Parallel composite heat storage structure and warmer for latent and sensible heat

Abstract

The application discloses a parallel composite heat storage structure and a warmer, wherein the parallel composite heat storage structure comprises a heat storage space with a certain heat exchange surface and a heat exchange direction, the heat storage space is filled with a first phase change material, and the first phase change material is arranged with a second phase change material at intervals, wherein the phase change points of the first phase change material and the second phase change material are different and are all lower than 200 DEG C. The application adopts a parallel type secondary heat storage design, wherein the first phase change material undertakes a main heat storage function, and the second phase change material undertakes a regulation and control function, heat compensation with stable temperature can be provided in the sensible heat release stage of the first phase change material, the sensible heat release temperature jump layer problem is effectively solved, and the sensible heat storage capacity utilization rate and the total energy density of the device are improved.

Description

Technical Field

[0001] This invention belongs to the field of new energy utilization technology, and in particular relates to a parallel composite heat storage structure and heater that combines latent and sensible heat. Background Technology

[0002] As people's living standards improve, the demand for winter heating is increasing. In areas without centralized heating, people rely heavily on electric heaters for warmth in winter. However, most current electric heaters are instant-on electric heaters, which have high electricity costs. To address the issue of high electricity costs for electric heaters, thermal storage heaters utilize off-peak electricity at night to store heat and release it when needed, gradually becoming a replacement for traditional heaters.

[0003] Existing thermal storage heaters primarily rely on sensible heat storage, which depends on the sensible heat in the storage medium. This results in a small heat storage capacity per unit volume, limiting the total heat storage within the heater's limited space and thus the duration of heating, insufficient to meet long daytime heating needs. Utilizing latent heat storage instead of sensible heat storage can effectively increase the energy density per unit volume, solving the problem of insufficient heating time caused by limited heat storage. Furthermore, latent heat storage provides stable temperature with minimal fluctuations during heat release, contributing to a more comfortable heating environment.

[0004] However, current low- and medium-temperature (melting point <200℃) latent heat storage materials generally have low thermal conductivity, which limits the heat release of phase change thermal storage modules. Furthermore, a significant thermocline problem exists during heat release, leading to low energy utilization efficiency. The thermocline problem refers to the difficulty in releasing internal heat when the temperature difference between the inside and outside of the phase change module reaches a certain level. Therefore, the key to solving this problem lies in controlling the temperature difference between the inside and outside of the module, allowing for a continuous release of heat. Summary of the Invention

[0005] Purpose of the invention: This invention provides a parallel composite heat storage structure and heater that combines latent and sensible heat to solve the current technical problems such as high heating costs, small heat storage capacity and large temperature fluctuations in sensible heat heaters, and the existence of a thermocline in latent heat storage materials when releasing heat.

[0006] Summary of the Invention: To achieve the above objectives, the present invention provides a parallel composite thermal storage structure that combines latent and sensible heat, including a thermal storage space with a heat exchange surface and a heat exchange direction. The thermal storage space is filled with a primary phase change material, and secondary phase change materials are arranged at intervals within the primary phase change material. The phase change points of the primary and secondary phase change materials are different and both are below 200°C.

[0007] The heat exchange surface of the heat storage space is not limited to one side of the space; it can also be inside the space, such as through heat exchange pipes. The heat exchange direction is perpendicular to the heat exchange surface. The primary and secondary phase change materials have different phase change points, allowing the secondary material to supplement heat when the primary material reaches a thermocline (preferably, the phase change point of the secondary material is about 10°C above the temperature threshold at which the primary material reaches a thermocline). This widens the temperature difference between the inside and outside of the primary material, enabling a continuous release of heat.

[0008] Optionally, the secondary phase change material is laid out in layers within the primary phase change material, with each layer extending along the heat transfer direction to at least half of the cross-section of the primary phase change material. The extended cross-sectional shape can be rectangular, circular, or other structures. In other embodiments, other distribution methods can also be used, such as arranging spherical secondary phase change materials at intervals within the primary phase change material.

