Patent Description:
In the past, heat storage apparatuses each having a heat storage material have been known. In facilities having heat sources, such as homes, offices, factories, or waste processing facilities, most of low-temperature exhaust heat of approximately <NUM> or less is discharged without being used. In order to effectively use such exhaust heat, it is required to use a heat storage material that stores low-temperature exhaust heat at a high density.

To satisfy this requirement, it is highly useful and preferable to use water at normal pressure, as a heat medium for the heat storage material. Thus, preferably, the heat storage material should have a melting point of <NUM> or less. As inorganic heat storage materials, inorganic hydrated salt, such as barium hydroxide octahydrate having a melting point of <NUM> and magnesium nitrate hexahydrate having a melting point of <NUM>, is present.

However, the inorganic hydrated salt has problems. That is, barium hydroxide octahydrate is specified as a deleterious substance, and magnesium nitrate hexahydrate corrodes metal. Therefore, these inorganic heat storage materials are not put to practical use. On the other hand, as organic heat storage materials, paraffin, fatty acids, sugar alcohol, etc., are present. However, paraffin, fatty acids, sugar alcohol, and other substances are not put to practical use because they have a small heat storage density because of the heat of fusion.

Patent Literature <NUM> discloses a heat storage material in which a mixture of a guest substance and water that is a host substance is cooled to produce a hydrate. Furthermore, in recent years, heat storage materials including hydrogel have been known. A heat storage material using hydrogel maintains a non-fluid property even in a temperature range above a phase transition temperature, and can stably maintain a non-fluid property even when being repeatedly cooled and heated such that its temperature varies to a lower temperature and a higher temperature through the phase transition temperature.

As such heat storage materials, Patent Literature <NUM> discloses a first gelled material, a second gelled material, and an inorganic or aqueous heat storage material that is held between the first gelled material and the second gelled material. The first gelled material is produced by crosslinking at least one polymer selected from polyacrylamide derivatives, polyvinyl alcohol, sodium polyacrylate, and sodium polymethacrylate. The second gelled material is polysaccharides, agar, or gelatin. Patent Literature <NUM> discloses a heat storage device including a heat exchanger that causes heat exchange to be performed between a heating fluid and a heat storage material to heat the heat storage material and store heat in the heat storage material Patent Literature <NUM> discloses a heat storage apparatus comprising as heat storage material a thermosensitive polymer gel including a thermosensitive polymer and water.

However, the heat storage materials disclosed in Patent Literature <NUM> and Patent Literature <NUM> have a small heat storage density. Thus, a thermal storage tank is made larger, and as a result, a heat storage apparatus including the thermal storage tank is also made larger. The thermal storage unit disclosed in Patent Literature <NUM> cannot be applied to a cooling apparatus, since a heat storage material cannot store cooling energy.

The present invention is applied to solve the above problems, and the object underlying the invention is to provide a heat storage apparatus that can be used in a cooling apparatus and is not made larger, as compared with existing heat source apparatuses.

A heat storage apparatus according to claim <NUM>.

According to the embodiment of the present invention, the heat storage material makes reversible hydrophilic-hydrophobic transition at a lower critical solution temperature, and the solvent included in the thermosensitive polymer gel is kept in a liquid state in the process of hydrophilic-hydrophobic transition. Thus, it is not made larger. Furthermore, a heat storage apparatus can store cooling energy in the heat storage material. The heat storage apparatus can thus be used in a cooling apparatus and is not made larger.

An embodiment of a heat storage apparatus according to the present invention will be described with reference to the drawings. The description concerning the embodiment is not limiting. In figures including <FIG> that will be referred to below, the relationships in size between components may be different from actual ones. In the following description, in order that the embodiment be easily understood, terms related to directions are used as appropriate. These terms are used only for explanation, that is, they are not limiting. As the terms expressing directions, for example, "upper", "lower", "right", "left", "front", and "back" are used.

