CN111777990A - Preparation and application of microcapsule type phase-change fluid applicable to low-temperature environment - Google Patents
Preparation and application of microcapsule type phase-change fluid applicable to low-temperature environment Download PDFInfo
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Abstract
The invention discloses a preparation method and application of a microcapsule type phase-change fluid used in a low-temperature environment. Firstly, synthesizing a fluid phase-change material and a water-soluble melamine prepolymer, then mixing the obtained water-soluble melamine prepolymer with a suspension and carrying out an emulsification reaction to obtain a reinforced composite heat transfer microcapsule; and uniformly mixing the obtained enhanced composite heat transfer microcapsule with the obtained fluid phase change material to obtain the microcapsule type phase change fluid applied to the low-temperature environment. Because the enhanced heat transfer composite microcapsule is added, the particle size change of the phase-change fluid is greatly reduced in the using process; and part of pure water is innovatively replaced by the 1, 2-propylene glycol with low toxicity, so that the freezing point of the solution is greatly reduced under the condition of keeping the original thermal conductivity as much as possible, and the phase-change fluid can normally run at low temperature even under severe cold conditions. In addition, the phase-change fluid greatly improves the heat transfer efficiency of the original phase-change material, is not easy to break down, can be used under various low voltages, and has a wide temperature adaptation range.
Description
Technical Field
The invention relates to the technical field of phase change materials, in particular to preparation and application of a microcapsule type phase change fluid capable of being used in a low-temperature environment.
Background
Phase Change Materials (PCMs), also called latent heat energy storage materials, refer to materials that absorb (release) a large amount of heat energy for energy storage when the phase changes, and among them, solid-liquid phase change materials are widely used.
Solid-liquid PCMs can be classified into three types, organic PCMs, inorganic PCMs, and composite PCMs, according to chemical composition classification.
The organic PCMs have good solid state formability, less material corrosiveness, more stable performance, less toxicity and difficult supercooling and phase separation.
The phase change microcapsule (MCPCM) is a new type working medium with the functions of absorbing or releasing latent heat, reducing the size of heat exchange equipment and the like, and the phase change material is encapsulated by utilizing the microcapsule technology and then mixed with a single-phase heat transfer working medium to prepare suspension.
After the phase-change material is microencapsulated, the heat conduction area of the phase-change material can be increased, the volume change in the phase-change process can be controlled, the defect that the phase-change material is easy to leak can be overcome, and certain heat conduction can be improved.
The phase-change energy storage (heat and cold) technology based on the phase-change microcapsule has the advantages of high energy storage density, large storage capacity, stable output energy and temperature, low cost, good chemical stability and the like.
Recently, the teams of hujiafeng, suhao and the like have achieved great results in the research aspect of phase change energy storage materials. The research results include Chinese patent publication CN105498652A (a heat transfer enhancing phase change microcapsule, a preparation method and application thereof), CN111059949A (a novel heat transfer enhancing composite phase change fluid, a preparation method and application thereof), CN110961054A (a preparation method and application of a composite microcapsule type phase change fluid for a high-voltage environment) and the like. The research direction of the team comprises microcapsule enhanced heat transfer, composite microcapsule type phase-change fluid preparation, high voltage resistance of a fluid phase-change material and the like, and the research is more prone to researching that the phase-change fluid can be suitable for various environments.
Today, high molecular organic phase change materials are still under development, and although phase change fluids used in high voltage environments are available, the use of phase change materials under low temperature conditions has not been much studied.
How to enable the phase-change material to normally operate in all weather, not to freeze and to keep better thermal performance in northern or severe cold areas, even areas with large day-night temperature difference becomes the key point of research. At present, most phase-change fluid cooling liquids can not work below zero centigrade, and a lot of research on the phase-change fluid cooling liquids is not available at home and abroad for a while.
Disclosure of Invention
The invention aims to overcome the defects that most of the existing phase-change fluid cooling liquids can not normally work under the conditions of large day and night temperature difference or extreme coldness and below zero DEG C, and provides preparation and application of a microcapsule type phase-change fluid for a low-temperature environment.
