Technology for regulating and controlling phase change heat transfer of cold storage material by inducing nano Fe3O4 through magnetic field and application

Abstract

The invention belongs to the technical field of inorganic eutectic phase change materials, and discloses a novel magnetic phase change cold storage material, a preparation method thereof and a magnetic control cold storage material phase change heat transfer technology. The preparation method comprises the following steps: pouring sodium formate, potassium chloride and deionized water into a beaker, and stirring in a water bath environment of 30 DEG C by using a magnetic stirrer until the materials are completely dissolved to obtain an inorganic salt solution A; adding nano Fe3O4 into the inorganic salt solution A in a room temperature environment, and dispersing for 1 hour by using an ultrasonic dispersion instrument to obtain a magnetic phase change cold storage material B; and adding a surfactant into the magnetic phase change cold storage material B, and dispersing for 2 hours by using an ultrasonic dispersion instrument to obtain a magnetic phase change cold storage material C, thereby completing the preparation. The invention discloses a preparation method of a novel magnetic phase change cold storage material based on sodium formate / potassium chloride, the prepared magnetic phase change cold storage material can be packaged in equipment such as a refrigerated container and a refrigerator car, and the problems that a single inorganic salt solution is large in supercooling degree, serious in phase separation, poor in cycling stability and the like are solved. In addition, the prepared magnetic phase change cold storage material can be coupled with an alternating magnetic field, the controllability of the phase change heat transfer process of the phase change material is achieved, and the application of the magnetic phase change cold storage material in cold chain transportation is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal energy storage, and specifically relates to a magnetic phase change cold storage material, a preparation method thereof, a technology for regulating phase change heat transfer of a cold storage material by magnetic field-induced nano-Fe3O4, and applications thereof. Background Art

[0002] Due to the non-sustainability of traditional fossil energy and serious environmental pollution, the development of renewable energy is the only way to solve energy shortage, improve the environment and promote human development. Currently, solar energy, water energy, wind energy, etc. are relatively mature in development and application, but these renewable energies all have defects such as intermittency and instability due to irresistible factors such as time and geography. Therefore, energy storage technology has become an important part of the development of renewable energy.

[0003] So far, temperature fluctuations have always been the most important factors affecting the quality and shelf life of aquatic products during low-temperature preservation. As a clean energy material, phase change materials can perform latent heat exchange at a constant temperature to achieve the storage and release of cold energy. However, there are still the following problems in the application of phase change materials in the cold chain: supercooling leads to a decrease in energy utilization efficiency, leakage during the solid-liquid phase change material process, and slow cooling release rate due to low thermal conductivity. In addition, Fe3O4 nanoparticles with unique superparamagnetism can provide a new function of rapid magnetothermal conversion for composite phase change materials under an applied alternating magnetic field due to the Brownian effect. Summary of the Invention

[0004] The purpose of the present invention is to provide a technology for regulating phase change heat transfer of a cold storage material by magnetic field-induced nano-Fe3O4 and its applications to solve one or more of the above-mentioned technical problems. In the technical solution provided by the present invention, a preparation method of a novel magnetic phase change cold storage material based on a sodium formate / potassium chloride solution is disclosed, which overcomes problems such as large supercooling degree, serious phase separation and poor cycle stability of a single inorganic salt solution. In addition, the prepared magnetic phase change cold storage material can be coupled with an alternating magnetic field to achieve the controllability of the phase change heat transfer process of the phase change material, and expand the application of the magnetic phase change cold storage material in cold chain transportation.

[0005] To achieve the above object, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a preparation method of a magnetic phase change cold storage material, including the following steps: Step 1, pour sodium formate, potassium chloride and deionized water into a beaker, and stir with a magnetic stirrer in a water bath environment at 30°C until completely dissolved to obtain an inorganic salt solution A; Step 2, add nano-Fe3O4 to the inorganic salt solution A at room temperature, and disperse it with an ultrasonic disperser for 1 hour to obtain a magnetic phase change cold storage material B; Step 3, at room temperature, add the surfactant to the magnetic phase change cold storage material B, and disperse it with an ultrasonic disperser for 2 hours to obtain the magnetic phase change cold storage material C, thus completing the preparation.

