Heat storage device

Abstract

To provide a heat storage device capable of suppressing deterioration of heat transfer efficiency between a latent heat storage material and a heat exchange body without greatly increasing the weight and volume of the heat storage device even when the volume of the latent heat storage material decreases due to solidification of the latent heat storage material.SOLUTION: A heat storage device comprises: a container 1 in which a latent heat storage material 30 is encapsulated; a pipe 10 through which a heat medium flows so as to be able to exchange heat with the latent heat storage material 30 in the container 1; thermally conductive flexible sheets 20, 21 with one end attached to an outer peripheral surface of the pipe 10; and a nucleation trigger that is arranged in the latent heat storage material 30, and breaks down a supercooled state of the latent heat storage material. The pipe 10 has an inlet part 11 and an outlet part 15 for the heat medium in the container 1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat storage device.

Background Art

[0002] Conventionally, when starting the engine of a moving body such as a vehicle, in order to promote warm-up to improve fuel efficiency and purify exhaust gas, or to improve heating performance, the heat energy discharged from the moving body is temporarily stored in a latent heat storage material and used. Various heat storage devices have been proposed.

[0003] For example, as a heat storage device, Patent Document 1 describes a latent heat storage device including a sealed container and a heat exchanger having a heat transfer tube that forms a flow path of a heat medium passing from the outside of the container through the inside of the container to the outside of the container. A latent heat storage material is accommodated inside the container, and an immiscible liquid having a lower specific gravity than the latent heat storage material and being immiscible with the latent heat storage material is accommodated inside the container. The latent heat storage material and the immiscible liquid are accommodated in a layered manner such that the latent heat storage material is in the lower layer and the immiscible liquid is in the upper layer with respect to the gravitational direction, and the heat exchanger is configured to straddle the immiscible liquid and the latent heat storage material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The latent heat storage material has a mechanism of extracting heat by changing between a solid phase and a liquid phase. However, the specific gravity is different between the liquid phase and the solid phase, and when the latent heat storage material changes from the liquid phase to the solid phase, the volume of the latent heat storage material decreases. In a container filled with the latent heat storage material, if a gap is generated between the heat exchanger and the latent heat storage material due to the volume reduction of the latent heat storage material caused by the phase change, there is a problem that the heat transfer efficiency between the latent heat storage material and the heat exchanger decreases.

[0006] In Patent Document 1, in order to solve this problem, even if a gap is generated between the latent heat storage material and the heat exchanger, since the immiscible liquid enters the gap, the heat exchange efficiency between the latent heat storage material and the heat exchanger is improved compared to the state where the gap remains as a void, and the decrease in the heat transfer efficiency between the latent heat storage material and the heat exchanger due to the gap is suppressed. However, in the heat storage device of Patent Document 1, since it is necessary to put a liquid different from the latent heat storage material in the device, there is a problem that the weight and volume of the heat storage device increase. Further, when the latent heat storage material stores heat, sensible heat increases, so there is a problem that extra energy is required.

[0007] Therefore, in view of the above problems, the present invention aims to provide a heat storage device that can suppress a decrease in the heat transfer efficiency between a latent heat storage material and a heat exchanger without significantly increasing the weight and volume of the heat storage device, even if the volume of the latent heat storage material decreases due to solidification of the latent heat storage material.

Means for Solving the Problems

[0008] To achieve the above object, a heat storage device according to the present invention includes a container in which a latent heat storage material is enclosed, a nucleation trigger for collapsing the supercooled state of the latent heat storage material, the nucleation trigger being disposed in the latent heat storage material in the container, a pipe through which a heat medium flows in a heat-exchangeable manner with the latent heat storage material in the container, the pipe having an inlet portion and an outlet portion of the heat medium in the container, and a heat-conductive flexible sheet having one end attached to the outer peripheral surface of the pipe.

Effects of the Invention

[0009] According to the present invention as described above, by providing a pipe through which a heat medium flows in a heat-exchangeable manner with the latent heat storage material in the container and attaching one end of a heat-conductive flexible sheet to the outer peripheral surface thereof, the flexible sheet follows the volume contraction due to solidification of the latent heat storage material, preventing the formation of a gap between the latent heat storage material, so that a decrease in the heat transfer efficiency with the solid latent heat storage material can be suppressed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0011] Hereinafter, with reference to the accompanying drawings, an embodiment of a heat storage device according to the present invention will be described.

