A composite phase change heat storage large capsule and its preparation method

Abstract

The present invention belongs to the technical field related to phase change heat storage materials, and discloses a composite phase change heat storage large capsule and a preparation method thereof. The capsule includes a spherical core layer and a shell layer wrapped outside the core layer, and a cavity is formed between the core layer and the shell layer; the material of the core layer is an expanded vermiculite-based composite phase change heat storage material, and the expanded vermiculite-based composite phase change heat storage material includes the following component raw materials in parts by mass: 60-75 parts of KCl-Na2SO4 eutectic salt, 25-40 parts of expanded vermiculite; the material of the shell layer is modified alumina ceramic, and the modified alumina ceramic includes the following component raw materials in parts by mass: 80-90 parts of alumina mixed powder, 10-20 parts of acrylic resin and 0.1-2 parts of fumed silica. The phase change heat storage large capsule provided by the present invention can effectively solve the leakage problem of the phase change material during the high-temperature phase change process, thereby reducing the corrosive effect on the metal container and prolonging the service life of the metal container.

Description

Technical Field

[0001] The present invention belongs to the technical field related to phase change heat storage materials, and more specifically, relates to a composite phase change heat storage large capsule and a preparation method thereof. Background Art

[0002] At present, the total amount of industrial waste heat is huge, but the utilization efficiency of waste heat resources is relatively low, which is one of the main reasons for the high unit energy consumption of industrial products. The heat storage technology stores various energies in heat storage materials first and releases the stored energy when needed, which is an important means to solve the mismatch between energy supply and demand and improve energy utilization efficiency. The phase change heat storage technology utilizes the change of enthalpy during the phase change process of materials to store and release heat. This technology has the advantages of large heat storage density, stable temperature during the charging / discharging process, easy operation and control, etc., and is one of the heat storage technologies with great application potential at present.

[0003] Compared with other phase change materials, inorganic salt-based phase change materials have a relatively high heat storage temperature range and lower prices, and have great advantages in the field of medium and high temperature heat storage. At present, the inorganic salt phase change materials with a phase change temperature near 500°C are generally NaCl-CaCl2 eutectic salt and Li2CO3-Na2CO3 eutectic salt. The price of NaCl-CaCl2 eutectic salt is very low, but according to the research of Tian et al., its phase change latent heat is only 178.4 J / g, and CaCl2 has strong hygroscopicity, which is difficult to meet the actual application; Li2CO3-Na2CO3 eutectic salt has a high phase change latent heat (>300 J / g), but as one of the raw materials of lithium batteries, the price of Li2CO3 has been high, and the cost required in actual application is huge. Therefore, it is necessary to provide an inorganic salt phase change material with a phase change temperature near 500°C, which has high phase change latent heat and heat storage performance while the raw materials are cheap and easily available.

[0004] In addition, the vast majority of inorganic salt-based phase change materials have strong corrosivity, are prone to leakage during the phase change process and cause serious corrosion to the encapsulation materials, resulting in their difficulty in large-scale application. Porous materials usually have a high porosity and a large specific surface area, which can provide a large number of attachment sites for inorganic salts, and the unique network structure in porous materials can effectively prevent the leakage of inorganic salts by virtue of its capillary force and surface tension. However, during the use of the composite phase change material obtained by adsorbing inorganic salts with porous materials, the inorganic salts on its surface will still cause serious corrosion to the metal containers in contact with it at high temperatures, greatly reducing the service life of the metal containers. Therefore, reasonable strategies are also needed to reduce or avoid the corrosion of the phase change material to the metal containers. Summary of the Invention

