A directional heat-conducting, anisotropic porous silicon carbide ceramic skeleton, a preparation method thereof and application thereof in a directional thermal management composite phase change material

Abstract

The present application relates to a kind of directional heat conduction, anisotropic porous silicon carbide ceramic framework and its preparation method and application in directional heat management composite phase change material.The preparation method of the porous silicon carbide ceramic framework includes the following steps: slurry preparation, the slurry contains silicon carbide fiber, slurry infusion: prepared slurry is induced to infiltrate and is infused in porous polyurethane mold by multitype driven guiding laminar flow field;Sintering.The present application improves the directional heat conduction performance of silicon carbide skeleton material by introducing silicon carbide fiber and optimizing the preparation method, the skeleton can be used to prepare directional heat management composite phase change material, greatly improve the thermal conductivity of the directional heat transfer strengthening direction of composite phase change material, save phase change time, reduce the phase change temperature difference of distributed solar energy single-tank energy storage system, improve its energy storage rate.

Description

Technical Field

[0001] This invention relates to the field of molten salt phase change energy storage technology, specifically to a directional thermally conductive, anisotropic porous silicon carbide ceramic framework, its preparation method, and its application in directional thermal management composite phase change materials. Background Technology

[0002] The advantages of solar energy as a renewable energy source are being increasingly recognized, and solar thermal power generation technology is experiencing rapid iteration. Currently, the primary energy storage method used in solar thermal energy storage is dual-tank molten salt phase change energy storage. This type of storage offers significant advantages, including high energy density, low saturated vapor pressure, superior high-temperature stability, and low viscosity, and is widely used in tower, trough, dish, and existing Fresnel-type solar thermal power generation energy storage facilities. Dual-tank energy storage, which uses separate hot and cold molten salt tanks, is simple in structure, technologically mature, and highly adaptable, and has also gained widespread application. Single-tank energy storage technology, however, faces limitations in technological development. For a long time, solar thermal power technology has primarily focused on centralized thermal power technology, mainly due to the dependence of thermal power systems on energy collection power and storage density. Larger-scale solar collectors will achieve significant cost-effectiveness due to their volume effect.

[0003] However, in this context, the application of dual-tank energy storage in small-scale energy storage facilities faces significant technical limitations. The complex dual-tank piping makes it difficult to match with small-scale energy storage facilities. This not only leads to insufficient energy density and low storage efficiency of the thermal medium, preventing it from being heated to a sufficient temperature, but also presents a significant cost crisis, hindering the effective promotion of solar thermal energy storage technology. Furthermore, the distributed nature of solar thermal energy resources, due to the inherent characteristics of solar energy, greatly limits the application scope and development of solar thermal energy storage.

[0004] Single-tank energy storage integrates the management of both hot and cold molten salt tanks within a single storage vessel, providing unified control over the energy storage medium. With its lower initial investment cost and smaller footprint, single-tank energy storage systems offer significant cost-effectiveness and space efficiency, making them particularly suitable for space-constrained applications. Furthermore, installation and maintenance are simple and quick due to the limited number of components. The high operational flexibility of single-tank systems allows for rapid adaptation to changing heat demands, making them suitable for applications requiring rapid energy release or absorption. These advantages make single-tank energy storage applicable to most energy storage projects, from small-scale residential heating to medium-to-large-scale industrial applications. With proper insulation design, heat loss is relatively low, further enhancing its competitiveness in the energy storage field.

[0005] However, single-tank energy storage technology currently faces three core technical limitations: First, the challenge of controlling the thermocline in single-tank systems. Thermocline control primarily requires ensuring the smallest possible vertical temperature gradient in the upper region; however, improving the uniformity of molten salt temperature in a specific direction without adding excessive flow field disturbance is the core issue. Second, reliability issues under high temperature gradients. The Haynes series nickel-based superalloys commonly used in current solar molten salt thermal storage are not only expensive, but also suffer from thermal stress damage under high temperature gradients within single-tank energy storage systems, significantly reducing the reliability of the system. Third, the issue of heat collection efficiency. Since single-tank thermal storage uses a single molten salt tank instead of a dual molten salt tank, it places higher demands on the efficient energy storage medium. Simply using a low thermal conductivity heat transfer medium will further exacerbate the thermocline control and thermal stress damage problems inherent in single-tank technology.

