooling, the carrying capacity and storage volume of the cooling working fluid are typically strictly limited. Therefore, relying solely on the sensible heat and latent heat of vaporization of pure water is insufficient to further improve the heat absorption capacity per unit mass or volume of the working fluid.

[0004] To improve the cooling performance of water-based working fluids, various additive modification methods have been proposed in the prior art. For example, dispersing metal oxides, carbon materials, or silicon-based nanoparticles in water can improve the thermal conductivity or heat transfer characteristics of the working fluid to some extent; adding organic co-solvents such as ethylene glycol and propylene glycol to water can also adjust the boiling point, freezing point, and interfacial transport behavior of the working fluid. However, particulate additives may agglomerate, deposit, or clog during high-temperature evaporation and porous channel flow, thereby increasing the risk of pressure drop and deteriorating heat transfer; although water-soluble organic co-solvents can regulate boiling behavior, their addition will change the proportion of the water phase and may adversely affect the overall evaporative heat absorption capacity of the system.

[0005] In addition to the heat absorption and heat exchange performance during operation, the actual sweating cooling working fluid also needs to consider its storage stability and engineering applicability under non-operating conditions. For example, water-based working fluids are prone to water evaporation in open or semi-open storage environments, leading to component drift; there may also be a risk of microbial contamination during long-term storage or repeated use; at the same time, the working fluid needs to maintain compatibility with structural materials such as porous ceramics, metals, or composite materials. Existing water-based working fluid modification schemes mostly focus on a single heat exchange index or a single energy-saving effect, and there is still room for improvement in simultaneously considering phase change heat absorption capacity, flow boiling heat exchange, anti-evaporation, antibacterial properties, and material compatibility.

[0006] Therefore, it is necessary to provide a liquid additive suitable for water-based sweating cooling and its application method, which can improve the phase change heat absorption capacity of water-based working fluids without introducing solid particles, while taking into account the flow boiling heat transfer in porous media, moisture retention in non-working state, microbial inhibition, and compatibility with porous materials. Summary of the Invention

[0007] This invention addresses the shortcomings of existing water-based evaporative cooling media in high heat flux density thermal protection applications by proposing an aqueous solution that enhances the latent heat of liquid water and its applications.

[0008] The technical solution adopted by the present invention to solve the above problems is: the aqueous solution for enhancing the latent heat of liquid water described in the present invention is a hydrophilic ionic liquid composed of organic cations and anions.

[0009] Furthermore, the organic cation is one or more of imidazolium ions, pyridinium ions, organic ammonium ions, phosphonium ions, and choline ions.

[0010] Furthermore, the organic anion is one or more of the following: carboxylate, hydroxycarboxylate, sulfonate, sulfate, phosphate, and halide.

[0011] The present invention describes an aqueous solution for enhancing the latent heat of liquid water, which is used in the preparation of a sweating cooling water-based working fluid. After the liquid additive is added to the water, a modified water-based sweating cooling working fluid is formed.

[0012] Furthermore, the mass fraction of the liquid additive in the modified water-based sweating cooling medium is 5% to 20%.

[0013] Furthermore, modified water-based sweating cooling media are used for sweating cooling of porous media.

[0014] Furthermore, the porous medium is one of ceramic porous media, metal porous media, silicon-based porous media, or composite porous media.

[0015] Furthermore, the ceramic porous medium is one of alumina-based ceramics, zirconia-based ceramics, or silicon carbide-based composite ceramics.

[0016] The method for preparing an aqueous solution that enhances the latent heat of liquid water according to the present invention is achieved through the following steps: Step 1: Weigh out the liquid additive and water; Step 2: Add the liquid additive to water and stir until a homogeneous solution is formed to obtain a water-based sweating cooling medium.

[0017] Furthermore, the mass fraction of the liquid additive in step 1 is 5% to 20%.