[0006] A further improvement in the preparation method of the present invention lies in that In the inorganic salt solution A, the mass fraction of sodium formate is 20% - 25%, the mass fraction of potassium chloride is 10% - 15%, and the mass fraction of deionized water is 60% - 70%.

[0007] A further improvement in the preparation method of the present invention lies in that The nano-Fe3O4 serves both as a nucleating agent to reduce the supercooling degree and as a magnetic particle to be regulated by a magnetic field.

[0008] A further improvement in the preparation method of the present invention lies in that The surfactant is one of cetyltrimethylammonium bromide and sodium dodecylbenzenesulfonate, which improves the dispersibility of nano-Fe3O4.

[0009] A further improvement in the preparation method of the present invention lies in that In the magnetic phase change cold storage material B, the mass fraction of nano-Fe3O4 is 0.2% - 1.0%.

[0010] A further improvement in the preparation method of the present invention lies in that In the magnetic phase change cold storage material C, the mass fraction of the surfactant is 0.4% - 1.2%.

[0011] A further improvement in the preparation method of the present invention lies in that The phase change temperature of the prepared magnetic phase change cold storage material is -20°C to -30°C.

[0012] In the second aspect, a composite phase change cold storage material prepared by the preparation method according to any one of the first aspects of the present invention is provided.

[0013] In the third aspect, the present invention also discloses an application of a magnetic phase change cold storage material. The cold storage material is the magnetic phase change cold storage material prepared by the above method, and the application is in cold chain logistics. In the field of cold chain logistics, the magnetic phase change cold storage material can be encapsulated on the inner wall of a refrigerated box or a refrigerated truck. During short-distance refrigerated logistics transportation, the magnetic phase change cold storage material releases cold through phase change, enabling the refrigerated box or refrigerated truck to maintain a relatively low temperature for a long time and meeting the requirements of short-distance cold chain logistics transportation.

[0014] A further improvement in the application method of the present invention lies in that The addition of the nano-Fe3O4 improves the thermal conductivity of the magnetic phase change cold storage material, and the effect is more significant in the application of short-distance cold chain logistics transportation.

[0015] Fourthly, the present invention also discloses a technology for regulating phase change heat transfer of a cold storage material by magnetic field-induced nano-Fe3O4. The cold storage material is the magnetic phase change cold storage material prepared by the above method, and the magnetic field is an alternating magnetic field with adjustable magnetic field intensity. In this technical solution, during the solidification and melting processes of the phase change cold storage material, different intensities of magnetic fields are added to induce nano-Fe3O4 to regulate the phase change process of the material, realizing the controllability of the phase change temperature and phase change time to meet the cooling requirements in different cold chain transportation environments.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a preparation method of a novel magnetic phase change cold storage material based on a sodium formate / potassium chloride solution. The prepared magnetic phase change cold storage material has the advantages of suitable phase change temperature, high phase change latent heat, high thermal conductivity, small supercooling degree, no phase separation and excellent cycle stability; the prepared magnetic phase change cold storage material can be subsequently applied to the cold chain logistics field, enabling a refrigerated box or a refrigerated truck to maintain a low temperature for a long time and meeting the requirements of short-distance cold chain logistics transportation.

[0017] More specifically, taking the sodium formate / potassium chloride solution as the base solution has the advantage of high latent heat; using nano-Fe3O4 as the nucleating agent improves the supercooling problem of the magnetic phase change cold storage material; using cetyltrimethylammonium bromide and the like as surfactants and thickeners to inhibit phase separation and at the same time improve the dispersion of nano-Fe3O4; the preparation method of the present invention is simple, the raw materials are easily available, the method steps are few, and the operation difficulty is low, which can greatly reduce the process cost.

