Novel tree-shaped fin vertical phase change heat storage device and evaluation method thereof

Abstract

The invention relates to a novel tree-shaped fin vertical phase change heat storage device and an evaluation method thereof, and the novel tree-shaped fin vertical phase change heat storage device comprises a heat storage shell, heat exchange tubes and heat exchange fins. And a heat exchange tube is arranged in the heat storage shell. The heat exchange fins comprise a first main fin, a second main fin and a third main fin which are connected in sequence; the length direction of the first main fins, the length direction of the second main fins and the length direction of the third main fins are consistent with the axial direction of the heat exchange pipes. The first main fins are connected with the heat exchange tubes, and the width direction of the first main fins is consistent with the radial direction of the heat exchange tubes. The heat exchange fins further comprise first branch fins and second branch fins, the first branch fins and the second branch fins are arranged on the first main fins, the first branch fins are located between the two second main fins, and the second branch fins are perpendicular to the first main fins. By arranging the first branch fins and the second branch fins on the first main fins, under the condition that the total volume of the heat exchange fins is not changed, melting dead angles are eliminated, and the heat storage efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of heat generating devices, and in particular to a novel tree-shaped fin vertical phase-change heat storage device and an evaluation method thereof. Background Art

[0002] As a clean energy with abundant reserves and easy access, renewable energy such as solar energy and wind energy has an important impact on the energy consumption structure. However, such renewable energy is volatile and unstable, and its storage and scheduling have always been the main problems restricting its large-scale utilization. Latent heat storage (LHS) technology using solid-liquid phase change materials (PCM) stands out for its high heat storage density, wide phase change temperature range, easy and stable temperature control, rich and diverse types of phase change energy storage materials, and high cost performance. It has been widely used in building energy conservation, waste heat recovery, solar energy utilization, electronic equipment cooling, power systems and other fields, and is one of the forward-looking technologies to promote future energy development.

[0003] However, most PCM thermal storage materials generally have the disadvantage of low thermal conductivity, which seriously affects the energy storage efficiency of the thermal storage system. Therefore, how to improve the device structure and improve the melting performance of PCM, and store heat in PCM quickly and efficiently to achieve efficient heat exchange has always been a hot topic of research. Summary of the invention

[0004] The present invention provides a novel tree-shaped fin vertical phase change thermal storage device and an evaluation method thereof, aiming to solve the problem of low thermal storage efficiency caused by melting dead corners in thermal storage devices in the prior art.

[0005] In order to solve the above problems, the present invention provides a novel tree-shaped fin vertical phase-change heat storage device, which comprises: a heat storage shell, a heat exchange tube and a heat exchange fin; The heat exchange tube is arranged in the heat storage shell; The heat exchange fins include a first main fin, a second main fin and a third main fin which are connected in sequence; the length directions of the first main fin, the second main fin and the third main fin are consistent with the axial direction of the heat exchange tube; the first main fin is connected to the heat exchange tube, and the width direction of the first main fin is consistent with the radial direction of the heat exchange tube; The heat exchange fins further include a first branch fin and a second branch fin both arranged on the first main fin, the first branch fin is located between two of the second main fins, and the second branch fin is perpendicular to the first main fin; The space between the heat storage shell and the heat exchange fins is filled with heat storage material.

[0006] Preferably, the second branch fins are disposed on opposite sides of the first main fin, and the two second branch fins are located on the same plane.

[0007] Preferably, the angle between the first fin and the second fin is 90°.

[0008] Preferably, the first branch fin and the second branch fin have the same thickness, the width of the third main fin is 2.8 times the width of the first branch fin, and the width of the second branch fin is half the width of the first main fin.

[0009] Preferably, two second main fins are provided at one end of the first main fin.

[0010] Preferably, at least two third main fins are provided at one end of the second main fin.

[0011] Preferably, the widths of the first main fin, the second main fin and the third main fin are arranged in an increasing manner.