<FIG> is a circuit diagram of a heat storage system <NUM> according to Embodiment <NUM>. The heat storage system <NUM> uses a heat storage apparatus <NUM> to perform air cooling or air heating at a heat transfer terminal <NUM>. The heat storage system <NUM> includes a heat source <NUM>, a heating/cooling pump <NUM>, a circulation pump <NUM>, the heat storage apparatus <NUM>, a heating/cooling fluid, and a heat utilization fluid.

A lower joint <NUM> of a heating/cooling pipe <NUM> is connected to the heat source <NUM> by an inlet pipe <NUM> via the heating/cooling pump <NUM>. The heat source <NUM> is connected to an upper joint <NUM> of the heating/cooling pipe <NUM> by an outlet pipe <NUM>. As a result, a heat source circuit <NUM> is provided, and the heating/cooling fluid circulates in the heat source circuit <NUM>.

The heat source <NUM> generates heat, and is, for example, an electric heater or a vapor compression heat pump that is driven by power. The heat source <NUM> heats the heating/cooling fluid that flows thereinto through the inlet pipe <NUM>. The heating/cooling pump <NUM> is used to transfer the heating/cooling fluid. The heating/cooling pump <NUM> transfers, to the heat source <NUM>, the heating/cooling fluid that flows through the inlet pipe <NUM>, causes the heating/cooling fluid that flows out of the heat source <NUM> to flow through the outlet pipe <NUM>, and transfers the heating/cooling fluid to the heating/cooling pipe <NUM>.

The circulation pump <NUM> is used to transfer the heating/cooling fluid. The circulation pump <NUM> transfers, to the heat storage apparatus <NUM>, the heat utilization fluid that flows through a return pipe <NUM>, causes the heat utilization fluid that flows out of the heat storage apparatus <NUM> to flow through a feed pipe <NUM>, and transfers the heat utilization fluid to the heat transfer terminal <NUM>. The heating/cooling fluid is, for example, water, an antifreeze, such as ethylene glycol or propylene glycol, or refrigerant, such as HFC or CO<NUM>.

A lower joint <NUM> of a heat utilization pipe <NUM> is connected to the heat transfer terminal <NUM> by the return pipe <NUM> via the circulation pump <NUM>. An upper joint <NUM> of the heat utilization pipe <NUM> is connected to the heat transfer terminal <NUM>, which is a heat utilization terminal, by the feed pipe <NUM>. As a result, a utilization circuit <NUM> is provided, and the heat utilization fluid circulates in the utilization circuit <NUM>. The heat utilization fluid is, for example, water or an antifreeze, such as ethylene glycol or propylene glycol.

The heat transfer terminal <NUM> is, for example, a floor heating panel, a fan coil unit, or a hot water radiator panel. The heat transfer terminal <NUM> is an example of a heat utilization terminal, and cooling energy or heating energy transferred from the heat utilization fluid in the heat transfer terminal <NUM> is utilized in, for example, air cooling or air heating.

<FIG> is a sectional view of a heat storage apparatus <NUM> according to Embodiment <NUM>. <FIG> is a perspective view of the heat storage apparatus <NUM> according to Embodiment <NUM>. As illustrated in <FIG>, the heat storage apparatus <NUM> includes a container <NUM> and a heat exchanger <NUM>. The container <NUM> is, for example, substantially cuboid, is made of stainless steel (SUS), and has a thickness of <NUM>.

The container <NUM> is filled with a heat storage material <NUM>. The container <NUM> houses the heat exchanger <NUM>. In an upper surface and a lower surface of the container <NUM>, a plurality of openings (not illustrated) are provided into which the heating/cooling pipe <NUM> and the heat utilization pipe <NUM> of the heat exchanger <NUM> are inserted.

The heat exchanger <NUM> is, for example, a fin-and-tube heat exchanger, and includes the heating/cooling pipe <NUM>, the heat utilization pipe <NUM>, and a plurality of fins <NUM>. The heating/cooling pipe <NUM> is, for example, a cylindrical or flat tube made of metal such as SUS or Cu. In the heating/cooling pipe <NUM>, a heating/cooling fluid to heat or cool the heat storage material <NUM> flows. The heating/cooling pipe <NUM> is inserted into the openings formed in the upper surface and the lower surface of the container <NUM>, and extends from the inside of the container <NUM> to the outside thereof.