[0005] In view of the above defects or improvement requirements of the prior art, the present invention provides a composite phase change heat storage large capsule and a preparation method thereof. The method combines KCl-Na2SO4 eutectic salt and expanded vermiculite in a certain proportion to form a spherical core layer, and then wraps a layer of modified alumina micelle on the spherical core layer. After heat treatment, a high-temperature composite phase change heat storage large capsule is obtained. The phase change heat storage large capsule provided by the present invention can effectively solve the leakage problem of phase change materials during high-temperature phase change, thereby reducing the corrosive effect on metal containers and extending the service life of metal containers. At the same time, it also has a high phase change latent heat and excellent thermal cycle performance.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a composite phase change heat storage large capsule, which includes a spherical core layer and a shell layer wrapped outside the core layer, and a cavity is formed between the core layer and the shell layer; the core layer is made of an expanded vermiculite-based composite phase change heat storage material, and the expanded vermiculite-based composite phase change heat storage material includes the following component raw materials in parts by mass: 60-75 parts of KCl-Na2SO4 eutectic salt, 25-40 parts of expanded vermiculite; the shell layer is made of modified alumina ceramics, and the modified alumina ceramics include the following component raw materials in parts by mass: 80-90 parts of alumina mixed powder, 10-20 parts of acrylic resin, and 0.1-2 parts of fumed silica.

[0007] Further, the KCl-Na2SO4 eutectic salt is prepared by melting and blending potassium chloride and sodium sulfate, and the mass ratio of potassium chloride to sodium sulfate is 1:(1.22-1.25).

[0008] Further, the alumina mixed powder includes the following components in mass percentage: 20.36 wt.% of 2μm alumina, 22.92 wt.% of 5μm alumina, and 56.72 wt.% of 40μm alumina.

[0009] Further, the mesh number of the expanded vermiculite is 300-800 mesh; the specific surface area of the fumed silica is 200-400m 2 / g.

[0010] Further, the total amount of KCl-Na2SO4 eutectic salt and expanded vermiculite is 100 parts; the total amount of alumina mixed powder and acrylic resin is 100 parts.

[0011] Further, the phase change temperature of the core layer is greater than 522°C.

[0012] According to another aspect of the present invention, there is provided a preparation method of the composite phase change heat storage large capsule as described above, and the preparation method mainly includes the following steps:

[0013] a), Mix the eutectic salt of KCl-Na2SO4 and expanded vermiculite evenly and then sinter them to obtain sintered powder;

[0014] b), Press the sintered powder into a green body by an isostatic press, and then sinter the green body to obtain a spherical core layer;

[0015] c), Stir and mix the alumina mixed powder and acrylic resin. After mixing evenly, add fumed silica, continue stirring until a fluid colloid is formed, then evacuate the air. Repeat the stirring and evacuation steps 4 to 6 times in sequence to obtain a modified alumina micelle;

[0016] d), Wrap the modified alumina micelle on the spherical core layer prepared in step b), and obtain a composite phase change heat storage macro-capsule after sintering.

[0017] Further, the mixing in step a) is ball milling. The rotation speed of the ball mill is 200 - 300 r / min, and the ball milling time is 30 - 120 min; during sintering, first heat up to 120 - 150 °C and keep warm for 1 - 2 h, then heat up to 550 - 600 °C and keep warm for 2 - 3 h.

[0018] Further, in step b), the pressure for pressing into shape is 20 - 30 Mpa, and the pressure holding time for pressing into shape is 3 - 5 min.

[0019] Further, in step c), the stirring and mixing is carried out by a vacuum stirrer or a glass rod. The stirring time for stirring and mixing is 5 - 10 min; in step d), first heat up to 300 - 400 °C and keep warm for 1 - 2 h, then heat up to 700 °C - 720 °C and keep warm for 3 - 4 h.

[0020] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the composite phase change heat storage macro-capsule provided by the present invention and its preparation method mainly have the following beneficial effects:

[0021] 1. In the present invention, the eutectic salt of KCl-Na2SO4 and expanded vermiculite are combined in a certain proportion and made into a spherical core layer, and then a layer of modified alumina micelle is wrapped on the spherical core layer. After heat treatment, a high-temperature composite phase change heat storage macro-capsule is obtained. Among them, a cavity is formed between the core layer and the shell layer. The cavity can adapt to the expansion of the phase change material in the core layer during the phase change process, avoiding the problem of the rupture of the macro-capsule.