[0012] Preferably, the thicknesses of the first main fin, the second main fin and the third main fin are arranged in decreasing order.

[0013] Preferably, the heat storage shell is cylindrical in shape, and the center line of the heat exchange tube is collinear with the center line of the heat storage shell.

[0014] Preferably, the present invention further provides an evaluation method for a novel tree-shaped fin vertical phase-change thermal storage device, the evaluation method being implemented based on the novel tree-shaped fin vertical phase-change thermal storage device as described above, and the evaluation method comprising: Nusselt number N u Indicates the intensity of convective heat transfer during the melting process: ; in, q w ( t ) represents the heat flux density on the inner wall of the heat exchange tube, L e Indicates the distance between the outer wall of the heat exchange tube and the inner wall of the heat storage shell. T hs Indicates the temperature of the heat source in the heat exchange tube. T 0 represents the initial temperature of the heat storage device, λ PCM Indicates the thermal conductivity of the heat storage material; Total energy storage E ( t ) represents the total amount of thermal energy stored in the system, including the sensible heat storage of the heat storage material and heat exchange fins and the latent heat storage of the phase change material: ; in, T PCM and T fin It is the body temperature of the heat storage material and heat exchange fins when the heat storage material is completely melted; m PCM 、m fin Respectively represent the mass of heat storage material and heat exchange fin; L represents the latent heat of the thermal storage material; C PCM , C fin represent the specific heat capacity of the heat storage material and the heat exchange fins respectively; The thermal energy storage efficiency of the system is expressed as: ;

[0015] in, t full Indicates the time it takes for the thermal storage material to completely melt.

[0016] The present invention arranges a first branch fin and a second branch fin on a first main fin, and the first branch fin is located between two second main fins, and the first branch fin and the second branch fin are not further connected to other fins. While ensuring that the total volume of the heat exchange fins remains unchanged, the melting dead corner is eliminated and the heat storage efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a cross-sectional view of the novel tree-shaped fin vertical phase-change thermal storage device of the present invention; Figure 2 It is a schematic diagram of the structure of the heat exchange tube and the heat exchange fin in the present invention; Figure 3 A top view of the heat exchange tube and the heat exchange fin in the present invention; Figure 4 It is a top view of a traditional tree-shaped heat dissipation fin in the prior art; Figure 5 It is a top view of a rectangular heat dissipation fin in the prior art; Fig. 6A This is the melting cloud diagram of the top cross section of the heat storage device at 4560s for the new tree-shaped heat dissipation fins of the present invention; Figure 6B This is the melting cloud diagram of the middle cross section of the heat storage device at 4560s for the new tree-shaped heat dissipation fins of the present invention; Figure 6C This is the melting cloud diagram of the cross section at the bottom of the heat storage device at 4560s for the new tree-shaped heat dissipation fins of the present invention; Fig. 7A The melting cloud diagram of the top cross section of the heat storage device at 4560s for the conventional tree-shaped fins in the prior art; Figure 7B This is the melting cloud diagram of the middle cross section of the heat storage device at 4560s for the conventional tree-shaped fins in the prior art; Figure 7C The melting cloud diagram of the bottom cross section of the heat storage device at 4560s for the conventional tree-shaped fins in the prior art; Figure 8 The liquid phase rate variation curves of rectangular fins, traditional tree-shaped fins and new tree-shaped fins; Fig. 9 The Nusselt number curves of rectangular fins, traditional tree-shaped fins and new tree-shaped fins vary with liquid phase ratio; Fig.10 This is a comparison chart of the total energy storage and energy storage rate of rectangular fins, traditional tree-shaped fins and new tree-shaped fins.