At both ends of the heating/cooling pipe <NUM>, respective joints <NUM> are provided (see <FIG>). The type of the joints <NUM> can be appropriately changed depending on the configuration of the heat storage system <NUM> including the heat storage apparatus <NUM>. For example, quick fastener joints or Swagelok joints can be used as the joints <NUM>. Since the joints <NUM> are provided at the heating/cooling pipe <NUM>, it is possible to easily connect the heat storage apparatus <NUM> to the inlet pipe <NUM> and the outlet pipe <NUM>.

The heat utilization pipe <NUM> is, for example, a cylindrical or flat pipe made of metal such as SUS or Cu. In the heat utilization pipe <NUM>, a heat utilization fluid to receive heat from the heat storage material <NUM> flows. The heat utilization pipe <NUM> is inserted into openings formed in an upper surface and a lower surface of the container <NUM>, and extends from the inside of the container <NUM> to the outside thereof. At both ends of the heat utilization pipe <NUM>, joints <NUM> are provided (see <FIG>).

The type of the joints <NUM> can be appropriately changed depending on the configuration of the heat storage system <NUM> including the heat storage apparatus <NUM>. For example, quick fastener joints or Swagelok joints can be used as the joints <NUM>. Since the joints <NUM> are provided at the heat utilization pipe <NUM>, it is possible to easily connect the heat storage apparatus <NUM> to the return pipe <NUM> and the feed pipe <NUM>.

The fins <NUM> are, for example, plate fins made of metal such as SUS or Al, and arranged substantially parallel to each other. In the fins <NUM>, openings (not illustrated) are provided. The heating/cooling pipe <NUM> and the heat utilization pipe <NUM> are inserted into the openings of the fins <NUM> arranged substantially parallel to each other.

The heat exchanger <NUM> causes heat exchange to be performed between the heating/cooling fluid and the heat storage material <NUM>, thereby heating or cooling the heat storage material <NUM> to store heat in the heat storage material <NUM>, and also causes heat exchange to be performed between the heat utilization fluid and the heat storage material <NUM>, thereby receiving heat from the heat storage material <NUM> and causing the heat storage material <NUM> to transfer heat therefrom.

The heat exchanger <NUM> may have any configuration as long as the heat exchanger <NUM> can cause the heat storage material <NUM> to be heated and to transfer heat. The shape and material of the heat exchanger <NUM> can be changed appropriately. For example, the heat exchanger <NUM> may be configured such that the fins <NUM> are not provided and the heating/cooling pipe <NUM> and the heat utilization pipe <NUM> are arranged at a high density. Furthermore, the heat exchanger <NUM> may be configured such that the following layers are stacked together: a layer through which the heating/cooling fluid flows; a layer through which the heat utilization fluid flows; and a layer filled with the heat storage material <NUM>.

The heat storage material <NUM> has a thermosensitive polymer gel including a thermosensitive polymer <NUM> and a solvent selected from the group consisting of water <NUM>, an organic solvent, and a compound of water <NUM> or organic solvents. The heat storage material <NUM> transfers heat or receives heat when the thermosensitive polymer <NUM> adsorbs or desorbs water <NUM>. After the thermosensitive polymer <NUM> is hydrophobized, the density of the thermosensitive polymer <NUM> is higher than that of water <NUM>. The density of thermosensitive polymer <NUM> containing hydrophobized bubbles is lower than that of water <NUM>.

Next, the heat storage material <NUM> will be described in detail. The heat storage material <NUM> makes a reversible hydrophilic-hydrophobic transition at a lower critical solution temperature, and the solvent included in the thermosensitive polymer gel is kept in a liquid state during the process of hydrophilic-hydrophobic transition. The lower critical solution temperature is abbreviated as a LCST. The thermosensitive polymer <NUM> exhibits a hydrophilic property at a temperature below the LCST, and exhibits a hydrophobic property at a temperature above the LCST. In other words, the thermosensitive polymer <NUM> makes a reversible hydrophilic-hydrophobic transition at the lower critical solution temperature.