[0022] 2. Using spherical alumina with different particle sizes to form an alumina mixed powder is to fill the voids generated when the large-particle-size alumina microparticles come into contact with each other with small-particle-size alumina, making the alumina stack more densely. This not only reduces the voids and thus reduces the air thermal resistance, but also makes the sintered shell layer more dense.

[0023] 3. Crosslink the alumina mixed powder with acrylic resin to form a micelle with excellent fluidity and plasticity, which is as convenient to wrap the core layer as dough. After high-temperature sintering, the acrylic resin is decomposed and no organic matter remains.

[0024] 4. Modify the alumina micelle with fumed silica. The high specific surface area of fumed silica gives it strong adsorption force and surface energy. After sintering, a smooth and firm shell can be formed, and Si-O-Si bond connections are also formed between the particles, binding the alumina more densely, significantly improving the encapsulation performance of the alumina shell layer. At the same time, use KCl-Na2SO4 eutectic salt as the phase change material, which is not only cheap and easily available, but also has a high phase change latent heat near 500°C. By compounding with expanded vermiculite and using the porous structure of expanded vermiculite to adsorb KCl-Na2SO4 eutectic salt, it not only provides a high phase change latent heat but also has excellent thermal cycling performance.

[0025] 5. The phase change temperature of the KCl-Na2SO4 eutectic salt provided by the present invention is 522.8°C, and the phase change latent heat is 220.6 J / g; the phase change temperature of the internal core layer of the high-temperature composite phase change heat storage large capsule provided by the present invention is above 522°C, and the phase change latent heat is above 150 J / g, having a relatively high phase change temperature and phase change latent heat; after 100 heating-cooling cycles, the phase change temperature still remains above 522°C (almost unchanged), and the phase change latent heat is above 150 J / g (the retention rate reaches 97.9%, and the loss rate is 2.1%), having excellent thermal cycling performance; moreover, after 100 heating-cooling cycles, the appearance of the high-temperature composite phase change heat storage large capsule remains intact, without cracking and salt leakage, showing excellent structural stability. At the same time, after corroding 316 stainless steel at 650°C for 100 h, compared with the core layer, it can significantly reduce the corrosive effect on the metal container and extend its service life, showing excellent encapsulation performance. Brief Description of the Drawings

[0026] Figure 1 (a) in it is the structural diagram of the product obtained in Example 1; (b) is the structural diagram after cutting the product obtained in Example 1;

[0027] Figure 2 is the SEM diagram of the core layer of the composite phase change heat storage large capsule provided in Example 1 of the present invention;

[0028] Figure 3 Schematic diagram of the product obtained in Example 1 after heating-cooling cycles;

[0029] Figure 4 is the DSC curve diagram of the internal core layer and KCl-Na2SO4 eutectic salt of the product obtained in Example 1 before and after heating-cooling cycles;

[0030] Figure 5 In (a), it is a schematic diagram of the product obtained in Example 1 after corroding 316 stainless steel for 100 h; in (b), it is a schematic diagram of the expanded vermiculite-based high-temperature phase change heat storage material after corroding 316 stainless steel for 100 h.

[0031] Figure 6 Schematic diagram of the product obtained in Comparative Example 1. Specific implementation manners

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] The present invention provides a composite phase change heat storage large capsule, which includes a spherical core layer and a shell layer wrapped outside the core layer, and a cavity is formed between the core layer and the shell layer; the material of the core layer is an expanded vermiculite-based high-temperature composite phase change heat storage material, and the expanded vermiculite-based high-temperature composite phase change heat storage material includes the following component raw materials in parts by mass: 60-75 parts of KCl-Na2SO4 eutectic salt, 25-40 parts of expanded vermiculite; the material of the shell layer is modified alumina ceramic, and the modified alumina ceramic includes the following component raw materials in parts by mass: 80-90 parts of alumina mixed powder, 10-20 parts of acrylic resin and 0.1-2 parts of fumed silica.

