heat storage device

Abstract

The heat storage device (1) of the present invention comprises a latent heat storage material (10) and a container (20). The latent heat storage material (10) is water-soluble. The container (20) contains the latent heat storage material (10) and uses aluminum or an aluminum alloy as the main material. The container (20) has a joint (22) and a first coating (24). For the joint (22), the first coating (24) covers at least the joint (22) on the inner surface of the container (20). A first element and fluorine are present on the surface (24a) of the first coating (24). The first element is an element other than aluminum that has a lower ionization tendency than potassium.

Description

Technical Field

[0001] This invention relates to a heat storage device. Background Technology

[0002] Previously, heat storage devices using water-soluble latent heat storage materials were known.

[0003] For example, Patent Document 1 describes a heat storage device comprising multiple heat storage bodies filled with a latent heat storage material whose main component is hydrate. The heat storage bodies are formed from a heat storage container and the latent heat storage material. Alumina is a suitable material for the heat storage container.

[0004] Furthermore, Patent Document 2 describes a vacuum insulation material comprising a heat storage material and a gas-barrier membrane. In this vacuum insulation material, the heat storage material is sealed under reduced pressure within the gas-barrier membrane. The heat storage material is a hydrate such as sodium acetate hydrate. The gas-barrier membrane may contain, for example, a sealing layer, a gas-barrier layer, and a resin film layer layered together. The gas-barrier layer is a metal foil or a vapor-deposited film, and may contain aluminum.

[0005] Patent document 3 describes a cold storage device comprising a double-walled container and a cold storage agent. The double-walled container is constructed by flanged outer and inner containers made of metal. The interior of the double-walled container is filled with a cold storage agent that freezes at a specified temperature. The outer container and inner container are formed from thin aluminum alloy sheets with an anodized coating on their surfaces and back sides.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2006-284031

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-109424

[0010] Patent Document 3: Japanese Utility Model Application Publication No. 58-129479 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] The present invention provides a heat storage device that is advantageous from the viewpoint of the stability of supercooling of the latent heat storage material, in which the container for storing latent heat storage material is made of aluminum or aluminum alloy as the main material and has a joint.

[0013] Solution for solving the problem

[0014] The heat storage device of the present invention comprises:

[0015] Water-soluble latent heat storage materials; and

[0016] A container that houses the aforementioned latent heat storage materials and uses aluminum or aluminum alloy as the main material.

[0017] The aforementioned container has: a joint, and a first film covering at least the joint on the inner surface of the aforementioned container.

[0018] The surface of the aforementioned first coating contains: a first element other than aluminum that has a lower ionization tendency than potassium; and fluorine.

[0019] Invention Effects

[0020] The aforementioned heat storage device is advantageous from the viewpoint of the stability of the supercooling of latent heat storage materials. Attached Figure Description

[0021] Figure 1 This is a cross-sectional view of the heat storage device according to Embodiment 1.

[0022] Figure 2 A diagram illustrating the heat utilization system of Embodiment 2. Detailed Implementation

[0023] (Insights that form the basis of this invention)

[0024] In heat storage devices, containers made primarily of aluminum or aluminum alloys and having joints are considered for storing latent heat storage materials. In this case, flux or other additives are used to form the joints. However, according to the research of the present inventors, it has been newly discovered that the stability of the latent heat storage material stored in the container is compromised by the use of flux or other additives.

[0025] It is believed that the supercooling stability of latent heat storage materials is easily compromised due to the dissolution of aluminum ions from the container into the latent heat storage material. Therefore, in order to suppress the dissolution of aluminum ions from the container into the latent heat storage material, it is considered to form a passivation state by performing aluminum anodizing and boehmite treatment on the inner surface of the container. On the other hand, it is believed that a passivation state is not easily formed on the inner surface of the container where flux or other additives used in the formation of the joint are applied, as the flux or other additives dissolve into the latent heat storage material, exposing the main material of the container to the latent heat storage material. As a result, it is believed that aluminum ions dissolve into the latent heat storage material from the periphery of the joint, thereby compromising the supercooling stability of the latent heat storage material. Therefore, the inventors have conducted numerous repeated experiments and have newly discovered that by including a specified element on the surface of the coating covering the joint, the supercooling stability of the latent heat storage material can be improved, thus proposing the heat storage device of the present invention.