The invention is realized by the following technical scheme:
a preparation method of microcapsule type phase-change fluid used in low-temperature environment comprises the following preparation steps:
(1) mixing an emulsifier, a nucleating agent, 1, 2-propylene glycol, pure water and glycerol according to a certain sequence and operation, adding a certain amount of nano aluminum nitride or nano aluminum oxide (one or two of the nano aluminum nitride and the nano aluminum oxide) to obtain a turbid solution, then uniformly mixing the turbid solution with a phase-change material to obtain a suspension, and cooling the suspension to room temperature to obtain a fluid phase-change material;
(2) uniformly mixing melamine and a formaldehyde solution, adjusting the solution to be alkaline, heating and stirring until the solution becomes transparent, adding water, and continuing to react to obtain a water-soluble melamine prepolymer;
(3) uniformly mixing the water-soluble melamine prepolymer obtained in the step (2) with an emulsifier and water, adjusting the obtained mixed solution to be acidic, adding the suspension obtained in the step (1), carrying out an emulsification reaction, adding an alkali to adjust the pH value of the system to be 6-9 after the reaction is finished, and obtaining the enhanced composite heat transfer microcapsule;
(4) and (3) uniformly mixing the reinforced composite heat transfer microcapsule obtained in the step (3) with the fluid phase change material obtained in the step (1) to obtain the microcapsule type phase change fluid applicable to a low-temperature environment.
The mixing in the step (1) is carried out after preheating to 75 ℃.
The emulsifier in the step (1) is at least one of arabic gum powder, nonoxynol, polyoxyethylene lauryl ether, dodecyl heptapolyethylene glycol ether, hexadecyl 1,3 propylene glycol ether, cetyl polyether-12, stearyl polyether-2, stearyl polyether-20, stearyl polyether-100 and oleyl polyether-8.
Preferably, the two or three emulsifiers are used in the step (1), and when the emulsifiers are nonoxynol and ceteth, the mass ratio is 1: 1-6: 1, preferably 2: 1-3: 1; when the emulsifier is cetyl polyether-12, stearyl polyether-100 and oleyl polyether-8, the mass ratio is 1:1: 1-6: 1: 2; more preferably 3:1: 1.
the nucleating agent in the step (1) is at least one of polyvinyl cyclobutane, polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, polycyclopentene, polystyrene, polyvinyl alcohol, polypropylene alcohol, oleyl alcohol polyoxyethylene ether and magnesium stearate.
The volume ratio of the 1, 2-propylene glycol obtained in the step (1) to the fluid phase-change material obtained in the step (1) is as follows: 35-65: 100, preferably: 47-60: 100.
Preferably, when the nucleating agent in the step (1) is polyvinyl alcohol, oleyl alcohol polyoxyethylene ether or magnesium stearate, the mass ratio of the polyvinyl alcohol, the oleyl alcohol polyoxyethylene ether, the magnesium stearate and the glycerol to the 1, 2-propylene glycol aqueous solution is 2-8: 0.5-3: 1-6: 3-10: 150, preferably 4-5: 1-1.5: 2-3: 3-6: 150, and more preferably 5:1:2:5: 150. The mass fraction of the polyvinyl alcohol (hydrolyzed) is preferably 86-89%.
The mass-volume ratio of the emulsifier, the nucleating agent, the glycerol and the 1, 2-propylene glycol aqueous solution in the step (1) is 1-6: 30, preferably 1-2: 1-2: 1-2: 30. (the units are grams)
The mass ratio of the nano aluminum nitride to the turbid solution in the step (1) is 1: 100-300; the mass ratio of the nano alumina to the turbid solution is 1: 100-300.
The phase-change material in the step (1) can be selected from paraffin, higher fatty acid and higher fatty acid ester. Can be at least two of paraffin, dodecyl myristate, tridecyl pentadecate, tetradecyl palmitate, tridecyl heptadecanoate, tetradecyl octadecanoate, tetradecyl myristate, hexadecyl hexadecanoate, polymethyl methacrylate and stearic acid.
Preferably, the phase change material in the step (1) is tetradecyl palmitate, tetradecyl stearate and hexadecyl palmitate with the mass ratio of 3: 6: 8, a mixture of; or the mixture of tetradecyl palmitate and tetradecyl stearate with the mass ratio of 1: 2; or a mixture of dodecyl myristate and tridecyl pentadecate in a mass ratio of 1: 2; or a mixture of tetradecyl palmitate and tridecyl heptadecanoate with the mass ratio of 1: 2; or a mixture of tetradecyl octadecanoate and hexadecyl hexadecanoate with the mass ratio of 3: 4.
The mass ratio of the nucleating agent to the phase-change material in the step (1) is 1: 2-6, preferably 1:3 to 5, and more preferably 1: 3.