[0018] In the magnetic control phase change heat transfer technology disclosed by the present invention, a magnetic control phase change heat transfer device composed of a magnetic phase change cold storage material and a magnetic field generator is disclosed, which can regulate the solidification and melting processes of the phase change material. Specifically, with the increase of the alternating magnetic field intensity, the solidification temperature of the magnetic phase change cold storage material gradually increases, while the melting temperature gradually decreases. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art; obviously, the following drawings are some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0020] Figure 1 It is a schematic flow chart of the preparation of a novel magnetic phase change cold storage material based on a sodium formate / potassium chloride solution in the preferred example of the present invention.

[0021] Figure 2It is a schematic diagram of the DSC (Differential Scanning Calorimetry) curve of the sodium formate / potassium chloride / iron tetroxide composite phase change energy storage material with different iron tetroxide nanoparticle contents in the embodiments of the present invention; Figure 3 It is a schematic diagram of the cooling curve of the sodium formate / potassium chloride / iron tetroxide composite phase change energy storage material with different iron tetroxide nanoparticle contents in the embodiments of the present invention; Figure 4 It is a schematic diagram of the DSC curve of the sodium formate / potassium chloride / iron tetroxide / sodium dodecylbenzenesulfonate composite phase change energy storage material with different sodium dodecylbenzenesulfonate contents in the embodiments of the present invention; Figure 5 It is an XRD spectrogram of the novel magnetic phase change energy storage material in the embodiments of the present invention; Figure 6 It is a graph showing the change in the central temperature of the crucian carp samples in the refrigerator during cooling using the novel magnetic phase change energy storage material in the embodiments of the present invention; Figure 7 It is a schematic diagram of the magnetic control phase change heat transfer device in the embodiments of the present invention; Figure 8 It is the solidification curve of the magnetic phase change energy storage material under the action of alternating magnetic fields with different intensities in the embodiments of the present invention. Detailed implementation manners

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0023] Please refer to Figure 1 , a preparation method of a novel magnetic phase change energy storage material provided by an embodiment of the present invention, specifically a preparation method of a novel magnetic phase change energy storage material based on a sodium formate / potassium chloride solution, includes the following steps: Step 1: Pour sodium formate, potassium chloride and deionized water into a beaker, and stir them with a magnetic stirrer in a water bath environment at 30 °C until completely dissolved to obtain inorganic salt solution A. Among them, in the inorganic salt solution A, the mass fraction of sodium formate is 22 wt%, the mass fraction of potassium chloride is 12 wt%, and the mass fraction of deionized water is 66 wt%.

[0024] Step 2: At room temperature, add nano-Fe3O4 as a nucleating agent to the inorganic salt solution A obtained in Step 1, and disperse it with an ultrasonic disperser for 1 hour to obtain magnetic phase change energy storage material B. Among them, in the magnetic phase change energy storage material B, the mass fraction of nano-Fe3O4 is 0.6 wt%.

[0025] Step 3: At room temperature, add sodium dodecylbenzenesulfonate as a surfactant to the magnetic phase change energy storage material B obtained in Step 2, and disperse it with an ultrasonic disperser for 2 hours to obtain magnetic phase change energy storage material C, thus completing the preparation. Among them, in the magnetic phase change energy storage material C, the mass fraction of sodium dodecylbenzenesulfonate is 1.2 wt%.

[0026] In the technical solution disclosed in the embodiment of the present invention, nano-Fe3O4 is used to improve the supercooling of the composite phase change material, and sodium dodecylbenzenesulfonate is used to improve the dispersibility of nano-Fe3O4, thereby constructing a new type of magnetic phase change material system.

[0027] In the further verification scheme of the embodiment of the present invention, the molten composite phase change material is cooled and solidified at a constant temperature of -40 °C in a glass sample bottle, and its cooling curve is measured.