As the thermosensitive polymer <NUM>, the following can be used: partially acetylated polyvinyl alcohol; polyvinyl methyl ether; methyl cellulose; polyethylene oxide; polyvinyl methyl oxazolidinone; poly N-ethyl acrylamide; poly N-ethyl methacrylamide; poly N-n-propyl acrylamide; poly N-n-propyl methacrylamide; poly N-isopropyl acrylamide; poly N-isopropyl methacrylamide; poly N-cyclopropyl acrylamide; poly N-cyclopropyl methacrylamide; poly N-methyl-N-ethyl acrylamide; poly N,N-diethyl acrylamide, poly N-methyl-N-isopropyl acrylamide; poly N-methyl-N-n-propyl acrylamide; poly N-acryloylpyrrolidine; poly-N-acryloylpiperidine; poly N-<NUM>-ethoxyethyl acrylamide; poly N-<NUM>-ethoxyethyl methacrylamide; poly N-<NUM>-methoxypropyl acrylamide; poly N-<NUM>-methoxypropyl methacrylamide; poly N-<NUM>-ethoxypropyl acrylamide; poly N-<NUM>-ethoxypropyl methacrylamide; poly N-<NUM>-isoproxylpropyl acrylamide; poly N-<NUM>-isoproxylpropyl methacrylamide; poly N-<NUM>-(<NUM>-methoxyethoxy)propyl acrylamide; poly N-<NUM>-(<NUM>-methoxyethoxy)propyl methacrylamide; poly N-tetrahydrofurfuryl acrylamide; poly N-tetrahydrofurfuryl methacrylamide; poly N-<NUM>-methyl-<NUM>-methoxyethyl acrylamide; poly N-<NUM>-methyl-<NUM>-methoxyethyl methacrylamide; poly N-<NUM>-methoxymethylpropyl acrylamide; poly N-<NUM>-methoxymethylpropyl methacrylamide; poly N-(<NUM>,<NUM>-)dimethoxyethyl)-N-methyl acrylamide; poly N-(<NUM>,<NUM>-dioxolan-<NUM>-ylmethyl)-N-methyl acrylamide; poly N-<NUM>-acryloyl-<NUM>,<NUM>-dioxa-<NUM>-aza-spiro[<NUM>,<NUM>]decane; poly N-<NUM>-methoxyethyl-N-ethyl acrylamide; poly N-<NUM>-methoxyethyl-N-n-propyl acrylamide; poly N-<NUM>-methoxyethyl-N-isopropyl acrylamide; and poly N,N-di(<NUM>-methoxyethyl) acrylamide.

The thermosensitive polymer <NUM> has a crosslinked structure, and has, at its molecular end, at least one functional group selected from the group consisting of a hydroxy group, a sulfonate group, an oxysulfonate group, a phosphate group, and an oxyphosphate group. The molar ratio between repeating units that form the thermosensitive polymer <NUM>, the functional group, and the unit of the crosslinked structure falls within the range of <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM>. Regarding the thermosensitive polymer <NUM>, it is preferable that the molar ratio between the repeating units that form the thermosensitive polymer, the functional group, and the unit of the crosslinked structure fall within the range of <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM>.

In the case where the percentage of the repeating units is too high, the heat storage density decreases. The case where the percentage of the repeating units is high corresponds to the case where when the total molecular weight of the repeating units, the functional group and the unit of the crosslinked structure is <NUM> mol%, the percentage of the repeating units exceeds <NUM> mol%.

By contrast, when the percentage of the repeating units is too low, the LCST is not exhibited. The case where the percentage of the repeating units is low corresponds to the case where when, for example, the total amount of the repeating unit, the functional group and the unit of the crosslinked structure is <NUM> mol%, the percentage of the repeating unit is below <NUM> mol%.

