High-thermal-conductivity and high-stability preparation method of composite phase change heat storage material suitable for high-temperature heat storage

Abstract

The invention relates to a preparation method of a NaNO3 / Ca (NO3) 2-based composite phase change heat storage material with high thermal conductivity and high stability. The NaNO3 / Ca (NO3) 2-based composite phase change heat storage material comprises the following components: NaNO3 / Ca (NO3) 2 serving as a heat storage / release material, a reinforced heat conduction agent, a nucleating agent, an active agent and a stable thickening agent. The preparation method comprises the following steps: preparing a heat storage / release material NaNO3 / Ca (NO3) 2 according to a molar ratio of 7: 3, heating to a molten state, adding a reinforced heat conduction agent, a nucleating agent, an active agent and a stable thickening agent, and uniformly stirring to obtain the required composite phase change heat storage material. The heat conduction performance and stability of the heat storage material can be greatly improved, especially the thickening agent can improve the dispersion uniformity of the reinforced heat conduction agent and the nucleating agent active agent, and storage of medium-temperature industrial waste heat and solar heat and the requirement of users for heat consumption are met.

Description

Technical Field

[0001] The present application relates to a technology in the field of phase change heat storage, specifically a preparation method for improving the stability of a phase change heat storage material of a nitrate type having high efficiency and low cost. Background Art

[0002] With the depletion of traditional fossil fuels and the emergence of pollutant emissions, the world is facing severe challenges in climate and even human survival. The development of renewable energy is a major need for implementing energy conservation and emission reduction strategies, but renewable energy is strongly affected by weather changes. Thermal storage technology can effectively solve the problem of wind and solar power abandonment caused by the discontinuity of renewable energy.

[0003] Phase change thermal storage materials store and release thermal energy in the form of latent heat. The phase change process occurs in a narrow temperature range, so the material responds to thermal energy. Phase change thermal storage materials can store solar heat and release it when needed, reducing carbon emissions. Since electricity production and consumption vary at different times, the load of the power system changes, and there are peak and valley differences. By converting electrical energy into thermal energy, heat is stored in the form of phase change heat. The demand for steam in industry is huge. If solar heat and valley electricity can be used to convert heat into heat to store it in phase change thermal storage materials, the huge operating costs of enterprises due to steam demand can be greatly reduced, which will generate huge economic and environmental benefits and have broad application prospects.

[0004] Among many phase change heat storage materials, nitrate and its composite salts have an exothermic temperature ranging from 100 degrees Celsius to 300-400 degrees Celsius, which is very suitable for heat storage and heat release to generate industrial steam, especially NaNO3 sodium nitrate and Ca(NO3)2 A mixed salt of calcium nitrate, which is inexpensive and has a phase transition temperature of around 210 to 220 degrees Celsius, is very suitable for generating industrial steam. Summary of the invention

[0005] This application aims at the problems of low thermal conductivity, phase separation and supercooling of NaNO3 / Ca(NO3)2 composite phase change materials, and proposes a modified material with improved heat release density and heat release rate and a preparation method thereof, which can improve the above-mentioned shortcomings.

[0006] This application is implemented through the following technical solutions: The present application relates to a composite phase change heat storage and release material with high heat storage and release density, high thermal conductivity and high stability, the components of which are: NaNO3 / Ca(NO3)2 composite phase change materials in different proportions as heat storage / release materials, an activator, a nucleating agent, an enhanced thermal conductivity agent and a stability regulator.

[0007] Preferably, the NaNO3 / Ca(NO3)2 composite phase change materials with different ratios have a molar ratio of NaNO3:Ca(NO3)2 of 7:3 after considering the purity.

[0008] Preferably, the enhanced thermal conductor is expanded graphite or metal particles, more preferably nano-metal particles.

[0009] Preferably, the nucleating agent is SiO2, more preferably 10-100 nm nano powder SiO2.

[0010] Preferably, the active agent is zeolite or covalent organic frameworks (COFs); more preferably, it is zeolite powder.

[0011] Preferably, the stabilizing thickener is bentonite.

[0012] Preferably, in terms of mass percentage, the exothermic material NaNO3 / Ca(NO3)2 composite phase change material is 92-96%, the enhanced thermal conductor is 1~2%, the nucleating agent is 1~2%, the active agent is 1~2% and the stabilizing thickener is 1~2%; further preferably, the NaNO3 / Ca(NO3)2 composite phase change material is 96%, the enhanced thermal conductor is 1%, the nucleating agent is 1%, the active agent is 1% and the stabilizing thickener is 1%.