[0006] In the current research context, adding micro / nano high thermal conductivity fibers to composite phase change materials and directionally combing them can effectively reduce the high thermal resistance and high temperature gradient caused by large spans in specific directions. However, effectively combing and orienting micro / nano particles in three-dimensional space remains a challenging task. Summary of the Invention

[0007] To address the shortcomings of existing anisotropic phase change materials in the field of molten salt phase change energy storage, this invention improves the preparation method of silicon carbide ceramic skeletons for existing composite phase change materials. By using fiber-directed reinforcement, the directional thermal conductivity can be improved, thereby ultimately enhancing the thermal conductivity, energy storage efficiency, and reliability of the composite phase change material.

[0008] In a first aspect, the present invention provides a method for preparing a porous silicon carbide ceramic framework with directional thermal conductivity and anisotropy, comprising the following steps:

[0009] S1 Slurry Formulation: The slurry is composed of a mixture of solid and liquid phase components, wherein the solid phase component consists of silicon carbide fibers, silicon carbide particles, and sintering aids; and the liquid phase component consists of a mixture of deionized water, dynamic viscosity control agent, defoamer, and crosslinking agent.

[0010] S2 slurry injection: The prepared slurry is induced and injected into a porous polyurethane mold by a multi-type driven laminar flow field;

[0011] S3 sintering: After the mold is dried, it is sintered in an air atmosphere in a muffle furnace to obtain the silicon carbide ceramic skeleton.

[0012] By introducing silicon carbide fibers into the slurry and then combining it with multi-type driven laminar flow field-induced infusion, an anisotropic porous ceramic skeleton with oriented silicon carbide fibers can be obtained, thereby improving thermal conductivity.

[0013] The solid phase consists of ceramic components in the framework, primarily silicon carbide, combined with appropriate ceramic additives. Commonly used ceramic additives such as alumina, yttrium oxide, and combinations thereof can be selected.

[0014] The liquid phase is mainly adjusted by deionized water and dynamic viscosity control agent, combined with defoamer and crosslinking agent to adjust the slurry viscosity and stability, which facilitates subsequent flow field induction injection.

[0015] Because it is a porous mold, a driving guide is required for better pouring and directional alignment. Traditional soaking methods can only produce isotropic materials. Therefore, preferably, the multi-type driven laminar flow field refers to using laminar flow fields of various driving types to guide the slurry into the porous mold for wetting and pouring. This can be achieved through servo electric cylinder drive, gravity guidance, or centrifugal guidance via a rotary platform, or a combination of one or more of these methods.

[0016] The servo electric cylinder drives the laminar flow field. First, it needs to be fixed inside a tubular container of the same shape by interference fit. The servo electric cylinder pushes the piston rod to push the silicon carbide ceramic slurry carrying silicon carbide fibers inside the tube to fully fill the porous polyurethane mold.

[0017] The gravity-guided low-speed laminar flow field is achieved by fixing a flexible mold inside a tubular container of the same shape with an interference fit, so that the wall of the tubular container is vertical, and the upper end of the container is filled with silicon carbide ceramic slurry carrying silicon carbide fibers. After a period of guidance, the flow field guidance process is completed.

[0018] The rotation platform guides the laminar flow field orientation using a geared motor. The axis of the tubular container with the same shape as the mold is fixed to the center line of a circle assumed to be coaxial on the rotating platform axis. Then, the polyurethane foam mold is fixed inside the container at the end away from the axis of the rotating axis.

[0019] Preferably, in step S1, the solid phase component consists of 5-10 parts by weight of silicon carbide fiber, 75-80 parts by weight of silicon carbide particles, and 15 parts by weight of sintering aid; the sintering aid consists of 8 parts by weight of kaolin, 4 parts by weight of alumina, and 3 parts by weight of yttrium oxide; the liquid phase component is a mixture of 92 parts by weight of deionized water, 2 parts by weight of 10wt% NaOH solution, 2 parts by weight of glycerol, and 4 parts by weight of polyvinyl alcohol; the weight ratio of the solid phase component to the liquid phase component is 35-40:10-15.