[0026] (Summary of one aspect of the present invention)

[0027] The heat storage device according to the first aspect of the present invention comprises:

[0028] Water-soluble latent heat storage materials; and

[0029] A container that houses the aforementioned latent heat storage materials and uses aluminum or aluminum alloy as the main material.

[0030] The aforementioned container has: a joint, and a first film covering at least the joint on the inner surface of the aforementioned container.

[0031] The surface of the aforementioned first coating contains: a first element other than aluminum that has a lower ionization tendency than potassium; and fluorine.

[0032] According to the first method, the first element and fluorine are present on the surface of the first coating covering at least the joint. Therefore, the first coating is not easily dissolved in the water-soluble latent heat storage material, and easily inhibits the dissolution of aluminum ions from the periphery of the joint into the latent heat storage material. Thus, in the heat storage device according to the first method, the supercooling of the latent heat storage material is easily stabilized.

[0033] In the second aspect of the present invention, for example, in the heat storage device according to the first aspect, the aforementioned first coating has a potassium-rich portion, which is located closer to the aforementioned joint than the aforementioned surface in the thickness direction of the aforementioned first coating, and has a potassium concentration, in atomic percent, higher than the specific concentration of potassium in the aforementioned surface. According to the second aspect, the potassium concentration in the surface of the first coating is lower than the potassium concentration in the potassium-rich portion, so even if the first coating comes into contact with the latent heat storage material, the first coating is more reliably less likely to dissolve in the latent heat storage material. Therefore, the dissolution of aluminum ions from the periphery of the joint into the latent heat storage material can be more reliably suppressed, and the supercooling of the latent heat storage material is easily stabilized.

[0034] In the third aspect of the present invention, for example, in the heat storage device involved in the first or second aspect, the solubility of the aforementioned first element fluoride in water at 20°C may be lower than the solubility of potassium fluoride in water at 20°C. According to the third aspect, even if the first coating contacts the latent heat storage material, the first coating is more reliably less likely to dissolve in the latent heat storage material. Therefore, the dissolution of aluminum ions from the periphery of the joint into the latent heat storage material can be more reliably suppressed, and the supercooling of the latent heat storage material is easily stabilized.

[0035] In the fourth aspect of the present invention, for example, in the heat storage device involved in any one of the first to third aspects, the aforementioned first element can be at least one selected from the group consisting of sodium, calcium, magnesium, zinc, and iron. According to the fourth aspect, even if the first coating contacts the latent heat storage material, the first coating is more reliably less likely to dissolve in the latent heat storage material. Therefore, the dissolution of aluminum ions from the periphery of the joint into the latent heat storage material can be more reliably suppressed, and the supercooling of the latent heat storage material is easily stabilized.

[0036] In the fifth aspect of the present invention, for example, in the heat storage device according to any one of the first to fourth aspects, the aforementioned container may have a second coating formed on the inner surface of the aforementioned container away from the aforementioned joint. On the surface of the aforementioned second coating, at least one of the following may be present: alumina, aluminum hydroxide, alumina hydrate, and a substance containing a second element having a lower ionization tendency than potassium and fluorine. According to the fifth aspect, even if the second coating comes into contact with the latent heat storage material, the second coating is not easily dissolved in the latent heat storage material. Therefore, the dissolution of aluminum ions from the main material of the container into the latent heat storage material can be suppressed, and the supercooling of the latent heat storage material is easily stabilized.

[0037] In the sixth aspect of the present invention, for example, in the heat storage device according to the fifth aspect, the aforementioned substance containing the aforementioned second element and fluorine may be present on the surface of the aforementioned second coating. The solubility of the aforementioned second element fluoride in water at 20°C may be lower than that of potassium fluoride in water at 20°C. According to the sixth aspect, even if the second coating comes into contact with the latent heat storage material, the second coating is more reliably less likely to dissolve in the latent heat storage material. As a result, the dissolution of aluminum ions from the main material of the container into the latent heat storage material can be more reliably suppressed, and the supercooling of the latent heat storage material is more easily stabilized.

