A micron-sized graphite microsphere-based composite phase change material and its preparation method

Abstract

This invention discloses a micron-sized graphite microsphere-based composite phase change material and its preparation method. This invention relates to the field of phase change material technology. The preparation method includes the following steps: S1, dispersing nano-graphite and nano-cellulose in deionized water and then ball-milling to obtain a nano-graphite-cellulose mixed solution; S2, using an electronic atomizer to spray the nano-graphite-cellulose mixed solution into a container filled with liquid nitrogen, then sieving the microspheres in the container and freeze-drying the microspheres to obtain micron-sized graphite microspheres; S3, immersing the micron-sized graphite microspheres in molten phase change material for a period of time and then hot-filtering to obtain the micron-sized graphite microsphere-based composite phase change material. In this invention, by ball-milling nano-graphite and nano-cellulose and then spraying the prepared microspheres using an electronic atomizer, a micro-aerogel porous structure is formed, which better absorbs phase change material, significantly improving heat storage capacity and thermal conductivity, and maintaining a high phase change enthalpy value even after multiple cycles.

Description

Technical Field

[0001] This invention relates to the field of phase change materials technology, and in particular to a micron-sized graphite microsphere-based composite phase change material and its preparation method. Background Technology

[0002] Latent heat storage technology, using phase change materials (PCMs) as thermal storage components, is widely used in fields such as solar energy storage, industrial waste heat recovery, and building energy conservation. Leakage is a major obstacle to the application of PCMs; encapsulating porous materials to prepare shaped composite PCMs is an important method to solve this problem.

[0003] The material and size of porous materials themselves greatly affect the performance of composite phase change materials. In the existing technology, microsphere matrix encapsulation is often used to prepare shaped composite phase change materials. Common methods for producing microspheres include emulsion solvent evaporation, phase separation, spray drying, and membrane emulsification. Microspheres prepared by spray drying are generally obtained by spraying a mixed solution into an inert gas or high-temperature gas to obtain a powder structure, which cannot form porous aerogel microspheres, resulting in problems such as low loading rate and difficulty in improving the original performance. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by proposing a micron-sized graphite microsphere-based composite phase change material and its preparation method.

[0005] The present invention discloses a method for preparing a micron-sized graphite microsphere-based composite phase change material, comprising the following steps:

[0006] S1. Nanographite and nanocellulose are dispersed in deionized water and then ball-milled to obtain a nanographite-cellulose mixed solution.

[0007] S2. Use an electronic atomizer to spray the nano-graphite cellulose mixture into a container filled with liquid nitrogen, then sieve the microspheres in the container and freeze-dry the microspheres to obtain micron-sized graphite microspheres.

[0008] S3. After immersing micron-sized graphite microspheres in molten phase change material for a period of time, the micron-sized graphite microsphere-based composite phase change material is obtained by heat filtration.

[0009] Furthermore, the mass ratio of nanographite to nanocellulose is 1-10:1.

[0010] Furthermore, the mass-to-volume ratio of nanographite to deionized water is 1-10:100g / ml.

[0011] Furthermore, the ball milling speed is 400-600 r / min, and the time is 2-4 h.

[0012] Furthermore, the phase change material is paraffin.

[0013] Further, the specific operation of step S3 is as follows: first, put the micron-sized graphite microspheres and phase change material into a container and then evacuate in a vacuum drying oven, and then react at 80°C for 2 hours to obtain micron-sized graphite microsphere-based composite phase change material, and then perform hot filtration in an oven at 80°C.

[0014] Furthermore, freeze-dry for 72 hours.

[0015] A micron-sized graphite microsphere-based composite phase change material prepared using the above-described preparation method.

[0016] Furthermore, the loading rate of the phase change material in the micron-sized graphite microsphere-based composite phase change material is 65%-70%.

[0017] This invention involves ball milling and emulsifying a solution of nano-graphite and nano-cellulose to form an emulsion in the mixed solution. The sprayed droplets can then be cooled in liquid nitrogen to form microspheres. The nozzle of the electronic atomizer is at the micrometer level, ensuring that the sprayed droplets are also at the micrometer level, and the final microspheres are also at the micrometer level.

[0018] In preparing the composite phase change material, the present invention first evacuates the material to remove the air from the microspheres, so that the high-temperature molten paraffin liquid can flow smoothly into the pores of the microspheres. The microporous structure of the microspheres can bind the PW through capillary force to prevent the PW from leaking due to the molten phase change.

[0019] In this invention, microspheres are prepared by mixing and ball milling nano-graphite and nano-cellulose and then spraying them out using an electronic atomizer. Due to the formation of a micro-aerogel porous structure, the microspheres are better able to absorb phase change materials, thereby improving the loading rate. Moreover, because graphite is also used as the raw material for the microspheres, the heat storage capacity and thermal conductivity of the micron-sized graphite microsphere-based composite phase change material are greatly improved, and it still has a high phase change enthalpy value after multiple cycles. Attached Figure Description

[0020] Figure 1 A photograph of the micron-sized graphite microspheres prepared according to this invention.