The unit of the crosslinked structure is introduced by applying a cross-linker in the process of producing the thermosensitive polymer <NUM>, such as partially acetylated polyvinyl alcohol or polyvinyl methyl ether described above. The cross-linker may be referred to as a cross-linkable monomer. As the cross-linker, for example, the following are present: N,N'-methylenebisacrylamide; N,N'-diallylacrylamide; N,N'-diacryloylimide, N,N'-dimethacryloylimide; triallylformal; diallyl naphthalate; ethylene glycol diacrylate; ethylene glycol dimethacrylate; various polyethylene glycol di(meth)acrylates; propylene glycol diacrylate; propylene glycol dimethacrylate; various polypropylene glycol di(meth)acrylates; <NUM>,<NUM>-butylene glycol diacrylate; <NUM>,<NUM>-butylene glycol dimethacrylate; <NUM>,<NUM>-butylene glycol dimethacrylate; various butylene glycol di(meth)acrylates; glycerol dimethacrylate; neopentyl glycol dimethacrylate; trimethylolpropane triacrylate; trimethylolpropane trimethacrylate; tetramethylolmethane tetramethacrylate; and divinyl derivatives; such as divinylbenzene.

The organic solvent is selected from polar organic solvents, and preferably, should be selected from the group consisting of alcohols, such as methanol, ethanol, propanol, isopropanol, isopentanol, and <NUM>-methoxyethanol; ketones, such as acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl isopropyl ketone, and methyl isoamyl ketone; ethers, such as ethylene glycol monobutyl ether, and propylene glycol monomethyl ether; methyl acetate; ethyl acetate; propyl acetate; n-butyl acetate; chloroform; acetonitrile; glycerol; dimethyl sulfoxide; N,N-dimethylformamide; tetrahydrofuran; pyridine; <NUM>,<NUM>-dioxane; dimethylacetamide; N-methylpyrrolidone; propylene carbonate; and mixtures thereof.

The organic solvent is selected from nonpolar organic solvents, and preferably, should be selected from the group consisting of benzene, chlorobenzene; o-dichlorobenzene; toluene; o-xylene; dichloromethane; <NUM>,<NUM>,<NUM>-trichlorotrifluoroethane; pentane; cyclopentane; hexane; cyclohexane; heptane; isooctane; diethyl ether; petroleum ether; pyridine; carbon tetrachloride; fatty acids; fatty acid esters; and mixtures thereof. Furthermore, the organic solvent is selected from oils, and preferably, should be selected from the group consisting of vegetable oils, essential oils, petrochemical oils, synthetic oils, and mixtures thereof. When an oil is used as the organic solvent, the organic solvent may be referred to as a lipophilic solvent. Otherwise, the organic solvent may be a mixture of at least one kind of polar organic solvent or nonpolar organic solvent and at least one kind of oil.

The thermosensitive polymer gel includes a building block expressed by the following general Formula (<NUM>);
<CHM>.

In the heat storage material <NUM>, the molar ratio between the building block expressed by general Formula (<NUM>) or general Formula (<NUM>), X which is the functional group, and the building block expressed by general Formula (<NUM>) is <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM>, and preferably should be <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM>. In the case where the percentage of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>) is too high, the heat storage density is low.

The case where the percentage of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>) is high corresponds to the case where the percentage of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>) exceeds <NUM> mol% when, for example, the total molecular weight of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>), X which is the functional group, and the building block expressed by general Formula (<NUM>) is <NUM> mol%.

By contrast, in the case where the percentage of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>) is too low, an LCST is not exhibited. The case where the percentage of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>) is low corresponds to the case where the percentage of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>) is below <NUM> mol% when, for example, the total molecular weight of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>), X which is the functional group, and the building block expressed by general Formula (<NUM>) is <NUM> mol%. In Embodiment <NUM>, the molar ratio between the building block expressed by general Formula (<NUM>) or general Formula (<NUM>), X which is the functional group, and the building block expressed by general Formula (<NUM>) is a theoretical value calculated from the amount of prepared material.

The heat storage material <NUM> has only to contain a building block expressed by general Formula (<NUM>) or general Formula (<NUM>), X that is the functional group, and the structural unit expressed by general Formula (<NUM>) at the above molar ratio. The number of repetitions of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>) and the order in which the building blocks are bonded are not limited. In general, the number of repetitions of the building block expressed by general Formula (<NUM>) or general Formula (<NUM>) is an integer that falls within the range of <NUM> to <NUM>.

