A ceramic macrocapsule with a topological cavity structure, a preparation method thereof, and its application in heat storage

Abstract

The present invention discloses a ceramic macrocapsule with a topological cavity structure, a preparation method thereof, and an application in a phase change heat storage macrocapsule, belonging to the field of phase change energy storage technology. The present invention solves the technical problem that the ceramic shell fin macrocapsule obtained by the topological optimization method is difficult to apply in actual application due to its complex structure. The present invention utilizes the reverse design structural characteristics of the paraffin block and adopts a sacrificial paraffin template method to create a cavity with a topological optimization structure inside the ceramic macrocapsule, overcoming the process difficulties of making the topological optimization result into an internal ceramic fin structure. It has the advantages of being fast and cheap, and at the same time, it has great potential in large-scale production of complex shapes, and can realize industrial production. When the ceramic macrocapsule with a topological cavity structure prepared by the present invention is used as a phase change heat storage macrocapsule, it also has the advantages of shortening the heat storage time and increasing the heat storage rate.

Description

Technical Field

[0001] The present invention relates to a ceramic macrocapsule with a topological cavity structure, a preparation method thereof, and an application thereof in a phase change heat storage macrocapsule. The present invention belongs to the field of phase change energy storage technology, and specifically relates to the technical field of preparation and application of ceramic macrocapsules of phase change materials that can be applied to the recovery of waste heat from high-temperature industries such as glass, ironmaking, and steelmaking, or to concentrated solar power generation and energy storage systems. Background Art

[0002] Thermal energy storage technology can effectively solve the energy supply and demand mismatch problem caused by the intermittent and volatile limitations of renewable energy, maximize the energy efficiency of the system, and reduce the cost of energy utilization. In most cases, phase change materials need to be encapsulated to overcome their increased corrosion and poor stability during the heat storage and release process. At present, most phase change materials used in heat storage systems are macro-encapsulated in steel-based metal shells, and this system has been proven to be a very effective heat storage method. However, high-temperature phase change materials represented by molten salts will still cause severe high-temperature corrosion to the inside of the steel-based capsule after multiple cycles, seriously affecting the life of the heat storage unit. In addition, the inherent low thermal conductivity of phase change materials will lead to a decrease in the energy storage efficiency of the system.

[0003] In recent years, high thermal conductivity composite phase change materials prepared by combining phase change materials and ceramic porous media with carbon-based thermal conductivity enhancement materials are considered to be a good way to solve these problems. Unfortunately, carbon materials cannot withstand high temperatures for a long time. On the other hand, the molten salt content of most composite phase change materials is less than 50%, which will lead to a decrease in energy storage density and a significant increase in storage costs. In contrast, ceramic large capsules with higher energy storage density and more reliable sealing are more suitable for large-scale applications.

[0004] In large capsules, fins are widely used to expand the internal heat transfer surface area and produce excellent performance during the system's heat storage process. For example, embedding pins inside the capsule can reduce the phase change time of the phase change material by 27%. Among the many fin layouts, the shell fins obtained by topology optimization method have a huge improvement in design because the layout of the fins does not need to rely on the initial configuration and has a high degree of freedom. However, the fins recommended based on the optimization results are usually too complex for practical applications. Therefore, it is of great significance to explore an economical and effective method to realize the actual preparation of ceramic large capsules with topologically optimized cavities to achieve rapid heat transfer of phase change materials. Summary of the Invention

[0005] The present invention addresses the technical problem that the existing large ceramic shell fin capsules obtained by the topological optimization method are difficult to apply in actual applications due to their complex structure. The present invention provides a large ceramic capsule with a topological cavity structure, a preparation method thereof, and an application in a phase change heat storage large capsule.

[0006] The technical solution of the present invention:

[0007] One of the purposes of the present invention is to provide a ceramic macrocapsule with a topological cavity structure, which comprises an integrated ceramic shell and ceramic fins, and a topological cavity structure enclosed by the ceramic shell and the ceramic fins; the shape of the macrocapsule is spherical or convex polyhedron.

[0008] The second object of the present invention is to provide a method for preparing the above-mentioned ceramic macrocapsule with a topological cavity structure. The specific preparation steps are as follows:

[0009] S1, creating a ceramic macrocapsule structure with a topological cavity structure, and using silicone as the material to prepare a silicone mold according to the created structure;

[0010] S2, pouring molten paraffin into a silicone mold, solidifying, and demolding to obtain a paraffin block with a reverse design structure, and connecting the paraffin block to one end of a resin rod of a certain length;

[0011] S3, placing the paraffin block in a mold with the same shape as the ceramic shell layer, with the movable end of the resin rod located outside the mold, then pouring ceramic slurry into the mold, immersing the paraffin block in the ceramic slurry, curing, and demolding to obtain a green body;

[0012] S4, heating the green body in a water bath, removing the resin rod, leaving a filling hole at the top of the green body, and completely melting the paraffin inside. During the water bath heating process, since the density of liquid paraffin is lower than that of water, the density difference causes the liquid paraffin to float out of the filling hole, and then freeze-drying is performed. After the freeze-drying treatment, pre-sintering is performed to obtain a pre-sintered body;

[0013] S5, placing the pre-calcined body in an inert atmosphere for sintering to obtain a ceramic macrocapsule with a topological cavity structure.

