Phase change heat storage ball with built-in curved rib and preparation method thereof

Abstract

The application relates to a phase change heat storage ball with built-in curved ribs and a preparation method thereof. The phase change heat storage ball comprises a spherical heat storage unit shell (1), a curved high-thermal-conductivity rib (2) and a phase change material (3). The curved high-thermal-conductivity rib (2) is arranged in the spherical heat storage unit shell (1), and the phase change material (3) is filled in the spherical heat storage unit shell (1). The curved high-thermal-conductivity rib (2) has at least one layer. The preparation is mainly implemented through a 3D printing technology. Compared with the prior art, the application has the advantages of simple preparation process, high energy storage density and the like, and can effectively improve the power density in the charging and discharging process of the phase change heat storage system.

Description

Technical Field

[0001] This invention relates to the field of energy storage systems, specifically to a phase change thermal storage ball with built-in curved fins and its preparation method. Background Technology

[0002] Thermal energy storage technology is one of the effective methods to address the mismatch in time, space, and intensity between energy demand and supply during the utilization of renewable energy. Phase change thermal energy storage systems based on solid-liquid phase change materials (PCMs) utilize the enormous energy released during the phase change process, exhibiting characteristics such as high energy storage density, high energy utilization efficiency, and stable operating temperature. They have broad application prospects in fields such as solar thermal utilization, waste heat recovery, electronic device cooling, and energy conservation in building heating and air conditioning.

[0003] In thermal storage systems, achieving both high energy storage density and high power density is often difficult. For thermal storage systems based on solid-liquid phase change materials (PCTs), the energy storage density is high, but due to the typically low thermal conductivity of PCTs, the power density during the charge-and-discharge process is usually low. Encapsulating PCTs within spherical storage units can effectively increase the heat exchange area between the PCT and the heat exchange fluid, thereby improving the power density during the charge-and-discharge process. However, due to the low thermal conductivity of PCTs, a significant temperature difference still exists within the storage unit, leaving considerable room for improvement in both power density and heat exchange efficiency.

[0004] Methods to enhance the heat transfer performance of phase change thermal storage units mainly include using composite phase change materials and adding high thermal conductivity fins. Preparing composite phase change materials with expanded graphite or foamed metals can effectively improve the equivalent thermal conductivity of the composite phase change material, reduce the internal temperature gradient of the thermal storage unit, and increase the power density of the thermal storage unit. However, the phase change material filling rate is significantly reduced in expanded graphite-based composite phase change materials, resulting in a significant decrease in the energy storage density of the phase change thermal storage unit. Furthermore, foamed metal-based composite phase change materials are difficult to effectively encapsulate within spherical phase change thermal storage units. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a phase change thermal storage ball with built-in curved fins, which has a simple preparation process, high energy storage density, and can effectively improve the power density during the charging and discharging process of the phase change thermal storage system, as well as its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] This invention addresses the problem of large internal temperature gradients and low power density in spherical phase change thermal storage units during the charging and discharging process. It proposes a spherical phase change thermal storage unit with built-in double-layer curved fins. This design effectively reduces the internal thermal resistance of the spherical phase change thermal storage unit, increases the heat transfer rate during the charging and discharging process, and further improves the heat transfer efficiency of the thermal storage system. It is suitable for waste heat recovery and utilization, solar thermal utilization, and other fields. The specific solution is as follows:

[0008] A phase change thermal storage sphere with built-in curved fins, the phase change thermal storage sphere comprising a spherical thermal storage unit shell, curved high thermal conductivity fins, and a phase change material;

[0009] The curved high thermal conductivity fins are disposed inside the spherical thermal storage unit shell, and the phase change material is filled inside the spherical thermal storage unit shell.

[0010] Furthermore, the curved high thermal conductivity fin has at least one layer.

[0011] Furthermore, the curved high thermal conductivity fins have at least two layers.

[0012] Furthermore, the curved high thermal conductivity fin is a double-layer curved fin.

[0013] Furthermore, in the aforementioned double-layer curved high thermal conductivity fins, there are six outer curved fins and six inner curved fins. The center of curvature of the outer curved fins is on the same horizontal plane as the center of the sphere, 17.54 mm from the center of the sphere, with a radius of curvature of 30.54 mm and an arc of 1.808; the center of curvature of the inner curved fins is on the same horizontal plane as the center of the sphere, 60 mm from the center of the sphere, with a radius of curvature of 65 mm and an arc of 0.756.

