Bionic self-regulating heat accumulator

Abstract

The application discloses a kind of bionic self-regulation heat accumulator, comprising: shell, heat exchange pipeline, reinforcing fin and external ultrasonic module. Heat exchange pipeline is arranged in the center of shell, and its two ends are inlet and outlet, and the outside of pipe is filled with phase change material;Reinforcing fin is uniformly arranged around heat exchange pipeline, and is designed into fractal arrow structure, imitates the main vein and dry of self-blade, the length and thickness of its adjacent level bifurcation satisfy self-similarity law, and non-uniform half-open half-closed hole is also opened on fin, and the aperture and hole density change in steps along the direction of gravity;External ultrasonic module is arranged in steps on the outer wall of shell along the direction of gravity.The application significantly improves the heat transfer efficiency and heat storage rate of phase change material through the cooperative design of fractal arrow-shaped reinforcing fin and non-uniform half-open half-closed hole array, combined with external gradient ultrasonic module, and achieves the purpose of self-adaptive convective heat transfer regulation by means of shape memory material self-driven thermal deformation, improves the heat storage performance and stability of system under different working conditions.

Description

Technical Field

[0001] This invention relates to the field of thermal storage, specifically to a biomimetic self-regulating thermal storage device that is equipped with high-efficiency biomimetic fins and achieves adaptive convective heat transfer regulation by means of shape memory material self-driven thermal deformation. Background Technology

[0002] The inherent intermittency and volatility of renewable energy sources such as solar and wind power place higher demands on energy storage systems. Latent heat storage technology has emerged to address this need. Based on the characteristic of phase change materials (PCMs) absorbing or releasing heat during phase change, this technology achieves an effective balance between high heat storage density, minimal temperature variation, and reasonable cost. Moreover, developing latent heat storage devices not only helps improve energy efficiency and promotes a low-carbon economy, but also reduces dependence on fossil fuels, thereby alleviating environmental pressure. Therefore, by optimizing PCM performance, improving storage device structural design, and enhancing system integration efficiency, latent heat storage technology is expected to play a crucial role in the future energy system.

[0003] It should be noted that the fatigue thermal conductivity of most phase change materials (except liquid metals and their alloys) severely limits the energy efficiency of latent heat storage devices. Therefore, researchers both domestically and internationally have conducted extensive research on heat transfer enhancement technologies for latent heat storage devices, which can be mainly divided into two categories: active and passive. Active enhancement technologies rely on external energy input, and typical methods include mechanical stirring, ultrasonic vibration, and the application of magnetic and electric fields. However, these technologies are still under development, and their reliability and maturity need to be verified. They also impose stringent requirements on system complexity and integration. In contrast, passive enhancement technologies improve heat transfer performance through the self-optimization of materials or structures, requiring no external energy input. These systems are simple and highly maintainable, and are therefore widely used in engineering fields. Common methods include using highly conductive additives, using extended surfaces (such as fins), employing microencapsulated fluidized beds, and using a tiered arrangement of various phase change materials. Among these, fractal fins, as a passive enhancement method that mimics the fractal structure design found in nature, show great potential in thermal management applications. Its multi-level, self-similar branched structure enables efficient heat transport from the root to the entire phase change material region, which not only significantly enhances heat conduction, but also fully fills the space through a complex flow channel network, further strengthening the extensibility of heat transport.

[0004] Although existing research has proposed various fractal fin designs to improve the heat transfer efficiency of latent heat storage devices, current technologies still suffer from the following drawbacks. First, significant temperature stratification exists in the longitudinal direction of the storage device. Due to the low thermal conductivity of the phase change material and insufficient natural convection driving force, uneven temperature distribution occurs along the gravity direction, with higher temperatures at the top and lower temperatures at the bottom. This not only reduces energy storage efficiency but also increases system heat loss. Second, while the complex structure of the fractal fins increases the heat conduction area, it also restricts the flow range of the liquid phase change material, significantly inhibiting the development of natural convection and resulting in inconsistent natural convection intensities in the lateral and longitudinal directions. Furthermore, current latent heat storage devices generally lack the ability to adaptively adjust the heat transfer rate based on external heat load. Their fixed heat transfer characteristics cause slow response at high loads and passive energy waste at low loads, making it difficult to adapt to the high-efficiency operation requirements under varying load scenarios. Therefore, there is an urgent need to develop a new generation of latent heat storage technology. Summary of the Invention