[0034] The KCl-Na2SO4 eutectic salt is prepared by melting and blending potassium chloride and sodium sulfate. The mass ratio of potassium chloride to sodium sulfate is 1:(1.22-1.25), more preferably 1:1.222. The eutectic salt obtained by controlling the above ratio can make its phase change latent heat reach the maximum. If the above mass ratio is too low or too high, the phase change latent heat of the phase change material will be reduced. The melting temperature is preferably 550-600 °C, specifically 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C. After melting and blending, it is cooled to room temperature to obtain the KCl-Na2SO4 eutectic salt.

[0035] The mass fraction of the KCl-Na2SO4 eutectic salt is 60-75 parts, specifically 60 parts, 61 parts, 62 parts, 63 parts, 64 parts, 65 parts, 66 parts, 67 parts, 68 parts, 69 parts, 70 parts, 71 parts, 72 parts, 73 parts, 74 parts, 75 parts.

[0036] The mesh number of the expanded vermiculite is 300 - 800 mesh, more preferably 400 mesh. The dosage of the expanded vermiculite in the core layer is 25 - 40 parts, specifically 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts.

[0037] The contents of the components in the alumina mixed powder are as follows: 2μm alumina 20.36wt.%, 5μm alumina 22.92wt.%, 40μm alumina 56.72wt.%. The alumina is preferably spherical α-phase alumina. The dosage of the alumina mixed powder in the shell layer is 80 - 90 parts, specifically 80 parts, 81 parts, 82 parts, 83 parts, 84 parts, 85 parts, 86 parts, 87 parts, 88 parts, 89 parts, 90 parts.

[0038] The dosage of the acrylic resin in the shell layer is 10 - 20 parts, specifically 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts. The fumed silica can be either hydrophilic or hydrophobic. The specific surface area of the fumed silica is preferably 200 - 400m 2 / g, more preferably 400m 2 / g. The dosage of the fumed silica in the shell layer is 0.1 - 2 parts, specifically 0.1 part, 1 part, 1.5 parts, 2 parts.

[0039] In this embodiment, the total dosage of the KCl-Na2SO4 eutectic salt and the expanded vermiculite is preferably 100 parts; the total dosage of the alumina mixed powder and the acrylic resin is preferably 100 parts.

[0040] The present invention also provides a preparation method of the composite phase change heat storage macro-capsule as described above. The preparation method mainly includes the following steps:

[0041] a) Mix the KCl-Na2SO4 eutectic salt with the expanded vermiculite, sinter after mixing evenly, and grind into powder after sintering to obtain a sintered powder.

[0042] Before use, the KCl-Na2SO4 eutectic salt and the expanded vermiculite are preferably dried in advance. The drying temperature is preferably 100°C - 150°C, more preferably 120°C; the drying time is preferably ≥24h. After drying, store in sealed and dry condition for standby.

[0043] The mixing is preferably ball milling mixing, which can be specifically carried out in a planetary ball mill. In this embodiment, the rotation speed of the ball mill is preferably 200 - 300 r / min, and specifically can be 200 r / min, 210 r / min, 220 r / min, 230 r / min, 240 r / min, 250 r / min, 260 r / min, 270 r / min, 280 r / min, 290 r / min, 300 r / min. The ball milling time is preferably 30 - 120 min, and specifically can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min. After ball milling, a powder sintered product is obtained.

[0044] The sintering regime is preferably: first heat up to 120 - 150 °C and hold for 1 - 2 h, then heat up to 550 - 600 °C and hold for 2 - 3 h. Among them, the heating rate of the first heating is preferably 5 - 8 °C / min, and specifically can be 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min; the target temperature of the first heating is specifically 120 °C, 130 °C, 140 °C, 150 °C; the holding time after the first heating is specifically 1 h, 1.5 h, 2 h. The heating rate of the second heating is preferably 3 - 5 °C / min, and specifically can be 3 °C / min, 4 °C / min, 5 °C / min; the target temperature of the second heating is specifically 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C; the holding time after the second heating is specifically 2 h, 2.5 h, 3 h. After sintering, a sintered product is obtained. In this embodiment, after sintering, it is preferably followed by cooling and grinding to obtain a powdered sintered product, and then subsequent processes are carried out.