The LCST of the heat storage material <NUM> can be set to fall within a wide range from <NUM> to <NUM> according mainly to the kind of R<NUM> and R<NUM> in general Formula (<NUM>) or general Formula (<NUM>). In general Formula (<NUM>), preferably, R<NUM> should be a hydrogen atom in order that the thermosensitive polymer <NUM> be easily produced. In general Formula (<NUM>), preferably, R<NUM> should be an N-<NUM>-isopropoxypropyl group in order that thermosensitivity be further improved.

In general Formula (<NUM>) or general Formula (<NUM>), X can be a functional group selected from the group consisting of a hydroxy group, a sulfonate group, an oxysulfonate group, a phosphate group, and an oxyphosphate group so as to satisfy the above molar ratio. It is preferable that of these functional groups, an oxysulfonate group be selected in order that radical polymerization be further improved.

In general Formula (<NUM>), preferably, q should be <NUM> in order that the heat storage density be further increased. The atoms in the covalent bonds in general Formula (<NUM>) or general Formula (<NUM>) and general Formula (<NUM>) may be formed by bonding the same kind of building blocks, may be formed by bonding different kinds of building blocks, or may partially form a branch structure. However, other branch structures can be applied.

The heat storage material <NUM> can be produced by radial polymerization of a polymerizable monomer expressed by the following general Formula (<NUM>),
<CHM>.

The polymerizable monomer expressed by general Formula (<NUM>) provides the building block expressed by general Formula (<NUM>). The following are specific examples of the polymerizable monomer: N-<NUM>-isopropoxypropyl (meth)acrylamide; and N-<NUM>-methoxymethylpropyl (meth)acrylamide. Of these, preferably, N-<NUM>-isopropoxypropyl acrylamide, and N-<NUM>-methoxymethylpropyl acrylamide should be applied. "([M]eth)acryl" means methacryl or acryl. The polymerizable monomer expressed by general Formula (<NUM>) provides the building block expressed by general Formula (<NUM>). The following are specific examples of this polymerizable monomer: N-acryloyl piperidine; and N-methacryloyl piperidine. Of these, preferably, N-acryloyl piperidine should be applied.

The cross-linker expressed by general Formula (<NUM>) provides the building block expressed by general Formula (<NUM>). The following are specific examples of the cross-linker: N,N'-methylenebisacrylamide; N,N'-ethylenebisacrylamide; and N,N'-(trimethylene)bisacrylamide.

As the radial polymerization method, it is possible to use a bulk polymerization method, a solution polymerization method, an emulsion polymerization method, or other known methods. Of the polymerization initiators described above, preferably, potassium persulfate and ammonium persulfate should be used because they have good reactivity. Furthermore, it is possible to achieve rapid radical polymerization at low temperature using a combinational of a polymerization initiator, such as N,N,N',N'-tetramethylethylenediamine or N,N-dimethylparatoluidine, and the polymerization initiator described above.

The following are examples of solvents for use in radical polymerization: water; methanol; ethanol; n-propanol, isopropanol; <NUM>-butanol; isobutanol; hexanol; benzene; toluene; xylene; chlorobenzene; dichloromethane; chloroform; carbon tetrachloride; acetone; methyl ethyl ketone; tetrahydrofuran; dioxane; acetonitrile; dimethyl sulfoxide; N,N-dimethylformamide; and N,N-dimethylacetamide. Of these solvents, preferably water should be used in order that the heat storage density be further increased. In general, it suffices that the radical polymerization reaction is performed at a temperature of <NUM> to <NUM> for <NUM> minutes to <NUM> hours.

When the radial polymerization is performed using water <NUM> as a solvent, particularly preferably, the total concentration of the polymerizable monomer expressed by general Formula (<NUM>) or general Formula (<NUM>), the cross-linker expressed by general Formula (<NUM>), and the polymerization initiator should be <NUM> mol/L to <NUM> mol/L in order that the heat storage density be further increased. In the case where the total concentration is less than <NUM> mol/L, the heat storage density of a produced heat storage material <NUM> may be small. By contrast, in the case where the total concentration is exceeds <NUM> mol/L, the produced heat storage material <NUM> may not exhibit the LCST.