[0014] Furthermore, the diameter of the spherical thermal storage unit shell is 50 mm, and the shell thickness is 0.5-2.0 mm.

[0015] Furthermore, the diameter of the curved high thermal conductivity fins is not less than 1 mm, and they occupy 1-9% of the volume fraction of the spherical thermal storage unit shell. Preferably, it is 3-9%, more preferably 5-9%. The specific diameter of the fins is adjusted according to their volume fraction in the spherical phase change thermal storage unit.

[0016] Furthermore, the spherical thermal storage unit shell and the curved high thermal conductivity fins are made of the same material, namely stainless steel or aluminum alloy. To facilitate the 3D printing of the curved high thermal conductivity fins together with the spherical thermal storage unit shell, the curved high thermal conductivity fins should be made of the same material as the spherical thermal storage unit shell.

[0017] Furthermore, the phase change material includes paraffin, erythritol, butylene tertrol, sebacic acid, urea, high-density polyethylene, maleic acid, oxalic acid, hydroquinone, potassium nitrate, sodium nitrate, sodium nitrite, sodium carbonate, potassium carbonate, or lithium carbonate.

[0018] A method for preparing a phase change thermal storage ball with built-in curved fins as described in claim 1, the method comprising the following steps:

[0019] Through 3D printing, the main body of the spherical phase change thermal storage unit shell with curved high thermal conductivity fins and an opening at the top, as well as the spherical crown part that matches the opening, are obtained.

[0020] The phase change material is filled into the main body of the spherical phase change thermal storage unit shell through the opening, heated in a constant temperature chamber for 0.5-2 hours to completely melt the phase change material, and then cooled to completely solidify the phase change material.

[0021] The spherical phase change thermal storage unit shell body is welded and sealed to the spherical crown part by laser welding to obtain a phase change thermal storage sphere with built-in curved ribs.

[0022] When heating the main shell of the spherical phase change thermal storage unit filled with phase change material in a constant temperature chamber and cooling it at room temperature, the opening should be kept facing upwards. If necessary, a fixing device made of metal frame can be installed to prevent leakage of phase change material.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The built-in curved high thermal conductivity fins of the present invention can effectively reduce the equivalent thermal resistance inside the spherical phase change thermal storage unit during the heat charging and heat release process while ensuring that the phase change material has a high filling rate, thereby increasing the power density of the thermal storage unit and having good heat storage and heat release capabilities.

[0025] (2) The present invention generates a spherical thermal storage unit with built-in double-layer curved high thermal conductivity fins by 3D printing, which can simplify the fin manufacturing and processing process, while ensuring that the curved fins can be tightly connected with the shell of the spherical phase change thermal storage unit, eliminating the contact thermal resistance between the curved fins and the shell of the spherical phase change thermal storage unit.

[0026] (3) The present invention can ensure the airtightness of the spherical phase change thermal storage unit by sealing the spherical phase change thermal storage unit by laser welding, and prevent the phase change material from leaking during the charging and discharging process.

[0027] (4) The raw materials of the present invention are easy to obtain, the production process is simple, and it is easy to carry out large-scale preparation. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the phase change thermal storage ball of the present invention;

[0029] Figure 2 The average liquid phase fraction change during the heat charging process of the spherical phase change thermal storage unit with built-in ribs of different shapes in Example 1;

[0030] Figure 3 The average liquid phase fraction change during the heat release process of the spherical phase change thermal storage unit with built-in ribs of different shapes in Example 1;

[0031] Figure 4 The average liquid phase fraction change of the spherical phase change thermal storage unit with built-in double-layer curved fins under different fin volume fractions in Example 1 during the heat charging process;

[0032] Figure 5 The average liquid phase fraction change of the spherical phase change thermal storage unit with built-in double-layer curved fins under different fin volume fractions in Example 1 during the heat release process;

[0033] Figure 6 This is a cross-sectional view of the phase change thermal storage ball of the present invention;

[0034] As indicated by the labels in the figure: 1-Spherical thermal storage unit shell; 3-Phase change material; 21-Inner curved high thermal conductivity fin; 22-Outer curved high thermal conductivity fin. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0036] A phase change heat storage ball with built-in curved fins, such as Figure 1 , 6 The phase change thermal storage sphere comprises a spherical thermal storage unit shell 1, curved high thermal conductivity fins 2, and a phase change material 3. The curved high thermal conductivity fins 2 are disposed inside the spherical thermal storage unit shell 1, and the phase change material 3 is filled inside the spherical thermal storage unit shell 1. There are six outer curved fins and six inner curved fins. The center of curvature of the outer curved fins is on the same horizontal plane as the center of the sphere, 17.54 mm from the center, with a radius of curvature of 30.54 mm and an arc of 1.808. The center of curvature of the inner curved fins is on the same horizontal plane as the center of the sphere, 60 mm from the center, with a radius of curvature of 65 mm and an arc of 0.756.