[0018] The beneficial effects of this invention are: 1. This invention proposes a method for applying liquid additives to regulate the phase change endothermic behavior of water-based working fluids based on non-covalent interactions. The liquid additives can form a homogeneous solution with water and, through hydrogen bonding, ion-dipole interactions, dipole-dipole interactions, or other non-covalent interactions, alter the local solvation environment, liquid-phase network confinement, or gas-liquid interface escape behavior of the water component. This results in a higher effective vaporization enthalpy for the water component during evaporation, thereby improving the phase change endothermic capacity of the water-based working fluid.

[0019] 2. The liquid additive described in this invention does not introduce solid particles. The resulting modified water-based sweating cooling medium is a homogeneous solution, suitable for porous media sweating cooling structures, and beneficial for its stable transport in porous channels.

[0020] 3. The modified water-based diaphoretic cooling medium of the present invention can balance phase change heat absorption capacity and porous medium flow boiling heat transfer performance. In a specific embodiment of the present invention, when 1-ethyl-3-methylimidazolium acetate is used as a liquid additive, the resulting 10% modified water-based diaphoretic cooling medium exhibits higher effective vaporization enthalpy of water component, higher total evaporative heat absorption of the system, and higher two-phase heat transfer coefficient in the stable flow boiling region compared to pure water.

[0021] 4. The modified water-based sweating cooling medium of the present invention exhibits good service stability and engineering applicability. In a specific embodiment of the present invention, when 1-ethyl-3-methylimidazolium acetate is used as a liquid additive, the resulting medium shows lower water evaporation loss compared to pure water and has an inhibitory effect on microbial growth; at the same time, under immersion test conditions, no significant additional surface damage was observed to be introduced into representative porous materials such as alumina-based ceramics, zirconia-based ceramics, and silicon carbide-based composite ceramics. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the principle of the liquid additive described in this invention enhancing the performance of water-based sweating cooling fluids; Figure 2 The graph shows the DSC / TG test results for pure water and 10% modified water-based sweating cooling medium. Figure 3 The graph shows the evaporative heat absorption test results of modified water-based sweating cooling media with different mass fractions. Figure 4 This is a graph showing the test results of the heat transfer performance of the modified water-based sweating cooling medium in a porous media flow boiling experiment; Figure 5 This is a graph showing the evaporation loss test results of the modified water-based sweating cooling medium under non-working conditions; Figure 6 This is a graph showing the test results of the antibacterial properties of the modified water-based sweating cooling medium; Figure 7This is a graph showing the immersion compatibility test results between the modified water-based sweating cooling medium and the porous ceramic material. Detailed Implementation

[0023] Specific implementation method one: as follows Figure 1 As shown in the figure, the aqueous solution for enhancing the latent heat of liquid water described in this embodiment is a hydrophilic ionic liquid composed of organic cations and anions.

[0024] The liquid additive is an effective vaporization enthalpy-enhancing liquid additive for water components, capable of forming a homogeneous solution with water. The liquid additive contains functional groups, ionic groups, or molecular structural units that can interact with water molecules through hydrogen bonding, ion-dipole interactions, dipole-dipole interactions, or other non-covalent interactions that can enhance the liquid phase constraint of water components.

[0025] The liquid additive can alter the local solvation environment, liquid network constraint, or gas-liquid interface escape behavior of the water component, causing the water component in the modified water-based sweating cooling medium to exhibit a higher effective vaporization enthalpy during evaporation than that of the water-based medium without the liquid additive.

[0026] The organic cation is one or more of imidazolium ions, pyridinium ions, organic ammonium ions, phosphonium ions, and choline ions.

[0027] Organic anions are one or more of the following: carboxylate, hydroxycarboxylate, sulfonate, sulfate, phosphate, and halide.

[0028] Specific Implementation Method Two: In this implementation method, an aqueous solution that enhances the latent heat of liquid water is used to prepare a sweating cooling water-based working fluid. After the liquid additive is added to the water, a modified water-based sweating cooling working fluid is formed.

[0029] The liquid additive has a mass fraction of 5% to 20% in the modified water-based sweating cooling medium, preferably 10%.

[0030] Modified water-based sweating cooling medium is used for sweating cooling of porous media. The modified water-based sweating cooling medium flows through the porous media and absorbs heat in the heated area, resulting in vaporization and / or flow boiling.