[0028] In the further application scheme of the embodiment of the present invention, the obtained new type of magnetic phase change energy storage material can be filled in a cold storage bag as an energy storage unit for use in a cold storage system, such as a refrigerator, a refrigerated truck, etc. The preparation method is simple and easy to use.

[0029] Exemplarily, the cold storage system includes a magnetic phase change energy storage material encapsulated in a refrigerator, as Figure 7 shown.

[0030] Further specifically exemplarily, a magnetic control phase change heat transfer device is provided, which uses an alternating current power supply to supply an electromagnetic field generator to generate an alternating magnetic field. By controlling the output voltage of the alternating current power supply, the intensity of the alternating magnetic field is changed, and the phase change process of the magnetic phase change energy storage material is controlled to meet the cooling demand under different refrigeration environments.

[0031] In the specific embodiment of the present invention, a sodium formate / potassium chloride / iron oxide composite phase change energy storage material is prepared according to the following mass fraction ratio; among them, the specific mass ratio of sodium formate, potassium chloride and iron oxide is listed in Table 1. The DSC measurement results of the prepared sodium formate / potassium chloride / iron oxide composite phase change energy storage material are asFigure 2 As shown, the cooling curve is as Figure 3 shown.

[0032] Table 1. Mass ratio of sodium formate / potassium chloride / iron tetroxide Sample Sodium formate (g) Potassium chloride (g) Iron oxide (g) Deionized water (g) <![CDATA[SF-PC / 0.2%Fe3O4]]> 2.2 1.2 0.02 6.6 <![CDATA[SF-PC / 0.4%Fe3O4]]> 2.2 1.2 0.04 6.6 <![CDATA[SF-PC / 0.6% Fe3O4]]> 2.2 1.2 0.06 6.6 <![CDATA[SF-PC / 0.8%Fe3O4]]> 2.2 1.2 0.08 6.6 <![CDATA[SF-PC / 10%Fe3O4]]> 2.2 1.2 0.10 6.6 From Figure 2 it can be seen that sodium formate / potassium chloride / iron tetroxide shows a single endothermic peak during the melting process, proving that sodium formate and potassium chloride have extremely close phase transition temperatures. The DSC curves of the phase change materials with 0.2wt% and 0.4wt% iron tetroxide show no obvious changes, indicating that the addition of low-concentration nano-Fe3O4 has little effect on the thermal properties of sodium formate / potassium chloride / iron tetroxide. On the contrary, when the mass fraction of nano-Fe3O4 reaches 1.0wt%, the phase transition temperature range of sodium formate / potassium chloride / iron tetroxide becomes wider, which may be due to the influence of microscopic forces such as surface adsorption force of nano-Fe3O4.

[0033] From Figure 3 it can be seen that the enhanced thermal conductivity provided by nano-Fe3O4 and its role as a heterogeneous nucleating agent during the crystallization process of sodium formate / potassium chloride / iron tetroxide significantly reduce the supercooling degree of sodium formate / potassium chloride / iron tetroxide. The supercooling degree of SF-PC without adding nano-Fe3O4 is 5.78 °C, while those of SF-PC / 0.4%Fe3O4 and SF-PC / 0.8%Fe3O4 are reduced to 1.62 °C and 1.23 °C respectively. In addition, SF-PC / 0.2%Fe3O4, SF-PC / 0.4%Fe3O4, SF-PC / 0.8%Fe3O4 and SF-PC / 1.0%Fe3O4 have similar phase transition temperatures (about -24.0 °C) to SF-PC. While SF-PC / 0.6%Fe3O4 has the lowest phase transition temperature (-25.14 °C) and a longer cooling curve plateau, indicating its excellent cold storage capacity during the cooling process.