[0009] The reason for not completely isolating the upper and lower layers of primary phase change material is that the secondary phase change material in the middle is more expensive, making complete isolation even more costly. Additionally, a full-scale isolation of the secondary phase change material would block natural convection between the upper and lower layers, hindering heat exchange. Although the upper and lower layers are not completely isolated, the isolation extends at least to the center of the primary phase change material (i.e., at least half of the cross-section) to improve the heat release rate at the center of the phase change thermal storage module.

[0010] Optionally, the primary phase change material and the secondary phase change material are separated by a material with high thermal conductivity (preferably greater than 100 W / (m*K)) to form an independent space for encapsulating the secondary phase change material. The partition material with high thermal conductivity acts like a fin, which can also solve the problem of low thermal conductivity within the phase change material to some extent.

[0011] Optionally, the side of the secondary phase change material closest to the heat exchange surface is separated by a material with low thermal conductivity (it is recommended that the thermal conductivity be less than 1W / (m*K)) to weaken the external heat dissipation of the secondary phase change material, thereby ensuring that the heat of the secondary phase change material can be replenished into the primary phase change material during the heat exchange process.

[0012] Optionally, the secondary phase change material is composited with anisotropic thermally conductive materials (the thermally conductive materials are not limited, such as graphite skeletons, fins, heat pipes, etc.), so that the thermal conductivity of the secondary phase change material in the heat transfer direction is lower than that in the vertical direction, thereby enhancing the heat transfer between the primary and secondary phase change materials and weakening the external heat dissipation of the secondary phase change material.

[0013] Optionally, the primary phase change material is incorporating an isotropic thermally conductive material (the thermally conductive material is not limited, such as graphite skeleton, fins, nanoparticles, etc.), so that the thermal conductivity of the primary phase change material is consistent in all directions, thereby improving the internal thermal conductivity of the primary phase change material and enhancing the release of heat from the phase change thermal storage module.

[0014] In addition, the present invention also provides a parallel composite heater that combines latent and sensible heat, including a heater, a heat storage box and a shell, wherein the heat storage box is provided with the above-mentioned parallel composite heat storage structure, and the heater is disposed in the heat storage box. The heat storage box is encapsulated in the shell, and an air inlet and outlet channel is formed between the heat storage box and the shell.

[0015] Optionally, the heat storage box is provided with a high thermal conductivity structure on the side near the air inlet and outlet channels to enhance heat exchange between the heat storage box and the air inlet and outlet.

[0016] Optionally, the high thermal conductivity structure includes a liquid-filled tank filled with a high thermal conductivity liquid (it is recommended that the thermal conductivity be greater than 150W / (m*K)). The outer shell is also provided with a liquid storage tank that communicates with the liquid-filled tank, and the liquid storage tank is provided with a control device for controlling the flow of the high thermal conductivity liquid between the liquid-filled tank and the liquid storage tank.

[0017] Optionally, the control device includes a sealed piston, a control push rod, and a driver arranged inside the liquid storage tank. The driver drives the sealing piston to rise and fall by controlling the push rod, thereby adjusting the pressure inside the liquid storage tank.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0019] 1. The parallel composite structure that combines latent and sensible heat has the following effect: it uses the latent and sensible heat of the heat storage material for heating at the same time. It adopts a parallel two-stage heat storage design, in which the primary phase change material undertakes the main heat storage function, and the secondary phase change material undertakes the regulation function. It can provide heat compensation with a stable temperature during the sensible heat release stage of the primary phase change material, effectively solve the thermocline problem of sensible heat release, and improve the utilization rate of sensible heat storage and the total energy density of the device.

[0020] 2. The anisotropic heat transfer enhancement design has the following effect: by enhancing the heat transfer between the primary and secondary phase change materials, the external heat dissipation of the secondary phase change material is weakened, the temperature control effect of the secondary phase change material is improved, and the effective utilization rate of the sensible heat storage of the device is increased.