The mol ratio of the melamine in the step (2) to the pure formaldehyde in the formaldehyde solution is 1: 2-1: 10, and preferably 1: 3-1: 5.
And (2) the alkalinity is pH 8-9.
And (2) heating to 65-70 ℃.
And (3) the amount of the water used in the step (2) is 1-3 times of the mass of the methanol solution.
And (3) the continuous reaction in the step (2) is carried out for 20-50 min at the original temperature.
The mass ratio of the water-soluble melamine prepolymer to the emulsifier in the step (3) is 1: 1-1: 5, preferably 1: 2-1: 3.
and (3) the water is used in an amount which is enough for completely dissolving the water-soluble melamine prepolymer and the emulsifier.
And (3) adjusting the mixed solution to be acidic by using at least one of sulfuric acid, hydrochloric acid, oxalic acid, acetic acid, benzoic acid, formic acid and succinic acid, wherein the acidity is 1-6.
The mass ratio of the suspension liquid to the water-soluble melamine prepolymer in the step (3) is 1: 1-6: 1; preferably 1: 1-3: 1; more preferably 1:1 to 2.5: 1.
The emulsification reaction process in the step (3) is as follows: firstly, an emulsifier is used for stirring and emulsifying at 40-50 ℃ and 3000-4000 r/min for 20-50 min, then the temperature is raised to 60-75 ℃, and a turbulent stirring paddle is used for stirring and reacting at 2500-3500 r/min for 3-5 h.
Step (2) the base of step (3) is independently at least one of lithium hydroxide, potassium hydroxide, sodium hydroxide, calcium hydroxide, triethylamine and ammonia water.
In the step (4), the mass ratio of the capsule to the fluid phase-change material is 0.1: 1-0.5: 1, preferably 0.1: 1-0.2: 1.
The microcapsule type phase-change fluid for the low-temperature environment is prepared by the method;
the microcapsule phase-change fluid prepared by the invention can be applied to the field of heat storage and transfer under low-temperature and low-voltage conditions.
Compared with the prior art, the invention has the following advantages and effects:
(1) the novel fluid phase-change material prepared by the invention is emulsion, and because paraffin, higher fatty acid ester, higher fatty acid and the like are used as the phase-change material, the latent heat of phase change is higher than that of other organic phase-change materials, the stability is better, and the heat conductivity is higher.
(2) The novel phase change fluid microcapsule prepared by the invention is a white, off-white or black uniform sphere, and the average particle size is 0.1-10 mu m; the water mass content is less than or equal to 5 percent; the critical stress is 0-900 mN, and the mechanical property is good.
(3) The microcapsule type phase-change fluid applied to the low-temperature environment has a simple preparation process, controls the mechanical property of the microcapsule through a process technology, can avoid the loss caused by excessive microcapsule breakage in the processes of storage, transportation and landfill, and improves the recycling efficiency.
(4) The invention coats the phase-change material by the microcapsule technology, reduces the flammability and the liquid fluidity of the phase-change material, avoids the loss of the phase-change material, and prepares the novel phase-change fluid microcapsule which is more stable and more beneficial to storage; the core material is mixed with a heat transfer enhancer, so that the heat transfer efficiency can be improved.
(5) According to the invention, the change of the particle size of the phase-change material in the single use process can be reduced by mixing the enhanced heat transfer composite microcapsule and the phase-change material, and because the microcapsule and the phase-change material are mixed with the enhanced heat transfer agent in a certain proportion, the heat conductivity of the organic phase-change material can be greatly improved after mixing, and the service life of the phase-change material in the use process is prolonged.
(6) The microcapsule phase-change fluid applied to the low-temperature environment has the residual formaldehyde content lower than 5%, is environment-friendly and harmless to the environment, and compared with ethylene glycol which can be used for anti-freezing purpose as well, the microcapsule phase-change fluid which is selected by using 1, 2-propylene glycol as one of main solvents has lower toxicity and is more environment-friendly and green, and can be widely applied to the field of heat storage and transfer.