[0013] The present application relates to a method for preparing the above-mentioned composite phase change heat storage and release material. First, the NaNO3 / Ca(NO3)2 composite phase change material is heated to a molten state at about 240°C. In the molten state, it is subjected to ultrasonic stirring treatment together with an enhanced thermal conductor, a nucleating agent, an activator, and a stabilizing thickener to obtain a high-efficiency composite phase change heat storage material.

[0014] The stirring treatment is achieved by stirring the rotor during heating with a magnetic stirrer; The high temperature melting treatment is preferably heated to 240° C. in a muffle furnace and heated at a constant temperature for 1 hour; The ultrasonic treatment is achieved by evacuating the vacuum to below 0.5 MPa and ultrasonically treating at an ultrasonic frequency of 100-500 Hz for 30-60 min; Among them, the phase change temperature of the above-mentioned phase change material prepared in the present application is 196-217°C, and the equivalent thermal conductivity can be increased from the original about 0.5 W / (m • K) to about 2 W / (m • K).

[0015] The present application relates to the application of the above-mentioned composite phase change heat storage and release material, which can be used in waste heat utilization, solar thermal storage, power peak regulation and other aspects.

[0016] Compared with existing nitrate phase change materials and technologies, this application has the following advantages: High heat storage and release rate. During heat storage and release, due to the effect of the thickener, the nano-metal powder can be evenly dispersed, and there will be no metal powder deposition. The heat transfer rate is greatly improved, which can fully ensure the uniformity of heat transfer during the heat storage and release process, improve the overall heat transfer rate, and store or release more heat in the same time.

[0017] During the heat storage and release process, the activator and the nucleating agent work together to improve the nucleation efficiency of the phase change heat storage material and reduce the supercooling, making the entire heat storage and release more stable and the heat transfer more stable.

[0018] The thickener makes the aforementioned thermal conductivity enhancer, active agent and nucleating agent dispersed more evenly, and the composite phase change heat storage material is also mixed more evenly, and there will be no problem of material separation after a certain number of cycles, which greatly improves the cycle life and stability of the composite phase change heat storage material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The composite phase change heat storage material prepared according to Example 1; Figure 2 This is a DSC thermal performance test diagram of the composite phase change heat storage material obtained according to Example 1; Figure 3 The stability test results of the composite phase change heat storage material prepared in Example 1; Implementation

[0020] Example 1

[0021] This embodiment includes the following steps: Step 1, weigh 25 g of Ca(NO3)2·4H2O (analytical grade, Sinopharm Chemical Reagent Co., Ltd.) and 21 g of NaNO3 (analytical grade, Sinopharm Chemical Reagent Co., Ltd.), stir and mix, then place in an electric heating furnace and heat at 50°C until Ca(NO3)2·4H2O melts. Continue to add NaNO3 and it will also dissolve to form a transparent liquid. After stirring evenly, increase the temperature to 300°C and heat for 5 hours to fully evaporate the water, then cool to room temperature to obtain a mixed salt sample, which is stored in a desiccator.

[0022] Step 2, add 0.48g of enhanced thermal conductive nano-metal powder (copper powder is used in this embodiment, but not limited to copper powder), 0.48g of nucleating agent SiO2, 0.48g of activating agent zeolite, and 0.48g of stabilizing thickener bentonite (natural sodium-based bentonite is used in this embodiment, but not limited to sodium-based bentonite) to the NaNO3 / Ca(NO3)2 composite phase change material obtained in step 1, and perform preliminary mechanical stirring and mixing together.

[0023] Step 3, heating the insufficiently mixed material obtained in step 2 to 260° C. (not less than 230° C.) in a muffle furnace and heating at a constant temperature for 1 hour.

[0024] Step 4, subjecting the molten material obtained in step 3 to ultrasonic treatment in a molten state, ultrasonically treating the material at an ultrasonic frequency of 100-500 Hz for 30-60 minutes to achieve ultrasonic stirring, and cooling the material to room temperature after ultrasonic stirring treatment to obtain a high-efficiency composite phase change heat storage material with a NaNO3 / Ca(NO3)2 ratio of 96%.