[0021] 3. The integrated design of the heat storage device and the high thermal conductivity fluid push rod structure has the following effect: During the heat storage stage, the push rod structure is controlled to rise, driving the high thermal conductivity fluid back into the liquid storage tank, turning the liquid-filled tank into a rarefied air state, thus achieving the heat preservation function; During the heat release stage, the push rod structure is controlled to descend, injecting the high thermal conductivity fluid into the liquid-filled tank through the through hole, working in conjunction with the fins to achieve efficient release of latent heat. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the external structure of the parallel composite heater in an embodiment of the present invention;

[0023] Figure 2 This is a perspective view of the parallel composite heater in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the internal box structure during the heat storage stage in an embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the internal box structure during the heat release stage in an embodiment of the present invention;

[0026] Figure 5 This is a partial longitudinal sectional view of the parallel composite thermal storage structure in an embodiment of the present invention;

[0027] Figure 6 This is a graph showing the average temperature change of the heat exchange surface during the heat release process using a primary phase change thermal storage structure, a latent and apparent composite thermal storage structure, and a latent and apparent composite superimposed anisotropic graphite skeleton in Embodiment 1 of the present invention.

[0028] Figure 7 This is a graph showing the average temperature change of the heat exchange surface during the heat release process using a primary phase change thermal storage structure, a latent and apparent composite thermal storage structure, and a latent and apparent composite superimposed anisotropic graphite skeleton in Embodiment 2 of the present invention.

[0029] The diagram includes: 1-control switch, 2-cover plate, 3-cold air inlet, 4-bracket, 5-side cover, 6-screw, 7-warm air outlet, 8-control push rod, 9-sealed piston, 10-high thermal conductivity liquid, 11-through hole, 12-fin, 13-secondary phase change material, 14-liquid filling tank, 15-electric heating rod, 16-primary phase change material, 17-liquid storage tank, 18-heat storage tank, 19-aerogel. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Furthermore, in the description of the present invention, terms such as "first-level," "second-level," "first," and "second" are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0031] like Figure 1-2 The image shown is a parallel composite heater that combines latent and sensible heat generation, provided in this embodiment. It mainly consists of an internal housing and an external encapsulation structure.

[0032] Internal box structure such as Figure 4 As shown, the liquid filling tank 14 and the heat storage tank 18 are arranged side by side, and the liquid storage tank 17 is located on one side of the liquid filling tank 14 and the heat storage tank 18. Figure 3 As shown, the thermal storage tank 18 adopts a parallel composite thermal storage structure that combines latent and sensible heat, and an electric heating rod 15 is provided to provide heat to the parallel composite thermal storage structure. The thermal storage tank 18 and the liquid-filled tank 14 are connected by a heat exchange surface (except for the heat exchange surface, the other surfaces of the thermal storage tank 18 are insulated surfaces). The liquid-filled tank 14 has a high thermal conductivity structure (copper fins 12 are provided on the heat exchange surface of the liquid-filled tank 14). The liquid-filled tank 14 is filled with a high thermal conductivity liquid 10. The bottom of the liquid storage tank 17 and the liquid-filled tank 14 are connected by a through hole 11. The top of the liquid storage tank 17 is provided with a sealing piston 9, a control push rod 8, and an actuator (not shown in the figure). The actuator drives the sealing piston 9 to rise and fall through the control push rod 8, thereby realizing the pressure adjustment in the liquid storage tank 17.

[0033] External packaging structure such as Figure 1 As shown, the control switch 1, screw 6, cover plate 2, side cover 5, and bracket 4 are common structural components with an overall design size of 600*500*200mm. The heat storage tank 18 has dimensions of 400*450*140mm, the liquid storage tank 17 has dimensions of 100*450*15mm, and the liquid filling tank 14 has a thickness of 1mm. The volume ratio of the two is 3.75, which allows for rapid filling and discharging of high thermal conductivity fluids. The left side of the outer casing has a warm air outlet 7 and a cold air inlet 3, forming an air intake and exhaust channel between the liquid filling tank 14 and the outer casing. The cold air inlet 3 and the warm air outlet 7 have 10 70*30mm vents. The bracket 4 has a height of 100mm. The control switch 1 controls the charging rate and the switching of the charging and discharging modes. Cold air expands and rises under heating, flowing out through the warm air outlet 7. Cold air below rises and enters the heater, expands after heating, and flows out, achieving circulation. In practice, an air circulation pump can be added as needed to increase heating power.