(7) The microcapsule phase-change fluid applied to the low-temperature environment can work at the lowest temperature of-20 to-50 ℃ without freezing or solidifying, and the microcapsule phase-change fluid added with the insulating material can move smoothly without influencing other thermal properties, mechanical properties and the like, and has enhanced insulating property, so that the microcapsule phase-change fluid can work on equipment under severe cold conditions.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
The property characterization method of the microcapsule type phase-change fluid applied to the low-temperature environment, which is prepared by the invention, comprises the following steps: testing of appearance: observing and recording under natural light; average particle size: a Malvern particle size analyzer; amount of residual formaldehyde: measuring with ultraviolet spectrophotometer; the critical stress was measured with a micro-control system (Model 403A); the moisture measurements were performed according to GB/T6283-1986. Phase transition temperature and latent heat of phase transition: measured with a differential thermal scanner (DSC); step-size curve: measuring with a low-temperature constant-temperature tank; thermal conductivity: measuring with a thermal constant analyzer; and (3) cyclic stability: measuring by using a high-low temperature alternating test box; freezing point test: testing by using a freezing point tester; and (3) voltage resistance testing: measured with a high voltage test transformer.
Example 1
The microcapsule phase-change fluid applied to the low-temperature environment can be prepared for a direct-contact heat accumulator, and the raw material formula is shown in table 1.
Table 1: example 1 raw material formulation
(1) All raw materials (deionized water, 1, 2-propylene glycol, phase change material, emulsifier and nucleating agent) for preparing the core material phase change material are preheated to 75 ℃.
(2) Mixing preheated phase-change material such as esters such as tetradecyl palmitate, and stirring at low speed for 15min with a stirrer to obtain dispersed phase to obtain a first solution; then adding preheated emulsifier and nucleating agent such as steareth-10, steareth-30, steareth-40, steareth-50, steareth-100, steareth-20, steareth-2, polyvinyl alcohol, oleyl polyoxyethylene ether, magnesium stearate and glycerin into the previously mixed 1, 2-propanediol solution, and adding 0.2g of nano-aluminum nitride. The temperature was maintained and stirring continued until the solution became cloudy, yielding a second solution.
(3) And (3) mixing the two solutions in the step (2), then placing the mixture into a high-speed shearing emulsifying machine for high-speed treatment for 5min, and continuously stirring and cooling to room temperature to obtain a suspension.
(4) Weighing melamine and formaldehyde solution according to a formula, adding the melamine and then adding the formaldehyde into a three-neck flask, stirring and mixing, adding a proper amount of triethylamine to adjust the pH value of the system to be 8-9, heating and stirring the melamine-formaldehyde mixed solution in a water bath at 65 ℃, enabling the system to become transparent after about 10min, adding distilled water with the same mass as the formaldehyde solution, and continuously reacting for 50min to obtain the transparent low-molecular-weight water-soluble melamine prepolymer.
(5) Weighing the emulsifier Arabic gum powder according to the formula, adding the emulsifier Arabic gum powder and the melamine prepolymer into a beaker, adding 1L of distilled water, stirring at low speed at room temperature until the mixture is completely dissolved, adjusting the pH value to 4 by using dilute hydrochloric acid, adding the emulsion obtained in the step (3), and emulsifying at 40 ℃ for 20min at the rotating speed of 3000r/min by using an emulsifying machine. The temperature of the water bath is raised to 60 ℃, and then the stirring is carried out by a turbulence stirring paddle at the rotating speed of 2500 r/min. After the reaction was continued for 3 hours, the reaction was stopped by adjusting the pH to 10 with a sodium hydroxide solution (10%), thereby obtaining the heat transfer enhancing composite microcapsule of the present example.
(6) And (3) mixing the reinforced composite microcapsule prepared in the step (5) and the phase-change material prepared in the step (3) according to the mass ratio of 10%, and stirring and uniformly mixing to obtain the microcapsule type phase-change fluid applied to the low-temperature environment.
The microcapsule phase-change fluid applied to the low-temperature environment prepared in the experimental example is a uniform sphere, the average particle size is 1-10 microns, the moisture mass content is less than or equal to 5%, the critical stress is 1-50 mN, the elastic modulus is 1.9-2.0 GPa, the capsule shell failure stress is 50-55 MPa, the mechanical property is good, the residual formaldehyde content is less than 5%, the heat conductivity coefficient of the fluid phase-change material is 0.2-1.0W/m/DEG C, the phase-change latent heat is more than or equal to 165J/g, and the freezing point of the fluid phase-change material is as follows: and (3) testing the high-pressure stability at the temperature of less than or equal to-20 ℃: more than or equal to 200V.
Example 2
The microcapsule phase-change fluid newly applied to the low-temperature environment can be used for preparing a solar photovoltaic photo-thermal battery plate, and the formula of the raw materials is shown in table 2.
