Enhanced heat transfer type phase change energy storage device

Abstract

The invention relates to a phase change energy storage device, in particular to an enhanced heat transfer type phase change energy storage device which comprises energy storage cavity subunits, a phase change material, a runner cover plate, runner side plates and fractal fins. The phase change materials are respectively filled in the energy storage cavity subunits; the fractal fins are fixed on the inner wall surfaces of the energy storage cavity subunits; the flow channel cover plates are installed above and below the energy storage cavity subunits respectively, the flow channel side plates are installed on the left side and the right side of the energy storage cavity subunits respectively, communicated flow channels are arranged in the flow channel cover plates and the flow channel side plates respectively, the flow channel cover plates at the upper end and the lower end are provided with flow channel outlets and flow channel inlets respectively, and flow channel partition plates are installed in the flow channels of the flow channel side plates; a strengthening element round protrusion is arranged in the runner, and an external magnetic field element is fixed to the outer side of the runner side plate. The latent heat energy storage device is based on active magnetic field strengthening and passive structure strengthening, the heat transfer rate of the phase change material can be increased, the heat transfer performance of the system can be improved, and therefore the heat exchange efficiency of a heat source and the energy storage device is improved.

Description

Technical Field

[0001] The present invention relates to a phase change energy storage device, in particular to an enhanced heat transfer type phase change energy storage device. Background Art

[0002] As a strategic resource that countries around the world focus on reserving, fossil energy occupies an important position in the early industrial development of mankind. However, with the progress of society and the development of science and technology, the disadvantages of fossil energy continue to emerge. At present, the use of fossil energy has caused the global temperature to continue to rise, causing irreparable damage to the environment on which human beings depend for survival. Using new energy to replace fossil energy has become one of the important policies of various countries. However, most new energy sources have the characteristics of intermittent, instability, and low energy density during utilization, such as solar energy. In order to overcome these problems, it is necessary to carry out research on energy storage technology, and it is particularly important to use a good thermal energy storage strategy to improve the utilization efficiency of new energy.

[0003] Traditional thermal energy storage strategies are divided into three types: sensible heat storage, latent heat storage and chemical energy storage. Among them, latent heat storage uses phase change materials to achieve energy storage, which has the advantages of low price, stable temperature, high energy storage density, long cycle life, and wide application range. However, the thermal conductivity of phase change materials is low, which greatly limits the heat transfer efficiency of latent heat storage technology during energy storage and release. Summary of the invention

[0004] The purpose of the present invention is to provide a phase change energy storage device with enhanced heat transfer to solve the shortcomings of the prior art that the low thermal conductivity of the phase change material limits the heat transfer efficiency of the latent heat energy storage technology during energy storage and release.

[0005] The purpose of the present invention is achieved by adopting the following technical scheme: a heat transfer enhanced phase change energy storage device, comprising an energy storage cavity subunit, a phase change material, a flow channel cover plate, a flow channel side plate, a fractal fin, and a flow channel partition plate; the phase change material is respectively filled in the energy storage cavity subunit; a plurality of fractal fins are independently fixed on the inner wall surface of the energy storage cavity subunit; the flow channel cover plate is respectively installed above and below the energy storage cavity subunit, and the flow channel side plates are respectively installed on the left and right sides of the energy storage cavity subunit, and the flow channel cover plate and the flow channel side plates are respectively provided with connected flow channels, and the flow channel cover plate at the upper end is provided with a flow channel outlet communicating with the flow channel, and the flow channel cover plate at the lower end is provided with a flow channel inlet communicating with the flow channel; the flow channel partition plate is also installed in the flow channel of the flow channel side plate along the longitudinal direction; a reinforcing element circular protrusion for improving the heat transfer rate of the heat exchange fluid is also provided in the flow channel.

[0006] A further technical solution of the present invention is that the energy storage cavity subunit is a rectangular parallelepiped, and the energy storage cavity subunit is designed according to a modular structure, and the energy storage cavity subunits are sequentially connected in series in an up-and-down arrangement.