[0012] As shown in FIGS. 1 to 3, the heat storage device of the present embodiment mainly includes a container 1 in which a latent heat storage material 30 is enclosed, a pipe 10 through which a heat medium circulates so as to be heat-exchangeable with the latent heat storage material 30 in the container 1, heat-conductive flexible sheets 20 and 21 having one end attached to the outer peripheral surface of the pipe 10, and a nucleation trigger (not shown) disposed in the latent heat storage material 30 in the container 1 for collapsing the supercooled state of the latent heat storage material 30.

[0013] Container 1 may be able to withstand heating and cooling for causing a phase change of the latent heat storage material between the solid phase and the liquid phase, and the material and structure of the container for housing the latent heat storage material in a conventional heat storage device may be used. For example, as the material, resins having heat insulation properties such as phenolic resin and engineering plastics can be mentioned. In FIG. 1, the case where the material of container 1 is transparent is shown, but the present invention is not limited thereto and may be opaque. As shown in FIG. 1, the structure of container 1 preferably has a three-dimensional shape that is long in one direction, and may have any other three-dimensional shape such as a rectangular shape or a cylindrical shape in addition to the rectangular shape.

[0014] As the latent heat storage material 30 enclosed in container 1, there is no particular limitation as long as it is a substance that, when heated above its melting point in the solid phase, changes to the liquid phase, and then, even when cooled below the melting point, continues to maintain the liquid phase as a supercooled state and can store the heat absorbed during heating as latent heat. For example, calcium chloride hydrate, sodium acetate hydrate, sodium sulfate hydrate, etc. are preferable.

[0015] The pipe 10 through which the heat medium flows has an inlet portion 11 and an outlet portion 15 of the heat medium in container 1, and as shown in FIG. 1, both are arranged on one surface (ceiling surface 1a) of container 1. Further, the pipe 10 includes a feed pipe portion 11 extending from the inlet portion 11 on the ceiling surface 1a toward the bottom surface 1b on the opposite side, a return pipe portion 14 extending from the outlet portion 15 on the ceiling surface 1a toward the bottom surface 1b on the opposite side, and a plurality of branch pipe portions 13 that are in fluid communication with each other between the feed pipe portion 11 and the return pipe portion 14. The branch pipe portions 13 are arranged in a meandering manner so as to reciprocate a plurality of times between one side surface 1c and the other side surface 1d of container 1 in order to maximize the contact area with the latent heat storage material 30 enclosed in container 1.

[0016] The heat medium is not particularly limited as long as it can recover heat from the latent heat storage material. For example, a refrigerant generally used in a heat pump, an air conditioning system, etc. can be used.

[0017] Flexible sheets 20 are respectively attached to the branch pipe portions 13. Although the branch pipe portions 13 are arranged in a meandering manner within the container 1, it is still difficult to sufficiently recover heat from the latent heat storage material 30 near the inner wall surface of the container 1 that is far from the branch pipe portions 13. By attaching the flexible sheet 20 with heat conductivity to the branch pipe portions 13 in this way, heat can be sufficiently recovered from the latent heat storage material 30 at a position far from the branch pipe portions 13.

[0018] The flexible sheet 20 is not particularly limited as long as it is flexible and has heat conductivity. For example, a graphite sheet, a carbon fiber sheet, a silicone sheet, an acrylic sheet, etc. can be used. Further, in order for the flexible sheet 20 to efficiently exchange heat from the latent heat storage material 30 near the inner wall surface of the container 1, the density of the flexible sheet 20 is preferably equal to or lower than the density of the latent heat storage material 30 so that the tip of the flexible sheet 20 does not droop and extends toward the inner wall surface of the container 1, for example, in the horizontal direction.

[0019] Also, as shown in FIGS. 1 and 2, a flexible sheet 21 extending toward the corner of the container 1 is attached to the branch pipe portion 13 located on the bottom surface 1b side of the container 1 so that heat can be efficiently exchanged from the latent heat storage material 30 near the corner of the container 1.

[0020] The tips of the flexible sheets 20 and 21 may contact the inner wall surface or the corner of the container 1. The base ends of the flexible sheets 20 and 21 are adhered to the branch pipe portions 13 by an adhesive or an adhesive tape. The adhesive and the adhesive tape are not particularly limited as long as they have heat conductivity. For example, as the adhesive, a commercially available adhesive such as a cyanoacrylate-based adhesive can be used, and as the adhesive tape, a commercially available adhesive tape such as a silicone-based adhesive tape, an acrylic-based adhesive tape, or one with enhanced heat conductivity by blending a metal filler can be used.

[0021] The proximal ends of the flexible sheets 20 and 21 may be adhered to the upper end or the lower end of the branch pipe portion 13. Further, in the present embodiment, both of the flexible sheets 20 and 21 are attached to the branch pipe portion 13. However, the present invention is not limited to this, and the flexible sheet may be attached to any type of pipe as long as it is a pipe through which a heat medium flows.