[0037] The curved high thermal conductivity fins 2 are layered at least once. The spherical thermal storage unit shell 1 has a diameter of 50 mm and a shell thickness of 0.5-2.0 mm. The curved high thermal conductivity fins 2 have a diameter of not less than 1 mm and occupy 1-9% of the volume fraction of the spherical thermal storage unit shell 1. Preferably, it is 3-9%, more preferably 5-9%. The specific diameter of the fins is adjusted according to their volume fraction in the spherical phase change thermal storage unit.

[0038] The spherical thermal storage unit shell 1 and the curved high thermal conductivity fin 2 are made of the same material, namely stainless steel or aluminum alloy. In order to facilitate the 3D printing of the curved high thermal conductivity fin 2 together with the spherical thermal storage unit shell 1, the curved high thermal conductivity fin 2 should be made of the same material as the spherical thermal storage unit shell 1.

[0039] Phase change material 3 includes paraffin, erythritol, butylene tertrol, sebacic acid, urea, high-density polyethylene, maleic acid, oxalic acid, hydroquinone, potassium nitrate, sodium nitrate, sodium nitrite, sodium carbonate, potassium carbonate, or lithium carbonate.

[0040] A method for preparing a phase change thermal storage ball with built-in curved fins, the method comprising the following steps:

[0041] Through 3D printing, the main body of the spherical phase change thermal storage unit shell with curved high thermal conductivity fins and an opening at the top, as well as the spherical crown part that matches the opening, are obtained.

[0042] The phase change material 3 is filled into the main body of the spherical phase change thermal storage unit shell through the opening, heated in a constant temperature chamber for 0.5-2 hours to completely melt the phase change material 3, and then cooled to completely solidify the phase change material 3.

[0043] The spherical phase change thermal storage unit shell body is welded and sealed to the spherical crown part by laser welding to obtain a phase change thermal storage sphere with built-in curved ribs.

[0044] When heating the main shell of the spherical phase change thermal storage unit filled with phase change material in a constant temperature chamber and cooling it at room temperature, the opening should be kept facing upwards. If necessary, a fixing device made of metal frame can be installed to prevent leakage of phase change material.

[0045] Example 1

[0046] The spherical phase change thermal storage unit with built-in high thermal conductivity fins mainly consists of a spherical thermal storage unit shell, high thermal conductivity fins, and a phase change material. Aluminum alloy is used as the material for both the spherical thermal storage unit shell and the high thermal conductivity fins, possessing high strength, thermal stability, and good thermal conductivity. The phase change thermal storage unit has a diameter of 50 mm and a shell thickness of 1 mm. The phase change material selected is paraffin wax, with a melting point of 81℃ and a density of 0.785 g / cm³. 3 .

[0047] Optimization Design of the Shape and Dimensions of Curved High Thermal Conductivity Fins Inside the Phase Change Thermal Storage Unit: First, the shape and dimensions of the double-layer curved high thermal conductivity fins inside the phase change thermal storage unit were initially designed. The heat charging and releasing processes of this phase change thermal storage unit at a constant wall temperature were calculated through numerical simulation. Based on the changes in liquid phase fraction at various locations inside the thermal storage unit obtained from numerical calculations, and adhering to the principle of fins being located near the area with the worst heat transfer, the curvature, position, and number of curved fins were continuously adjusted. This ensured that the average liquid phase fraction maintained a high rate of change during the heat charging and releasing processes, thereby improving the heat transfer performance of the phase change thermal storage unit. Considering the changes in the average liquid phase fraction within the phase change thermal storage unit during both heat charging and releasing processes, the optimal shape and dimensions of the double-layer curved high thermal conductivity fins inside the spherical phase change thermal storage unit were finally obtained. Figure 1 The image shows a spherical phase change thermal storage unit with a built-in optimized design of double-layer curved high thermal conductivity fins.