[0031] Among them, porous media are one of ceramic porous media, metal porous media, silicon-based porous media or composite porous media.

[0032] Among them, the porous ceramic medium is one of alumina-based ceramics, zirconia-based ceramics, or silicon carbide-based composite ceramics.

[0033] Specific Implementation Method 3: The preparation method of the water-based sweating cooling working fluid described in this implementation method is achieved through the following steps: Step 1: Weigh out the liquid additive and water; the liquid additive should be 5%~20% by mass. Step 2: Add the liquid additive to water and stir until a homogeneous solution is formed to obtain a water-based sweating cooling medium.

[0034] Example In the following examples, 1-ethyl-3-methylimidazolium acetate is referred to as [EMIM]OAc, water is deionized water, and mass fraction refers to the mass percentage of [EMIM]OAc in the final modified water-based sweating cooling medium.

[0035] "Heat sink" refers to the total heat absorbed by the working fluid within a predetermined temperature range through heating, vaporization, or evaporation processes. It can be expressed as heat absorption per unit mass or heat absorption per unit volume.

[0036] "Effective vaporization enthalpy of water component" refers to the contribution of water component to evaporation endothermic reaction, obtained by normalizing the water component mass based on thermal analysis test results. This parameter is used to characterize the apparent endothermic capacity of water component during evaporation in the presence of additives, and does not represent a change in the intrinsic vaporization enthalpy of pure water.

[0037] The water may be deionized water, distilled water, pure water, or purified water; in the following embodiments, deionized water is used as the aqueous phase.

[0038] Example 1 Preparation of 10% modified water-based sweating cooling medium with [EMIM]OAc as liquid additive Weigh 10 parts by mass of [EMIM]OAc and 90 parts by mass of deionized water, add the [EMIM]OAc to the deionized water, and stir at room temperature until completely mixed to obtain a 10% modified water-based sweating cooling medium. The resulting medium is a transparent and homogeneous solution.

[0039] This working fluid can be transported into a porous medium as a water-based evaporative cooling medium, where it absorbs heat in the heated area and undergoes vaporization and / or fluid boiling.

[0040] Example 2 Preparation of modified water-based sweating cooling working fluids with different mass fractions Following the method in Example 1, [EMIM]OAc and deionized water were weighed to prepare 5%, 15%, and 20% modified water-based sweating cooling media. All samples formed homogeneous solutions after stirring at room temperature.

[0041] Pure water was used as Test Example 1, without the addition of [EMIM]OAc. Pure [EMIM]OAc can be used as a reference sample for liquid additives in thermal analysis tests.

[0042] Test Example 1 Evaporation heat absorption performance test Combined with appendix Figure 2-3 This test method is described below. The evaporative endothermic behavior of the working fluids obtained in Test Example 1, Example 1, and Example 2 was tested using simultaneous DSC / TG thermal analysis. Baseline correction was performed before testing. The samples were placed in a perforated aluminum crucible to allow the gaseous products to escape during evaporation. The test was conducted under a nitrogen atmosphere, with an initial temperature of 24°C and a heating rate of 5°C / min, continuing heating until the evaporation process was complete and the mass change stabilized.

[0043] The test results show that the total heat absorption of pure water in Test Example 1 is 2580 J / g, which is close to the theoretical value of 2574.88 J / g for water to be heated from 24℃ to the boiling point and completely vaporized. The deviation is about 0.2%, indicating that this thermal analysis method can be used for quantitative comparison of the heat absorption capacity of water-based working fluids during evaporation.

[0044] Compared to Test Example 1, the heat absorption temperature range of the 10% ionic liquid modified water-based sweating cooling medium obtained in Example 1 is significantly widened. After normalization by the mass of the water component, its effective vaporization enthalpy of the water component is increased by 18.91% relative to pure water; calculated by the total mass of the medium, its total heat absorption by evaporation is 2812 J / g, corresponding to a 9.21% increase in total heat sink based on mass; and calculated by combining the density of 1.038 g / cm³, its total heat sink based on volume is increased by 13.36%.