[0022] As the nucleation trigger, for example, a curved plate made of a metal having elasticity may be used. Such a curved plate can collapse the supercooled state of the latent heat storage material in the supercooled state by changing its shape such as inversion, and initiate a phase change from the liquid phase to the solid phase, that is, nucleation. The nucleation trigger is preferably disposed at one end in the longitudinal direction of the container 10. For example, it may be disposed on the bottom surface in the vertically long container 10, and particularly preferably at the center of the bottom surface.

[0023] With reference to FIG. 4 schematically showing the heat storage and heat release of the heat storage device having such a configuration, an explanation will be given. First, for the heat storage device in a state where heat storage is completed and before heat release, as shown in FIG. 4(a), the liquid-phase latent heat storage material 31 is accommodated in the container 1, and the flexible sheet 20 attached to the pipe 10 through which the heat medium flows extends substantially horizontally in the latent heat storage material 30.

[0024] Next, when the heat storage device releases heat, nucleation occurs in the liquid-phase latent heat storage material 31 by a nucleation trigger (not shown), the latent heat storage material 31 is solidified, and heat release occurs. Then, as shown in FIG. 4(b), the inside of the container 1 becomes entirely the solid-phase latent heat storage material 32 and the heat release is completed. However, the volume of the solid-phase latent heat storage material 32 is smaller than that of the liquid phase. At this time, since the flexible sheet 20 flexibly follows the volume contraction of the latent heat storage material 32, it is possible to prevent a gap from being formed between the latent heat storage material 32 and the flexible sheet 20. The flexible sheet 20 extends near the inner wall surface of the container 1 as described above. Therefore, heat can be efficiently transferred from the latent heat storage material 32 at a position far from such a pipe 10 to the pipe 10 through which the heat medium flows via the flexible sheet 20.

[0025] In contrast, the case where a metal fin is attached to a pipe through which a heat medium flows instead of a flexible sheet will be described with reference to FIG. 5. Before heat dissipation is performed after heat storage is completed, in the heat storage device in the state shown in FIG. 5(a), a liquid-phase latent heat storage material 31 is accommodated in the container 1, and the metal fin 40 attached to the pipe 10 extends horizontally in the latent heat storage material 31, similar to the flexible sheet 20.

[0026] Next, when heat dissipation of the heat storage device is performed, nucleation occurs in the liquid-phase latent heat storage material 31 by a nucleation trigger (not shown), and the latent heat storage material 31 is solidified. Then, as shown in FIG. 5(b), the entire inside of the container 1 becomes a solid-phase latent heat storage material 32 and the volume decreases. At this time, since the metal fin 40 is rigid, a gap is generated between the metal fin 40 and the latent heat storage material 32 due to the volume contraction of the latent heat storage material 32. This gap significantly reduces the heat transfer efficiency between the latent heat storage material 32. In addition, since the heat capacity increases in the metal fin 40, there is also a problem that the temperature rise becomes slow.

[0027] In this way, by attaching the flexible sheet 20 instead of the metal fin 40 to the pipe 10, it is possible to prevent a gap from being generated between the latent heat storage material 32 whose volume decreases due to solidification, and thus, it is possible to suppress a decrease in the heat transfer efficiency to the pipe 10 through which the heat medium flows.

[0028] For heat storage of the heat storage device, first, the solid-phase latent heat storage material 32 is heated above the melting point so that the entire inside of the container 1 becomes a liquid-phase latent heat storage material 31. Next, the latent heat storage material 31 is cooled below the melting point to be in a supercooled state. Thereby, again, a ready state for heat dissipation as shown in FIG. 4(a) is achieved. In this way, the heat storage device can repeat heat dissipation and heat storage.

[0029] Note that the above heating and cooling of the latent heat storage material can be performed, for example, by once removing the heat medium from the pipe and flowing a high-temperature fluid through the pipe to heat the latent heat storage material, and flowing a low-temperature fluid through the pipe to cool the latent heat storage material. Alternatively, heat transfer means to the latent heat storage material such as a heat transfer plate extending into the latent heat storage material through the container may be separately provided to perform heating and cooling of the latent heat storage material.

Example

[0030] Hereinafter, examples and comparative examples of the present invention will be described.

