Magnetic field controllable undercooled crystallization composite material, preparation method thereof and heat storage application

Abstract

The application belongs to the field of heat storage and specifically relates to a supercooled plastic crystal composite material with controllable magnetic field and a preparation method and heat storage application thereof. The supercooled plastic crystal composite material with controllable magnetic field is prepared by mixing the supercooled plastic crystal with controllable pressure and magnetic powder, and then the magnetic powder is attracted by the magnetic field to generate stress on the supercooled plastic crystal, so that the phase change of the non-contact magnetic field-induced plastic crystal composite material is realized in this indirect way. Accordingly, the combination of the supercooled plastic crystal material and the magnetic powder can solve the limitation of the current supercooled plastic crystal material-induced phase change mode, realize the non-contact and non-damage type of the magnetic field-controllable phase change heat release, and greatly expand the application scenarios of the supercooled plastic crystal material.

Description

Technical Field

[0001] This invention belongs to the field of thermal energy storage applications, specifically relating to a magnetic field-controllable supercooled plastic crystal composite material, its preparation method, and its thermal energy storage applications. Background Technology

[0002] For future carbon neutrality and development, there is an urgent need to develop decarbonized thermal storage systems. Globally, winter heating and hydrothermal heating account for 60% of building energy consumption, representing the energy required for human life and thermal comfort. Heating or cooling in homes can be replaced by sustainable solar-thermal energy. However, the significant time mismatch between abundant summer solar energy and high winter heating demand, especially in some extreme climate regions, presents a major technological obstacle to harvesting solar energy for heating. Therefore, developing new energy storage methods for interseasonal thermal storage is crucial to mitigating this time-heat mismatch.

[0003] Supercooled plastic crystal materials exhibit an irreversible compressive effect, specifically manifested in the high-temperature endothermic transformation to a glassy phase. However, this glassy phase can be maintained at temperatures far below the phase transition point, and the phase transition can be exothermically achieved at low temperatures (hundreds of J / kg) with relatively small pressure. -1 k -1 Therefore, utilizing the irreversible compressive effect of such supercooled plastic crystal materials holds promise for achieving long-term, wide-temperature-range, and cross-regional heat storage. While plastic crystal materials exhibit excellent thermodynamic properties, their widespread application is limited by contact-based pressure control. Currently, phase transitions are mainly induced by pressure or prolonged ultrasound. However, this contact-based or prolonged stress-induced phase transition method inevitably causes irreversible damage to the material, thus reducing its lifespan. Therefore, introducing a non-contact field to controllably induce phase transitions while avoiding damage to the material would greatly improve the application flexibility of supercooled plastic crystal materials. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a magnetically controllable supercooled plastic crystal composite material and its heat storage application. By uniformly mixing and grinding a plastic crystal material with a supercooled phase with NbFeB and Fe3O4 magnetic powders in a certain mass ratio, a composite phase change material is prepared. This method can use a small magnetic field to induce a phase change in the supercooled plastic crystal composite material.

[0005] The present invention adopts the following technical solution:

[0006] A magnetic field-controllable supercooled plastic crystal composite material, which is composed of a plastic crystal material with a supercooled phase and magnetic powder.

[0007] The supercooled crystal-forming material is erythritol (C4H).10 O4, magnesium chloride hexahydrate MgCl2·6H2O, adipic acid HOOC(CH2)4COOH, galactitol C6H 14 One or more of O6 and 2-amino-2-methyl-1,3-propanediol H2N(CH3)C(CH2OH)2(AMP).

[0008] The magnetic powder is one or more of NdFeB, Fe3O4, Fe, SmCo, and NdNiCo, and the mass percentage of the magnetic powder is 20-90%, preferably 20-80%, and more preferably 20-60%.

[0009] A method for preparing a magnetically controllable supercooled crystalline composite material is characterized by: mixing and grinding a crystalline material with a supercooled phase and magnetic powder, heating it to above the glass phase transition temperature, holding it at that temperature, and then naturally cooling it to room temperature.

[0010] Furthermore, the particle size of the ground magnetic powder is less than 10 μm, preferably 0.1 to 10 μm, and the particle size of the ground plastic crystal material with supercooled phase is between 100 and 500 μm.

[0011] Furthermore, the heating temperature is above the phase transition temperature of the glass phase, preferably 10 to 50°C above the phase transition temperature of the glass phase, and the holding time is 1 to 3 minutes.

[0012] The application of a magnetic field-controllable supercooled plastic crystal composite material as a heat storage material is characterized in that the application process includes the heat release process and the heat storage process of the supercooled plastic crystal composite material.

[0013] Furthermore, the exothermic process involves applying an external magnetic field to the supercooled plastic crystal composite material to induce a phase transition and release heat.

[0014] When the magnetic field strength is 40-60 mT and the induction time is 1-3 min, 0.5-2% strain can be generated for 0.5-1 g of supercooled plastic crystal composite material. After that, a phase transition begins to occur. After the phase transition is triggered, the phase transition of the material has spontaneous diffusion. After 100 s, the material completes the phase transition and generates a temperature change of 100-120 °C / g.