[0038] In the seventh aspect of the present invention, for example, in the heat storage device according to the fifth aspect, the aforementioned substance containing the aforementioned second element and fluorine may be present on the surface of the aforementioned second coating. The aforementioned second element may be at least one selected from the group consisting of sodium, calcium, magnesium, zinc, and iron. According to the seventh aspect, even when the second coating comes into contact with the latent heat storage material, the second coating is more reliably less likely to dissolve in the latent heat storage material. As a result, the dissolution of aluminum ions from the main material of the container into the latent heat storage material can be more reliably suppressed, and the supercooling of the latent heat storage material is easily stabilized.

[0039] In the eighth aspect of the present invention, for example, in the heat storage device according to any one of the first to seventh aspects, the aforementioned latent heat storage material may contain a metal salt or a hydrate of a metal salt as the main component. According to the eighth aspect, the latent heat storage material is easily stabilized by supercooling.

[0040] In the ninth aspect of the present invention, for example, in the heat storage device according to the eighth aspect, the aforementioned latent heat storage material may contain sodium acetate as a main component. According to the ninth aspect, the supercooling of the latent heat storage material is more easily and reliably stabilized.

[0041] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The embodiments described below are merely illustrative, and the present invention is not limited to these embodiments.

[0042] (Implementation Method 1)

[0043] Figure 1This is a cross-sectional view of the heat storage device 1 according to Embodiment 1. Figure 1 As shown, the heat storage device 1 includes a latent heat storage material 10 and a container 20. The latent heat storage material 10 is water-soluble. The container 20 houses the latent heat storage material 10, using aluminum or an aluminum alloy as the main material. For example, the main material has the largest mass in the container 20. The container 20 has a joint 22 and a first coating 24. The joint 22 is, for example, a portion formed by joining various components using methods such as brazing and fusion. The first coating 24 covers at least the joint 22 on the inner surface of the container 20. On the surface 24a of the first coating 24, there is a first element having a lower ionization tendency than potassium, and fluorine. The first element is an element other than aluminum.

[0044] The heat storage device 1 typically utilizes the supercooling of the latent heat storage material 10 to store latent heat. Therefore, for the heat storage device 1, stable supercooling of the latent heat storage material 10 is advantageous.

[0045] like Figure 1 As shown, the first coating 24 is in contact with the latent heat storage material 10, for example. By presenting the first element and fluorine on the surface 24a, substances that are not easily soluble in the latent heat storage material 10 are readily present. Therefore, the first coating 24 is not easily soluble in the water-soluble latent heat storage material 10, and the dissolution of aluminum ions from the periphery of the joint 22 into the latent heat storage material 10 is easily suppressed. As a result, the supercooling of the latent heat storage material 10 is easily stabilized.

[0046] like Figure 1 As shown, the first coating 24 has, for example, a potassium-rich portion 24b. The potassium-rich portion 24b is located closer to the joint 22 in the thickness direction of the first coating 24 than the surface 24a. Furthermore, the potassium concentration in the potassium-rich portion 24b, on an atomic percent basis, is higher than the potassium concentration in the surface 24a. In other words, the potassium concentration in the surface 24a is lower than the potassium concentration in the potassium-rich portion 24b. Therefore, even when the first coating 24 contacts the latent heat storage material 10, the first coating 24 is more reliably less likely to dissolve in the latent heat storage material 10. Thus, the dissolution of aluminum ions from the periphery of the joint 22 into the latent heat storage material 10 can be more reliably suppressed, and the supercooling of the latent heat storage material is easily stabilized. Moreover, by having the potassium-rich portion 24b located close to the joint 22, the joint 22 is maintained in the desired state, and the strength of the joint 22 is easily maintained at a high level.

[0047] The first element is not limited to a specific element as long as it has a lower ionization tendency than potassium. The solubility of the fluoride of the first element in water at 20°C is not limited to a specific value; for example, it may be lower than the solubility of potassium fluoride in water at 20°C. In this case, substances that are not easily soluble in the latent heat storage material 10, such as the first element and fluorine present on the surface 24a of the first coating 24, are more likely to be present on the surface 24a. Therefore, even if the first coating 24 contacts the latent heat storage material 10, the first coating 24 is more reliably less likely to dissolve in the latent heat storage material 10. This more reliably suppresses the dissolution of aluminum ions from the periphery of the joint 22 into the latent heat storage material 10, and facilitates the stabilization of supercooling of the latent heat storage material 10.