[0007] A further technical solution of the present invention is: the phase change material is filled into the energy storage cavity subunit from top to bottom in the order of decreasing melting point.

[0008] A further technical solution of the present invention is that the fractal fin is a simple geometric structure designed according to a functional relationship or a complex bionic structure designed according to topological optimization theory.

[0009] A further technical solution of the present invention is: the structural parameters of the fractal fin are defined by the first-level length L0, the first-level width W0, the branch length Ln, the branch width Wn, the bifurcation angle θ, and the number of bifurcations k, wherein n is the nth-level fractal fin; the ratio between the branch length Ln and Ln-1 satisfies formula ①, and the ratio between the branch width Wn and Wn-1 satisfies formula ②; ①, ②.

[0010] A further technical solution of the present invention is: the flow channel adopts a reciprocating layout design, and the reciprocating layout includes baffle-type and S-shaped flow channels.

[0011] A further technical solution of the present invention is that the protrusion of the strengthening element is in the shape of a semi-sphere, a semi-ellipsoid, a raindrop or a boss.

[0012] A further technical solution of the present invention is: the heat exchange fluid flowing in the flow channel is a magnetic heat exchange fluid; the phase change material in the energy storage cavity subunit is a magnetic phase change material; an external magnetic field element for regulating the heat transfer characteristics of the magnetic heat exchange fluid in the flow channel and the magnetic phase change material in the energy storage cavity subunit is also fixed on the outer side of the flow channel side plate, and the external magnetic field element is an electromagnet or a permanent magnet.

[0013] A further technical solution of the present invention is that the magnetic phase change material filled in the energy storage cavity subunit is a mixture of ferroferric oxide and paraffin, or a mixture of iron powder and paraffin, or a mixture of iron microspheres and paraffin.

[0014] A further technical solution of the present invention is that the magnetic heat exchange fluid in the flow channel is water-based magnetic fluid nano-ferroferric oxide-water.

[0015] Due to the adoption of the above scheme, the present invention has the following beneficial effects compared with the prior art: The present invention arranges fractal fins inside the energy storage cavity subunit, and greatly improves the heat transfer rate of the phase change material through the synergy of strengthening the local natural convection induced by the fins in the early stage of melting and strengthening the thermal conductivity throughout the melting process.

[0016] The present invention installs flow channel partitions and a certain number of reinforcing element protrusions along the longitudinal direction inside the flow channel of the device. The flow channel partitions are used to divide the flow channel into reciprocating flow channels, which can extend the residence time of the heat exchange fluid in the flow channel. The reinforcing element protrusions can disturb the heat exchange fluid in the flow channel, induce longitudinal vortices through flow separation and reattachment, destroy the thermal boundary layer of the heat exchange flow channel, and improve the heat transfer rate between the heat exchange fluid and the wall.

[0017] The present invention uses a magnetic heat exchange fluid in the flow channel. Under the action of the magnetic field, the magnetic particles will form a chain structure. These chain structures can form disturbances in the fluid, increase the turbulence of the magnetic heat exchange fluid, and thus improve the heat exchange efficiency. The present invention uses a magnetic phase change material in the energy storage cavity subunit. By adjusting the magnetic field strength, magnetic field direction and magnetic field operation mode, the directional migration of the magnetic phase change material and the destruction of the solid-liquid phase interface can be achieved, thereby improving the energy storage rate of the energy storage device.

[0018] The present invention fills the phase change material into the energy storage cavity subunit from top to bottom in the order of decreasing melting point, which can fully utilize the positive effect of natural convection on the melting process, not only enabling the upper energy storage cavity subunit to more effectively absorb the heat of the lower energy storage cavity subunit, but also further improving the temperature uniformity of different energy storage cavity subunits of the device.

[0019] The energy storage device and energy storage cavity subunits of the present invention adopt a modular structure, are easy to disassemble and integrate, can be combined in series or in parallel, have a compact and simple structure, are easy to operate, and have a low cost.