[0020] Preferably, in step S1, the silicon carbide fiber has a diameter of 5-10 μm and an aspect ratio of 5-20, and the silicon carbide particle has a particle size of 10-15 μm.

[0021] The particle size of the sintering aid is selected based on the size of the silicon carbide, and is usually close to or smaller than the silicon carbide particle size. For example, it can be 1-3 μm, etc.

[0022] Preferably, the liquid phase component should be added to the solid phase component in multiple batches while stirring, in order to obtain a better dispersion effect.

[0023] Preferably, in step S2, the multi-type driven laminar flow field includes a servo electric cylinder driven laminar flow field, a gravity-guided low-speed laminar flow field, and a rotary platform-guided laminar flow field.

[0024] Preferably, the operation sequence of each flow field is as follows: servo-driven laminar flow field, gravity-guided low-speed laminar flow field, and rotary platform-guided laminar flow field. First, a servo-driven laminar flow field is used for initial slurry injection to ensure that the porous polyurethane mold is filled with the silicon carbide ceramic slurry carrying silicon carbide fibers and to directionally comb the silicon carbide fibers. Then, a gravity-guided low-speed laminar flow field is used to further comb the silicon carbide fibers within the mold along the internal structure of the porous polyurethane mold. After this gravity-guided low-speed laminar flow field, a rotary platform provides centrifugal force to guide the laminar flow field, displacing excess slurry and further guiding the fiber combing process to completion.

[0025] More preferably, the operation sequence of each flow field is as follows: servo electric cylinder drives laminar flow field, gravity guides low-speed laminar flow field, and rotary platform guides laminar flow field. After the steps of servo electric cylinder driving laminar flow field, gravity guiding low-speed laminar flow field and rotary platform guiding laminar flow field are completed, gravity guiding low-speed laminar flow field is used for compensation to ensure that the total weight of the slurry in the porous polyurethane mold is met.

[0026] Preferably, in the laminar flow field driven by the servo electric cylinder, the push rod speed is 0-5 mm / s.

[0027] Preferably, in the gravity-guided low-speed laminar flow field, the viscosity of the ceramic slurry needs to be adjusted to be between 500-1500 mPa·s to ensure that the low-speed laminar flow can proceed smoothly. This can be achieved by adding liquid phase components or by adding deionized water separately.

[0028] Preferably, in the laminar flow field guided by the rotary platform, the rotational speed of the rotary platform is 150 r / min.

[0029] Preferably, in step S2, the porous polyurethane mold is soaked in a 15wt% NaOH solution for ≥16 hours before injection to facilitate slurry impregnation.

[0030] Preferably, the porous polyurethane mold is made of polyurethane foam formed by laser ablation and shearing, and the pore size can be divided into three levels: PPI=1.5, PPI=2.5, and PPI=3.5. The laser power can be set to 20W, and the laser scanning speed is adjusted according to the thickness of the composite phase change material.

[0031] Preferably, in step S3, the air atmosphere sintering process in the muffle furnace includes the following processes: initial heating stage, from room temperature to 700°C; oxidation process, from 700°C to 850°C after 100 minutes; heating process, from 850°C to 1400°C after 3 hours; sintering process: maintaining at 1400°C for 2 hours; and hot annealing process: cooling steadily to 600°C after 4.5 hours, and then cooling to room temperature after 2 hours.

[0032] Preferably, in step S3, the drying temperature is 60-100℃ and the drying time is 10-14h.

[0033] In a second aspect, the present invention also provides a silicon carbide ceramic framework prepared by the above-described preparation method.

[0034] In a third aspect, the present invention also provides a directional thermal management composite phase change material, which is composed of the aforementioned silicon carbide ceramic framework and phase change material.

[0035] Preferably, the phase change material is an inorganic salt, including one or more of nitrates, carbonates, and chlorides in any proportion.

[0036] Preferably, the phase change material is a KNO3-NaNO3-NaNO2 molten salt.