[0018] [Description of Reference Numerals] 1: heat storage shell; 10: melting dead corner; 2: heat exchange tube; 3: heat exchange fin; 31: first main fin; 32: second main fin; 33: third main fin; 34: first branch fin; 35: second branch fin. DETAILED DESCRIPTION

[0019] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0020] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0021] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0022] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] like Figure 1 and Figure 2 As shown, the present invention provides a novel tree-shaped fin vertical phase-change heat storage device, which comprises: a heat storage shell 1, a heat exchange tube 2 and a heat exchange fin 3. The heat storage shell 1 is provided with a heat exchange tube 2. The heat storage material is filled between the heat storage shell 1 and the heat exchange fin 3. The heat exchange fin 3 comprises a first main fin 31, a second main fin 32 and a third main fin 33 which are connected in sequence; the length direction of the first main fin 31, the second main fin 32 and the third main fin 33 is consistent with the axial direction of the heat exchange tube 2; the first main fin 31 is connected to the heat exchange tube 2, and the width direction of the first main fin 31 is consistent with the radial direction of the heat exchange tube 2. The heat exchange fin 3 also comprises a first branch fin 34 and a second branch fin 35 which are both arranged on the first main fin 31, the first branch fin 34 is located between the two second main fins 32, and the second branch fin 35 is perpendicular to the first main fin 31.

[0024] The technical solution of the present invention is roughly as follows: the heat exchange tube 2 in the heat storage shell 1 is hollow to form an HTF flow channel, and the heat exchange fin 3 is connected to the outside. The space formed between the heat exchange fin 3 and the heat storage shell 1 is filled with heat storage material. The heat source is introduced into the HTF flow channel, and the heat of the heat source is transferred to the heat storage material through the heat exchange fin 3 to melt the heat storage material, store thermal energy by using the latent heat of phase change, and perform subsequent heat exchange by using the stored thermal energy. In a preferred embodiment, the heat storage material is a solid-liquid phase change material (PCM), and the heat storage material is mostly a crystalline hydrated salt, paraffin or fatty acid phase change material. The shape of the heat storage shell is cylindrical, and the center line of the heat exchange tube is collinear with the center line of the heat storage shell.

[0025] In the existing heat storage device, the cross section of the heat exchange fins 3 is mostly tree-shaped, and the heat storage material has a melting dead corner 10 during the melting process, which makes the heat storage efficiency low. Fig. 7A , Figure 7B , Figure 7CAs shown, the phase interface distribution of the cross section at the upper, middle and lower positions in the axial direction of the conventional tree-shaped fin phase change energy storage unit at 4560s of melting, from which it can be seen that there are multiple melting dead corners 10 between the two first main fins 31 and between the two second main fins 32, especially in the bottom area where the natural convection effect is relatively weakest, which will lead to poor heat transfer in the actual three-dimensional phase change energy storage unit in the later stage of melting.

[0026] The present invention arranges a first branch fin 34 and a second branch fin 35 on the first main fin 31, and the first branch fin 34 is located between the two second main fins 32, and the first branch fin 34 and the second branch fin 35 are not further connected to other fins. While ensuring that the total volume of the heat exchange fin 3 remains unchanged, the melting dead corner 10 is eliminated and the heat storage efficiency is improved.

[0027] In a preferred embodiment, second branch fins 35 are disposed on opposite sides of the first main fin 31, and the two second branch fins 35 are located on the same plane. The angle between the first branch fin 34 and the second branch fin 35 is 90°. The first branch fin 34 and the second branch fin 35 have the same thickness, the width of the third main fin 33 is 2.8 times the width of the first branch fin 34, and the width of the second branch fin 35 is half the width of the first main fin 31.

[0028] Further, two second main fins 32 are arranged at one end of the first main fin 31. At least two third main fins 33 are arranged at one end of the second main fin 32. The widths of the first main fin 31, the second main fin 32 and the third main fin 33 are arranged in an increasing manner. The thicknesses of the first main fin 31, the second main fin 32 and the third main fin 33 are arranged in a decreasing manner.