[0031] Using the heat storage device shown in FIGS. 1 to 3, the heat transfer efficiency during heat dissipation of the heat storage device was tested. After placing a nucleation trigger at the center of the bottom surface of the container, a latent heat storage material was injected into the container. As the latent heat storage material, sodium acetate trihydrate (C2H3NaO2·3H2O) was used. As the nucleation trigger, a metal curved disk used in commercially available recycled heat packs was used. Then, the piping was switched, and a high-temperature refrigerant was flowed through the heating operation of the heat pump outside the device to heat the latent heat storage material to 58 °C or higher than the melting point, and after making all the latent heat storage material into a liquid state, this time the piping was switched and a low-temperature refrigerant was flowed through the cooling operation of the heat pump, and it was gently cooled to a supercooled state. Next, the nucleation trigger was pushed with a rod from the upper opening of the container to cause nucleation, and at the same time, a low-temperature refrigerant was flowed through the piping again. Then, while observing the behavior of the latent heat storage material through the transparent container, the temperature of the refrigerant at the inlet and outlet of the piping and the temperature of the latent heat storage material in the container were measured over time. The measurement results of the temperature are shown in FIG. 6.

[0032] Also, as a comparative example, except for the point that a flexible sheet was not attached, using the heat storage device shown in FIGS. 1 to 3, a test was conducted in the same manner as in the example, and the behavior of the latent heat storage material was observed and the temperature at a predetermined position was measured. The measurement results of the temperature are shown in FIG. 7.

[0033] In the example, as shown in FIG. 6, the temperature at the inlet, outlet of the piping, and the latent heat storage material was T0 at the time of nucleation t1, but due to the heat dissipation of the latent heat storage material caused by nucleation, the latent heat storage material reached temperature T at time t2 after a short period of time.

[0034] Also, in the example, as shown in FIG. 6, the temperature at the inlet, outlet of the piping, and the latent heat storage material was T0 at the time of nucleation t1, but due to the heat dissipation of the latent heat storage material caused by nucleation, the latent heat storage material reached temperature T at time t2 after a short period of time.x rose, and since the refrigerant was heated by the latent heat storage material, the temperature at the outlet of the pipe was lower than that but was temperature T a rose. On the other hand, since the low-temperature refrigerant was introduced into the pipe simultaneously with nucleation, the temperature at the inlet of the pipe reached temperature T at time t2 after a short period of time z and dropped. Then, from time t3 when all of the latent heat storage material became solid phase, the temperature of the latent heat storage material dropped rapidly, and the temperature at the outlet of the pipe also dropped rapidly almost simultaneously with the latent heat storage material.

[0035] On the other hand, in the comparative example, as shown in FIG. 7, the temperatures of the inlet, outlet of the pipe, and the latent heat storage material, which were temperature T0 at the time of nucleation t1, were such that the latent heat storage material reached temperature T at time t2 after a short period of time due to nucleation x and rose, but the temperature at the outlet of the pipe only rose to a temperature T that was even lower than in the case of the example b . Then, the temperature at the outlet of the pipe dropped rapidly at time t5, which was considerably earlier than the time when all of the latent heat storage material became solid phase. On the other hand, the temperature of the latent heat storage material did not drop significantly even after the time when all of the latent heat storage material became solid phase.

[0036] Thus, in the comparative example, although the temperature at the outlet of the pipe dropped early, the temperature of the latent heat storage material did not drop at all times because a large number of voids were generated between the branch pipe portion and the latent heat storage material, resulting in a significant decrease in the heat transfer efficiency between the branch pipe portion and the latent heat storage material and heat remaining in the latent heat storage material. On the other hand, in the example, the temperature at the outlet of the pipe dropped together with the temperature of the latent heat storage material, and no heat remained in the latent heat storage material because the flexible sheet was able to prevent the generation of voids between the latent heat storage material and prevent a decrease in the heat transfer efficiency.

Explanation of Reference Numerals

[0037] 1 Heat storage container 10 Pipe 11 Inlet portion 12 Feed pipe portion 13 Branch pipe portion 14 Return pipe portion 15 Outlet portion 20, 21 Flexible sheet 30, 31, 32 Latent heat storage material 40 Metal fin

Claims

1. a container filled with a latent heat storage material; a nucleation trigger for collapsing the supercooled state of the latent heat storage material, the nucleation trigger being disposed within the latent heat storage material in the container; a pipe through which a heat medium flows in a heat-exchangeable manner with the latent heat storage material in the container, the pipe having an inlet portion and an outlet portion of the heat medium in the container; a heat-conductive flexible sheet having one end attached to the outer peripheral surface of the pipe and a heat storage device comprising the same.

2. The heat storage device according to claim 1, wherein the other end of the flexible sheet is disposed facing the inner wall surface of the container.

3. The heat storage device according to claim 1 or 2, further comprising a heat transfer means to the latent heat storage material.

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