[0021] Figure 2 A photograph of the micron-sized graphite microsphere-based composite phase change material prepared according to this invention.

[0022] Figure 3 These are the DSC diagrams for Examples 1-5.

[0023] Figure 4a -e is the BET diagram for Examples 1-5.

[0024] Figure 5These are scanning electron microscope (SEM) images of Examples 1-5; where (a)-(b) are SEM images of Example 1, (c)-(d) are SEM images of Example 2, (e)-(f) are SEM images of Example 3, (g)-(h) are SEM images of Example 4, and (i)-(j) are SEM images of Example 5. Detailed Implementation

[0025] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0026] This invention is achieved using the following technical solution, including the following process steps:

[0027] (1) Preparation of micron-sized graphite microsphere precursor mixed solution

[0028] Add 30 g of 2% solids nanocellulose aqueous solution to a 100 ml beaker, then add 30 mL of deionized water to the beaker and mix. Add 0.6 g, 1.8 g, 3 g, 4.2 g and 5.4 g of nanographite to the mixture. Stir with a magnetic stirrer for 30 min, then place the solution in a planetary ball mill and ball mill for 3 h at a speed of 500 r / min. Pour the resulting mixed solution into a 100 ml beaker to obtain a nanographite cellulose mixed solution.

[0029] (2) Preparation of micron-sized graphite microspheres

[0030] Add 60ml of the obtained nano-graphite cellulose mixed solution to the purchased electronic atomizer for preparation. Pour 2L of liquid nitrogen into a Dewar flask for later use. Use the electronic atomizer to spray the nano-graphite cellulose mixed solution into the Dewar flask containing liquid nitrogen. After spraying 10ml, stop the electronic atomizer, wait five minutes, and then spray again. After all the solution has been sprayed, wait another five minutes. Pour the excess liquid nitrogen from the Dewar flask back into the liquid nitrogen storage bottle. Place a sieve between the Dewar flask and the liquid nitrogen storage bottle, pour the prepared microspheres onto the sieve, transfer them to a beaker, seal with filter paper, and dry in a freeze dryer for 72 hours to obtain micron-sized graphite microspheres. Figure 1 As shown.

[0031] (3) Preparation of microsphere-based composite phase change materials

[0032] Weigh 1g of micron-sized graphite microsphere powder and 3g of paraffin wax into a beaker; place the beaker in a vacuum drying oven, evacuate the vacuum, and react at 80℃ for 2 hours to obtain a micron-sized graphite microsphere-based paraffin wax composite phase change material. Then, perform hot filtration in an oven at 80℃ to finally obtain the micron-sized graphite microsphere-based composite phase change material. Figure 2 As shown.

[0033] Example 1

[0034] Weigh 0.6g of nano-graphite powder, 30g of 2wt.% cellulose solution, and 30ml of deionized water into a 100ml beaker. Stir the solution in the beaker on a magnetic stirrer for half an hour. Then, place the mixture in the beaker into a ball mill and mill for 3 hours. Remove the mixture from the ball mill jar and use an electronic atomizer to spray 60ml of the solution into liquid nitrogen in a Dewar flask in six 10ml portions, with each portion spaced five minutes apart. Place the frozen microspheres into a vacuum freeze dryer and dry for 72 hours to obtain micron-sized graphite microspheres.

[0035] After hot filtration, micron-sized graphite microspheres and excess paraffin were combined to obtain a composite phase change material with a melting enthalpy of 117.3 J / g, a solidification enthalpy of 113.9 J / g, a thermal conductivity of 0.6235 W / (m·K), a specific surface area of ​​16.5332 m² / g, a pore volume of 0.318644 cm³ / g, and an average pore size of 28.8965 nm.

[0036] Example 2

[0037] Weigh 1.8g of nano-graphite powder, 30g of 2wt.% cellulose solution and 30ml of deionized water, and the rest is the same as in Example 1.

[0038] The obtained composite phase change material has a melting enthalpy of 137.2 J / g, a solidification enthalpy of 132.5 J / g, a thermal conductivity of 0.6772 W / (m·K), and according to BET testing, a specific surface area of ​​69.2373 m² / g, a pore volume of 0.668389 cm³ / g, and an average pore size of 35.3571 nm.

[0039] Example 3

[0040] Weigh 3g of nano-graphite powder, 30g of 2wt.% cellulose solution and 30ml of deionized water into a 100ml beaker. The rest is the same as in Example 1.

[0041] The obtained composite phase change material has a melting enthalpy of 121.7 J / g, a solidification enthalpy of 116.2 J / g, a thermal conductivity of 0.7325 W / (m·K), and according to BET testing, a specific surface area of ​​62.2777 m² / g, a pore volume of 0.533866 cm³ / g, and an average pore size of 31.8875 nm.