Table 2: example 2 raw material formulation
(1) All raw materials (deionized water, 1, 2-propylene glycol, phase-change material, emulsifier, nucleating agent and the like) for preparing the core material phase-change material are preheated to 75 ℃.
(2) Mixing preheated phase change material such as esters such as pentadecanoic acid tridecyl ester, and stirring at low speed for 15min with a stirrer to prepare dispersed phase to obtain a first solution; then adding preheated emulsifier and nucleating agent such as nonoxynol, polyoxyethylene lauryl alcohol ether, ceteth-12, polyvinyl cyclobutane, magnesium stearate and glycerin into the mixed solution of 1, 2-propylene glycol, and adding 0.4g of nano-alumina. The temperature was maintained and stirring continued until the solution became cloudy, yielding a second solution.
(3) And (3) mixing the two solutions in the step (2), then placing the mixture into a high-speed shearing emulsifying machine for high-speed treatment for 5min, and continuously stirring and cooling to room temperature to obtain a suspension.
(4) Weighing melamine and formaldehyde solution according to a formula, adding the melamine and then adding the formaldehyde into a three-neck flask, stirring and mixing, adding a proper amount of triethylamine to adjust the pH value of the system to be 8-9, heating and stirring the melamine-formaldehyde mixed solution in a water bath at 65 ℃, enabling the system to become transparent after about 10min, adding distilled water with the same mass as the formaldehyde solution, and continuously reacting for 50min to obtain the transparent low-molecular-weight water-soluble melamine prepolymer.
(5) Weighing the emulsifier Arabic gum powder according to the formula, adding the emulsifier Arabic gum powder and the melamine prepolymer into a beaker, adding 1L of distilled water, stirring at low speed at room temperature until the mixture is completely dissolved, adjusting the pH value to 4 by using dilute hydrochloric acid, adding the emulsion obtained in the step (3), and emulsifying at the rotating speed of 3500r/min and the temperature of 40 ℃ for 20min by using an emulsifying machine. The temperature of the water bath is raised to 60 ℃, and then a turbulent stirring paddle is used for stirring at the rotating speed of 3000 r/min. After the reaction was continued for 3 hours, the reaction was stopped by adjusting the pH to 10 with a sodium hydroxide solution (10%), thereby obtaining the heat transfer enhancing composite microcapsule of the present example.
(6) And (3) mixing the heat transfer enhancement composite microcapsule prepared in the step (5) and the phase-change material prepared in the step (3) according to the mass ratio of 10%, and stirring and uniformly mixing to obtain the microcapsule type phase-change fluid applied to the low-temperature environment.
The microcapsule phase-change fluid applied to the low-temperature environment prepared in the experimental example is a uniform sphere, the average particle size is 0.6-7 microns, the water mass content is less than or equal to 5%, the critical stress is 3-20 mN, the elastic modulus is 1.95-2.05 GPa, the capsule shell failure stress is 51-56 MPa, the mechanical property is good, the residual formaldehyde content is less than 5%, the heat conductivity coefficient is 0.4-1.2W/m/DEG C, the phase-change latent heat is more than or equal to 170J/g, and the freezing point of the fluid phase-change material is as follows: and (3) testing the high-pressure stability at the temperature of less than or equal to-30 ℃: more than or equal to 400V.
Example 3
The microcapsule phase-change fluid applied to the low-temperature environment of the embodiment is prepared and can be used in a circulating cooling system of a converter valve, and the formula of the raw materials is shown in table 3.
Table 3: example 3 raw material formulation
(1) All raw materials (deionized water, 1, 2-propylene glycol, phase-change material, emulsifier, nucleating agent and the like) for preparing the core material phase-change material are preheated to 75 ℃.
(2) Mixing preheated phase-change material such as ester acids such as paraffin, and stirring with a stirrer at low speed for 15min to prepare dispersed phase to obtain a first solution; then adding the preheated emulsifier and nucleating agent such as dodecyl heptapolyethylene glycol ether, hexadecyl 1,3 propylene glycol ether, oleyl polyether-8, polyvinyl-2-methylcyclohexane, poly 3-methyl-1-butene, polycyclopentene, glycerin and the like into the mixed 1, 2-propylene glycol solution in advance, and adding 0.7g of nano-aluminum nitride and 0.7g of nano-aluminum oxide. The temperature was maintained and stirring continued until the solution became cloudy, yielding a second solution.
(3) And (3) mixing the two solutions in the step (2), then placing the mixture into a high-speed shearing emulsifying machine for high-speed treatment for 5min, and continuously stirring and cooling to room temperature to obtain a suspension.