[0020] In summary, the present invention is a novel latent heat energy storage device based on active magnetic field enhancement and passive structural enhancement. At the same time, different energy storage cavity sub-units in the device use phase change materials with different melting points. Through the synergy of the main external field heat transfer enhancement method and the clever selection of phase change materials, not only the heat transfer rate of the phase change material can be improved, but also the overall heat transfer performance of the system can be increased, thereby enhancing the heat exchange efficiency between the heat source and the energy storage device.

[0021] The technical features of an enhanced heat transfer phase change energy storage device of the present invention are further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 : A schematic diagram of the three-dimensional structure of a heat transfer enhanced phase change energy storage device of the present invention; Figure 2 : A front cross-sectional view of a heat transfer enhanced phase change energy storage device of the present invention; Figure 3 : Figure 2 Left view of; Figure 4 : A schematic diagram of the structure of the flow channel described in Example 1; Figure 5 : Schematic diagram of the structure of the fractal fin described in Example 1.

[0023] In the above drawings, the descriptions of the reference numerals are as follows: 1-flow channel inlet, 2-flow channel cover plate, 3-flow channel side plate, 4-subunit below the energy storage cavity, 5- energy storage cavity middle subunit, 6- energy storage cavity upper subunit, 7- external magnetic field element, 8-channel outlet, 9-fractal fin, 10-reinforcement element protrusion, 11-channel partition, 12-reciprocating sub-channel. DETAILED DESCRIPTION Embodiment 1

[0024] Reference Figures 1 to 5 The present embodiment relates to an enhanced heat transfer phase change energy storage device, comprising an energy storage cavity subunit, a phase change material, a flow channel cover plate 2, a flow channel side plate 3, an external magnetic field element 7, a fractal fin 9, an enhanced element protrusion 10, and a flow channel partition 11. Among them: The energy storage cavity subunit is a rectangular parallelepiped, and adopts a modular structure, including an upper subunit 6 of the energy storage cavity, a middle subunit 5 of the energy storage cavity, and a lower subunit 4 of the energy storage cavity, which are arranged in series from top to bottom, and thermal conductive silicone grease is used to fill the space between the subunits.

[0025] The phase change material is filled into the upper subunit 6 of the energy storage cavity, the middle subunit 5 of the energy storage cavity, and the lower subunit 4 of the energy storage cavity from top to bottom in the order of decreasing melting point; the positive effect of natural convection on the melting process can be fully utilized, which can not only enable the upper energy storage cavity subunit to more effectively absorb the heat of the lower energy storage cavity subunit, but also further improve the temperature uniformity of different energy storage cavity subunits of the device.

[0026] There are multiple fractal fins 9, which are independently welded and fixed on the inner wall surface of the energy storage cavity subunit to improve the heat transfer rate of the phase change material. The fractal fins 9 are simplified based on the veins of leaves in nature. In order to simplify the bionic fractal structure, the fractal fins in this embodiment 1 are simple geometric structures designed according to functional relationships and machined according to regular shapes. Its structural parameters are defined by the first-level length L0, the first-level width W0, the branch length Ln, the branch width Wn, the bifurcation angle θ, and the number of bifurcations k, where n is the nth-level fractal fin; the ratio between the branch length Ln and Ln-1 satisfies formula ①, and the ratio between the branch width Wn and Wn-1 satisfies formula ②; ①, ②.

[0027] By adopting the fractal fins 9, the heat transfer rate of the phase change material can be greatly improved by strengthening the local natural convection induced by the fractal fins in the early stage of melting and strengthening the thermal conductivity throughout the melting process. The optimization of local natural convection and thermal conductivity can be further achieved by adjusting the above-mentioned structural parameters of the fractal fins 9.