[0045] b) Press the sintered product powder into a green body using an isostatic press, and then sinter the green body to obtain a spherical core layer.

[0046] The pressing and forming is preferably carried out in an isostatic press. Through pressing and forming, a spherical green body is obtained. The pressure of the pressing and forming is preferably 20 - 30 Mpa, and specifically can be 20 Mpa, 21 Mpa, 22 Mpa, 23 Mpa, 24 Mpa, 25 Mpa, 26 Mpa, 27 Mpa, 28 Mpa, 29 Mpa, 30 Mpa. The pressure holding time of the pressing and forming is preferably 3 - 5 min, specifically 3 min, 4 min, 5 min.

[0047] After obtaining the green body by the above pressing and forming, sinter the green body. The sintering regime is the same as that in step a). After sintering, a spherical core layer is obtained.

[0048] c) stirring and mixing the alumina mixed powder and acrylic resin, adding fumed silica after mixing evenly, continuing stirring until a fluid colloidal state is formed, and then evacuating the mixture, repeating the stirring and evacuating steps 4 to 6 times in sequence to obtain modified alumina micelles.

[0049] The aluminum oxide mixed powder and the fumed silicon dioxide are preferably dried in advance before use. The drying temperature is preferably 100-150° C., more preferably 120° C. The drying time is preferably ≥ 24 hours. After drying, the mixture is sealed and dried for storage for future use.

[0050] The stirring and mixing is preferably carried out by a vacuum stirrer or a glass rod, more preferably by a glass rod. In the present embodiment, the stirring time of the stirring and mixing is preferably 5 to 10 minutes, specifically 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, and 10 minutes; the vacuuming time is preferably 30 to 60 seconds each time, specifically 30 seconds, 40 seconds, 50 seconds, and 60 seconds. The stirring and vacuuming steps are preferably repeated 4 to 6 times, specifically 4 times, 5 times, and 6 times. After repeated stirring and vacuuming, modified alumina micelles are obtained.

[0051] d) Wrapping the modified alumina micelle outside the spherical core layer prepared in step b), and sintering to obtain a high-temperature composite phase-change heat storage large capsule.

[0052] The wrapping method is preferably a manual ball-rubbing method, specifically, embedding the spherical core layer into the modified alumina micelle and rubbing it into a spherical shape by hand.

[0053] The sintering method is preferably: first heat up to 300-400℃ and keep warm for 1-2h, then heat up to 700℃-720℃ and keep warm for 3-4h. Among them, the heating rate of the first heating is preferably 3-5℃ / min, specifically 3℃ / min, 4℃ / min, 5℃ / min; the target temperature of the first heating can be specifically 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃; the insulation time after the first heating can be specifically 1h, 1.5h, 2h. The heating rate of the second heating is preferably 3-5℃ / min, specifically 3℃ / min, 4℃ / min, 5℃ / min; the target temperature of the second heating can be specifically 700℃, 710℃, 720℃; the insulation time after the second heating can be specifically 3h, 3.5h, 4h. After sintering, a high-temperature composite phase-change heat storage large capsule is obtained.

[0054] The present invention is further described in detail with reference to specific examples. In the following examples, the mesh size of the expanded vermiculite is 400 mesh, the specific surface area of ​​the fumed silica is 400 m 2 / g. The KCl-Na2SO4 eutectic salt is obtained by melting and blending potassium chloride and sodium sulfate in a mass ratio of 1:1.222 at 600 °C and then cooling to room temperature. The alumina mixed powder is composed of the following components in mass percentage: 20.36% of 2μm alumina, 22.92% of 5μm alumina, and 56.72% of 40μm alumina, which are mixed together. The fumed silica, expanded vermiculite, alumina mixed powder, and KCl-Na2SO4 eutectic salt are all pre-dried before use, dried at 120 °C for more than 24 h, sealed and stored in a dry place for standby.