[0034] like Figure 3As shown, during the nighttime heat storage phase, the control push rod 8 moves upward, and the high thermal conductivity liquid 10 (in this example, Great Wall thermal oil L-QB-300) flows back into the liquid storage tank 17 through the through hole 11 under air pressure, making the air in the liquid-filled tank 14 rarefied and providing good heat preservation. The phase change material gradually melts under the heating action of the electric heating rod 15, and electrical energy is converted into latent heat and sensible heat stored in the phase change material. When the average temperature of the phase change region reaches the set upper temperature limit, the electric heating rod 15 stops working, and the heat storage phase ends.

[0035] like Figure 4 As shown, during the heat release phase, the control push rod 8 descends, and the high thermal conductivity liquid 10 flows from the liquid storage tank 17 into the liquid filling tank 14. The high thermal conductivity fluid, combined with the high thermal conductivity fins 12, fully exchanges heat with the heat storage tank 18 on the right, releasing heat in a timely manner. In addition, there is a direct heating phase, where heat storage and heating occur simultaneously. During this phase, the control push rod 8 descends, and the high thermal conductivity liquid 10 flows from the liquid storage tank 17 into the liquid filling tank 14. The heating effect of the electric heating rod 15 allows the phase change material to store heat while simultaneously providing heating.

[0036] Parallel composite thermal storage structures, such as Figure 3 As shown, the heat storage box 18 is filled with primary phase change material 16, and secondary phase change material 13 is arranged at intervals in the primary phase change material 16 (the black filling in the heat storage box 18 in the figure represents the primary phase change material 16, and the white blank space represents the secondary phase change material 13). The primary phase change material 16 and the secondary phase change material 13 have different phase change points and are both below 200°C.

[0037] like Figure 5 As shown, the secondary phase change material 13 is layered and laid flat within the primary phase change material 16, with each layer extending laterally from the side closest to the heat exchange surface (since the heat exchange surface is vertical, the heat exchange direction is laterally) to 3 / 4 of the cross-section of the primary phase change material 16 (i.e., its length in the x-direction is approximately 3 / 4 of the primary phase change material, and its length in the y-direction is the same as that of the primary phase change material). Furthermore, the primary phase change material 16 and the secondary phase change material 13 are separated by a material with high thermal conductivity (e.g., copper), forming an independent space encapsulating the secondary phase change material 13.

[0038] Two specific embodiments of the thermal storage structure will be given below.

[0039] Example 1:

[0040] In this embodiment, the primary phase change material 16 is solid paraffin RT80 (melting point approximately 354.15 K), which is composited with isotropic expanded graphite (porosity 90%, thermal conductivity 50 W / (m*K) in all directions) to achieve high thermal conductivity in all directions; the secondary phase change material 13 is D-mannitol (melting point approximately 440.15 K), which is composited with an anisotropic thermally conductive material, wherein the anisotropic thermally conductive material is expanded graphite (porosity 90%, thermal conductivity 50 W / (m*K) in the z direction, and thermal conductivity 25 W / (m*K) in the xy direction), so that the high thermal conductivity of the secondary composite phase change material is distributed along the longitudinal direction, and heat is mainly transferred along the longitudinal direction. At the same time, in order to further block transverse heat transfer, a low thermal conductivity aerogel 19 (thermal conductivity 0.012 W / (m*K)) is provided on the left side of the secondary phase change material 13.