[0037] Preferably, the mass ratio is KNO3:NaNO3:NaNO2 = 53:7:40.

[0038] Preferably, the ternary nitrate melting process uses a nitrogen atmosphere for protected pouring and heating to 160°C until melting, wherein the pouring process requires preheating the container to above 145°C, and the preparation process should use a container made of nickel-based Hastelloy or high-temperature ceramic material.

[0039] The beneficial effects of this invention are as follows:

[0040] This invention improves the directional thermal conductivity of silicon carbide framework materials by optimizing the preparation method, and can prepare porous silicon carbide frameworks with directional thermal conductivity and anisotropy. These frameworks can be used to prepare high thermal conductivity composite phase change materials with directional heat transfer enhancement and thermal management anisotropy, which greatly improves the thermal conductivity of the directional heat transfer enhancement direction of the thermal composite phase change material, saves phase change time, reduces the phase change temperature difference of distributed solar single-tank energy storage systems, and improves their energy storage efficiency. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating the fabrication process of a directional thermally conductive, anisotropic porous silicon carbide ceramic framework according to an embodiment of the present invention.

[0042] Figure 2 This is a schematic diagram of the preparation process of anisotropic composite phase change material for directional heat transfer enhancement and thermal management in Application Example 1 of the present invention.

[0043] Figure 3 This is a SEM image of the anisotropic composite phase change material for directional heat transfer enhancement and thermal management in Application Example 1 of the present invention.

[0044] Figure 4 A comparison chart of thermal conductivity for Application Example 1 and Comparative Application Examples 1, 2, and 3;

[0045] Figure 5 The experimental setup for testing the maximum temperature difference and phase transition time, as well as the comparison diagram of the heating process at each temperature measurement point in Application Example 1 and Application Comparative Example 3;

[0046] Figure 6 The graph shows a comparison of the energy storage rates of Application Example 1 and Comparative Examples 1, 2, and 3. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are one module of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0049] Example 1: A directional thermally conductive, anisotropic porous silicon carbide ceramic framework

[0050] A directional thermally conductive, anisotropic porous silicon carbide ceramic framework, reference Figure 1 Its preparation method is as follows:

[0051] (1) Mold preparation

[0052] A porous polyurethane mold with dimensions of 50mm*50mm*50mm and a pore size of PPI=25 was prepared by laser ablation shearing. After preparation, the mold surface was activated by soaking in a 15wt% NaOH solution for 16 hours.

[0053] (2) Preparation of silicon carbide ceramic slurry carrying silicon carbide fibers

[0054] First, prepare the solid phase composition of the slurry by mixing 10 parts by mass of silicon carbide fiber (diameter 5-10μm, aspect ratio 5-20), 75 parts by mass of silicon carbide particles with a particle size of 10μm, 8 parts by mass of kaolin (1000 mesh), 4 parts by mass of alumina (1000 mesh), and 3 parts by mass of yttrium oxide (1000 mesh).

[0055] Next, the liquid phase components are prepared by mixing 92 parts by mass of deionized water, 2 parts by mass of 10wt% NaOH solution, 2 parts by mass of glycerol, and 4 parts by mass of polyvinyl alcohol to form a slurry liquid phase.

[0056] Finally, mix 74 parts by weight of solid material and 26 parts by weight of liquid material and stir thoroughly with a magnetic stirrer to form a slurry. The liquid component should be added to the stirring system in multiple batches.

[0057] (3) Injection.

[0058] The prepared silicon carbide ceramic slurry was induced and impregnated into a porous polyurethane mold by a multi-type driven laminar flow field. The flow field orientation operation sequence was as follows: servo-electric cylinder driven laminar flow field, gravity-guided low-speed laminar flow field, rotary platform-guided laminar flow field, and gravity-guided low-speed laminar flow field. The gravity-guided low-speed laminar flow field lasted for 20 minutes. The viscosity of the silicon carbide ceramic slurry was adjusted to 500-1500 mPa·s by adding deionized water. In the servo-electric cylinder driven laminar flow field, the push rod speed was 0-5 mm / s. In the rotary platform-guided laminar flow field, the rotary platform speed was 150 r / min.