[0055] Example 1:

[0056] 1. Preparation

[0057] S1. Pour 0.7 g of KCl-Na2SO4 eutectic salt and 0.3 g of expanded vermiculite into a ball milling jar, and then ball mill and mix them in a planetary ball mill at a speed of 220 rpm for 1 h to obtain a uniform mixture powder; transfer the powder mixture to a corundum crucible, place it in a muffle furnace, heat it to 120 °C at a rate of 5 °C / min and hold for 2 h, then heat it to 600 °C at a rate of 5 °C / min and hold for 2 h; then, cool it to room temperature with the furnace, and then transfer it to a mortar and grind for 5 min to obtain a sintered powder.

[0058] S2. Pour the sintered powder into a mold, place it in an isostatic press and press it at a pressure of 20 Mpa for 4 min to obtain a core layer blank. Place the core layer blank in a muffle furnace, heat it to 120 °C at a rate of 5 °C / min and hold for 2 h, then heat it to 600 °C at a rate of 5 °C / min and hold for 2 h; then, cool it to room temperature with the furnace to obtain a spherical core layer.

[0059] S3. Add 1 g of acrylic resin to 10 g of alumina mixed powder, stir and mix evenly, then add 0.15 g of fumed silica, and continue to stir until a fluid colloid is formed. Then, use a vacuum mixer to evacuate for 30 s to extract the air in the colloid and crosslink it; then, repeat the stirring and evacuation steps 5 times in sequence to obtain a modified alumina micelle.

[0060] S4. Wrap 2 g of the modified alumina micelle outside the spherical core layer prepared in step S2, place it in a muffle furnace, heat it to 400 °C at a rate of 3 °C / min and hold for 2 h to remove the acrylic resin in the blank, then heat it to 700 °C at a rate of 5 °C / min and hold for 3 h; then, cool it to room temperature with the furnace to obtain a high-temperature composite phase change heat storage capsule.

[0061] 2. Characterization and testing

[0062] (1) Appearance, internal and microscopic characterization

[0063] The obtained high-temperature composite phase change heat storage capsules were respectively subjected to appearance observation, internal observation, and microstructure characterization of the core layer by scanning electron microscopy. The results are shown respectively as Figure 1 and Figure 2 shown. It can be seen from (b) in Figure 1 that there is a certain cavity structure between the core layer and the shell layer. The cavity structure can adapt to the expansion of the core layer phase change material during the phase change process, avoiding the problem of capsule rupture. It can be seen from Figure 2 that the KCl-Na2SO4 eutectic salt has been embedded in the layered structure of expanded vermiculite. Appearance observation was carried out on the high-temperature composite phase change heat storage capsules after 100 heating-cooling cycles (each time heating to 600 °C and then cooling to room temperature); as shown in Figure 3 shown, it can be seen that the appearance of the high-temperature composite phase change heat storage capsules after thermal cycling remains intact, without rupture and salt leakage, showing excellent structural stability.

[0064] (2) Performance testing

[0065] ⅰ. The core layer powders of the KCl-Na2SO4 eutectic salt and the prepared product were respectively taken and put into a Netzsch STA449F3 TG-DSC comprehensive analyzer for thermal property analysis. The results are shown in Figure 4 ;

[0066] It can be seen from Figure 4 that the phase change temperature of the KCl-Na2SO4 eutectic salt is 522.8 °C, and the phase change latent heat is 220.6 J / g. The phase change temperature of the core layer of the prepared product is 523.4 °C, and the phase change latent heat is 153.8 J / g; compared with the KCl-Na2SO4 eutectic salt, the phase change temperature difference is small, and the phase change latent heat also maintains about 69.7%, proving that the addition of expanded vermiculite hardly affects the phase change temperature and phase change latent heat of the KCl-Na2SO4 eutectic salt and has good chemical compatibility.