[0014] It is further defined that the initial model is constructed using the COMSOL platform in S1, and the solid isotropic material rule with penalty is used for optimization to obtain a ceramic macrocapsule structure with a topological cavity structure.

[0015] Further limiting, the optimization formula is as follows:

[0016] min:

[0017] st0≤∫ Ω ρ e dΩ≤γA

[0018] ρ min ≤ρ e ≤1

[0019] Where, γ is the volume ratio of the ceramic area; ρ e is the ceramic area density; K SIMP represents thermal conductivity; ρ min is the minimum pseudo density to avoid the occurrence of singular matrices; Ω is the design domain; A is the area of ​​the design domain.

[0020] Further limit, the optimization convergence criterion is 10 -6 , the maximum number of iterations is 500.

[0021] It is further defined that the connection method between the paraffin block and the resin rod in S2 is: one end of the resin rod is placed on a heating platform at 150°C and heated for 10 seconds, then brought into contact with the paraffin block and cooled.

[0022] It is further defined that the ceramic powder, dispersant, monomer, cross-linking agent and water are mixed, and then ball-milled at 200 rpm for 12 hours using ZrO2 balls. After the ball-milling treatment is completed, degassing is carried out under vacuum stirring, and then an initiator and a catalyst are added, and stirred for 1 minute to obtain a ceramic slurry.

[0023] It is further defined that the initiator and the catalyst are added 1 minute before pouring the ceramic slurry.

[0024] It is further defined that the curing temperature in S3 is 50° C. and the curing time is 20 min.

[0025] It is further defined that the pre-sintering conditions in S4 are: heating to 600° C. at a heating rate of 0.5° C. / min and keeping the temperature for 2 h.

[0026] It is further defined that the sintering temperature in S5 is 1550° C. and the sintering time is 10 h.

[0027] The third object of the present invention is to provide an application of the above-mentioned ceramic large capsule with a topological cavity structure. Specifically, the phase change material is injected into the topological cavity of the large capsule, and after being sealed with glass powder, it is used as a phase change heat storage large capsule.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention utilizes the reverse design structural characteristics of the paraffin block and adopts the sacrificial paraffin template method to create a cavity with a topologically optimized structure inside the ceramic macrocapsule, overcoming the process difficulty of making the topological optimization result into an internal ceramic fin structure. It has the advantages of being fast and inexpensive, and at the same time has great potential in the large-scale production of complex shapes, and can realize industrial production.

[0030] (2) The large capsule preparation method provided by the present invention only requires the preparation of a small amount of silicone molds to support the production of batch ceramic capsules, greatly reducing the process cost.

[0031] (3) The ceramic macrocapsules with topological cavity structure prepared by the present invention are used as phase change heat storage macrocapsules. When the ceramic volume ratio is 25%, the heat storage time is shortened by 62.8% and the heat storage rate is increased by 101.5%; when the ceramic volume ratio is 45%, the heat storage time is shortened by 76% and the heat storage rate is 129.3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Comparison diagram of the initial model constructed in Example 1 and the structure after topology optimization;

[0033] Figure 2 This is a diagram of a silicone mold prepared according to the structure created in Example 1;

[0034] Figure 3 This is a paraffin block diagram with a reverse design structure obtained in Example 1;

[0035] Figure 4 Comparison diagram of the green body before and after pre-sintering and sintering in Example 1; (a) is a top view, (b) is a cross-sectional view, (c) and (d) are SEM images of the pre-sintered and sintered samples, respectively;

[0036] Figure 5 This is a before and after comparison of the phase change material encapsulated in the ceramic large capsule obtained in Example 1;

[0037] Figure 6 The heat storage process of a large capsule with a topological cavity structure and a topological cavity structure filled with paraffin wax and placed in a constant temperature water bath at 65°C over time;

[0038] Figure 7 The heat storage process of filling paraffin into a large capsule without a topological cavity structure and placing it in a constant temperature water bath at 65°C over time;

[0039] Figure 8 (a) is a schematic diagram of the design domain in Example 1; (b) is a schematic diagram of the actual design domain obtained by the COMSOL platform. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0041] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0042] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0043] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0044] Example 1

[0045] This embodiment takes a large alumina ceramic capsule with an internal ceramic fin volume ratio of 45% as an example.