[0041] The preparation process of the primary composite phase change material is as follows:

[0042] 1) Mix the paraffin wax and expanded graphite thoroughly by stirring and place them in a beaker;

[0043] 2) Place both in a 90℃ constant temperature water bath (for secondary composite phase change materials, place in a 180℃ oil bath), and stir continuously during the paraffin melting process to allow the liquid paraffin to be fully adsorbed into the pores of the expanded graphite (for secondary composite phase change materials, a whole piece of anisotropic expanded graphite is required, and mannitol is slowly infiltrated into it).

[0044] 3) Use microwave oscillation and heating for 30 minutes, stirring constantly, to stabilize the material properties;

[0045] 4) Remove the beaker and allow it to cool naturally at room temperature for more than 2 hours to obtain the composite phase change material.

[0046] In other embodiments, the preparation method of the composite phase change material is not limited. The phase change material and the reinforcing means (graphite skeleton is used here) can also be combined by other standard preparation methods to prepare a new composite material, so that the material has the functions of both materials and can maintain the stability of properties.

[0047] Because the phase change point of the secondary phase change material 13 is higher than that of the primary phase change material 16, during the heat release process in the heat storage box 18, in the first stage, the primary phase change material 16 releases liquid sensible heat, while the secondary phase change material 13 reaches its phase change temperature first, undergoing a latent heat phase change. The sensible and latent heat combine to resolve the temperature jump problem. In the second stage, the temperature of the primary phase change material 16 gradually decreases, releasing solid latent heat. The solid secondary phase change material 13 replenishes the heat of the primary phase change material 16, thus slowing down the rate of temperature decrease of the primary phase change material 16.

[0048] In this embodiment, the temperature changes on the heat release side of the phase change material during the heat release process were compared under various conditions, based on the dimensions of the heat storage box 18, the physical properties of the heat storage material, and the arrangement of the graphite skeleton. For example... Figure 6 As shown, the baseline is 333.15K, at which the minimum design power of the heater, 500W, is achieved. Under the same convective heat transfer conditions (forced convection, wind speed 5m / s, external temperature 273.15K, pressure 1atm), compared to a single-stage phase change thermal storage structure, the latent-heating composite thermal storage structure effectively solves the thermocline problem, extends the heating time to 10840s (above the minimum heating power), and improves energy utilization (i.e., η2 = 73.58%). Adding a graphite skeleton to the latent-heating composite structure further extends the heating time to 14600s and improves energy utilization (i.e., η3 = 80.85%). In summary, the novel phase change thermal storage structure combining latent-heating composite and a graphite skeleton can effectively improve heater performance.

[0049] Example 2:

[0050] In this embodiment, the primary phase change material 16 is made of solid paraffin RT80 (melting point approximately 354.15 K), which is composited with isotropic expanded graphite (porosity 90%, thermal conductivity 50 W / (m*K) in all directions); the secondary phase change material 13 is made of solid paraffin RT70 (melting point approximately 343.15 K), which is composited with an anisotropic thermally conductive material, wherein the anisotropic thermally conductive material is expanded graphite (porosity 90%, thermal conductivity 50 W / (m*K) in the z-direction, and thermal conductivity 25 W / (m*K) in the xy-direction), so that the high thermal conductivity of the secondary composite phase change material is distributed along the longitudinal direction, and the heat is mainly transferred along the longitudinal direction. At the same time, in order to block the transverse heat transfer, a low thermal conductivity aerogel (thermal conductivity 0.012 W / (m*K)) is provided on the left side of the secondary phase change material 13.

[0051] Because the phase change point of the primary phase change material 16 is higher than that of the secondary phase change material 13, during the heat release process in the heat storage box 18, in the first stage, the primary phase change material 16 reaches its phase change temperature first and undergoes a latent heat phase change, while the secondary phase change material 13 releases liquid sensible heat. The sensible and latent heat combine, and the temperature remains basically in equilibrium. In the second stage, the temperature of the primary phase change material 16 gradually decreases, releasing solid sensible heat, while the secondary phase change material 13 undergoes a latent heat phase change, replenishing the heat of the primary phase change material 16. This slows down the rate of temperature decrease of the primary phase change material 16, thus resolving the thermocline problem.