[0048] The solubility of potassium fluoride in water at 20°C is 949 g / L. g / L refers to grams per liter. The solubility of elemental fluorides in water at 20°C can be, for example, below 400 g / L, below 300 g / L, below 200 g / L, below 100 g / L, or below 50 g / L.

[0049] The first element is, for example, at least one selected from the group consisting of sodium, calcium, magnesium, zinc, and iron. In this case, even if the first coating 24 contacts the latent heat storage material 10, the first coating 24 is more reliably less likely to dissolve in the latent heat storage material 10. Therefore, the dissolution of aluminum ions from the periphery of the joint 22 into the latent heat storage material 10 can be more reliably suppressed, and the supercooling of the latent heat storage material is easily stabilized. It should be noted that the solubility of fluorides of these elements in water at 20°C is shown in Table 1.

[0050] [Table 1]

[0051]

[0052] The concentration of the first element in surface 24a is not limited to a specific value. For example, the concentration P of the first element in surface 24a... P Atom percentage divided by the concentration of fluorine atoms in surface 24a, P FS The value P obtained by atomic percentage P / P FS Not limited to a specific value. Value P P / P FS For example, a value greater than 0.015 and less than 0.30. Value P P / P FS It can also be greater than 0.018. Value P P / P FS It can also be below 0.295. The concentration of a specific element in surface 24a can be determined, for example, by energy-dispersive X-ray spectroscopy (SEM-EDX) using a scanning electron microscope.

[0053] The concentration of potassium in surface 24a is not limited to a specific value. For example, the concentration of potassium in surface 24a may be 10 atomic percent or less, or it may be 5 atomic percent or less, or it may be 3 atomic percent or less. The concentration of potassium in surface 24a may also be 0 atomic percent.

[0054] The concentration of potassium in potassium-rich section 24b is not limited to a specific value. For example, the concentration P of potassium atoms in potassium-rich section 24b... K The concentration P is calculated by dividing the atomic percentage by the number of fluorine atoms in surface 24a. FR The value P obtained by atomic percentage K / P FR Not limited to a specific value. Value P K / P FR For example, values ​​above 0.14 and below 1.

[0055] like Figure 1 As shown, container 20 has, for example, a second coating 26. The second coating 26 is formed on the inner surface of container 20 away from joint 22. At least one of the following is present on the surface 26a of the second coating 26: selected from alumina, aluminum hydroxide, alumina hydrate, and a substance containing a second element and fluorine. The second element has a lower ionization tendency than potassium.

[0056] like Figure 1 As shown, the second coating 26 is in contact with the latent heat storage material 10, for example. The surface 26a is configured as described above, so even if the second coating 26 contacts the latent heat storage material 10, the second coating 26 is not easily dissolved in the latent heat storage material 10. Therefore, the dissolution of aluminum ions from the main material of the container 20 into the latent heat storage material 10 can be suppressed, and the supercooling of the latent heat storage material 10 can be easily stabilized.

[0057] For example, a substance containing a second element and fluorine may be present on the surface 26a of the second coating 26. The second element is not limited to a specific element as long as it has a lower ionization tendency than potassium. The solubility of the fluoride of the second element in water at 20°C is not limited to a specific value; for example, it may be lower than the solubility of potassium fluoride in water at 20°C. In this case, even if the second coating 26 contacts the latent heat storage material 10, the second coating 26 is more reliably less likely to dissolve in the latent heat storage material 10. Therefore, the dissolution of aluminum ions from the main material of the container 20 into the latent heat storage material 10 can be more reliably suppressed, and the supercooling of the latent heat storage material 10 is easily stabilized.

[0058] The second element is, for example, at least one selected from the group consisting of sodium, calcium, magnesium, zinc, and iron. In this case, even if the second coating 26 comes into contact with the latent heat storage material 10, the second coating 26 is more reliably less likely to dissolve in the latent heat storage material 10. As a result, the dissolution of aluminum ions from the main material of the container 20 into the latent heat storage material 10 can be more reliably suppressed, and the supercooling of the latent heat storage material 10 is more easily stabilized.