[0015] Furthermore, the heat storage process involves heating the supercooled plastic crystal composite material after heat release to a temperature above the phase transition point of the glass phase, preferably 10 to 50°C above the phase transition point, holding it at that temperature for 1 to 3 minutes, and then naturally cooling it to room temperature.

[0016] Advantages and beneficial effects of the present invention:

[0017] This invention utilizes the pressure-controlled properties of supercooled plastic crystals. After mixing them with magnetic powder, a magnetic field can attract the magnetic powder, thereby inducing stress in the supercooled plastic crystals. This indirectly achieves a non-contact, magnetically induced phase transition in the plastic crystal composite material. Therefore, combining this type of supercooled plastic crystal material with magnetic powder is expected to overcome the limitations of current methods for inducing phase transitions in supercooled plastic crystal materials, achieving non-contact and non-destructive, magnetically controlled exothermic phase transitions. This will greatly expand the application scenarios of supercooled plastic crystal materials. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the technical principle of phase transformation of the supercooled plastic crystal composite material under the induction of a small magnetic field according to the present invention;

[0019] Figure 2 This is a non-contact full-field strain test diagram of the supercooled plastic crystal composite material prepared in Example 1;

[0020] Figure 3 This is a photograph of the phase transition of the supercooled plastic crystal composite material prepared in Example 1 under the induction of a small magnetic field;

[0021] Figure 4 This is a photograph of the phase transition of the supercooled plastic crystal composite material prepared in Example 2 under the induction of a small magnetic field. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] The purpose of this invention is to provide a method for preparing a magnetic field-controllable supercooled plastic crystal composite material and its heat storage application, the specific implementation of which is as follows.

[0024] Preparation of magnetically controllable supercooled plastic crystal composite materials

[0025] Example 1

[0026] S1: Select a plastic crystal material with a supercooled phase, such as erythritol C4H 10 O4, magnesium chloride hexahydrate MgCl2·6H2O, adipic acid HOOC(CH2)4COOH, galactitol C6H 14 One or more of O6, 2-amino-2-methyl-1,3-propanediol H2N(CH3)C(CH2OH)2(AMP); in this embodiment, 2-amino-2-methyl-1,3-propanediol H2N(CH3)C(CH2OH)2(AMP) is used as a plastic crystal material with a supercooled phase.

[0027] S2: The supercooled crystalline material and magnetic powder are mixed in a certain mass ratio, using magnetic NdFeB as the magnetic powder. The mass of the supercooled crystalline material is 0.5g, and the mass of the magnetic powder is 0.125g. After mixing, the mixture is mechanically ground for 10 minutes under N2 protection to ensure uniform mixing. After grinding, the particle size of the supercooled crystalline material is between 100-500μm, and the particle size of the NdFeB magnetic powder is between 5-10μm.

[0028] S3: The material obtained in S2 is heated. In this embodiment, the heating temperature is selected as 100°C. In particular, in the heating step, the heating temperature needs to exceed the phase transition temperature point (88°C) of the glass phase change material to put it in a high-temperature plastic crystal state. The heating time is 1 minute, and it is naturally cooled to room temperature to obtain its supercooled plastic crystal phase, that is, to obtain a magnetic field-controllable supercooled plastic crystal composite material.

[0029] Example 2

[0030] S1: Select a plastic crystal material with a supercooled phase, such as erythritol C4H 10 O4, magnesium chloride hexahydrate MgCl2·6H2O, adipic acid HOOC(CH2)4COOH, galactitol C6H 14 One or more of O6, 2-amino-2-methyl-1,3-propanediol H2N(CH3)C(CH2OH)2(AMP); in this embodiment, 2-amino-2-methyl-1,3-propanediol H2N(CH3)C(CH2OH)2(AMP) is used as a plastic crystal material with a supercooled phase.

[0031] S2: The supercooled crystalline material and magnetic powder are mixed in a certain mass ratio, with Fe3O4 powder as the magnetic powder. The mass of the supercooled crystalline material is 0.5g, and the mass of the magnetic powder is 0.125g. After mixing, the mixture is mechanically ground for 10 minutes under N2 protection to ensure uniform mixing. After grinding, the particle size of the supercooled crystalline material is between 100-500μm, and the diameter of the Fe3O4 powder is between 200-300nm.

[0032] S3: The material obtained in S2 is heated. In this embodiment, the heating temperature is selected as 100°C. In particular, in the heating step, the heating temperature needs to exceed the phase transition temperature of the glass phase change material to put it in a high-temperature plastic crystal state. The heating time is 1 minute, and it is naturally cooled to room temperature to obtain its supercooled plastic crystal phase, that is, to obtain a magnetic field-controllable supercooled plastic crystal composite material.

[0033] Application example (thermal storage application process)

[0034] The application of the supercooled plastic crystal composite material in this invention as a heat storage material includes a heat release process and a heat storage process. The heat release process is induced by a magnetic field, and then the heat-released composite material is heated and cooled to achieve the heat storage process. This cycle is repeated so that the supercooled plastic crystal composite material can be reused under non-contact stress.