[0059] (4) Sintering

[0060] After drying at 80°C for 12 hours, the silicon carbide was sintered in an air atmosphere without pressure in a muffle furnace. The sintering process was divided into the following stages: the initial heating stage, from room temperature to 700°C; the oxidation process, slowly heating from 700°C to 850°C over 100 minutes to oxidize some of the silicon carbide to silicon oxide, providing conditions for the sintering neck formation stage; the heating process, heating from 850°C to 1400°C over 3 hours; the sintering process, maintaining at 1400°C for 2 hours; and the thermal annealing process, cooling steadily to 600°C over 4.5 hours, followed by cooling to room temperature over 2 hours, to obtain the silicon carbide ceramic skeleton.

[0061] Comparative Example 1: Isotropic porous silicon carbide ceramic framework

[0062] An isotropic porous silicon carbide ceramic framework is prepared by the following method:

[0063] (1) Mold preparation

[0064] A porous polyurethane mold with dimensions of 50mm*50mm*50mm and a pore size of PPI=25 was prepared by laser ablation shearing. After preparation, the mold surface was activated by soaking in a 15wt% NaOH solution for 16 hours.

[0065] (2) Preparation of silicon carbide ceramic slurry carrying silicon carbide fibers

[0066] First, prepare the solid phase composition of the slurry by mixing 10 parts by mass of silicon carbide fiber (diameter 5-10μm, aspect ratio 5-20), 75 parts by mass of silicon carbide particles with a particle size of 10μm, 8 parts by mass of kaolin (1000 mesh), 4 parts by mass of alumina (1000 mesh), and 3 parts by mass of yttrium oxide (1000 mesh).

[0067] Next, the liquid phase components are prepared by mixing 92 parts by mass of deionized water, 2 parts by mass of 10wt% NaOH solution, 2 parts by mass of glycerol, and 4 parts by mass of polyvinyl alcohol to form a slurry liquid phase.

[0068] Finally, mix 74 parts by weight of solid material and 26 parts by weight of liquid material and stir thoroughly with a magnetic stirrer to form a slurry. The liquid component should be added to the stirring system in multiple batches.

[0069] (3) Pouring: Immerse the porous polyurethane mold from step (1) into the ceramic slurry prepared in step (2), stir thoroughly, and squeeze out excess slurry to achieve a slurry filling rate of 0.22 g / cm³ in the mold. 3 .

[0070] (4) After drying at 80°C for 12 hours, the material was sintered in an air atmosphere without pressure in a muffle furnace. The sintering process was divided into the following stages: the initial heating stage, from room temperature to 700°C; the oxidation process, after 100 minutes, slowly heating from 700°C to 850°C to oxidize some silicon carbide to silicon oxide, providing conditions for the sintering neck formation stage; the heating process, after 3 hours, heating from 850°C to 1400°C; the sintering process: maintaining at 1400°C for 2 hours; the thermal annealing process: after 4.5 hours, the material was steadily cooled to 600°C, and then cooled to room temperature for 2 hours to obtain an isotropic high thermal conductivity composite phase change material (OCPCM) ceramic skeleton.

[0071] Comparative Example 2: Ordinary porous silicon carbide ceramic framework

[0072] A porous silicon carbide ceramic framework is prepared by the following method:

[0073] (1) Mold preparation

[0074] A porous polyurethane mold with dimensions of 50mm*50mm*50mm and a pore size of PPI=25 was prepared by laser ablation shearing. After preparation, the mold surface was activated by soaking in a 15wt% NaOH solution for 16 hours.

[0075] (2) Preparation of silicon carbide ceramic slurry carrying silicon carbide fibers

[0076] First, prepare the solid phase composition of the slurry by mass parts of 85 parts of silicon carbide particles with a particle size of 10μm, 8 parts of kaolin (1000 mesh), 4 parts of alumina (1000 mesh), and 3 parts of yttrium oxide (1000 mesh).