[0052] In this embodiment, the temperature changes on the heat release side of the phase change material during the heat release process were compared under various conditions, based on the aforementioned heat storage box dimensions, heat storage material properties, and graphite skeleton arrangement. For example... Figure 7As shown, the baseline is 333.15K, at which the minimum design power of the heater, 500W, is achieved. Under the same convective heat transfer conditions (forced convection, wind speed 5m / s, external temperature 273.15K, pressure 1atm), compared to a single-stage phase change heater, the latent heat transfer composite structure effectively solves the thermocline problem, extending the heating time to 8900s (above the minimum heating power) and improving energy utilization (i.e., η2 = 72.94%). Adding a graphite skeleton to the latent heat transfer composite structure further extends the heating time to 16650s and improves energy utilization (i.e., η3 = 81.74%). In summary, the novel phase change heat storage structure combining latent heat transfer composite and a graphite skeleton can effectively improve heater performance.

[0053] This heater can utilize off-peak electricity at night for heat storage, effectively reducing heating costs; the use of latent and apparent composite heat storage can effectively increase the heat storage capacity per unit volume, thereby extending heating time; the heater is stable and controllable, using a parallel composite structure to stabilize the heating temperature, alleviate the thermocline problem, improve the quality of warm air, and increase energy utilization efficiency and energy density; at the same time, the use of a heat transfer oil filling device can achieve free switching between on / off and heat storage / release stages.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A parallel composite heat storage structure for latent and sensible heat, characterized in that, The heat storage structure comprises a heat exchange surface and a heat exchange direction, a first phase change material is filled in a heat storage space, and a second phase change material is arranged in the first phase change material, wherein the phase change points of the first phase change material and the second phase change material are different and are both lower than 200 ℃, and the phase change point of the second phase change material is higher than the temperature threshold of the first phase change material by 10 ℃ when a thermocline occurs in the first phase change material; the second phase change material is layered and laid in the first phase change material, and each layer extends to at least 1 / 2 of the cross section of the first phase change material along the heat exchange direction; the side of the second phase change material close to the heat exchange surface is separated by a low thermal conductivity material; The second phase change material is compounded with an anisotropic thermal conductive material, so that the thermal conductivity of the second phase change material in the heat exchange direction is higher than the thermal conductivity perpendicular to the heat exchange direction, the heat exchange between the first phase change material and the second phase change material is strengthened, and the heat dissipation of the second phase change material is weakened.

2. The parallel composite heat storage structure according to claim 1, characterized in that, The first phase change material and the second phase change material are separated by a high thermal conductivity material.

3. The parallel composite heat storage structure according to claim 1, characterized in that, The first phase change material is compounded with an isotropic thermal conductive material, so that the thermal conductivities of the first phase change material in all directions are consistent.

4. A parallel compound heater for latent and sensible heat, characterized by, The heat storage structure comprises a heater, a heat storage box, and an outer shell, wherein the heat storage box is provided with the parallel composite heat storage structure according to any one of claims 1-3, the heater is arranged in the heat storage box, the heat storage box is encapsulated in the outer shell, and an air inlet and outlet channel is formed between the heat storage box and the outer shell.

5. The parallel compound heater of claim 4, wherein, The side of the heat storage box close to the air inlet and outlet channel is provided with a high thermal conductive structure.

6. The parallel compound heater of claim 5, wherein, The high thermal conductive structure comprises a liquid-filled box filled with a high thermal conductive liquid, the outer shell is further provided with a liquid storage box in communication with the liquid-filled box, and the liquid storage box is provided with a control device for controlling the flow of the high thermal conductive liquid between the liquid-filled box and the liquid storage box.

7. The parallel compound heater of claim 6, wherein, The control device comprises a sealing piston arranged in the liquid storage box, a control push rod, and a driver, the driver drives the sealing piston to rise and fall through the control push rod, thereby adjusting the pressure in the liquid storage box.

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