Bionic self-regulation heat reservoir

Abstract

The invention discloses a bionic self-regulation heat reservoir which comprises a shell, a heat exchange pipeline, strengthening fins and an external ultrasonic module. The heat exchange pipeline is arranged in the center of the shell, and the two ends of the heat exchange pipeline are an inlet and an outlet. The strengthening fins are evenly arranged on the periphery of the heat exchange pipeline and are designed to be of a constituent arrow structure, the main vein and the trunk meridian of a bionic self-blade are arranged, the forked length and thickness of the adjacent layers meet the self-similarity law, non-uniform semi-open and semi-closed holes are further formed in the fins, and the hole diameter and the hole density change in a stepped mode in the gravity direction. The external ultrasonic modules are arranged on the outer wall of the shell in the gravity direction in a stepped mode. Through the collaborative design of the fractal arrow-shaped reinforced fins and the non-uniform semi-open and semi-closed hole array and in combination with the external gradient ultrasonic module, the heat transfer efficiency and the heat storage and release rate of the phase change material are remarkably improved, and the purpose of self-adaptive convective heat transfer regulation is achieved by means of self-driven thermal deformation of the shape memory material; and the heat storage performance and stability of the system under different working conditions are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of heat storage, in particular to a bionic self-regulating heat storage device with high-efficiency bionic fins and self-driven thermal deformation of shape memory material to realize adaptive convection heat transfer regulation. BACKGROUND

[0002] Under the background of global energy structure accelerating towards green and low carbon, renewable energy such as solar and wind energy is crucial to achieve emission reduction and carbon neutralization. However, their inherent intermittency and volatility put higher requirements on energy storage systems. Latent heat storage technology emerges as the times require, which realizes an effective balance between high heat storage density, minimal temperature change and reasonable cost based on the characteristics of phase change materials absorbing or releasing heat during phase change. Moreover, the development of latent heat storage devices not only helps to improve energy utilization efficiency and promote the development of low-carbon economy, but also reduces the dependence on fossil fuels, thereby alleviating environmental pressure. Therefore, by optimizing the performance of phase change materials, improving the design of heat storage device structure and enhancing the efficiency of system integration, latent heat storage technology is expected to play a key role in future energy systems and provide strong technical support for achieving carbon neutralization and sustainable development.

[0003] It should be noted that the fatigue heat conduction ability of most phase change materials (except liquid metals and their alloys) severely limits the energy efficiency level of latent heat storage devices. For this reason, researchers at home and abroad have carried out extensive research on the heat transfer enhancement technology of latent heat storage devices, which can be divided into two categories: active and passive. Active enhancement technology relies on external energy input, typical methods include mechanical stirring, ultrasonic vibration and the application of magnetic and electric fields. However, these technologies are still in the development stage, and their reliability and maturity need to be verified, and they also pose strict requirements on system complexity and integration. In contrast, passive enhancement technology improves heat transfer performance through self-optimization of materials or structure without external energy input, and the system is simple and has high maintainability, so it is widely used in engineering. Common methods include the use of high-conductivity additives, the use of extended surfaces (such as fins), the use of microcapsule fluidized beds and the arrangement of multiple phase change materials in stages. Among them, fractal fins as a passive enhancement method that simulates the fractal structure design in nature show great potential in thermal management applications. Its multi-level, self-similar branch structure can realize efficient heat transport from the root to the entire phase change material area, not only significantly enhancing heat conduction, but also filling space through complex flow channel network, further enhancing the extensibility of heat transport.

[0004] Although the existing relevant research proposes a variety of different fractal fins to improve the heat transfer efficiency of latent heat storage, the existing technology still has the following technical defects. First, the storage has a clear temperature stratification problem in the longitudinal direction. Due to the low thermal conductivity of the phase change material and the insufficient natural convection driving force, the temperature distribution in the gravity direction of the storage is uneven, with higher temperature at the upper part and lower temperature at the lower part, which not only reduces the energy storage efficiency, but also increases the system heat loss. Second, the complex structure of the fractal fin not only increases the heat conduction area, but also limits the flow range of the liquid phase change material, significantly inhibiting the development of natural convection, resulting in inconsistent natural convection intensity in the horizontal and vertical directions. In addition, the current latent heat storage generally lacks the ability to adaptively regulate the heat transfer rate according to the external heat load. Its fixed heat transfer characteristics make the system respond slowly under high load, and passively cause energy waste under low load, making it difficult to meet the efficient operation requirements in variable load scenarios. Therefore, it is urgent to develop a new generation of latent heat storage technology to further provide key technical support for the realization of the double carbon strategy. SUMMARY