The heat storage material <NUM> of Embodiment <NUM> can achieve a relatively low thermal storage operation temperature (<NUM> or lower) and a high heat storage density. The reason for this seems to be as follows. The thermosensitive polymer <NUM> having a LCST exhibits hydrophilic nature at a temperature lower than the LCST or exhibits hydrophobic nature at a temperature above the LCST. The thermosensitive polymer <NUM> in the heat storage material <NUM> of Embodiment <NUM> has a high cross-link density and a highly close-packed structure at terminals of branched polymer.

Thus, the molecules of water adsorbed in the thermosensitive polymer <NUM> are arranged at a high density as in an existing thermosensitive polymer <NUM>, but are arranged at a low density at a temperature higher than the LCST. In the thermosensitive polymer <NUM> in the heat storage material <NUM> of Embodiment <NUM>, the density of the molecules arranged greatly varies. The above seems to be why the heat storage material <NUM> of Embodiment <NUM> can achieve a low thermal storage operation temperature as in the existing themosensitive polymer <NUM>, but also achieve a high heat storage density.

According to Embodiment <NUM>, the heat storage material <NUM> makes a reversible hydrophilic-hydrophobic transition at the lower critical solution temperature, and the solvent included in the thermosensitive polymer gel is kept in a liquid state in the process of hydrophilic-hydrophobic transition. Thus, it is not made larger. The heat storage material <NUM> can store cooling energy. The heat storage apparatus <NUM> can thus be used in a cooling apparatus and is not made larger.

During thermal storage in the heat storage material <NUM> and heat transfer from the heat storage material <NUM>, water <NUM> is in a liquid state. Because of this feature, the heat storage apparatus <NUM> requires neither a condenser that condenses and liquefies water vapor nor a water transfer passage through which liquid water flows. Thus, the heat storage apparatus <NUM> to be used in an air-conditioning apparatus or a cooling and heating apparatus can be made smaller.

The liquid water content of the heat storage material <NUM> of Embodiment <NUM> is not particularly limited; however, preferably, it should fall within the range of <NUM> mass% to <NUM> mass%. The liquid water content can be determined as follows: after the weight of the heat storage material <NUM> containing water is measured at room temperature, the heat storage material <NUM> is put in a constant temperature reservoir, water of the heat storage material <NUM> is evaporated in the constant temperature reservoir at a drying temperature of <NUM> to <NUM> until no liquid remains in the heat storage material <NUM> or the weight thereof no longer decreases, the weight of the heat storage material <NUM> is then measured, and a substance corresponding to a decrease in the weight is assumed to be fluid.

This method is called a loss-on-drying method. Furthermore, the heat storage material <NUM> of Embodiment <NUM> and Embodiment <NUM> may be made porous. In the case where the heat storage material <NUM> is made porous, the temperature-responsiveness is improved. As a method of making the heat storage material <NUM> porous, for example, the following method is present: a mixed solution that contains the polymerizable monomer, the cross-linker, the polymerization initiator as describe above, and a porogen (pore-forming agent) is prepared, a crosslinked structure is formed through the radical polymerization reaction, and the porogen is then removed by washing.

In the radical polymerization reaction using water <NUM> as a solvent, preferable porogen is a water-soluble carbohydrate, such as sucrose, maltose, cellobiose, lactose, sorbitol, xylitol, glucose, or fructose. A porogen composition containing such a water-soluble carbohydrate and polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol or a mixture thereof may be used. As another method of making the heat storage material <NUM> porous, a method of freeze-drying the thermosensitive polymer <NUM> containing fluid to remove the fluid is present.