(4) Weighing melamine and formaldehyde solution according to a formula, adding the melamine and then adding the formaldehyde into a three-neck flask, stirring and mixing, adding a proper amount of triethylamine to adjust the pH value of the system to be 8-9, heating and stirring the melamine-formaldehyde mixed solution in a water bath at 65 ℃, enabling the system to become transparent after about 10min, adding distilled water with the same mass as the formaldehyde solution, and continuously reacting for 50min to obtain the transparent low-molecular-weight water-soluble melamine prepolymer.
(5) Weighing the emulsifier Arabic gum powder according to the formula, adding the emulsifier Arabic gum powder and the melamine prepolymer into a beaker, adding 1L of distilled water, stirring at low speed at room temperature until the mixture is completely dissolved, adjusting the pH value to 4 by using diluted oxalic acid, adding the emulsion obtained in the step (3), and emulsifying at room temperature for 20min at the rotating speed of 4000r/min by using an emulsifying machine. The temperature of the water bath is raised to 65 ℃, and then a turbulent stirring paddle is used for stirring at the rotating speed of 3000 r/min. After the reaction was continued for 3 hours, the reaction was stopped by adjusting the pH to 10 with ammonia (10%), thereby obtaining the heat transfer enhancing composite microcapsule of the present example.
(6) And (3) mixing the reinforced composite microcapsule prepared in the step (5) and the phase-change material prepared in the step (3) according to the mass ratio of 15%, and stirring and uniformly mixing to obtain the microcapsule type phase-change fluid applied to the low-temperature environment.
The microcapsule phase-change fluid applied to the low-temperature environment prepared in the experimental example is a uniform sphere, the average particle size is 0.4-5 μm, the water mass content is less than or equal to 5%, the critical stress is 1-15 mN, the elastic modulus is 2.0-2.05 GPa, the capsule shell failure stress is 52-56 MPa, the mechanical property is good, the residual formaldehyde content is less than 5%, the heat conductivity coefficient is 0.5-1.4W/m/DEG C, the phase-change latent heat is more than or equal to 175J/g, and the freezing point of the fluid phase-change material is as follows: and (3) testing the high-pressure stability at the temperature of less than or equal to-40 ℃: the voltage is more than or equal to 600V.
Example 4
The microcapsule phase-change fluid applied to the low-temperature environment in this embodiment is prepared by using a factory heat exchange jacket, and the raw material formulation is shown in table 4.
Table 4: example 4 raw material formulation
(1) All raw materials (deionized water, 1, 2-propylene glycol, phase-change material, emulsifier, nucleating agent and the like) for preparing the core material phase-change material are preheated to 75 ℃.
(2) Mixing preheated phase change material such as esters and acids such as pentadecanoic acid tridecyl ester, and stirring at low speed for 15min with a stirrer to prepare dispersed phase to obtain a first solution; then adding the preheated emulsifier and nucleating agent such as stearyl alcohol polyether-100, nonoxynol, oleyl alcohol polyether-8, polypropylene alcohol, oleyl alcohol polyoxyethylene ether, magnesium stearate, glycerol and the like into the mixed 1, 2-propylene glycol solution in advance, and adding 1g of nano-scale aluminum nitride and 1g of nano-scale aluminum oxide. The temperature was maintained and stirring continued until the solution became cloudy, yielding a second solution.
(3) And (3) mixing the two solutions in the step (2), then placing the mixture into a high-speed shearing emulsifying machine for high-speed treatment for 5min, and continuously stirring and cooling to room temperature to obtain a suspension.
(4) Weighing melamine and formaldehyde solution according to a formula, adding the melamine and then adding the formaldehyde into a three-neck flask, stirring and mixing, adding a proper amount of triethylamine to adjust the pH value of the system to be 8-9, heating and stirring the melamine-formaldehyde mixed solution in a water bath at 65 ℃, enabling the system to become transparent after about 10min, adding distilled water with the same mass as the formaldehyde solution, and continuously reacting for 50min to obtain the transparent low-molecular-weight water-soluble melamine prepolymer.