[0005] In view of the above-mentioned technical problems, the present invention provides a biomimetic self-regulating heat storage device with high-efficiency biomimetic fins and adaptive convective heat transfer regulation by means of shape memory material self-driven thermal deformation. It not only solves the problems of temperature stratification in the direction of gravity and suppression of radial natural convection, but also realizes adaptive regulation of heat storage rate according to heat load.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A biomimetic self-regulating thermal energy storage device includes a shell, a phase change thermal energy storage material filled within the shell, and a heat exchange pipe penetrating the shell. Reinforcing fins are disposed on the heat exchange pipe, uniformly arranged around its perimeter. The reinforcing fins are designed with a fractal arrow structure, with each level of the arrow structure including one main vein and two sub-branches. A non-uniform array of semi-open and semi-closed holes is formed on the reinforcing fins. The aperture and pore density of the semi-open and semi-closed holes gradually increase along the direction of gravity. It can change the semi-open and semi-closed state under temperature control; an external ultrasonic module is also provided on the outer wall of the shell. The external ultrasonic module is composed of an array of ultrasonic transmitters. The array of ultrasonic transmitters is distributed in a stepped manner along the direction of gravity, with more ultrasonic transmitters at the bottom. During the melting process, the external ultrasonic module excites the liquid phase change material region to generate fluid disturbance to enhance natural convection heat transfer. At the same time, it induces the semi-open and semi-closed hole array to resonate at the same frequency to excite local semi-active forced convection, thereby realizing mixed convection to enhance heat transfer.

[0007] This invention relates to a biomimetic self-regulating heat storage device. An external ultrasonic module significantly enhances natural convection heat transfer in the liquid phase change material region by stimulating fluid disturbance within that region. Furthermore, based on the principle of resonance, it induces resonance in a semi-open / semi-closed array of holes, thereby stimulating semi-active forced convection in localized areas, ultimately forming mixed convection and achieving enhanced heat transfer.

[0008] In this invention, the cross-section of the shell is including but not limited to symmetrical polygons such as circles, quadrilaterals, and pentagons, and the heat exchange channel is spiral or straight tube. The materials of both include but are not limited to metals and alloys such as copper, aluminum, or stainless steel.

[0009] In this invention, the length and thickness of the adjacent-level bifurcation of the reinforced fin satisfy the fractal self-similarity law, the number of sub-bifurcation levels is 3-5, the length ratio of adjacent-level bifurcation is 1.5-2.0, and the thickness fractal dimension is 2-3.

[0010] In this invention, the semi-open and semi-closed hole is a cantilever beam structure formed by partial cutting. Its root is still connected to the reinforcing fin. The shape of the partial cutting is a circle, an ellipse or a part of a polygon. The size change rate of the semi-open and semi-closed hole in the direction of gravity does not exceed 50%, and the density change rate does not exceed 50%.

[0011] In this invention, the reinforced fins are made of shape memory alloy material, which makes the semi-open and semi-closed holes open due to thermo-mechanical coupling after exceeding the high temperature threshold, and the opening range is larger when the temperature is higher, so as to reduce the suppression of radial natural convection; while at the low temperature threshold, the semi-open and semi-closed holes close, ensuring that natural convection in the direction of gravity is fully developed and reducing the temperature stratification effect in the direction of gravity.

[0012] In this invention, the shape memory alloy material is a nickel-titanium alloy or a copper-based shape memory alloy, and its phase change temperature matches the operating temperature range of the heat storage device; the high temperature threshold is about 5°C above the melting point of the phase change material, and the low temperature threshold is about 10°C below the melting point of the phase change material (considering that some phase change materials have excessively high supercooling).

[0013] In this invention, the operating frequency range of the ultrasonic transmitter must include the natural frequency of the reinforcing fin material, and in the gradient distribution of the ultrasonic transmitter array in the direction of gravity, the number of transmitters in the lower region is 1.5 to 3 times that in the upper region.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses relatively simple fractal arrow fins to enhance the melting rate while reducing the complexity of the fins, thereby weakening the limiting effect on natural convection during the heat storage process.

[0015] 2. This invention utilizes the synergistic design of fractal arrow-shaped reinforcing fins and a non-uniform semi-open and semi-closed hole array, combined with an external gradient ultrasonic module, to simultaneously stimulate natural convection and local semi-active forced convection during the melting process, forming a hybrid convection enhancement mechanism that significantly improves the heat transfer efficiency and heat storage and release rate of the phase change material.