[0045] Test results for samples with different mass fractions showed that as the mass fraction of [EMIM]OAc increased from 5% to 10%, the total heat absorption per unit mass of the water-based system increased; however, when the mass fraction was further increased to 15% and 20%, the total heat absorption per unit mass decreased. This indicates that a 10% mass fraction achieves a better balance between improving the effective evaporative heat absorption capacity of the water component and maintaining sufficient water content.

[0046] Test Example 2 Porous media flow boiling heat transfer performance test Combined with appendix Figure 4 This section describes the testing method. To evaluate the flow and boiling performance of the working fluid obtained in Example 1 within a porous medium, a two-dimensional porous micro-model flow and boiling test platform based on a silicon-glass substrate was constructed. The working fluid was pumped into the porous test section, and a platinum resistance layer was placed on the back of the test section as a heater and temperature measuring element. Before testing, the working fluid and pipeline were degassed. The inlet temperature was 24°C, and the outlet pressure was atmospheric pressure.

[0047] Under the same flow rate and the same effective heat flux, the wall temperature and two-phase heat transfer coefficient of the pure water in Test Example 1 and the 10% ionic liquid modified water-based sweating cooling medium obtained in Example 1 were compared. When calculating the two-phase heat transfer coefficient, 100°C for pure water and 103.5°C for the medium in Example 1 were used as boiling reference temperatures, and the difference between the wall temperature and the corresponding boiling reference temperature was used to characterize the wall superheat.

[0048] Test results show that, in the stable flow boiling region, the working fluid obtained in Example 1 has a higher two-phase heat transfer coefficient than that in Test Example 1. At flow rates of 100, 150, and 200 g / min, the two-phase heat transfer coefficient of the working fluid obtained in Example 1 is increased by 25.75%, 20.10%, and 21.34% relative to pure water, respectively, with an average increase of 22.40%. This result indicates that the ionic liquid-modified water-based sweating cooling working fluid of the present invention can improve the phase change heat transfer performance during the flow boiling process of porous media.

[0049] Table 1 shows the increase in the two-phase heat transfer coefficient of the working fluid in Example 1 at different flow rates.

[0050]

[0051] Table 1. Increase in two-phase heat transfer coefficient of working fluid at different flow rates in Example 1 Test Example 3 Moisture evaporation loss test in non-working state Combined with appendix Figure 5 This test method is explained. The pure water of Test Example 1, the 10% ionic liquid modified water-based sweating cooling medium obtained in Example 1, and pure [EMIM]OAc were placed under open static conditions and the mass change was tested in a light-proof environment at 24°C.

[0052] The test results show that the mass of both the pure water in Test Example 1 and the working fluid in Example 1 decreases approximately linearly over time, but the mass loss rate of the working fluid in Example 1 is lower. The mass change of pure [EMIM]OAc under the same conditions is small, indicating that the mass loss of the working fluid in Example 1 mainly comes from water evaporation. After initial ionic liquid mass correction and normalization to the same initial water volume, the equivalent water evaporation rate of the working fluid in Example 1 is 1.01 g / d, and the evaporation rate of pure water in Test Example 1 is 1.19 g / d, representing a reduction of approximately 15% in water evaporation loss for the working fluid in Example 1. This result indicates that the ionic liquid-modified water-based sweating cooling working fluid of the present invention has good moisture retention capacity in non-working states.

[0053] Test Example 4 Antibacterial performance test Combined with appendix Figure 6This test method is explained below. The antibacterial properties of the working fluid obtained in Example 1 were evaluated using the plate count method. *Escherichia coli* ATCC 25922 was used as the test strain, and pure water was used as the test sample. Before testing, the pure water and the working fluid from Example 1 were filtered to remove bacteria. After mixing the bacterial suspension with pure water or the working fluid from Example 1, the mixture was incubated at 37°C for 24 h, followed by serial dilutions and plate counts.