[0048] Figure 2 and Figure 3 The changes in the average liquid fraction within a spherical phase change thermal storage unit during heat charging and discharging were compared for units without fins, with built-in straight fins, with built-in single-layer curved fins, and with built-in optimized double-layer curved fins. The figures show that, compared to other types of phase change thermal storage units, the phase change thermal storage unit with the optimized double-layer curved fins exhibits a faster increase in average liquid fraction during heat charging and a faster decrease during heat discharging, maintaining a consistently high rate of change in average liquid fraction. Therefore, its heat charging and discharging times are the shortest.

[0049] Furthermore, it can be observed that the average liquid phase fraction of the phase change thermal storage unit with built-in curved fins changes faster than that with built-in straight fins, indicating superior heat transfer performance. This is because curved fins have a larger surface area than straight fins, increasing the heat transfer rate. Simultaneously, during the phase change process, the phase interface gradually moves inward from the spherical shell in an ellipsoidal or spherical shape. Designing the fins to be curved, close to the phase interface, effectively conforms to the interface, ensuring good contact between the fins and the phase change material that has not undergone phase change, resulting in better enhanced heat transfer capacity. By comparing the changes in the average liquid phase fraction within the spherical phase change thermal storage unit with built-in double-layer curved fins and single-layer curved fins, it can be seen that double-layer curved fins have a better enhanced heat transfer effect than single-layer curved fins. This is mainly due to the larger heat transfer surface area of ​​double-layer curved fins compared to single-layer curved fins. While maintaining the same volume fraction, upgrading from double-layer to triple-layer curved ribs can further increase the heat transfer area between the ribs and the phase change material, thus enhancing the heat transfer performance of the spherical phase change thermal storage unit. However, at this point, the rib diameter is too small to be easily generated by 3D printing. Therefore, the enhanced heat transfer structure inside the spherical phase change thermal storage unit is designed as a double-layer curved rib structure, which is simple to manufacture and can significantly shorten the melting and solidification time of the phase change material within the unit, resulting in better heat storage and release capabilities.

[0050] Figure 4 and Figure 5 The changes in the average liquid phase fraction within a spherical phase change thermal storage unit with optimized double-layer curved fins during heat charging and releasing processes were compared at fin volume fractions of 1%, 3%, 5%, 7%, and 9%. As shown in the figure, once the fin volume fraction exceeds 5%, further increasing the fin volume fraction does not significantly accelerate the change in average liquid phase fraction during heat charging and releasing, and the charging and releasing times are not significantly shortened. To balance the energy storage density and power density of the phase change thermal storage unit, the volume fraction of the double-layer curved fins was determined to be 5%.

[0051] Fabrication of a spherical phase change thermal energy storage unit: The main body of the spherical thermal energy storage unit, with an internal double-layer curved fin, and the top spherical crown portion are fabricated using 3D printing. The main body of the shell is open at the top, allowing it to fit tightly against the crown portion. The double-layer curved high thermal conductivity fins account for 5% of the internal volume of the thermal energy storage unit. Paraffin wax is filled into the main body of the spherical phase change thermal energy storage unit with internal double-layer curved fins through the top opening. The weight change of the thermal energy storage unit before and after filling with phase change material is measured, resulting in a paraffin wax mass of 36.5 ± 0.5 g inside the thermal energy storage unit. The phase change material accounts for approximately 80% of the internal volume of the thermal energy storage unit. The thermal energy storage unit filled with phase change material is placed in a constant temperature chamber at 150℃ and heated for 2 hours to completely melt the phase change material. During this process, the phase change material is fixed by a metal frame, ensuring that the opening of the thermal energy storage unit always faces upwards. After heating, the constant temperature chamber is closed, and the temperature inside the chamber is allowed to drop to room temperature and the spherical phase change thermal energy storage unit is cooled for 2 hours to completely solidify the phase change material. Then, the upper opening of the spherical phase change thermal storage unit is welded to the spherical crown shell using laser welding. The heating and cooling process is repeated several times to test the airtightness of the spherical phase change thermal storage unit. In this way, a spherical phase change thermal storage unit with built-in double-layer curved fins can be generated, which can be used for heat storage and heat release in domestic solar water heaters.