[0077] Next, the liquid phase components are prepared by mixing 92 parts by mass of deionized water, 2 parts by mass of 10wt% NaOH solution, 2 parts by mass of glycerol, and 4 parts by mass of polyvinyl alcohol to form a slurry liquid phase.

[0078] Finally, mix 74 parts by weight of solid material and 26 parts by weight of liquid material and stir thoroughly with a magnetic stirrer to form a slurry. The liquid component should be added to the stirring system in multiple batches.

[0079] (3) Pouring: Immerse the porous polyurethane mold from step (1) into the ceramic slurry prepared in step (2), stir thoroughly, and squeeze out excess slurry to achieve a slurry filling rate of 0.22 g / cm³ in the mold. 3 .

[0080] (4) Sintering

[0081] After drying at 80℃ for 12 hours, the material was sintered in an air atmosphere without pressure in a muffle furnace. The sintering process was divided into the following stages: the initial heating stage, from room temperature to 700℃; the oxidation process, which slowly increased from 700℃ to 850℃ over 100 minutes to oxidize some silicon carbide to silicon oxide, providing conditions for the sintering neck formation stage; the heating process, which increased from 850℃ to 1400℃ over 3 hours; the sintering process, which was maintained at 1400℃ for 2 hours; and the thermal annealing process, which involved stable cooling to 600℃ over 4.5 hours, followed by cooling to room temperature over 2 hours, to obtain a common composite phase change material (CPCM) ceramic framework.

[0082] Application example: Preparation of composite phase change materials

[0083] Application Example 1

[0084] A preheated alumina ceramic container (inner diameter 50.5mm*50.5mm*50.5mm) was heated to 145℃. 53 parts by weight of potassium nitrate, 7 parts by weight of sodium nitrate, and 40 parts by weight of sodium nitrite were added to the preheated alumina ceramic container. The KNO3-NaNO3-NaNO2 ternary solar salt was then heated to melt under nitrogen protection.

[0085] An anisotropic high thermal conductivity composite phase change material (DCPCM) with directional heat transfer enhancement and thermal management is formed by immersing the ceramic skeleton prepared in Example 1 into a high-temperature alumina ceramic container.

[0086] Application Comparative Example 1

[0087] A preheated alumina ceramic container (inner diameter 50.5mm*50.5mm*50.5mm) was heated to 145℃. 53 parts by weight of potassium nitrate, 7 parts by weight of sodium nitrate, and 40 parts by weight of sodium nitrite were added to the preheated alumina ceramic container. The KNO3-NaNO3-NaNO2 ternary solar salt was then heated to melt under nitrogen protection.

[0088] The ceramic framework prepared in Comparative Example 1 was then immersed in a high-temperature alumina ceramic container to form an isotropic high thermal conductivity composite phase change material (OCPCM).

[0089] Application Comparative Example 2

[0090] A preheated alumina ceramic container (inner diameter 50.5mm*50.5mm*50.5mm) was heated to 145℃. 53 parts by weight of potassium nitrate, 7 parts by weight of sodium nitrate, and 40 parts by weight of sodium nitrite were added to the preheated alumina ceramic container. The KNO3-NaNO3-NaNO2 ternary solar salt was then heated to melt under nitrogen protection.

[0091] The ceramic framework prepared in Comparative Example 2 was then immersed in a high-temperature alumina ceramic container to form a common composite phase change material (CPCM).

[0092] Application of Comparative Example 3: Pure Molten Salt

[0093] A preheated alumina ceramic container (inner diameter 50.5mm*50.5mm*50.5mm) was heated to 145℃. 53 parts by weight of potassium nitrate, 7 parts by weight of sodium nitrate, and 40 parts by weight of sodium nitrite were added to the preheated alumina ceramic container. The KNO3-NaNO3-NaNO2 ternary solar salt was then heated to melt under nitrogen protection.

[0094] Test Results

[0095] Figure 3 The image shows an anisotropic composite phase change material (DCPCM) obtained in Application Example 1 of this invention. It can be clearly seen that silicon carbide fibers with a significantly consistent orientation are distributed on the surface of the composite phase change material skeleton and in the internal pores. This indicates that during the preparation of the ceramic skeleton, the silicon carbide fibers are tightly connected to the silicon carbide ceramic matrix through sintering and have orientation.