[0005] In view of the above technical problems, the present application provides a bionic self-regulating storage with efficient bionic fins and self-driven thermal deformation of shape memory materials to achieve adaptive convective heat transfer regulation, which not only solves the problems of temperature stratification in the gravity direction and inhibited radial natural convection, but also realizes adaptive regulation of the heat storage rate according to the heat load.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is: A bionic self-regulating storage, comprising a shell, a phase change storage material filled in the shell, and a heat exchange pipeline penetrating through the shell, characterized in that: a reinforcing fin is arranged on the heat exchange pipeline, the reinforcing fin is uniformly arranged around the heat exchange pipeline, the reinforcing fin is designed in a fractal arrow structure, each level of arrow structure includes one main vein and two sub-bifurcations; a non-uniform half-open half-closed hole array is opened on the reinforcing fin, the hole diameter gradually increases and the hole density also increases along the gravity direction, the half-open half-closed hole can change the half-open half-closed state under temperature control; an external ultrasonic module is further arranged on the outer wall of the shell, the external ultrasonic module is composed of an ultrasonic transmitter array, the ultrasonic transmitter array is distributed in steps along the gravity direction, the number of ultrasonic transmitters increases towards the lower part, the external ultrasonic module excites fluid disturbance in the liquid phase change material region to strengthen natural convection heat transfer during the melting process, while inducing the half-open half-closed hole array to resonate at the same frequency to excite local semi-active forced convection, thereby realizing mixed convection enhanced heat transfer.

[0007] The bionic self-regulating heat accumulator of the application, an external ultrasonic module greatly enhances the natural convection heat transfer in the region by exciting fluid disturbance of the liquid phase change material region. In addition, based on the principle of same frequency resonance, resonance of the semi-open semi-closed hole array is induced to excite semi-active forced convection in the local region, and finally mixed convection is formed to realize the effect of enhanced heat transfer.

[0008] In the application, the cross section of the shell includes but is not limited to a circular shape, a quadrilateral shape, a pentagonal shape and other symmetrical polygonal shapes, and the heat exchange flow channel is in a spiral shape or a straight pipe shape, and the materials of the two include but are not limited to copper, aluminum or stainless steel and other metal and alloy materials.

[0009] In the application, the length and thickness of the adjacent levels of the bifurcated strengthening fins satisfy the fractal self-similarity law, the level of the sub-bifurcation is 3-5, the length ratio of the adjacent levels of the bifurcation is 1.5-2.0, and the thickness fractal dimension is 2-3.

[0010] In the application, the semi-open semi-closed hole is a cantilever beam structure formed by partial cutting, the root part is still connected with the strengthening fin, the shape of the partial cutting is a part of a circular shape, an elliptical shape or a polygonal shape, and the size variation rate of the semi-open semi-closed hole in the gravity direction is not more than 50%, and the density variation rate is also not more than 50%.

[0011] In the application, the strengthening fin is made of a shape memory alloy material, so that the semi-open semi-closed hole is opened due to the thermal-mechanical coupling effect when the temperature exceeds a high temperature threshold, and the higher the temperature, the greater the opening amplitude, so as to reduce the inhibition of the radial natural convection; and the semi-open semi-closed hole is closed at a low temperature threshold to ensure the full development of the natural convection in the gravity direction and reduce the temperature stratification effect in the gravity direction.

[0012] In the application, the shape memory alloy material is a nickel-titanium alloy or a copper-based shape memory alloy, and the phase transition temperature matches the working temperature range of the heat accumulator; the high temperature threshold is about 5℃ higher than the melting point of the phase change material, and the low temperature threshold is about 10℃ lower than the melting point of the phase change material (considering the phenomenon of excessive supercooling of part of the phase change material).

[0013] In the application, the working frequency range of the ultrasonic wave transmitter must include the material self-vibration frequency of the strengthening fin, and in the step distribution of the ultrasonic wave transmitter array in the gravity direction, the number of transmitters in the lower region is 1.5-3 times that in the upper region.

[0014] Compared with the prior art, the application has the following beneficial effects: 1. The fractal arrow fin with relatively simple structure is used to strengthen the melting rate, and the complexity of the fin is reduced to weaken the limiting effect of the natural convection in the heat storage process.

[0015] 2.The application is a synergistic design of fractal arrow-shaped reinforced fins and non-uniform half-open half-closed hole arrays, combined with an external gradient ultrasonic module, which synchronously excites natural convection and local semi-active forced convection during the melting process, forming a hybrid convection enhancement mechanism, significantly improving the heat transfer efficiency and heat storage rate of phase change materials.

[0016] 3.The reinforced fins made of shape memory alloy can automatically adjust the opening state of the half-open half-closed holes according to the temperature, enhancing radial flow at high temperature and promoting gravity direction convection at low temperature, realizing self-adaptive regulation and control of the heat transfer path, effectively suppressing temperature stratification, and improving the heat storage performance and stability of the system under different working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Structure diagram of a bionic self-regulating heat accumulator Figure 2 Two-dimensional structure diagram of fractal arrow-shaped reinforced fins Figure 3 State diagram of half-open half-closed hole array: a) low heat flow; b) high heat flow In the figure: 1 heat exchange pipeline; 2 reinforced fin; 3 ultrasonic module; 4 heat accumulator shell; 5 half-open half-closed hole; 6 heat exchange medium inlet; 7 heat exchange medium outlet. DETAILED DESCRIPTION

[0018] In order to deepen the understanding of the application, we will further describe the application in combination with the drawings, and the embodiments are only used to explain the application and do not constitute a limitation on the protection scope of the application.