[0052] Example 2

[0053] The spherical thermal storage unit shell body and top spherical crown portion, optimized in Example 1 with built-in double-layer curved fins, were generated by 3D printing. The shell and fin materials were selected from aluminum alloy, which has high thermal conductivity. 48±0.5g of adipic acid (melting point 151℃, density 1.36g / cm³) was used. 3The adipic acid was filled into the thermal storage unit through the opening at the top, with a filling rate of 77%. The thermal storage unit filled with phase change material was then placed in a constant temperature chamber at 200°C for 2 hours to completely melt the phase change material. Subsequently, the thermal storage unit was left to stand at room temperature for 2 hours to allow the phase change material to completely solidify. The thermal storage unit was sealed by laser welding and subjected to multiple high-temperature and low-temperature cycle tests to verify its airtightness. The spherical phase change thermal storage unit with built-in double-layer curved fins produced by this method can be used in fields such as industrial waste heat recovery and utilization.

[0054] Example 3

[0055] Following the numerical calculation method in Example 1, the dimensions and shape of the double-layer curved fins inside the spherical thermal storage unit were optimized. The main body of the spherical thermal storage unit shell and the top spherical crown were obtained by 3D printing. The shell and fins were made of stainless steel, which has good strength, corrosion resistance, and thermal conductivity. 100±0.5g of a ternary mixed carbonate (Li₂CO₃-K₂CO₃-Na₂CO₃, mass ratio 32:35:33, melting point 395℃, density 2.31g / cm³) was used. 3 The powder was filled into the phase change thermal storage unit through the opening at the top, with a ternary mixed carbonate filling rate of 75%. The storage unit, after being filled with phase change material, was placed in a 500°C constant temperature chamber and heated for 2 hours to completely melt the phase change material. Subsequently, the storage unit was allowed to stand at room temperature for 1 hour to allow the phase change material to completely solidify. The storage unit was then sealed using laser welding and subjected to multiple high- and low-temperature cycle tests to verify its airtightness. The spherical phase change thermal storage unit with built-in double-layer curved fins produced by this method can be used in fields such as solar thermal utilization.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A phase change thermal storage ball with built-in curved fins, characterized in that, The phase change thermal storage ball includes a spherical thermal storage unit shell (1), curved high thermal conductivity fins (2), and phase change material (3); The curved high thermal conductivity fins (2) are disposed inside the spherical thermal storage unit shell (1), and the phase change material (3) is filled inside the spherical thermal storage unit shell (1); The curved high thermal conductivity rib (2) is a double-layer curved rib. In the double-layer curved rib, there are 6 outer curved ribs and 6 inner curved ribs. The curvature center of the outer curved rib is on the same horizontal plane as the center of the sphere, 17.54 mm away from the center of the sphere, with a curvature radius of 30.54 mm and an arc of 1.

808. The curvature center of the inner curved rib is on the same horizontal plane as the center of the sphere, 60 mm away from the center of the sphere, with a curvature radius of 65 mm and an arc of 0.

756. The diameter of the curved high thermal conductivity fin (2) is not less than 1 mm, and it occupies 1-9% of the volume of the spherical thermal storage unit shell (1).

2. The phase change thermal storage ball with built-in curved fins according to claim 1, characterized in that, The spherical thermal storage unit shell (1) has a diameter of 50 mm and a shell thickness of 0.5-2.0 mm.

3. A phase change thermal storage ball with built-in curved fins according to claim 1, characterized in that, The spherical thermal storage unit shell (1) and the curved high thermal conductivity fins (2) are made of the same material, namely stainless steel or aluminum alloy.

4. A phase change thermal storage ball with built-in curved fins according to claim 1, characterized in that, The phase change material (3) includes paraffin, erythritol, butylene tertrol, sebacic acid, urea, high-density polyethylene, maleic acid, oxalic acid, hydroquinone, potassium nitrate, sodium nitrate, sodium nitrite, sodium carbonate, potassium carbonate, or lithium carbonate.

5. A method for preparing a phase change thermal storage ball with built-in curved fins as described in claim 1, characterized in that, The method includes the following steps: The main body of the spherical phase change thermal storage unit shell with an opening at the top, the curved high thermal conductivity fins (2), and the spherical crown part that matches the opening were obtained by 3D printing. The phase change material (3) is filled into the main body of the spherical phase change thermal storage unit shell through the opening, heated in a constant temperature box for 0.5-2 hours to completely melt the phase change material (3), and then cooled to completely solidify the phase change material (3). The spherical phase change thermal storage unit shell body is welded and sealed to the spherical crown part by laser welding to obtain a phase change thermal storage sphere with built-in curved ribs.

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