[0028] The flow channel cover plate 2 is installed above and below the energy storage cavity subunit respectively; the flow channel side plate 3 is installed on the left and right sides of the energy storage cavity subunit respectively, the flow channel cover plate 2 and the flow channel side plate 3 are fixedly connected together by welding, and the flow channel cover plate 2 and the flow channel side plate 3 are respectively provided with connected flow channels, and the flow channel cover plate 2 at the upper end is welded with a flow channel outlet 8 communicating with the flow channel, and the flow channel cover plate 2 at the lower end is welded with a flow channel inlet 1 communicating with the flow channel; the heat exchange fluid passes through the flow channel inlet 1, the flow channel in the lower end flow channel cover plate 2, the flow channel in the flow channel side plate 3, and the flow channel in the upper end flow channel cover plate 2 in sequence, and goes out from the flow channel outlet 8. The flow channel adopts a reciprocating layout design, and the reciprocating layout is a baffle type and S-shaped flow channel. The flow channel partition 11 is also installed longitudinally in the flow channel of the flow channel side plate 3; this embodiment uses the flow channel partition 11 to divide the flow channel 3 into reciprocating sub-flow channels 12, which can extend the residence time of the heat exchange fluid in the flow channel and fully transfer the heat from the heat exchange fluid to the flow channel wall.

[0029] The reinforcing element protrusion 10 is also provided on the inner wall of the reciprocating sub-channel 12. The reinforcing element protrusion 10 is in the shape of a semi-sphere or a semi-ellipse or a raindrop or a boss. The reinforcing element protrusion 10 can disturb the heat exchange fluid. When the heat exchange fluid passes through the reinforcing element protrusion 10, the longitudinal vortex is induced by flow separation and reattachment near the reinforcing element protrusion 10, thereby increasing the local turbulent kinetic energy and destroying the thermal boundary layer of the heat exchange channel. At the same time, the reinforcing element protrusion 10 increases the heat exchange area between the channel wall and the channel, thereby improving the heat transfer rate between the heat exchange fluid and the channel wall from the two key factors of heat transfer coefficient and heat transfer area.

[0030] The heat exchange fluid flowing in the flow channel is a magnetic heat exchange fluid, and the phase change material in the energy storage cavity subunit is a magnetic phase change material; an external magnetic field element 7 is also fixed on the outside of the flow channel side plate 3, and the external magnetic field element 7 is an electromagnet or a permanent magnet. The external magnetic field element 7 is fixed to the outer wall of the flow channel cover plate 2 by bolts, or the external magnetic field element 7 is encapsulated in an aluminum shell and is integrally formed and combined with the energy storage cavity; when the heat exchange fluid and the phase change material contain magnetic materials, the external magnetic field element 7 can be used to regulate the heat transfer characteristics of the magnetic heat exchange fluid in the flow channel and the magnetic phase change material in the energy storage cavity, further improving the heat transfer rate.

[0031] The magnetic heat exchange fluid flowing in the flow channel is a water-based magnetic fluid nano-iron tetroxide-water. The nano-magnetic iron tetroxide not only improves the macroscopic thermal conductivity of the heat exchange fluid, but also forms a chain structure under the action of the magnetic field. These chain structures can form disturbances in the fluid, increase the turbulence of the magnetic heat exchange fluid, and thus improve the heat exchange efficiency. The magnetic phase change material in the energy storage cavity subunit adopts an iron microsphere-paraffin mixture. By adjusting the magnetic field strength, magnetic field direction and magnetic field operation mode, the directional migration of the magnetic iron microsphere-paraffin mixture and the destruction of the solid-liquid phase interface can be achieved, thereby improving the energy storage rate of the energy storage device.

[0032] As a variation of the first embodiment, the fractal fin 9 can be the simplified geometric structure mentioned above, which is convenient for traditional machining; or it can be a complex bionic structure designed according to topological optimization theory and manufactured by 3D printing, such as irregular tree-like fins or other irregular shape structures generated by topological optimization to meet specific heat exchange constraints.

[0033] As another variation of the first embodiment, the energy storage cavity subunits of the present invention may also be connected in parallel from left to right.