The thermosensitive polymer <NUM> of Embodiment <NUM> can also be produced by coating a metal surface of the inside in the container <NUM> with a mixed solution containing at least the polymerizable monomer, the cross-linker, and the polymerization initiator as described above, and causing radical polymerization. The metal is, for example, stainless steel, copper, or aluminum. The mixed solution may contain an activator for the metal surface, a coupling agent, or other agents. The thermosensitive polymer <NUM> can also be produced by emitting radial rays onto a coating of the mixed solution.

Embodiment <NUM> will be specifically described by referring to examples below, but Embodiment <NUM> is not limited to the examples.

In the examples, respective thermosensitive polymers <NUM> ware produced by heating aqueous solution of raw material with respective compositions indicated in table <NUM> in a nitrogen atmosphere while increasing a temperature from room temperature to <NUM> within one hour. After being dried, the thermosensitive polymer <NUM> of each example was subjected to equilibrium swelling in distilled water to form a thermosensitive polymer gel. The thermosensitive polymer gel was encased in an aluminum airtight container, the aluminum airtight container was sealed, and the endothermic peak temperature and the heat storage density of the thermosensitive polymer were measured with a differential scanning calorimeter. The abbreviations in table <NUM> represent the following compounds: A is N-<NUM>-isopropoxypropyl acrylamide; B is N-<NUM>-methoxymethylpropyl acrylamide; C is N-acryloyl piperidine: MBA is N,N'-methylenebis acrylamide; KPS is potassium persulfate; and TEMED is N,N,N',N'-tetramethylethylenediamine.

The results of the measurement are indicated in Table <NUM>.

As can be seen from the results in table <NUM>, the thermosensitive polymer gels produced in examples <NUM> to <NUM> had very low endothermic peak temperatures that fall within the range of <NUM> to <NUM> and high thermal storage densities that fall within the range of <NUM> J/g to <NUM> J/g. In other words, the thermosensitive polymer gels of examples <NUM> to <NUM> had high thermal storage densities from <NUM> J/g to <NUM> J/g, which were much higher than those of existing heat storage materials <NUM>, such as tetra-n-butyl ammonium bromide hydrate, at low thermal storage operation temperatures from <NUM> to <NUM>.

In the reversible hydrophilic-hydrophobic transition of the thermosensitive polymer gels at thermal storage operation temperatures, the water temperature was <NUM> to <NUM>, and water was in a liquid state. The thermosensitive polymer gels produced in comparative examples <NUM> to <NUM> had low endothermic peak temperatures that fall within the range of <NUM> to <NUM>, but had significantly low thermal storage densities that fall within the range of <NUM> J/g to <NUM> J/g.

Claim 1:
A heat storage apparatus comprising:
- a container (<NUM>) sealed, with a heat storage material (<NUM>) encased in the container (<NUM>), the heat storage material (<NUM>) including a thermosensitive polymer gel including a thermosensitive polymer (<NUM>) and a solvent selected from the group consisting of water, organic solvents, and compounds of water or organic solvents; and
- a heat exchanger (<NUM>) housed in the container (<NUM>), and configured to cause heat exchange to be performed between the heat storage material (<NUM>) and a heating/cooling fluid to heat or cool the heat storage material (<NUM>), and store heating energy or cooling energy in the heat storage material (<NUM>), the heat exchanger (<NUM>) being configured to cause heat exchange to be performed between the heat storage material (<NUM>) and a heat utilization fluid to receive heat from the heat storage material (<NUM>) and to transfer heat from the heat storage material (<NUM>),
- wherein the heat storage material (<NUM>) makes a reversible hydrophilic-hydrophobic transition at a lower critical solution temperature, and the solvent included in the thermosensitive polymer gel is kept in a liquid state in a process of hydrophilic-hydrophobic transition,
- wherein the thermosensitive polymer (<NUM>) has a crosslinked structure, and has, at a molecular terminal of the thermosensitive polymer (<NUM>), at least one functional group selected from the group consisting of a hydroxy group, a sulfonate group, an oxysulfonate group, a phosphate group, and an oxyphosphate group, and
- wherein a molar ratio between repeating units that form the thermosensitive polymer (<NUM>), the functional group, and a unit of the crosslinked structure falls within the range of <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM>.