[0059] The second element can be of the same kind as the first element, or it can be of a different kind.

[0060] The latent heat storage material 10 is not limited to a specific latent heat storage material as long as it is water-soluble. For example, the latent heat storage material 10 may contain a metal salt or a hydrate of a metal salt as its main component. Therefore, the latent heat storage material 10 readily exhibits the desired supercooling stability. In this specification, "main component" refers to the component with the highest content by mass.

[0061] Metal salts can be sodium salts, lithium salts, potassium salts, calcium salts, magnesium salts, barium salts, iron salts, or aluminum salts.

[0062] The latent heat storage material 10 may contain sodium acetate as a main component. Therefore, the latent heat storage material 10 can more reliably possess the desired supercooling stability.

[0063] The main component of the latent heat storage material 10 can also be a specified hydrate. For example, it can be a hydrate of the aforementioned metal salts. Examples of hydrates include: sodium sulfate decahydrate, sodium bisulfate monohydrate, lithium chlorate trihydrate, lithium perchlorate trihydrate, potassium fluoride dihydrate, potassium fluoride tetrahydrate, calcium chloride dihydrate, calcium chloride tetrahydrate, calcium chloride hexahydrate, lithium nitrate trihydrate, sodium sulfate decahydrate, sodium carbonate heptahydrate, sodium carbonate decahydrate, calcium bromide dihydrate, disodium hydrogen phosphate dihydrate, disodium hydrogen phosphate heptahydrate, disodium hydrogen phosphate dodecahydrate, ferric chloride tetrahydrate, ferric chloride hexahydrate, sodium thiosulfate pentahydrate, magnesium sulfate heptahydrate, lithium acetate dihydrate, sodium hydroxide monohydrate, barium hydroxide monohydrate, barium hydroxide octahydrate, sodium pyrophosphate decahydrate, trisodium phosphate hexahydrate, trisodium phosphate octahydrate, and trisodium phosphate dodecahydrate.

[0064] The latent heat storage material 10 may also contain stabilizers and other components such as water.

[0065] The heat storage device 1 may also include, for example, a supercooling relief device (not shown). By operating the supercooling relief device, the supercooling of the latent heat storage material 10 can be relieved at a desired time. The configuration of the supercooling relief device is not limited to a specific configuration as long as it can relieve the supercooling of the latent heat storage material 10. The supercooling relief device, for example, generates a physical action to relieve the supercooling of the latent heat storage material 10. The physical action can be the movement or vibration of a specified object, or it can be an electrical action.

[0066] An example of a method for manufacturing the heat storage device 1 will be described. First, the components constituting the container 20 are joined together to form a joint 22. The method for forming the joint 22 is not limited to a specific method. For example, the components are joined together by brazing. In brazing, for example, flux is applied to the portion forming the joint 22 between the components. The flux contains, for example, potassium, aluminum, and fluorine. The flux contains, for example, a eutectic of KAlF4 and K3AlF6. Then, the ambient temperature of the components constituting the container 20 is maintained at a temperature above a predetermined temperature for a predetermined time. As a result, the components contained in the flux melt, thereby joining the components constituting the container 20 together. Then, the portion formed by joining the components constituting the container 20 is subjected to heat treatment under predetermined conditions while in contact with a liquid containing the first element. In the heat treatment, the temperature of the liquid is adjusted to, for example, 100°C or higher. The heat treatment time is, for example, 1 minute to 3 hours. Thus, a container 20 having the joint 22 and the first coating 24 is obtained. Then, the latent heat storage material 10 is housed inside the container 20 to obtain the heat storage device 1. On the other hand, the latent heat storage material 10 can be used as a liquid containing the first element. In this case, the step of filling the container 20 with the latent heat storage material 10 after the formation of the first coating 24 can be omitted.