[0029] In addition, the present invention also provides an evaluation method for a novel tree-shaped fin vertical phase-change thermal storage device. The evaluation method is implemented based on the novel tree-shaped fin vertical phase-change thermal storage device as described above, and the evaluation method includes: Nusselt number N u Indicates the intensity of convective heat transfer during the melting process: ; in, q w ( t ) represents the heat flux density on the inner wall of the heat exchange tube, L e Indicates the distance between the outer wall of the heat exchange tube and the inner wall of the heat storage shell. T hs Indicates the temperature of the heat source in the heat exchange tube. T 0 represents the initial temperature of the heat storage device, λ PCMIndicates the thermal conductivity of the heat storage material; Total energy storage E ( t ) represents the total amount of thermal energy stored in the system, including the sensible heat storage of the heat storage material and heat exchange fins and the latent heat storage of the phase change material: ;

[0030] in, T PCM and T fin It is the body temperature of the heat storage material and heat exchange fins when the heat storage material is completely melted; m PCM 、m fin Respectively represent the mass of heat storage material and heat exchange fin; L represents the latent heat of the thermal storage material; C PCM , C fin represent the specific heat capacity of the heat storage material and the heat exchange fins respectively; The thermal energy storage efficiency of the system is expressed as: ;

[0031] in, t full Indicates the time it takes for the thermal storage material to completely melt.

[0032] Finally, the above evaluation method is used to evaluate the heat storage device of the present invention and the heat storage device in the prior art, specifically: The heat storage material is filled around the heat exchange fins 3. The heat storage shell 1 is tubular, that is, the diameter of the heat storage shell 1 is Φ out =120mm, inner tube outer diameter Φ in =30mm, the inner tube thickness Δr=6mm, the new tree-shaped heat exchange fins with the first fin 34 and the second fin 35 in this application, the traditional tree-shaped fins in the prior art, and the rectangular fins in the prior art are arranged around the inner tube, and HTF flows from the inner tube to exchange heat with the PCM heat storage material. Among them, the cross-sections of the new tree-shaped heat exchange fins (for the convenience of subsequent description, the heat exchange fins 3 in this application are referred to as the new tree-shaped heat exchange fins), the traditional tree-shaped fins, and the rectangular fins are respectively as follows: Figure 3 , Figure 4 as well as Figure 5 shown.

[0033] The melting cloud diagrams of the cross sections of the new tree-shaped heat exchange fins and the traditional tree-shaped fin phase change energy storage unit at the upper, middle and lower positions on the axial direction when melting for 4560s were extracted respectively.

[0034] like Fig. 6A, Figure 6B , Figure 6C The three figures represent the melting cloud diagrams of three cross sections of the new tree-shaped heat exchange fin at the top, middle and bottom positions.

[0035] like Fig. 7A , Figure 7B , Figure 7C The three figures represent the melting cloud diagrams of three cross sections of the traditional tree-shaped fin at the top, middle and bottom positions.

[0036] from Fig. 7A , Figure 7B , Figure 7C It can be seen that in the traditional tree-shaped heat sink, there is an obvious heat transfer dead angle between the two first main fins and between the two second main fins ( Figure 7B , Figure 7C The area marked with number 10 is a melting dead corner, which represents the unmelted heat storage material, and the area outside the melting dead corner represents the melted heat storage material), especially the bottom area where the natural convection effect is relatively weakest, which will lead to poor heat transfer in the actual three-dimensional phase change energy storage unit in the later stage of melting.

[0037] In order to compare the heat transfer efficiency of the new tree-shaped heat exchange fins and the traditional tree-shaped fins, the new tree-shaped heat exchange fins in this application are designed under the condition of keeping the total volume of the fins unchanged. The structural parameters of the new tree-shaped fins are shown in Tables 1 and Figure 3 shown.

[0038] Table 1:

[0039] Figure 3 In the figure: d1 represents the width of the first main fin, h1 represents the thickness of the first main fin; d2 represents the width of the second main fin, h2 represents the thickness of the second main fin; d3 represents the width of the third main fin, h3 represents the thickness of the third main fin; d1' represents the width of the first branch fin, h1' represents the thickness of the first branch fin; the above dimensions all represent the dimensions of the new tree-shaped heat exchange fins of the present application.