[0096] Figure 4The graph shows a comparison of the thermal conductivity of Application Example 1 and Comparative Examples 1, 2, and 3. The composite phase change material (DCPCM) prepared in Application Example 1 has a thermal conductivity of 1.94 W / m·K in the fiber orientation reinforcement direction, which is 228.8% higher than the thermal conductivity of pure molten salt in Comparative Example 3 (0.59 W / m·K), 20.5% higher than the isotropic high thermal conductivity composite phase change material (OCPCM) of Comparative Example 1 (without fiber orientation), and 28.5% higher than the ordinary composite phase change material Comparative Example 2 (CPCM). This demonstrates that the ceramic skeleton prepared in Example 1, due to the high orientation of the silicon carbide fibers, significantly improves the thermal conductivity of the composite phase change material DCPCM in the fiber orientation reinforcement direction.

[0097] Figure 5 The experimental setup for testing the maximum temperature difference and phase transition time is shown in the comparison diagram of the heating process at each temperature measurement point in Application Example 1 and Application Comparative Example 3. Among them, (a) is an overview of the experimental instruments, which mainly include an Agilent data acquisition instrument (Agilent 34970A, Keysight); a PID high-precision temperature controller (AT70X, Beijing Xinxin Industrial Control); and a regulated DC power supply (62024P-600-8, Chroma). Figure 5 (b) is the experimental platform. A groove (57mm*54mm*60mm) was cut inside the Al2O3 ceramic fiber insulation platform to place a high-temperature quartz square dish. A ceramic heater was placed on the front wall. Due to the corrosiveness of molten salt and the accuracy of the temperature measurement range, a K-type armored thermocouple was used to complete the temperature measurement. There are six temperature measurement points: the upper inner side of the front wall (the highest point of molten salt temperature, point P1), the lower inner side of the front wall (the point where the longitudinal temperature gradient of molten salt is determined, point P2), the upper left wall (the point where the upper part of the molten salt has passed the half-phase change, point P3), the lower right wall (the point where the upper part of the molten salt has melted past the half-phase change, point P4), the upper rear wall (the point where the upper part of the molten salt has completely changed phase, point P5), and the lower rear wall (the point where the phase change is completely changed, point P6).

[0098] Figure 5 (c) shows the experimental results of the maximum temperature difference and phase transition time of the anisotropic composite phase change material DCPCM applied in Example 1. Figure 5 (d) shows the experimental results of the maximum temperature difference and phase change time using the pure molten salt in Comparative Example 3. Compared to the pure molten salt in Comparative Example 3, the fiber-induced composite phase change material DCPCM can reduce the phase change time of a single-tank energy storage system by 36.25% under the same heating conditions. Furthermore, it can reduce the maximum internal temperature difference by 48.6% and the average temperature difference by 39.3%.

[0099] Compared to composite phase change materials (CPCM, comparative application example 2) without added silicon carbide fibers, the maximum temperature difference was reduced by 22.9%, the average temperature difference was reduced by 17.5%, and the phase change time under the same heating conditions was reduced by 19.6%.

[0100] Figure 6 The chart shows a comparison of the energy storage efficiency of Application Example 1 and Comparative Examples 1, 2, and 3. Compared to the pure molten salt in Comparative Example 3, the composite phase change material system DCPCM in Application Example 1 increases the energy storage efficiency of the distributed solar single-tank energy storage system by 108.2%. Compared to the ordinary composite phase change material (CPCM) in Comparative Example 2, the composite phase change material system DCPCM in Application Example 1 increases the energy storage efficiency of the distributed solar single-tank energy storage system by 31.3%. Compared to the isotropic high thermal conductivity composite phase change material (OCPCM) in Comparative Example 1, the composite phase change material system DCPCM in Application Example 1 increases the energy storage efficiency of the distributed solar single-tank energy storage system by 20.5% (energy storage rate is the average energy stored per unit time).

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions provided by the embodiments of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit provided by the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles provided by the embodiments of the present invention should be included within the protection scope provided by the embodiments of the present invention.