[0025] like Figure 1 As shown, the composite phase change heat storage material prepared in the above steps has a uniform macroscopic physical state and is a stable phase change heat storage material.

[0026] Example 2

[0027] This embodiment includes the following steps: Step 1, weigh 25 g of Ca(NO3)2·4H2O (analytical grade, Sinopharm Chemical Reagent Co., Ltd.) and 21 g of NaNO3 (analytical grade, Sinopharm Chemical Reagent Co., Ltd.), stir and mix, then place in an electric heating furnace and heat at 50°C until Ca(NO3)2·4H2O melts. Continue to add NaNO3 and it will also dissolve to form a transparent liquid. After stirring evenly, increase the temperature to 300°C and heat for 5 hours to fully evaporate the water, then cool to room temperature to obtain a mixed salt sample, which is stored in a desiccator.

[0028] Step 2, add 1g of enhanced thermal conductive nano-metal powder (copper powder is used in this embodiment, but not limited to copper powder), 1g of nucleating agent SiO2, 1g of activating agent zeolite, and 1g of stabilizing thickener bentonite (natural sodium-based bentonite is used in this embodiment, but not limited to sodium-based bentonite) to the NaNO3 / Ca(NO3)2 composite phase change material obtained in step 1, and perform preliminary mechanical stirring and mixing together.

[0029] Step 3, heating the insufficiently mixed material obtained in step 2 to 260° C. (not less than 230° C.) in a muffle furnace and heating at a constant temperature for 1 hour.

[0030] Step 4, subjecting the molten material obtained in step 3 to ultrasonic treatment in a molten state, ultrasonically treating the material at an ultrasonic frequency of 100-500 Hz for 30-60 minutes to achieve ultrasonic stirring, and cooling the material to room temperature after ultrasonic stirring treatment to obtain a high-efficiency composite phase change heat storage material with a NaNO3 / Ca(NO3)2 ratio of 92%.

[0031] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention, such as fine-tuning various added regulators, etc. The scope of protection of the present invention shall be based on the claims and shall not be limited to the above-mentioned specific implementation, and each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A composite phase change heat storage material based on NaNO3 / Ca(NO3)2, having good thermal conductivity and stability, characterized in that: The components are: NaNO3 / Ca(NO3)2 as heat storage / release material, enhanced thermal conductivity agent, nucleating agent, active agent, and stabilizing thickener.

2. The composite phase-change heat storage and release material according to claim 1 is characterized in that: The heat storage / release material NaNO3 / Ca(NO3)2 is prepared in a molar ratio of 7:

3.

3. The composite phase-change heat storage and release material according to claim 1 is characterized in that: The enhanced thermal conductor is one or more nano metal powders such as iron, copper, silver, gold, nickel, etc.

4. The composite phase-change heat storage and release material according to claim 1 is characterized in that: The nucleating agent is SiO2, and more preferably 10-100nm nano powder SiO2.

5. The composite phase-change heat storage and release material according to claim 1 is characterized in that: The active agent is zeolite powder.

6. The composite phase-change heat storage and release material according to claim 1 is characterized in that: The thickener is bentonite, for example, sodium bentonite, calcium bentonite, hydrogen bentonite, etc.; more preferably, natural sodium bentonite and calcium bentonite, but not limited to these two types of bentonite.

7. The composite phase-change heat storage and release material according to claim 1 is characterized in that: The NaNO3 / Ca(NO3)2 prepared in a molar ratio of 7:3 has a mass ratio of 92~96%, a reinforced thermal conductor 1-2%, a nucleating agent 1~2%, an active agent 1~2% and a stabilizing thickener 1~2%; further preferably, the NaNO3 / Ca(NO3)2 has a mass ratio of 96%, a reinforced thermal conductor 1%, a nucleating agent 1%, an active agent 1% and a stabilizing thickener 1%.

8. A method for preparing the composite phase-change heat storage and release material according to any of the above claims, characterized in that: NaNO3 / Ca(NO3)2 was prepared in a high temperature molten state at a molar ratio of 7:

3.

9. The method according to claim 8, wherein the mixture is stirred and mixed with the thermal conductivity enhancing agent, the nucleating agent, the activating agent and the stabilizing thickener in a molten state, and ultrasonic stirring can be used, but is not limited to ultrasonic stirring.

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