[0042] Example 4

[0043] Weigh 4.2g of nano-graphite powder, 30g of 2wt.% cellulose solution and 30ml of deionized water into a 100ml beaker, and follow the same procedure as in Example 1.

[0044] The obtained composite phase change material has a melting enthalpy of 127.9 J / g, a solidification enthalpy of 124.3 J / g, a thermal conductivity of 0.8023 W / (m·K), and according to BET testing, a specific surface area of ​​58.9647 m² / g, a pore volume of 0.507495 cm³ / g, and an average pore size of 31.9188 nm.

[0045] Example 5

[0046] Weigh 5.4g of nano-graphite powder, 30g of 2wt.% cellulose solution and 30ml of deionized water into a 100ml beaker, and follow the same procedure as in Example 1.

[0047] The obtained composite phase change material has a melting enthalpy of 102.3 J / g, a solidification enthalpy of 91.2 J / g, a thermal conductivity of 0.6323 W / (m·k), and according to BET testing, a specific surface area of ​​8.8841 m² / g, a pore volume of 0.149452 cm³ / g, and an average pore size of 25.7325 nm.

[0048] Comparative Example 1

[0049] Direct use of halloysite composite paraffin:

[0050] Weigh 3g of halloysite powder and combine it with paraffin wax, then heat filter it.

[0051] The obtained composite phase change material has a melting enthalpy of 72.2 J / g, a solidification enthalpy of -73.09 J / g, a thermal conductivity of 0.25 W / (m·K), and a loading rate of only 33.6%.

[0052] Comparative Example 2

[0053] The preparation of composite phase change materials involves replacing nano-graphite in the raw materials with halloysite.

[0054] Weigh 3g halloysite powder, 30g 2wt.% cellulose solution and 30ml deionized water into a 100ml beaker, and do the same as in Example 1.

[0055] The resulting composite phase change material has a melting enthalpy of -147.6 J / g, a solidification enthalpy of 150.8 J / g, an increased loading rate from 33.6% to 68%, and a thermal conductivity of 0.3266 W / (m·K).

[0056] Comparative Example 3

[0057] Directly using nano-graphite to composite paraffin:

[0058] Weigh 3g of nano-graphite and mix it with excess paraffin, then heat filter the mixture.

[0059] The obtained composite phase change material has a melting enthalpy of -77.53 J / g, a solidification enthalpy of 82.08 J / g, a thermal conductivity of 0.5022 W / (m·K), and a loading rate of only 38%.

[0060] Table 1. Enthalpy Comparison Table

[0061]

[0062] From the data in Table 1 and Figure 3 It can be seen that after microsphere preparation, the loading rate and thermal conductivity of the microsphere-based composite phase change material are significantly improved compared with the original composite phase change material. The heat storage performance of Example 2 is also the best among the five examples. As can be seen from Figure 4 and BET test data, the specific surface area, pore volume and average pore size of Example 2 are the largest among the five examples. This can explain the highest adsorption rate of phase change material in Example 2. As can be seen from the above data, as the ratio of nano-graphite to cellulose increases, the thermal performance of the composite phase change material first increases and then decreases.

[0063] For any points not covered above, existing technologies shall apply.

[0064] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a micron-sized graphite microsphere-based composite phase change material, characterized in that: Includes the following steps: S1. Nanographite and nanocellulose are dispersed in deionized water and then ball-milled to obtain a nanographite-cellulose mixed solution. S2. Use an electronic atomizer to spray the nano-graphite cellulose mixture into a container filled with liquid nitrogen, then sieve the microspheres in the container and freeze-dry the microspheres to obtain micron-sized graphite microspheres. S3. After immersing micron-sized graphite microspheres in molten phase change material for a period of time, the micron-sized graphite microsphere-based composite phase change material is obtained by hot filtration. The mass ratio of nanographite to nanocellulose is 1-10:1; The phase change material is paraffin.

2. The preparation method according to claim 1, characterized in that: The mass-to-volume ratio of nano-graphite to deionized water is 1-10:100g / ml.

3. The preparation method according to claim 1, characterized in that: The ball milling speed is 400-600 r / min, and the time is 2-4h.

4. The preparation method according to claim 1, characterized in that: The specific operation of step S3 is as follows: first, put the micron-sized graphite microspheres and phase change material into a container and then evacuate in a vacuum drying oven. Then, react at 80°C for 2 hours to obtain the micron-sized graphite microsphere-based composite phase change material, and then perform hot filtration in an oven at 80°C.

5. The preparation method according to claim 1, characterized in that: Freeze-dry for 72 hours.

6. A micron-sized graphite microsphere-based composite phase change material prepared by the preparation method according to any one of claims 1-5.

7. The micron-sized graphite microsphere-based composite phase change material as described in claim 6, characterized in that: The loading rate of phase change material in the micron-sized graphite microsphere-based composite phase change material is 65%-70%.

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