[0034] In the embodiments of the present invention, a series of phase change cold storage materials of sodium formate / potassium chloride / iron tetroxide / sodium dodecylbenzenesulfonate are prepared according to the following mass ratios; among them, the specific mass ratios of sodium formate, potassium chloride, iron tetroxide and sodium dodecylbenzenesulfonate are listed in Table 2. The DSC measurement results of the prepared sodium formate / potassium chloride / iron tetroxide / sodium dodecylbenzenesulfonate composite phase change cold storage material are as Figure 4 shown.

[0035] Table 2. Mass ratio of sodium formate / potassium chloride / iron tetroxide / sodium dodecylbenzenesulfonate Sample Sodium formate (g) Potassium chloride (g) Iron oxide (g) Deionized water (g) Sodium dodecylbenzenesulfonate (g) MPCMs-0.4 2.2 1.2 0.06 6.6 0.04 MPCMs-0.6 2.2 1.2 0.06 6.6 0.06 MPCMs-0.8 2.2 1.2 0.06 6.6 0.08 MPCMs-1.0 2.2 1.2 0.06 6.6 0.10 MPCMs-1.2 2.2 1.2 0.06 6.6 0.12 Please refer to Figure 5, is the XRD spectrum of MPCMs-1.2, showing the complete characteristic peaks of the combination of sodium formate, potassium chloride, sodium dodecylbenzenesulfonate, and iron tetroxide. Specifically, the diffraction peaks observed at 20.5°, 26.3°, 30.2°, 31.8°, 32.3°, 39.3°, 43.2°, 43.8°, and 49.0° correspond to the (110), (020), (111), (200), (002), (-221), (-130), (-131), and (131) crystal planes of sodium formate, respectively. The diffraction peaks appearing at 28.4°, 40.6°, and 66.5° correspond to the (200), (220), and (420) crystal planes of potassium chloride, respectively. The characteristic peaks of sodium dodecylbenzenesulfonate are not obvious in the diffraction pattern of sodium formate / potassium chloride / iron tetroxide / sodium dodecylbenzenesulfonate, which is due to the small content. The corresponding characteristic peaks can also be found for the other weaker diffraction peaks in MPCMs-1.2. It should be noted that after the interaction between sodium dodecylbenzenesulfonate and sodium formate / potassium chloride / iron tetroxide, the diffraction peak intensity of sodium formate / potassium chloride / iron tetroxide / sodium dodecylbenzenesulfonate increases, indicating that the crystallinity of sodium formate / potassium chloride / iron tetroxide / sodium dodecylbenzenesulfonate has been improved. In addition, no new diffraction peaks appear in the diffraction pattern of MPCMs-1.2, indicating that sodium dodecylbenzenesulfonate has no effect on the structure of the sodium formate / potassium chloride / iron tetroxide solution, and only simple physical adsorption occurs between substances during the composite process.

[0036] In the application solution of the embodiment of the present invention, the obtained novel magnetic phase change cold storage material is encapsulated in a self-refrigerating box to supply cold to crucian carp. The self-refrigerating box mainly consists of three parts: a foamed polypropylene outer shell, a foamed polystyrene heat insulation layer, and an aluminum film pearl cotton heat insulation layer. The outer shell is made of foamed polypropylene material with an internal size of 360 mm × 270 mm × 225 mm. Foamed polypropylene is an environmentally friendly compression buffer heat insulation material that can be recycled and has high mechanical strength. The foamed polystyrene is used as the heat insulation layer with a thickness of 50 mm, having the advantages of heat insulation, moisture proof, shock absorption, and excellent dielectric properties. The inner layer of the refrigerating box is covered with a 3-mm-thick aluminum film pearl cotton, which further inhibits the heat exchange between aquatic products and the external environment.