[0067] An example of how the heat storage device 1 is used will be described. Heat is supplied to the heat storage device 1 from the outside, thereby causing the latent heat storage material 10 to change from a solid phase to a liquid phase. Then, the supply of heat from the outside of the heat storage device 1 is stopped, and the temperature of the latent heat storage material 10 changes to a temperature lower than its melting point. In this case, the latent heat storage material 10 is in a supercooled state as it was in the liquid phase. Therefore, the latent heat storage material 10 accumulates latent heat in the liquid phase and in a supercooled state. At a predetermined time, the supercooling of the latent heat storage material 10 is released. As a result, the latent heat storage material 10 solidifies, and latent heat is released from the heat storage device 1 to the outside.

[0068] (Implementation Method 2)

[0069] Figure 2The diagram illustrates the heat utilization system 5 of Embodiment 2. The heat utilization system 5 includes a heat storage device 1, a heat source 2, and a heat exchanger 3. The heat storage device 1 is connected to the heat source 2 via a predetermined flow path, in a manner that allows a heat medium supplied by the heat source 2 to be supplied to the heat storage device 1. Furthermore, the heat storage device 1 is connected to the heat exchanger 3 via a predetermined flow path, in a manner that allows a heat medium heated by utilizing the latent heat released by the heat storage device 1 to be supplied to the heat exchanger 3.

[0070] According to the heat utilization system 5, the heat source 2 can be stored in the heat storage device 1 in the form of latent heat, and the latent heat can be supplied to the heat exchanger 3 for utilization.

[0071] Example

[0072] The present invention will now be described in detail based on embodiments. The present invention is not limited to any of the embodiments described below.

[0073] <Example 1>

[0074] Sodium acetate, water, and 1,2-butanediol were placed in a 60cm container according to the specified proportions. 3 The latent heat storage material was prepared by mixing sodium acetate in a screw-top bottle of a certain volume and dissolving it in a constant temperature bath adjusted to 75°C. Flux was sprayed onto the surface of an aluminum alloy A4343 sheet and heated to approximately 560°C in a nitrogen atmosphere furnace to obtain an aluminum alloy sheet with flux. The flux contained a eutectic of KAlF4 and K3AlF6. Next, the aluminum alloy sheet with flux was immersed in the latent heat storage material, and the screw-top bottle was sealed. The latent heat storage material was then heated for a specified time inside a constant temperature bath adjusted to 120°C. The screw-top bottle was then removed from the constant temperature bath to obtain the sample described in Example 1.

[0075] <Example 2>

[0076] The latent heat storage material was prepared in the same manner as in Example 1. Furthermore, in the same manner as in Example 1, the prepared aluminum alloy sheet with flux was immersed in an aqueous solution containing sodium acetate and heated for a specified time inside a constant temperature bath set to 120°C. Then, the aluminum alloy sheet with flux was removed from the aqueous solution, washed with water, and dried. The aluminum alloy sheet with flux treated in this way was then immersed in the latent heat storage material, and the screw-cap bottle was sealed to obtain the sample described in Example 2.

[0077] <Comparative Example 1>

[0078] The latent heat storage material was prepared in the same manner as in Example 1. Furthermore, in the same manner as in Example 1, the prepared aluminum alloy sheet with flux was immersed in water and heated for a specified time inside a constant temperature bath set to 120°C. Then, the aluminum alloy sheet with flux was removed from the warm water, washed, and dried. The aluminum alloy sheet with flux treated in this way was then immersed in the latent heat storage material, and the screw-cap bottle was sealed to obtain the sample according to Comparative Example 1.

[0079] <Comparative Example 2>

[0080] The latent heat storage material was prepared in the same manner as in Example 1. The aluminum alloy sheet with flux was immersed in the latent heat storage material while remaining in its original state, and the screw-top bottle was sealed to obtain the sample involved in Comparative Example 2.

[0081] Evaluation of Supercooling Stability

[0082] For the samples involved in each embodiment and each comparative example, sodium acetate seed crystals were used to crystallize the latent heat storage material. Then, the temperature of the latent heat storage material was maintained at 30°C inside a constant temperature bath, and then dissolved at 75°C for 4 hours. Next, the temperature of the latent heat storage material was maintained at -20°C for 12 hours. At this time, it was confirmed whether the latent heat storage material had crystallized. Five cycles were performed on each sample for evaluation. The results are shown in Table 2.