[0016] 3. The reinforced fins made of shape memory alloy can automatically adjust the opening state of the semi-open and semi-closed holes according to the temperature. At high temperatures, it enhances radial flow and promotes gravity convection at low temperatures, realizing adaptive control of the heat transfer path, effectively suppressing temperature stratification, and improving the heat storage performance and stability of the system under different operating conditions. Attached Figure Description

[0017] Figure 1 A schematic diagram of a biomimetic self-regulating thermal storage device Figure 2 Schematic diagram of the two-dimensional structure of the fractal arrow-reinforced fin. Figure 3 Schematic diagram of a semi-open / semi-closed aperture array: a) Low heat flux; b) High heat flux In the diagram: 1. Heat exchange pipe; 2. Reinforced fins; 3. Ultrasonic module; 4. Heat storage tank shell; 5. Semi-open / semi-closed orifice; 6. Heat exchange medium inlet; 7. Heat exchange medium outlet. Detailed Implementation

[0018] To enhance understanding of the present invention, we will now describe it in further detail with reference to the accompanying drawings. These embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0019] This embodiment provides a biomimetic self-regulating thermal energy storage device, such as... Figure 1 As shown in Figures 2 and 3, it includes: 1. Heat exchange pipe; 2. Reinforced fins; 3. Ultrasonic module; 4. Heat storage tank shell; 5. Semi-open / semi-closed orifice; 6. Heat exchange medium inlet; 7. Heat exchange medium outlet.

[0020] In one embodiment, the heat storage tank shell 4 is selected as a regular pentagon with a side length of 120mm. The heat exchange pipe 1 is arranged at the center of the heat storage tank shell 4 and is selected as a straight pipe. The two ends exposed in the shell are the heat exchange medium inlet 6 and the heat exchange medium outlet 7, respectively. The closed area formed by the two is filled with lauric acid phase change material.

[0021] In one embodiment, the ultrasonic module 3 is arranged on the outer wall of the heat storage tank shell 4 and consists of an array of ultrasonic transmitters. The ultrasonic transmitter array is distributed in a stepped manner along the direction of gravity, with more ultrasonic transmitters at the bottom. The number of transmitters in the lower region is 2.25 times that in the upper region, and the operating frequency range of the ultrasonic transmitters includes the natural frequency of the reinforcing fin material. The external ultrasonic module can induce strong disturbances in the liquid phase change material region and the semi-open / semi-closed hole array simultaneously through frequency modulation. During this process, the natural convection heat transfer in the liquid phase change material region is enhanced; at the same time, the semi-open / semi-closed hole array excites forced convection heat transfer in local areas through the same-frequency vibration mechanism. The synergistic effect of these two heat transfer modes forces the originally inefficient heat transfer mode, which is mainly based on pure natural convection, into a highly efficient mixed convection mode composed of natural convection and forced convection, thereby significantly accelerating the melting rate of the phase change material.

[0022] In one embodiment, reinforced fins 2 are evenly distributed around the heat exchange pipe 1. The reinforced fins 2 are designed as fractal arrow structures, biomimetic to the structure of the main vein and trunk in a blade transport system. Each branch is generated iteratively, and each level of bifurcation further divides into two sub-branches. The length and thickness of adjacent level bifurcations of the reinforced fins 2 satisfy the fractal self-similarity law. The sub-branches have three levels, the length ratio of adjacent level bifurcations is 1.81, the thickness fractal dimension is 3, and the bifurcation angle is chosen to be 72° (e.g., ...). Figure 2 The fractal arrow structure shown in the figure has its length and thickness dimensions for each branch.

[0023] In one embodiment, the reinforced fins 2 of the fractal arrow structure are made of a shape memory alloy, specifically a nickel-titanium alloy. Shape memory alloys are special metal alloys that can deform at low temperatures and recover their original pre-deformed shape upon heating. This phenomenon stems from the reversibility of their solid-solid phase transition, as well as their shape memory effect and superelastic properties. The nickel-titanium alloy is composed of nickel and titanium in a near equimolar ratio, exhibiting excellent superelasticity and shape memory effect, and its phase transition temperature matches the operating temperature range of the thermal storage device.