[0054] The test results showed that a large number of colonies appeared in the pure water group of Test Example 1 after incubation, while almost no obvious colony growth was observed in the working fluid treatment group of Example 1. The average result of three independent experiments showed that the viable bacteria concentration in the pure water group of Test Example 1 was 1.86 × 10⁻⁶. 9 CFU / mL, the viable bacterial concentration after treatment with the working medium in Example 1 was 3.33 × 10⁻⁶. 2 The CFU / mL corresponds to a 6.75-log decrease. This result indicates that the ionic liquid-modified water-based sweating cooling medium of the present invention can inhibit microbial growth, which is beneficial to reducing the risk of microbial contamination during the storage and reuse of water-based working media.

[0055] Test Example 5 Material compatibility testing Combined with appendix Figure 7 This test method is explained below. Alumina-based ceramics, zirconia-based ceramics, and silicon carbide-based composite ceramics were selected as representative porous materials to compare and evaluate the immersion compatibility of the pure water in Test Example 1 and the working medium obtained in Example 1. The ceramic samples were immersed in pure water and the working medium of Example 1, respectively, and sealed for 500 h at 24°C. After immersion, the samples were removed for surface morphology observation, mass change measurement, and surface elemental analysis.

[0056] Immersion test results showed that all three ceramic materials basically maintained their original pore wall contours and local surface textures after immersion in pure water and the working medium of Example 1. No obvious cracks, local peeling, significant surface roughening, or continuous deposits were observed. Compared with the pure water group, the working medium group of Example 1 did not show obvious additional surface damage.

[0057] The mass change results showed that the normalized mass changes of the three ceramic materials in both liquids were small, with absolute normalized mass changes below 0.17%. Surface elemental analysis results showed that the framework cation retention rates of the alumina-based ceramics, zirconia-based ceramics, and silicon carbide-based composite ceramics were all close to 100%, ranging from 99.85% to 101.70% overall. These results indicate that, under the test conditions of this embodiment, the ionic liquid-modified water-based sweating cooling medium of the present invention exhibits good material compatibility with the ceramic materials.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. An aqueous solution that enhances the latent heat of liquid water, characterized in that, The liquid additive is a hydrophilic ionic liquid composed of organic cations and anions.

2. The aqueous solution for enhancing the latent heat of liquid water according to claim 1, characterized in that, The organic cation is one or more of the following: imidazolium ion, pyridinium ion, organic ammonium ion, phosphonium ion, and choline ion.

3. An aqueous solution for enhancing the latent heat of liquid water according to claim 1, characterized in that, Organic anions are one or more of the following: carboxylate, hydroxycarboxylate, sulfonate, sulfate, phosphate, and halide.

4. The application of the liquid additive according to any one of claims 1 to 3, characterized in that, The liquid additive is used in the preparation of a sweating cooling water-based working fluid. After the liquid additive is added to water, a modified water-based sweating cooling working fluid is formed.

5. The application of an aqueous solution for enhancing the latent heat of liquid water according to claim 4, characterized in that, The mass fraction of liquid additives in modified water-based sweating cooling media is 5% to 20%.

6. The application of an aqueous solution for enhancing the latent heat of liquid water according to claim 4, characterized in that, Modified water-based sweating cooling medium is used for sweating cooling of porous media.

7. The application of an aqueous solution for enhancing the latent heat of liquid water according to claim 6, characterized in that, Porous media are one of the following: ceramic porous media, metal porous media, silicon-based porous media, or composite porous media.

8. The application of an aqueous solution for enhancing the latent heat of liquid water according to claim 7, characterized in that, Ceramic porous media are one of alumina-based ceramics, zirconia-based ceramics, or silicon carbide-based composite ceramics.

9. A method for preparing a water-based sweating cooling working fluid using the aqueous solution according to any one of claims 1 to 3, characterized in that, The specific steps include: Step 1: Weigh out the liquid additive and water; Step 2: Add the liquid additive to water and stir until a homogeneous solution is formed to obtain a water-based sweating cooling medium.

10. The method for preparing an aqueous solution that enhances the latent heat of liquid water according to claim 9, characterized in that, The mass fraction of the liquid additive in step 1 is 5% to 20%.

Images