[0037] As can be seen from Figure 6 , it takes only 2.53 hours for the temperature of crucian carp to reach -15°C in a refrigerating box filled with ordinary high polymer phase change materials (SPCMs), indicating that ordinary phase change materials cannot meet the short-distance transportation of frozen aquatic products. In the refrigerating box filled with sodium formate / potassium chloride, the refrigeration time is 15.30 hours when the temperature of crucian carp reaches -15°C. The time for MPCMs-1.2 to keep the temperature of crucian carp below -15°C is increased by 2.23 (14.6%) hours compared with sodium formate / potassium chloride, which benefits from the reduction of supercooling degree and the improvement of thermal conductivity.

[0038] In a specific embodiment of the present invention, a magnetically controlled phase change heat transfer device is provided, and an alternating current power supply is used to supply an electromagnetic field generator to generate an alternating magnetic field, as shown in the schematic diagram Figure 7 shown. By controlling the output voltage of the alternating current power supply to change the intensity of the alternating magnetic field, the phase change process of the magnetic phase change cold storage material is controlled to meet the cooling requirements under different refrigeration environments.

[0039] As can be seen from Figure 8 , the time for MPCMs-1.2 to reach the melting point is greatly affected by the alternating magnetic field. As the magnetic field intensity increases, the time for MPCMs-1.2 to reach the melting point becomes longer. In addition, as the magnetic field intensity increases, the melting point of MPCMs-1.2 gradually decreases. At magnetic field intensities of 0 mT, 1 mT, and 3 mT, the melting points of MPCMs-1.2 are -20.83 °C, -21.10 °C, and -21.25 °C, respectively. As the magnetic field intensity increases, the absorption and response of magnetic particles to the external magnetic field increase, which may enable the material to obtain sufficient energy for phase change at a lower temperature.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the specific implementation manners of the present invention can still be modified or equivalently replaced, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A preparation method of a magnetic phase change cold storage material, characterized in that, It includes the following steps: Step 1: Pour sodium formate, potassium chloride and deionized water into a beaker, and stir them with a magnetic stirrer in a 30°C water bath environment until completely dissolved to obtain inorganic salt solution A; Step 2: At room temperature, add nano-Fe3O4 to the inorganic salt solution A, and disperse it with an ultrasonic disperser for 1 hour to obtain magnetic phase change energy storage material B; Step 3: At room temperature, add a surfactant to the magnetic phase change energy storage material B, and disperse it with an ultrasonic disperser for 2 hours to obtain magnetic phase change energy storage material C, completing the preparation.

2. The preparation method of a composite phase change cold storage material according to claim 1, characterized in that, The nano-Fe3O4 serves both as a nucleating agent to reduce supercooling and as magnetic particles to be regulated by a magnetic field.

3. The preparation method of a composite phase change cold storage material according to claim 1, characterized in that, The surfactant is one of cetyltrimethylammonium bromide and sodium dodecylbenzenesulfonate, which improves the dispersibility of nano-Fe3O4.

4. The preparation method of a composite phase change cold storage material according to claim 1, wherein In the magnetic phase change energy storage material B, the mass fraction of nano-Fe3O4 is 0.2% - 1.0%.

5. The preparation method of a composite phase change cold storage material according to claim 1, characterized in that In the magnetic phase change energy storage material C, the mass fraction of the surfactant is 0.4% - 1.2%.

6. The preparation method of a composite phase change cold storage material according to claim 1, characterized in that, The phase change temperature of the prepared magnetic phase change energy storage material is -20°C to -30°C.

7. A composite phase change energy storage material prepared by the preparation method described in any one of claims 1 to 7.

8. The application method of the magnetic phase change cold storage material according to claim 8, characterized in that, The magnetic phase change energy storage material is used for cooling in cold chain transportation equipment such as refrigerators or refrigerated trucks.

9. A technique for regulating phase change heat transfer of a cold storage material by magnetic field-induced nano-Fe3O4, characterized in that, During the solidification and melting processes of the phase change energy storage material, magnetic fields with different intensities are added to induce nano-Fe3O4 to regulate the phase change process of the material, realizing the controllability of the phase change temperature and phase change time to meet the cooling requirements in different cold chain transportation environments.

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