Claims

1. A method for preparing a directional thermally conductive, anisotropic porous silicon carbide ceramic framework, characterized in that, Includes the following steps: S1 Slurry Preparation: The slurry is composed of a mixture of solid and liquid phase components. The solid phase composition consists of silicon carbide fibers, silicon carbide particles, and sintering aids; The liquid phase component is composed of deionized water, dynamic viscosity control agent, defoamer and crosslinking agent; S2 slurry injection: The prepared slurry is induced and injected into a porous polyurethane mold by a multi-type driven laminar flow field; the multi-type driven laminar flow field includes a combination of servo electric cylinder driven laminar flow field, gravity guided low-speed laminar flow field and rotary platform guided laminar flow field. S3 sintering: After the mold is dried, it is sintered in an air atmosphere in a muffle furnace to obtain the silicon carbide ceramic skeleton.

2. The method for preparing the silicon carbide ceramic framework according to claim 1, characterized in that, In step S1, the solid phase composition consists of 5-10 parts by weight of silicon carbide fiber, 75-80 parts by weight of silicon carbide particles and 15 parts by weight of sintering aid; the sintering aid consists of 8 parts by weight of kaolin, 4 parts by weight of alumina and 3 parts by weight of yttrium oxide. The liquid phase composition is a mixture of 92 parts by weight of deionized water, 2 parts by weight of 10 wt% NaOH solution, 2 parts by weight of glycerol and 4 parts by weight of polyvinyl alcohol. The weight ratio of the solid phase component to the liquid phase component is 35~40:10~15.

3. The method for preparing the silicon carbide ceramic framework according to claim 2, characterized in that, In step S1, the silicon carbide fiber has a diameter of 5-10 μm and an aspect ratio of 5-20, and the silicon carbide particle has a particle size of 10-15 μm.

4. The method for preparing a silicon carbide ceramic framework according to claim 1, characterized in that, In step S2, the operation sequence of each flow field is as follows: servo electric cylinder drives laminar flow field, gravity guides low-speed laminar flow field, and rotary platform guides laminar flow field.

5. The method for preparing the silicon carbide ceramic framework according to claim 4, characterized in that, In step S2, the operation sequence of each flow field is as follows: servo electric cylinder drives laminar flow field, gravity guides low-speed laminar flow field, rotary platform guides laminar flow field, and gravity guides low-speed laminar flow field.

6. The method for preparing the silicon carbide ceramic framework according to claim 4, characterized in that, In the laminar flow field driven by the servo electric cylinder, the push rod speed is greater than 0 mm / s and less than or equal to 5 mm / s. And / or in the gravity-guided low-speed laminar flow field, the viscosity of the ceramic slurry is adjusted to be between 500-1500 mPa·s. And / or in the laminar flow field guided by the rotary platform, the rotary platform rotation speed is 150 r / min.

7. The method for preparing a silicon carbide ceramic framework according to claim 1, characterized in that, In step S2, the porous polyurethane mold is soaked in a 15wt% NaOH solution for ≥16 hours before injection.

8. The method for preparing a silicon carbide ceramic framework according to claim 1, characterized in that, In step S3, the air atmosphere sintering and forming process in the muffle furnace includes the following processes: the initial heating stage, from room temperature to 700°C; the oxidation process, from 700°C to 850°C after 100 minutes. The heating process involved raising the temperature from 850℃ to 1400℃ over 3 hours. The sintering process involved maintaining the temperature at 1400℃ for 2 hours. The hot annealing process involved cooling the temperature steadily to 600℃ over 4.5 hours, followed by cooling to room temperature over 2 hours.

9. A porous silicon carbide ceramic framework with directional thermal conductivity and anisotropy prepared by the preparation method according to any one of claims 1-8.

10. A directional thermal management composite phase change material, characterized in that, It is composed of a silicon carbide ceramic framework as described in claim 9 and a phase change material.

11. The directional thermal management composite phase change material as described in claim 10, characterized in that, The phase change material is an inorganic salt, including one or more of nitrates, carbonates, and chlorides in any proportion.

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