(5) Weighing the emulsifier Arabic gum powder according to the formula, adding the emulsifier Arabic gum powder and the melamine prepolymer into a beaker, adding 1L of distilled water, stirring at low speed at room temperature until the mixture is completely dissolved, adjusting the pH value to 4 by using dilute hydrochloric acid, adding the emulsion obtained in the step (3), and emulsifying at the rotating speed of 4000r/min and the temperature of 40 ℃ for 20min by using an emulsifying machine. Then the temperature of the water bath is raised to 60 ℃, and a turbulent stirring paddle is used for stirring at the rotating speed of 3500 r/min. After the reaction was continued for 3 hours, the reaction was stopped by adjusting the pH to 10 with a potassium hydroxide solution (10%), thereby obtaining the heat transfer enhancing composite microcapsule of the present example.
(6) And (3) mixing the reinforced composite microcapsule prepared in the step (5) and the phase-change material prepared in the step (3) according to the mass ratio of 20%, and stirring and uniformly mixing to obtain the microcapsule type phase-change fluid applied to the low-temperature environment.
The microcapsule phase-change fluid applied to the low-temperature environment prepared in the experimental example is a uniform sphere, the average particle size is 0.1-2 μm, the water mass content is less than or equal to 5%, the critical stress is 1-10 mN, the elastic modulus is 2.05-2.10 GPa, the capsule shell failure stress is 53-57 MPa, the mechanical property is good, the residual formaldehyde content is less than 5%, the heat conductivity coefficient is 0.6-1.6W/m/DEG C, the phase-change latent heat is more than or equal to 180J/g, and the freezing point of the fluid phase-change material is as follows: and (3) testing the high-pressure stability at the temperature of less than or equal to-50 ℃: more than or equal to 750V.
As mentioned above, the invention firstly synthesizes the fluid phase-change material and the water-soluble melamine prepolymer, then mixes the obtained water-soluble melamine prepolymer with the suspension and carries out emulsification reaction to obtain the enhanced composite heat transfer microcapsule; and uniformly mixing the obtained enhanced composite heat transfer microcapsule with the obtained fluid phase change material to obtain the microcapsule type phase change fluid applied to the low-temperature environment.
The microcapsule type phase-change fluid applied to the low-temperature environment, which is prepared by the invention, has the advantage that the change of the particle size of the phase-change fluid is greatly reduced in the using process due to the addition of the enhanced heat transfer composite microcapsule.
In addition, the product innovatively changes part of pure water into 1, 2-propylene glycol with low toxicity, greatly reduces the freezing point of the solution under the condition of keeping the original thermal conductivity as much as possible, and enables the phase-change fluid to normally run under the conditions of low temperature and even severe cold.
In addition, the phase-change fluid is added with the nano-scale aluminum nitride or nano-scale aluminum oxide serving as the insulation strengthening heat transfer agent, so that the heat transfer efficiency of the original phase-change material is greatly improved, the phase-change material is not easy to break down, the phase-change material can be used under various low voltages, and the service life of the phase-change material is prolonged to a certain extent.
In addition, the phase-change fluid also has the advantages of high phase-change latent heat, flexible and adjustable phase-change temperature range, good stability and the like.
The embodiments of the present invention are not limited to the above-described embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.
Claims (10)
1. A preparation method of microcapsule type phase-change fluid capable of being used in low-temperature environment is characterized by comprising the following preparation steps:
(1) mixing an emulsifier, a nucleating agent, 1, 2-propylene glycol, water and glycerol in a certain sequence and operation, adding one or two of nanoscale aluminum nitride or aluminum oxide to obtain a turbid solution, uniformly mixing the turbid solution with a phase-change material to obtain a suspension, and cooling to room temperature to obtain a fluid phase-change material;
(2) uniformly mixing melamine and a formaldehyde solution, adjusting the solution to be alkaline, heating and stirring until the solution becomes transparent, adding water, and continuing to react to obtain a water-soluble melamine prepolymer;
(3) uniformly mixing the water-soluble melamine prepolymer obtained in the step (2) with an emulsifier and water, adjusting the obtained mixed solution to be acidic, adding the suspension obtained in the step (1), carrying out an emulsification reaction, adding an alkali to adjust the pH value of the system to be 6-9 after the reaction is finished, and obtaining the enhanced composite heat transfer microcapsule;
(4) and (3) uniformly mixing the reinforced composite heat transfer microcapsule obtained in the step (3) with the fluid phase change material obtained in the step (1) to obtain the microcapsule type phase change fluid applied to the low-temperature environment.