[0035] The principle of induced phase transition during the exothermic process is explained below: A magnetic field generated by a magnet induces a phase transition in the supercooled plastic crystal composite materials prepared in Examples 1 and 2. The magnitude of the induced magnetic field is 40 mT, and the duration is 4 min. The principle of induced phase transition is described below. Figure 1 Since the supercooled crystalline composite material is prepared by mixing a supercooled crystalline material with magnetic powder, during the magnetic field-induced phase transition, the magnetic powder in the supercooled crystalline composite material moves under the influence of a non-contact magnetic field, generating minute stress on the supercooled crystalline material. This induces the supercooled crystalline material to begin phase transition crystallization, ultimately forming an ordered crystalline phase and releasing a large amount of heat. The first 2 minutes of the induced phase transition are a process of stress and strain generation; after 2 minutes, the supercooled crystalline material begins the phase transition and releases heat.

[0036] Figure 2 The image shows the non-contact full-field strain (DIC) test results of the supercooled crystalline composite material prepared in Example 1 after being subjected to a 40mT magnetic field for 2 minutes. The strain is caused by the magnetic powder being subjected to stress by the magnetic field. The specific test procedure is as follows: The supercooled crystalline composite material prepared in Example 1 was placed in a square glass groove. White and black paint were then sprayed sequentially onto the sample to form a speckle image. A CCD camera was used to track (or match) the position changes of all pixels in the speckle image on the surface of the supercooled crystalline composite material under the influence of a 40mT magnetic field (with the magnet placed at the edge of the supercooled crystalline composite material) for 2 minutes to obtain the displacement vector of each pixel. This yielded the full-field strain of the supercooled crystalline composite material surface. The test results showed that the supercooled crystalline composite material could locally generate a strain of 0.5%–2% within 2 minutes under the induction of the magnet. 。 The strain analysis in DIC first uses an algorithm to match the coordinates of discrete spots in the acquired images, and then calculates the displacement vector of each discrete point on the deformed sample. Calculating the full-field strain requires differentiating the displacement. First, the obtained displacement data needs to be denoised and smoothed. Then, the strain in the image is calculated using the following strain calculation formula, where u and v represent the calculated displacements in the x and y directions, respectively.

[0037]

[0038] The magnetic field continued to induce a phase transition for 2 minutes. At this point, the supercooled plastic crystal composite material began to undergo a phase transition after generating sufficient strain. Figure 3 and Figure 4Images of the supercooled plastic crystal composite materials prepared in the two examples (where the supercooled plastic crystals are transparent and the magnetic powder is black) at different induction times after the phase transition begins. The images show that after the phase transition is triggered, the phase transition exhibits spontaneous diffusion. Within 100 seconds, both supercooled plastic crystal composite materials undergo a complete phase transition under a 40 mT magnetic field, transforming into a white, ordered crystalline phase. Infrared thermodynamic analysis of the phase transition process of the supercooled plastic crystal composite material in Example 1 revealed that 0.625 g of the supercooled plastic crystal composite material in Example 1 experienced a temperature change as high as 70.6 °C within 100 seconds.

[0039] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A magnetic field-controllable supercooled plastic crystal composite material, characterized in that: This material is composed of a supercooled crystalline material and magnetic powder; the magnetic powder in this material moves under the influence of a non-contact magnetic field and generates stress on the supercooled crystalline material to induce a phase transition; the magnetic powder accounts for 20-80% of the total mass. The supercooled crystal material is 2-amino-2-methyl-1,3-propanediol H2N(CH3)C(CH2OH)2 (AMP). The magnetic powder is one or more of NdFeB, Fe3O4, Fe, SmCo, and NdNiCo.

2. A method for preparing a magnetically controllable supercooled plastic crystal composite material as described in claim 1, characterized in that: Take a plastic crystal material with a supercooled phase and mix it with magnetic powder, grind it, heat it to above the glass phase transition temperature, keep it at the temperature, and let it cool naturally to room temperature; The particle size of the ground magnetic powder is 0.1~10μm, and the particle size of the ground plastic crystal material with supercooled phase is between 100~500μm; The heating temperature is 10-50°C above the phase transition temperature of the glass phase, and the holding time is 1-3 minutes.

3. The application of the magnetic field-controllable supercooled plastic crystal composite material as described in claim 1 as a heat storage material, characterized in that: The application process includes the exothermic process and the heat storage process of the supercooled plastic crystal composite material.

4. The application according to claim 3, characterized in that: The exothermic process involves applying an external magnetic field to the supercooled plastic crystal composite material to induce a phase transition and release heat.

5. The application according to claim 3, characterized in that: The heat storage process involves heating the supercooled plastic crystal composite material after heat release to 10-50°C above the phase change point temperature, holding it at that temperature for 1-3 minutes, and then allowing it to cool naturally to room temperature.

6. The application according to claim 3, characterized in that, The magnetic field strength is 40~60mT, and the induction time is 1~3min.

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