[0046] (1) The initial model was constructed using the COMSOL platform, and the solid isotropic material rule with penalty was used for optimization to obtain a ceramic macrocapsule structure with a topological cavity structure.

[0047] In order to find the best layout of ceramic materials to accelerate the heat transfer process inside a large capsule with a fixed porosity, the optimization design adopts the solid isotropic material rule with penalty and obtains a ceramic large capsule structure with a topological cavity structure. Figure 8 As shown in (a), the design domain will consist of the ceramic region (design density defined as 1) and the cavity region (design density defined as 0).

[0048] The optimization formula is as follows:

[0049] min:

[0050] st0≤∫ Ω ρ e dΩ≤γA

[0051] ρ min ≤ρ e ≤1

[0052] Where, ρ e is the design density; K SIMP is the thermal conductivity, which is expressed as ρ e function; γ is the volume ratio of the ceramic area; Ω is the design domain; A is the area of ​​the design domain in the two-dimensional physical model; ρ min is the minimum pseudo density to avoid a singular matrix.

[0053] The topological model is solved on the COMSOL platform. The moving asymptote method (MMA) is used for updating. In this embodiment, the design domain is as follows Figure 8(b) shows a square with a side length of 45 mm and an outer wall thickness of 2 mm. The penalty factor is 3, the filter radius is 0.0003 mm, the heat load is 20 W, the ceramic volume ratio is 45% according to the requirements, and the optimization convergence standard is 10 -6 , the maximum number of iterations is 500.

[0054] The optimization convergence criterion is 10 -6 , the maximum number of iterations is 500 times, the structures before and after optimization are as follows Figure 1 shown.

[0055] (2) Using silicone as the material, prepare a silicone mold according to the created structure, such as Figure 2 As shown, the molten paraffin is poured into the silicone mold, solidified, and demoulded to obtain a paraffin block with a reverse design structure, as shown Figure 3 The paraffin block is connected to one end of a resin rod of a certain length by placing one end of the resin rod on a heating platform at 150°C for 10 seconds, then immediately contacting the resin rod with the paraffin block to tightly bond the two, and then cooling.

[0056] (3) Place the paraffin block in a mold with the same shape as the ceramic shell, with the active end of the resin rod outside the mold. Then pour the ceramic slurry (note that pouring should be done within 4 minutes after adding the catalyst and initiator) into the mold, immerse the paraffin block in the ceramic slurry, and cure it at 50°C for 20 minutes. De-mold to obtain a green body.

[0057] The ceramic slurry preparation process is:

[0058] First, a monomer (acrylamide, 4 wt %, based on deionized water) and a cross-linking agent (N,N'-methylenebisacrylamide, the mass ratio of N,N'-methylenebisacrylamide to acrylamide is 1:10) were dissolved in deionized water and dispersed to obtain a solution.

[0059] Then, alumina ceramic powder (alumina, 60 Vol%, based on the volume of deionized water) and a dispersant (ammonium salt dispersant 4705, 0.5 wt%, based on the mass of the ceramic powder) were added to the solution.

[0060] Finally, ZrO2 balls were used for ball milling at 200 rpm for 12 h. After the ball milling treatment, the mixture was degassed under vacuum stirring. Then, an initiator (ammonium persulfate, 0.3 wt %, based on deionized water) and a catalyst (N,N,N',N'-tetramethylethylenediamine, 1 μL / g) were added and stirred for 1 min to obtain a ceramic slurry.

[0061] (4) The green body is placed in a water bath at 60°C for heating treatment, the resin rod is removed, and the internal paraffin is completely melted, and then the green body is freeze-dried at a condenser temperature of -35°C. After freeze-drying treatment, the temperature is increased to 600°C at a heating rate of 0.5°C / min and kept at this temperature for 2 hours to obtain a pre-burned body without organic additives.

[0062] (5) The pre-calcined body is placed in an argon atmosphere and heated to 1550°C for 10 hours to obtain a dense ceramic macrocapsule with a topological cavity structure. The comparison diagram of the pre-calcined body and the sintered body before and after treatment is shown in the figure below. Figure 4 As shown by Figure 4 It can be seen that due to the shrinkage of the ceramic shell during sintering at 1550℃, the size of the large capsules decreased slightly, but there was no cracking. The ceramic powder is not subjected to unidirectional force during the gel injection molding process, so the large capsules shrink evenly as a whole during sintering, and the ceramic in the cavity maintains the original volume ratio. Further analysis of the cross-section of the Al2O3 shell by SEM (c) and (d) shows that compared with the pre-fired shell, when the ceramic sample is sintered at 1550℃, the surface pores completely disappear, and only a few isolated small pores can be seen. The results show that the porous matrix has been infiltrated and blocked by the molten phase of the ceramic, which will provide sufficient mechanical properties for encapsulating the phase change material and also avoid leakage of the molten phase change material.