[0083] Evaluation of the surface condition of aluminum alloy sheets with flux

[0084] The surface of flux-coated aluminum alloy sheets for each sample before evaluation of overcooling stability was determined using a Hitachi High-Tech Corporation TM4000 Plus desktop microscope and an AZtecOne energy-dispersive X-ray analyzer manufactured by the same company. Based on the results of this measurement, the elemental content of each element on the surface of the flux-coated aluminum alloy sheets for each sample was determined. The results are shown in Table 3.

[0085] As shown in Table 2, for the samples involved in Examples 1 and 2, the supercooling of the latent heat storage material was maintained at -20°C for 12 hours throughout all 5 cycles, indicating that the supercooling of the latent heat storage material has high stability. On the other hand, for the sample involved in Comparative Example 1, although the supercooling of the latent heat storage material could be maintained for the specified time, it could not be maintained for the long period of 12 hours. In addition, the sample involved in Comparative Example 2 could not maintain supercooling at -20°C.

[0086] As shown in Table 3, fluorine and sodium were present on the surface of the flux-coated aluminum alloy sheets in the samples of Examples 1 and 2. On the other hand, sodium was not present on the surface of the flux-coated aluminum alloy sheets in the samples of Comparative Examples 1 and 2. It is believed that the presence of elements such as sodium and fluorine on the surface of the flux-coated aluminum alloy sheets in the samples of Examples 1 and 2 indicates the presence of substances that are not easily soluble in the latent heat storage material. This can be understood as the flux covering the aluminum alloy sheet not easily dissolving in the latent heat storage material, and the supercooling of the latent heat storage material in the samples of Examples 1 and 2 exhibits high stability. On the other hand, for the sample of Comparative Example 1, it is believed that a portion of the flux dissolved in the latent heat storage material, thereby causing aluminum ions to dissolve from the aluminum alloy. Therefore, it is believed that for the sample of Comparative Example 1, it is difficult to maintain the supercooling of the latent heat storage material at -20°C. Furthermore, for the sample of Comparative Example 2, it is believed that a portion of the flux also dissolved in the latent heat storage material, thereby causing aluminum ions to dissolve from the aluminum alloy into the latent heat storage material. Furthermore, it is believed that aluminum ions also dissolve from the areas of the aluminum alloy not covered by flux into the latent heat storage material. As a result, it is believed that the sample involved in Comparative Example 2 did not maintain supercooling of the latent heat storage material at -20°C.

[0087] [Table 2]

[0088]

[0089] [Table 3]

[0090]

Claims

1. A heat storage device, comprising: Water-soluble latent heat storage materials; and A container for storing the latent heat storage material, using aluminum or aluminum alloy as the main material. The container has: a joint, and a first coating covering at least the joint on the inner surface of the container. The surface of the first coating contains: a first element other than aluminum with a lower ionization tendency than potassium; and fluorine. The first coating has a potassium-rich portion located closer to the junction than the surface in the thickness direction of the first coating, and has a higher potassium concentration (in atomic percent) than that in the surface.

2. The heat storage device according to claim 1, wherein, The fluoride of the first element has a lower solubility in water at 20°C than the potassium fluoride in water at 20°C.

3. The heat storage device according to claim 1, wherein, The first element is selected from at least one of the group consisting of sodium, calcium, magnesium, zinc and iron.

4. The heat storage device according to claim 1, wherein, The container has a second coating formed on the inner surface of the container away from the joint. The surface of the second coating contains at least one of the following: aluminum oxide, aluminum hydroxide, aluminum oxide hydrate, and a substance containing a second element having a lower ionization tendency than potassium and fluorine.

5. The heat storage device according to claim 4, wherein, The substance containing the second element and fluorine is present on the surface of the second coating. The fluoride of the second element has a lower solubility in water at 20°C than the potassium fluoride in water at 20°C.

6. The heat storage device according to claim 4, wherein, The substance containing the second element and fluorine is present on the surface of the second coating. The second element is selected from at least one of the group consisting of sodium, calcium, magnesium, zinc, and iron.

7. The heat storage device according to claim 1, wherein, The latent heat storage material contains metal salts or hydrates of metal salts as its main components.

8. The heat storage device according to claim 7, wherein, The latent heat storage material contains sodium acetate as its main component.

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