[0040] In addition, as a comparison, the present application also uses the existing tree-shaped heat exchange fins as a reference. The structural parameters of the existing tree-shaped heat exchange fins are shown in Table 2 and Figure 4 shown.

[0041] Table 2:

[0042] Figure 4In the figure, d1 represents the width of the first main fin, h1 represents the thickness of the first main fin; d2 represents the width of the second main fin, h2 represents the thickness of the second main fin; d3 represents the width of the third main fin, h3 represents the thickness of the third main fin; the above dimensions are all represented as the dimensions of the traditional tree-shaped heat exchange fins.

[0043] Finally, as a comparison, the present application also uses the existing rectangular fins as a control. The existing tree-shaped fin structure parameters are shown in Table 3 and Figure 5 shown.

[0044] Table 3:

[0045] Figure 5 In the figure, d represents the width of the main fin, and h represents the thickness of the main fin; the above dimensions are all the dimensions of the traditional tree-shaped heat exchange fins.

[0046] Through simulation, the melting process of the heat storage material in three heat storage devices (the structures of the three heat storage devices are only different in the fins, and the fins of the three heat storage devices are new tree-shaped heat exchange fins, traditional tree-shaped heat exchange fins, and rectangular fins) and the related parameters in the melting process are calculated and recorded respectively.

[0047] The time taken for the heat storage materials to completely melt in the three heat storage devices was recorded respectively. The results are as follows: Figure 8 As shown, Figure 8 When the liquid fraction of the vertical axis is 1, it means that the heat storage material in the heat storage device is completely melted. Figure 8 The following conclusions can be drawn: First: The new tree-shaped heat exchange fins and traditional tree-shaped heat exchange fins increase the phase change heat transfer depth by expanding the heat transfer area. By changing the rectangular fin structure into a tree-shaped fin structure, the fin distribution is more uniform. Under the combined effect of the tree-shaped fin structure and the local heat conduction of the phase change material, the melting time is significantly shortened, which is 19% less than that of the rectangular fins.

[0048] Second: When the shape of the tree-shaped fins remains unchanged and the effective volume of the heat storage material remains unchanged, the melting time of the new tree-shaped heat exchange fins is reduced by 19.8% compared with the traditional tree-shaped heat exchange fins.

[0049] Calculate and record the Nusselt numbers of the three heat storage devices during heat storage. The results are as follows: Fig. 9 As shown, according to Fig. 9 The following conclusions can be drawn: Third: Comparing the Nusselt number, the Nusselt number of the new tree-shaped heat exchange fins is greater than that of the rectangular heat exchange fins and the traditional tree-shaped heat exchange fins during the entire melting process. During the melting process, the new tree-shaped heat exchange fins have a good promoting effect on the natural convection of the heat storage material.

[0050] Calculate and record the total amount of energy stored and the energy storage rate of the three heat storage devices during heat storage. The results are as follows: Fig.10 As shown, according to Fig.10 The following conclusions can be drawn: Fourth: Compared with rectangular heat exchange fins, the energy storage rate of the new tree-shaped heat exchange fins increased by 49%, while the total energy storage amount only decreased by 3.3%; and compared with traditional tree-shaped heat exchange fins, the energy storage rate of the new tree-shaped heat exchange fins increased by 26.4%, and the total energy storage amount increased by 1.4%.

[0051] The calculation of the above parameters is derived from the solution of the horizontal phase change thermal storage device model based on the continuity equation, momentum equation and energy equation by the fluid mechanics software calculation method.

[0052] It should be understood that the above description of the specific embodiments of the present invention is only for illustrating the technical route and features of the present invention, and its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, but the present invention is not limited to the above specific implementation methods. Any changes or modifications made within the scope of the claims of the present invention should be included in the protection scope of the present invention.