[0019] The present embodiment provides a bionic self-regulating heat accumulator, as shown in Figure 1 , 2, 3, which comprises: Heat exchange pipeline 1, reinforced fin 2, ultrasonic module 3, heat accumulator shell 4, half-open half-closed hole 5, heat exchange medium inlet 6, heat exchange medium outlet 7.

[0020] In one embodiment, the heat accumulator shell 4 is a regular pentagon with a side length of 120 mm, the heat exchange pipeline 1 is arranged at the center of the heat accumulator shell 4, and is selected as a straight pipe shape, and the two ends of the pipeline exposed to the shell are the heat exchange medium inlet 6 and the heat exchange medium outlet 7, respectively, and 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 accumulator shell 4, and is composed of an ultrasonic transmitter array, which is distributed in steps along the direction of gravity, with more ultrasonic transmitters in the lower part, the number of transmitters in the lower part being 2.25 times that in the upper part, and the working frequency range of the ultrasonic transmitters including the material self-vibration frequency of the reinforced fin. The external ultrasonic module can induce strong disturbance in the liquid phase change material region and the semi-open semi-closed hole array synchronously by frequency modulation. In this process, the natural convection heat transfer of the liquid phase change material region is strengthened; at the same time, the semi-open semi-closed hole array excites forced convection heat transfer in the local region through the same frequency vibration mechanism. The above two heat transfer modes work together to forcibly convert the original low-efficiency heat transfer mode dominated by pure natural convection into a high-efficiency 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, the reinforced fins 2 are uniformly distributed around the heat exchange pipes 1, and the reinforced fins 2 are designed as a fractal arrow structure, which simulates the structure of the main vein and stem in the bionic self-blade transport system, wherein each branch is generated by iteration, and each level of bifurcation is divided into two sub-bifurcations again. The length and thickness of adjacent bifurcations of the reinforced fins 2 satisfy the fractal self-similarity law, the level of the sub-bifurcations is 3, the length ratio of adjacent bifurcations is 1.81, the thickness fractal dimension is 3, and the bifurcation angle is selected as 72° (as shown in the fractal arrow structure Figure 2 in the figure, the length and thickness dimensions of each layer of bifurcations are given).

[0023] In one embodiment, the reinforced fins 2 of the fractal arrow structure are made of shape memory alloy, and nickel-titanium alloy is selected. Shape memory alloy is a special metal alloy that can be deformed at low temperature and restored to its original pre-deformed shape when heated. This phenomenon is due to the reversibility of solid-solid phase transition, as well as the shape memory effect and super-elasticity characteristics. The nickel-titanium alloy is composed of nickel and titanium in a near-equal molar ratio, has good super-elasticity and shape memory effect, and its phase transition temperature matches the working temperature range of the heat accumulator.

[0024] In one embodiment, the semi-open semi-closed holes 5 are opened on the surface of the fractal arrow fin made of shape memory alloy, first by mechanical milling to dig holes in the hole opening area, and then by partial cutting to form semi-open semi-closed holes 5 with cantilever beam structure, the root of the semi-open semi-closed holes 5 is still connected with the fractal arrow fin, and the shape of the partial cutting is a part 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, and the size variation rate along the direction of gravity is 30%, and the density variation rate is 15%. In addition, the semi-open semi-closed holes can change the semi-open semi-closed state under temperature control, open due to thermal-mechanical coupling effect when the temperature exceeds the high temperature threshold, and the opening degree continues to increase as the temperature further rises, thereby significantly relieving the inhibition of radial natural convection and enhancing the heat exchange capacity, such as Figure 3 a; and at the low temperature threshold, the semi-open semi-closed holes return to semi-closed, and as the temperature further decreases, the holes are further closed, thereby maintaining the full development of natural convection in the direction of gravity, effectively inhibiting the thermal stratification phenomenon caused by temperature gradient, 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 application, and the purpose is to enable those skilled in the art to implement it, but the above content does not limit the protection scope of the present application, any equivalent changes or modifications made according to the spirit and essence of the present application shall fall within the protection scope of the present application.

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.

2. The biomimetic self-regulating thermal energy storage device according to claim 1, characterized in that: The sub-branch A 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 shown is less than 90°.

3. The biomimetic self-regulating thermal energy storage device according to claim 1, characterized in that: The semi-open, semi-closed hole is a cantilever beam structure with a connecting root, formed by partial cutting.

4. The biomimetic self-regulating thermal energy storage device according to claim 3, characterized in that: 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.

5. A biomimetic self-regulating thermal energy storage device according to claim 3, 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.

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

7. 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%.

8. A biomimetic self-regulating thermal energy storage device according to any one of claims 1-7, characterized in that: The cross-section of the shell includes, but is not limited to, a circle, a quadrilateral, and a pentagon.

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

10. 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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