[0067] ⅱ. Thermal property analysis was carried out on the core layer of the high-temperature composite phase change heat storage capsules after 100 heating-cooling cycles. The results are also shown in Figure 4 . It can be seen that after 100 heating-cooling cycles, the phase change temperature of the core layer is 523.7 °C, and the phase change latent heat is 150.6 J / g. Its phase change temperature is almost unchanged before and after cycling, and the phase change latent heat retention rate reaches 97.9% and only loses 2.1%, proving that the encapsulation effect of the alumina ceramic shell and expanded vermiculite on the eutectic salt is significant, ensuring excellent thermal cycling performance of the composite phase change heat storage material.

[0068] ⅲ. In order to test the corrosion resistance of the prepared high-temperature composite phase change heat storage capsules, the capsules were contacted with 316 stainless steel and placed in a muffle furnace at 650 °C for 100 h. The results are shown inFigure 5 (a) in it. For comparison, the expanded vermiculite-based high-temperature composite phase change heat storage material (i.e., the core layer) was also contacted with 316 stainless steel and placed in a muffle furnace, and kept at a constant temperature of 650 °C for 100 h. The results are as Figure 5 shown in (b).

[0069] It can be seen from Figure 5 (a) that only some areas of the surface of 316 stainless steel were corroded after being contacted with the high-temperature composite phase change heat storage large capsule for 100 h. By calculating the mass of 316 stainless steel before and after corrosion, it was found that the weight gain was about 0.04%; it can be seen from Figure 5 (b) that the entire surface of 316 stainless steel was corroded after being contacted with the core layer for 100 h, and a large amount of easily exfoliated scale was generated. By calculating the mass of 316 stainless steel before and after corrosion, it was found that the weight gain was about 0.11%. Through comparison, it is concluded that the high-temperature phase change heat storage large capsule can reduce the corrosive effect on the metal container and extend its service life, which benefits from the good encapsulation and isolation performance of the alumina shell layer.

[0070] Example 2:

[0071] S1. Pour 0.65 g of KCl-Na2SO4 eutectic salt and 0.35 g of expanded vermiculite into a ball milling tank, and then ball mill and mix them in a planetary ball mill at 220 rpm for 1 h to obtain a uniform mixture powder; transfer the powder mixture to a corundum crucible, place it in a muffle furnace, heat it to 120 °C at a rate of 5 °C / min and hold for 2 h, and then heat it to 600 °C at a rate of 5 °C / min and hold for 2 h; then, cool it to room temperature with the furnace, and then transfer it to a mortar and grind it for 5 min to obtain a sintered powder.

[0072] S2. Pour the sintered powder into a mold, place it in an isostatic press and press it at a pressure of 20 Mpa for 4 min to obtain a core layer blank. Place the core layer blank in a muffle furnace, heat it to 120 °C at a rate of 5 °C / min and hold for 2 h, and then heat it to 600 °C at a rate of 5 °C / min and hold for 2 h; then, cool it to room temperature with the furnace to obtain a spherical core layer.

[0073] S3. Add 1 g of acrylic resin to 5 g of alumina mixed powder, stir and mix evenly, then add 0.2 g of fumed silica, continue to stir until a fluid colloid is formed, and then use a vacuum mixer to evacuate for 30 s to extract the air in the colloid and crosslink it; then, repeat the stirring and evacuation steps 5 times in sequence to obtain a modified alumina micelle.

[0074] S4. Wrap 2 g of modified alumina micelles around the spherical core layer obtained in step S2, place it in a muffle furnace, heat it to 400 °C at a rate of 3 °C / min and hold for 2 h to remove the acrylic resin in the green body, then heat it to 700 °C at a rate of 5 °C / min and hold for 3 h; then, cool it to room temperature in the furnace to obtain a high-temperature composite phase change heat storage macro-capsule.

[0075] Comparative Example 1:

[0076] Carry out according to Example 1, the difference is that no fumed silica is added in step S3.

[0077] Comparative Example 2:

[0078] Carry out according to Example 1, the difference is that the acrylic resin is replaced with sodium carboxymethyl cellulose in step S3.