[0034] As another variation of the first embodiment, the magnetic phase change material filled in the energy storage cavity subunit may also be a mixture of ferroferric oxide and paraffin or a mixture of iron powder and paraffin.

[0035] As another variation of the first embodiment, the phase change material may also be a general phase change material, that is, a material that absorbs and releases heat through phase change, such as paraffin, lauric acid, myristic acid, palmitic acid, stearic acid, etc.

Claims

1. A heat transfer enhanced phase change energy storage device, characterized in that: It includes an energy storage cavity subunit, a phase change material, a flow channel cover plate, a flow channel side plate, a fractal fin, and a flow channel partition plate; the phase change material is respectively filled in the energy storage cavity subunit; a plurality of fractal fins are independently fixed on the inner wall surface of the energy storage cavity subunit; the flow channel cover plate is respectively installed above and below the energy storage cavity subunit, and the flow channel side plates are respectively installed on the left and right sides of the energy storage cavity subunit, and the flow channel cover plate and the flow channel side plates are respectively provided with connected flow channels, and the flow channel cover plate at the upper end is provided with a flow channel outlet communicating with the flow channel, and the flow channel cover plate at the lower end is provided with a flow channel inlet communicating with the flow channel; the flow channel partition plate is also longitudinally installed in the flow channel of the flow channel side plate; a reinforcing element circular protrusion for improving the heat transfer rate of the heat exchange fluid is also provided in the flow channel.

2. The heat transfer enhanced phase change energy storage device according to claim 1, characterized in that: The energy storage cavity subunit is a rectangular parallelepiped, and the energy storage cavity subunit is designed according to a modular structure. The energy storage cavity subunits are sequentially connected in series in an up-and-down arrangement.

3. The heat transfer enhanced phase change energy storage device according to claim 2, characterized in that: The phase change material is filled into the energy storage cavity subunit from top to bottom in the order of decreasing melting point.

4. The heat transfer enhanced phase change energy storage device according to claim 1, characterized in that: The fractal fin is a simple geometric structure designed according to a functional relationship or a complex bionic structure designed according to topology optimization theory.

5. The heat transfer enhanced phase change energy storage device according to claim 4, characterized in that: The structural parameters of the fractal fin are defined by the first-stage length L0, the first-stage width W0, the branch length Ln, the branch width Wn, the bifurcation angle θ, and the number of bifurcations k, where n is the nth-stage fractal fin; The ratio between the branch length Ln and Ln-1 satisfies formula ①, and the ratio between the branch width Wn and Wn-1 satisfies formula ②; ①， ②。 6. The enhanced heat transfer type phase change energy storage device according to claim 1, characterized in that: The flow channel adopts a reciprocating layout design, and the reciprocating layout includes a baffle type and an S-shaped flow channel.

7. The enhanced heat transfer phase change energy storage device according to claim 1, characterized in that: The circular protrusion of the strengthening element is in the shape of a semi-sphere, a semi-ellipsoid, a raindrop or a boss.

8. The heat transfer enhanced phase change energy storage device according to claim 1, characterized in that: The heat exchange fluid flowing in the flow channel is a magnetic heat exchange fluid; the phase change material in the energy storage cavity subunit is a magnetic phase change material; an external magnetic field element for regulating the heat transfer characteristics of the magnetic heat exchange fluid in the flow channel and the magnetic phase change material in the energy storage cavity subunit is also fixed on the outer side of the flow channel side plate, and the external magnetic field element is an electromagnet or a permanent magnet.

9. The enhanced heat transfer type phase change energy storage device according to claim 8, characterized in that: The magnetic phase change material filled in the energy storage cavity subunit is a mixture of ferroferric oxide and paraffin, a mixture of iron powder and paraffin, or a mixture of iron microspheres and paraffin.

10. The enhanced heat transfer type phase change energy storage device according to claim 8, characterized in that: The magnetic heat exchange fluid in the flow channel is water-based magnetic fluid nano-ferroferric oxide-water.

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