[0063] (6) Pour the phase change material into the large capsule through the filling hole at the top and seal it with glass powder, as shown in Figure 5 As shown, a large phase change heat storage capsule is obtained.

[0064] In order to clearly demonstrate the thermal performance of the macrocapsules, paraffin was filled into the macrocapsules with topological cavity structures (prepared in this example) and the macrocapsules without topological cavity structures, and placed in a constant temperature water bath at 65°C to study the heat storage process. The results are as follows: Figure 6 As shown in Figure 7, Figure 6 and Figure 7 It can be seen that heat will be transferred to the interior of the microcapsule more quickly through the Al2O3 fins. Compared with traditional capsules, the introduction of Al2O3 fins significantly shortens the phase change time of paraffin. In this embodiment, the heat storage time of the sample with a volume ratio of 45% is 8.5 minutes, which is 76% shorter than the heat storage time of 35.4 minutes of the traditional capsule. According to the content of paraffin filled in the embodiment, the heat storage rate of the sample with a volume ratio of 45% is calculated based on the above time to be 4.7W, which is 129.3% higher than the heat storage rate of 2.05W of the traditional capsule.

[0065] Example 2

[0066] The difference between this embodiment and embodiment 1 is that the volume ratio of the internal ceramic fins is 25%, and the other parameter settings and process steps are the same as those in embodiment 1.

[0067] In order to clearly demonstrate the thermal performance of the large capsules, paraffin was filled into the top-less large capsules with a topological cavity structure (prepared in this example) and the large capsules without a topological cavity structure, and placed in a constant temperature water bath at 65°C to study the heat storage process. The results showed that the heat storage time of the large capsules with a topological cavity structure was 13.2 minutes, which was a 63% shortening of the heat storage time, and the heat storage rate was 4.13W, which was a 101.5% increase of the heat storage rate.

[0068] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a ceramic macrocapsule having a topological cavity structure, characterized in that: The large capsule includes an integrated ceramic shell and ceramic fins, and a topological cavity structure enclosed by the ceramic shell and the ceramic fins; the outer shape of the large capsule is a sphere or a convex polyhedron; The preparation method comprises: S1, creating a ceramic macrocapsule structure with a topological cavity structure, and using silicone as the material to prepare a silicone mold according to the created structure; In S1, the COMSOL platform was used to build the initial model, and the solid isotropic material rule with penalty was used for optimization to obtain a ceramic macrocapsule structure with a topological cavity structure; The optimization formula is as follows: Where, is the volume ratio of the ceramic area; ρ e is the ceramic area density; K SIMP represents thermal conductivity; ρ min is the minimum pseudo density to avoid the occurrence of singular matrices; Ω is the design domain; A is the area of ​​the design domain; S2, pouring molten paraffin into a silicone mold, solidifying, and demolding to obtain a paraffin block with a reverse design structure, and connecting the paraffin block to one end of a resin rod of a certain length; S3, placing the paraffin block in a mold with the same shape as the ceramic shell layer, with the movable end of the resin rod located outside the mold, then pouring ceramic slurry into the mold, immersing the paraffin block in the ceramic slurry, curing, and demolding to obtain a green body; S4, heating the green body in a water bath, removing the resin rod, and completely melting the paraffin inside, followed by freeze drying, and then pre-sintering to obtain a pre-sintered body; S5, placing the pre-calcined body in an inert atmosphere for sintering to obtain a ceramic macrocapsule with a topological cavity structure.

2. The preparation method according to claim 1, characterized in that The optimization convergence criterion is 10 -6 , the maximum number of iterations is 500.

3. The preparation method according to claim 1, characterized in that The paraffin block and the resin rod in S2 were connected by placing one end of the resin rod on a heating platform at 150°C for 10 seconds, then placing it in contact with the paraffin block and cooling it.

4. The preparation method according to claim 1, characterized in that The preparation method of the ceramic slurry in S3 is: ceramic powder, dispersant, monomer, cross-linking agent and water are mixed, and then ball-milled at 200 rpm for 12 hours using ZrO2 balls. After the ball-milling treatment is completed, degassing is carried out under vacuum stirring, and then an initiator and a catalyst are added, and stirred for 1 minute to obtain a ceramic slurry.

5. The preparation method according to claim 1, characterized in that The curing temperature in S3 is 50°C and the curing time is 20 minutes.

6. The preparation method according to claim 1, characterized in that The pre-sintering conditions in S4 are: heating to 600°C at a heating rate of 0.5°C / min and keeping warm for 2h; the sintering temperature in S5 is 1550°C and the time is 10h.

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