[0079] Compared with Examples 1-2, the comprehensive performance of the products obtained in Comparative Examples 1-2 becomes worse. In Comparative Example 1, due to the absence of fumed silica, the surface of the alumina shell layer of the obtained product is rougher and more porous than that of Example 1. As Figure 6 shown, by calculating the mass of 316 stainless steel before and after corrosion, it is found that the weight gain is 0.08%, and the corrosion resistance becomes worse; after replacing the acrylic resin with sodium carboxymethyl cellulose in Comparative Example 2, the colloidal fluidity is poor during step S3 and cannot crosslink, forming micelles with obvious granularity, so it is difficult to form an alumina ceramic shell layer. The results show that the use of fumed silica and acrylic resin in the present invention can effectively improve the performance of the macro-capsule.

[0080] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A large composite phase change heat storage capsule, characterized in that: The large composite phase change heat storage capsule includes a spherical core layer and a shell layer wrapped outside the core layer, and a cavity is formed between the core layer and the shell layer; the material of the core layer is an expanded vermiculite-based composite phase change heat storage material, and the expanded vermiculite-based composite phase change heat storage material is made of the following component raw materials in parts by mass: 60-75 parts of KCl-Na2SO4 eutectic salt, 25-40 parts of expanded vermiculite; the material of the shell layer is modified alumina ceramic, and the modified alumina ceramic is made of the following component raw materials in parts by mass: 80-90 parts of alumina mixed powder, 10-20 parts of acrylic resin and 0.1-2 parts of fumed silica; The preparation steps of the large composite phase change heat storage capsule are as follows: a), Mix KCl-Na2SO4 eutectic salt and expanded vermiculite evenly and then sinter to obtain sintered powder; b), Press the sintered powder into a green body by an isostatic press, and then sinter the green body to obtain a spherical core layer; c), Stir and mix the alumina mixed powder and acrylic resin, add fumed silica after mixing evenly, continue to stir until a fluid colloidal state is formed and then evacuate, and repeat the stirring and evacuation steps 4-6 times in sequence to obtain a modified alumina colloidal mass; d), Wrap the modified alumina colloidal mass on the spherical core layer prepared in step b), and obtain a large composite phase change heat storage capsule after sintering.

2. The composite phase change heat storage large capsule according to claim 1, characterized in that: The KCl-Na2SO4 eutectic salt is prepared by melting and blending potassium chloride and sodium sulfate, and the mass ratio of potassium chloride to sodium sulfate is 1:(1.22-1.25).

3. The composite phase change heat storage large capsule according to claim 1, wherein: The alumina mixed powder includes the following components in mass percentage: 20.36 wt.% of 2μm alumina, 22.92 wt.% of 5μm alumina, and 56.72 wt.% of 40μm alumina.

4. The composite phase change heat storage large capsule according to claim 1, characterized in that: The mesh number of the expanded vermiculite is 300 to 800 meshes; the specific surface area of the fumed silica is 200 to 400 m 2 / g.

5. The composite phase change heat storage large capsule according to any one of claims 1-4, characterized in that: The total amount of KCl-Na2SO4 eutectic salt and expanded vermiculite is 100 parts; the total amount of alumina mixed powder and acrylic resin is 100 parts.

6. The composite phase change heat storage large capsule according to any one of claims 1-4, characterized in that: The phase change temperature of the core layer is greater than 522 °C.

7. The composite phase change heat storage large capsule according to claim 1, wherein: The mixing in step a) is ball milling mixing, the rotation speed of the ball mill is 200-300 r / min, and the ball milling time is 30-120 min; during sintering, first heat up to 120-150 °C and keep warm for 1-2 h, then heat up to 550-600 °C and keep warm for 2-3 h.

8. The composite phase change heat storage large capsule according to claim 1, wherein: In step b), the pressure for pressing and forming is 20-30 Mpa, and the pressure holding time for pressing and forming is 3-5 min.

9. The composite phase change heat storage large capsule according to claim 1, wherein: In step c), the stirring and mixing is vacuum stirring or stirring with a glass rod, and the stirring time for stirring and mixing is 5-10 min; in step d), first heat up to 300-400 °C and keep warm for 1-2 h, then heat up to 700 °C-720 °C and keep warm for 3-4 h.

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