[0024] In one embodiment, a semi-open / semi-closed hole 5 is formed on the surface of a fractal arrow fin made of shape memory alloy. First, a hole is machined in the opening area, and then a semi-open / semi-closed hole 5 with a cantilever beam structure is formed by partial cutting. The root of the semi-open / semi-closed hole 5 remains connected to the fractal arrow fin, and the partially cut shape is a portion of a circle. The array of semi-open / semi-closed holes on the surface of the fractal arrow fin gradually increases in size and density along the direction of gravity, with a size change rate of 30% and a density change rate of 15% in the direction of gravity. Furthermore, the semi-open / semi-closed holes can change their semi-open / semi-closed state under temperature control. After exceeding a high-temperature threshold, they open due to thermo-mechanical coupling. As the temperature further increases, the degree of opening continues to increase, thereby significantly alleviating the suppression of radial natural convection and enhancing heat transfer capacity. Figure 3 a; At low temperature thresholds, the semi-open / semi-closed orifice returns to semi-closed, and as the temperature further decreases, the orifice closes further, thereby maintaining the full development of natural convection in the direction of gravity, effectively suppressing thermal stratification caused by temperature gradients, and improving the vertical thermal uniformity and thermal stability of the system, such as... Figure 3 b.

[0025] The above specific embodiments are only for illustrating the technical concept and structural features of the present invention, and are intended to enable those skilled in the art to implement them. However, the above content does not limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit and essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A biomimetic self-regulating thermal energy storage device, comprising a shell, a phase change thermal energy storage material filled within the shell, and a heat exchange pipe penetrating the shell, characterized in that: Reinforcing fins are provided on the heat exchange pipe, and the reinforcing fins are evenly arranged around the heat exchange pipe. The reinforcing fins are designed with a fractal arrow structure, and each level of the arrow structure includes one main vein and two sub-branches. A non-uniform semi-open and semi-closed hole array is formed on the reinforcing fins. The diameter of the semi-open and semi-closed hole array gradually increases along the direction of gravity, and the pore density also increases accordingly. The semi-open and semi-closed holes can change their semi-open and semi-closed state under temperature control. An external ultrasonic module is also provided on the outer wall of the shell. The external ultrasonic module consists of an array of ultrasonic transmitters. The ultrasonic transmitter array is distributed in a stepped manner along the direction of gravity, with more ultrasonic transmitters at the bottom. During the melting process, the external ultrasonic module excites fluid disturbance in the liquid phase change material region to enhance natural convection heat transfer. At the same time, it induces the semi-open and semi-closed hole array to resonate at the same frequency to excite local semi-active forced convection, thereby realizing mixed convection enhanced heat transfer. The semi-open and semi-closed hole is a cantilever beam structure with a connecting root formed by partial cutting. The reinforced fins are made of shape memory alloy material. The semi-open and semi-closed holes open due to thermo-mechanical coupling after exceeding the high temperature threshold. As the temperature further increases, the degree of opening continues to increase, thereby significantly alleviating the suppression of radial natural convection and enhancing the heat transfer capacity. The semi-open and semi-closed holes return to semi-closed at the low temperature threshold. As the temperature further decreases, the holes close further.

2. The biomimetic self-regulating thermal energy storage device according to claim 1, characterized in that: The sub-branching has 3-5 levels, the length ratio of adjacent level branches is 1.5-2.0, and the thickness fractal dimension is 2-3; the branching angle of the arrow structure is less than 90°.

3. The biomimetic self-regulating thermal energy storage device according to claim 1, characterized in that: The high temperature threshold is 5°C above the melting point of the phase change material, and the low temperature threshold is 10°C below the melting point of the phase change material.

4. The biomimetic self-regulating thermal energy storage device according to claim 1, characterized in that: The shape memory alloy material is a nickel-titanium alloy or a copper-based shape memory alloy.

5. A biomimetic self-regulating thermal energy storage device according to claim 4, characterized in that: The rate of change in size of the semi-open / semi-closed hole in the direction of gravity does not exceed 50%, and the rate of change in density also does not exceed 50%.

6. A biomimetic self-regulating thermal energy storage device according to any one of claims 1-5, characterized in that: The cross-section of the shell is circular, quadrilateral, or pentagonal.

7. A biomimetic self-regulating thermal energy storage device according to any one of claims 1-5, characterized in that: The heat exchange pipe is either spiral or straight.

8. A biomimetic self-regulating thermal energy storage device according to claim 1, characterized in that: The operating frequency range of the ultrasonic transmitter includes the natural frequency of the material of the reinforcing fin, and in the gradient distribution of the ultrasonic transmitter array in the direction of gravity, the number of transmitters in the lower region is 1.5-3 times that in the upper region.

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