Claims

1. A novel tree-shaped fin vertical phase change thermal storage device, characterized in that: The novel tree-shaped fin vertical phase-change heat storage device comprises: a heat storage shell (1), a heat exchange tube (2) and a heat exchange fin (3); The heat exchange tube (2) is arranged in the heat storage shell (1); The heat exchange fin (3) comprises a first main fin (31), a second main fin (32) and a third main fin (33) which are connected in sequence; the length direction of the first main fin (31), the second main fin (32) and the third main fin (33) is consistent with the axial direction of the heat exchange tube (2); the first main fin (31) is connected to the heat exchange tube (2), and the width direction of the first main fin (31) is consistent with the radial direction of the heat exchange tube (2); The heat exchange fin (3) further comprises a first branch fin (34) and a second branch fin (35) both arranged on the first main fin (31), the first branch fin (34) being located between the two second main fins (32), and the second branch fin (35) being perpendicular to the first main fin (31); A heat storage material is filled between the heat storage shell (1) and the heat exchange fins (3).

2. The novel tree-shaped fin vertical phase change thermal storage device according to claim 1 is characterized in that: The second branch fins (35) are arranged on opposite sides of the first main fin (31), and the two second branch fins (35) are located on the same plane.

3. The novel tree-shaped fin vertical phase change thermal storage device according to claim 2 is characterized in that: The included angle between the first fin (34) and the second fin (35) is 90°.

4. The novel tree-shaped fin vertical phase change thermal storage device according to claim 2 is characterized in that: The first branch fin (34) and the second branch fin (35) have the same thickness, the width of the third main fin (33) is 2.8 times the width of the first branch fin (34), and the width of the second branch fin (35) is half the width of the first main fin (31).

5. The novel tree-shaped fin vertical phase change thermal storage device according to any one of claims 1 to 4, characterized in that: Two second main fins (32) are arranged at one end of the first main fin (31).

6. The novel tree-shaped fin vertical phase change thermal storage device according to claim 5 is characterized in that: At least two third main fins (33) are provided at one end of the second main fin (32).

7. The novel tree-shaped fin vertical phase change thermal storage device according to any one of claims 1 to 4, characterized in that: The widths of the first main fin (31), the second main fin (32) and the third main fin (33) are arranged in an increasing manner.

8. The novel tree-shaped fin vertical phase change thermal storage device according to any one of claims 1 to 4, characterized in that: The thicknesses of the first main fin (31), the second main fin (32) and the third main fin (33) are arranged in a decreasing manner.

9. The novel tree-shaped fin vertical phase change thermal storage device according to any one of claims 1 to 4, characterized in that: The heat storage shell (1) is cylindrical in shape, and the center line of the heat exchange tube (2) is colinear with the center line of the heat storage shell (1).

10. A novel evaluation method for a tree-shaped fin vertical phase change thermal storage device, characterized in that: The evaluation method is implemented based on the novel tree-shaped fin vertical phase change thermal storage device according to any one of claims 1 to 9, and the evaluation method includes: Nusselt number N u Indicates the intensity of convective heat transfer during the melting process: ； in, q w ( t ) represents the heat flux density on the inner wall of the heat exchange tube (2), L e Indicates the distance between the outer wall of the heat exchange tube and the inner wall of the heat storage shell. T hs represents the temperature of the heat source in the heat exchange tube (2), T 0 represents the initial temperature of the heat storage device, λ PCM Indicates the thermal conductivity of the heat storage material; Total energy storage E ( t ) represents the total amount of thermal energy stored in the system, including the sensible heat storage of the heat storage material and the heat exchange fins (3) and the latent heat storage of the phase change material: ； in, T PCM and T fin is the body temperature of the heat storage material and the heat exchange fins (3) when the heat storage material is completely melted; m PCM 、m fin represent the mass of heat storage material and heat exchange fin (3) respectively; L represents the latent heat of the thermal storage material; C PCM , C fin represent the specific heat capacity of the heat storage material and the heat exchange fin (3) respectively; The thermal energy storage efficiency of the system is expressed as: ； in, t full Indicates the time it takes for the thermal storage material to completely melt.

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