2. The method of claim 1, wherein the microcapsule phase-change fluid is prepared by a method comprising:
the emulsifier in the step (1) is at least one of arabic gum powder, nonoxynol, polyoxyethylene lauryl ether, dodecyl heptapolyethylene glycol ether, hexadecyl 1,3 propylene glycol ether, cetyl polyether-12, stearyl polyether-2, stearyl polyether-100 and oleyl polyether-8;
the nucleating agent in the step (1) is at least one of polyvinyl cyclobutane, polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, polycyclopentene, polystyrene, polyvinyl alcohol, polypropylene alcohol, oleyl alcohol polyoxyethylene ether and magnesium stearate;
the phase-change material in the step (1) is at least two of dodecyl myristate, tridecyl pentadecate, tetradecyl palmitate, tridecyl heptadecanoate, tetradecyl octadecanoate, tetradecyl tetradecate, hexadecyl hexadecanoate, polymethyl methacrylate and stearic acid.
3. The method of claim 2, wherein the microcapsule phase-change fluid is prepared by a method comprising:
when the emulsifier in the step (1) is nonoxynol and ceteth, the mass ratio is 1: 1-6: 1; when the emulsifier is cetyl polyether-12, stearyl polyether-100 and oleyl polyether-8, the mass ratio is 1:1: 1-6: 1: 2;
the volume ratio of the 1, 2-propylene glycol obtained in the step (1) to the fluid phase-change material obtained in the step (1) is as follows: 35-65: 100;
when the nucleating agent in the step (1) is polyvinyl alcohol, oleyl alcohol polyoxyethylene ether and magnesium stearate, the mass ratio of the polyvinyl alcohol, the oleyl alcohol polyoxyethylene ether, the magnesium stearate, the glycerol and the 1, 2-propylene glycol aqueous solution is 2-8: 0.5-3: 1:6:3:10: 150;
in the step (1), the phase-change material is tetradecyl palmitate, tetradecyl stearate and hexadecyl palmitate, and the mass ratio of the tetradecyl palmitate to the hexadecyl palmitate is 3: 6: 8, a mixture of; or the mixture of tetradecyl palmitate and tetradecyl stearate with the mass ratio of 1: 2; or a mixture of dodecyl myristate and tridecyl pentadecate in a mass ratio of 1: 2; or a mixture of tetradecyl palmitate and tridecyl heptadecanoate with the mass ratio of 1: 2; or a mixture of tetradecyl octadecanoate and hexadecyl hexadecanoate with the mass ratio of 3: 4.
4. The method of claim 3, wherein the microcapsule phase-change fluid is prepared by a method comprising:
the mass-volume ratio of the emulsifier, the nucleating agent, the glycerol and the 1, 2-propylene glycol aqueous solution in the step (1) is 1-6: 1-6: 30, of a nitrogen-containing gas;
the mass ratio of the nano aluminum nitride to the turbid solution in the step (1) is 1: 100-300; the mass ratio of the nano alumina to the turbid solution is 1: 100-300;
the mass ratio of the nucleating agent to the phase-change material in the step (1) is 1: 2-6.
5. The method of claim 3, wherein the microcapsule phase-change fluid is prepared by a method comprising: the molar ratio of the melamine to the pure formaldehyde in the formaldehyde solution in the step (2) is 1: 2-1: 10, and the amount of the water is 1-3 times of the mass of the organic solvent.
6. The method of claim 3, wherein the microcapsule phase-change fluid is prepared by a method comprising:
the mass ratio of the water-soluble melamine prepolymer to the emulsifier in the step (3) is 1: 1-1: 5;
the mass ratio of the suspension liquid in the step (3) to the water-soluble melamine prepolymer is 1: 1-6: 1.
7. The method of claim 3, wherein the microcapsule phase-change fluid is prepared by a method comprising:
in the step (4), the mass ratio of the capsule to the fluid phase-change material is 0.1: 1-0.5: 1, preferably 0.1: 1-0.2: 1.
8. The method of claim 3, wherein the microcapsule phase-change fluid is prepared by a method comprising:
the acidity in the step (3) is pH 1-6;
the emulsification reaction process in the step (3) is as follows: firstly, an emulsifier is used for stirring and emulsifying at 40-50 ℃ and 3000-4000 r/min for 20-50 min, then the temperature is raised to 60-75 ℃, and a turbulent stirring paddle is used for stirring and reacting at 2500-3500 r/min for 3-5 h.
9. A microcapsule type phase-change fluid applied to a low-temperature environment is characterized in that: prepared by the method of any one of claims 1 to 8.
10. The microcapsule phase-change fluid as claimed in claim 9, which is used in low-temperature environment, and is used in the field of heat storage and transmission power equipment.
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