heat storage

Abstract

To provide a technique for holding a phase change material in a silica porous body and storing heat which improves stability of heat storage.SOLUTION: A heat storage body having a spherical silica porous body in which a plurality of substantially columnar pores are formed has a phase change material in the plurality of pores of the spherical silica porous body, wherein in the spherical silica porous body, the plurality of pores have uniform porous sizes, and are radially arranged toward the surface from the center of the spherical porous body.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat storage body having a spherical silica porous body.

Background Art

[0002] Conventionally, a technique for retaining a phase change material in a solid for heat storage has been proposed (see, for example, Patent Document 1, Non-Patent Documents 1 and 2).

[0003] Patent Document 1 discloses a hard-shell microencapsulated latent heat transport material in which a phase change substance is encapsulated in non-porous hollow silica particles. Non-Patent Document 1 discloses a technique for confining a phase change substance inside the pores of mesoporous silica. Non-Patent Document 2 discloses a material in which LiOH is supported in the pores of mesoporous silica having water vapor adsorption performance.

Prior Art Documents

Patent Documents

[0004] [[ID=—]]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technology described in Patent Document 1 had problems with the packing density and dispersibility of the capsule particles, and sufficient heat storage stability could not be obtained. In the technology described in Non-Patent Document 1, leakage of erythritol as a heat storage material from the pores was confirmed. In the technology described in Non-Patent Document 2, a sufficient hydration reaction (=heat dissipation) rate could not be obtained. Thus, stable heat storage was difficult even with the technologies described in Patent Document 1 and Non-Patent Documents 1 and 2.

[0007] In view of the above issues, the objective is to provide a technology that improves the stability of heat storage in a technology that stores phase change material in a silica porous body for heat storage. [Means for solving the problem]

[0008] The present invention has been made to solve at least some of the above-mentioned problems and can be realized in the following forms.

[0009] (1) According to one embodiment of the present invention, a heat storage body is provided having a spherical silica porous body in which a plurality of substantially cylindrical pores are formed. The heat storage body has a phase change material in the plurality of pores of the spherical silica porous body, and in the spherical silica porous body, the plurality of pores have a uniform pore diameter and are arranged radially from the center toward the surface of the spherical silica porous body.

[0010] According to this configuration, multiple pores are arranged radially from the center toward the surface of the spherical silica porous body, so compared to, for example, the honeycomb-shaped silica porous body described in Non-Patent Document 1, Since one end of the pore is not open, leakage of the phase change material can be suppressed. Because the shape of the pore is approximately cylindrical, the phase change material is held by capillary force, and even if it liquefies due to melting, leakage to the outside can be suppressed, improving the stability of retention. As a result, the stability of heat storage in the heat storage body can be maintained.

[0011] (2) The heat storage body of the above form, wherein the phase change material may be at least one of sugar alcohol and paraffin. Since sugar alcohol has a large heat storage density, a heat storage body having good heat storage properties can be provided. Paraffin has a small degree of supercooling, so a decrease in heat storage efficiency can be suppressed.

[0012] Note that the present invention can be realized in various forms. For example, it can be realized in the form of a heat transport system using a heat storage body, a system including the heat transport system, and the like.

Brief Description of Drawings

[0013] [Figure 1] It is an explanatory diagram conceptually showing the heat storage of the heat storage body of one embodiment of the present invention. [Figure 2] It is an explanatory diagram conceptually showing the configuration of the spherical silica porous body of the present embodiment. [Figure 3] It is a SEM image of the spherical silica porous body. [Figure 4] It is a pore size distribution curve of the spherical silica porous body. [Figure 5] It is an explanatory diagram conceptually showing the enlargement of the pore size of the spherical silica porous body. [Figure 6] It is a SEM image of the non-spherical silica porous body used for the heat storage body of the comparative example. [Figure 7] It is a pore size distribution curve of the non-spherical silica porous body used for the heat storage body of the comparative example. [Figure 8] It is a diagram showing the physical properties of the phase change materials used in the examples and the comparative example. [Figure 9] It is a diagram showing the pore specifications of the heat storage bodies of the examples and the comparative example and the amount of the phase change material. [Figure 10] It is a diagram showing the TGA curve of the phase change material. [Figure 11] It is a diagram showing the DSC curve of the phase change material. [Figure 12] It is a diagram showing the SDC endothermic peak of the heat storage bodies of Example 1 and the comparative example. [Figure 13]It is a diagram showing the SDC heat absorption peak of the heat storage body of Example 2 and the comparative example.

Embodiment for Carrying Out the Invention

[0014] FIG. 1 is an explanatory diagram conceptually showing heat storage in the heat storage body 1 of an embodiment of the present invention. In FIG. 1, a part of the heat storage body 1 is cut away to illustrate the internal structure. The heat storage body 1 includes a spherical silica porous body 100 having a plurality of pores 10 and a phase change material 200 present in the pores 10. The shape of the pores 10 of the spherical silica porous body 100 is substantially cylindrical. The plurality of pores 10 have a uniform pore diameter and are arranged radially from the center to the surface of the spherical silica porous body 100. In the figure, some of the pores 10 and some of the phase change material 200 are labeled, and the labeling of other parts is omitted. FIG. 1 conceptually shows the heat storage body 1, and the number of pores may be more or less than that shown. Also, although an example in which the phase change material 200 is filled throughout the pores 10 is illustrated, the phase change material 200 may be filled in a part of the pores 10.

[0015] The phase change material 200 absorbs and releases latent heat in response to a temperature change. The heat storage body 1 absorbs and releases heat by utilizing the phase change (solid, liquid) of the phase change material 200. Specifically, when the phase change material 200 held in the spherical silica porous body 100 changes from the solid phase change material 200S (upper part of FIG. 1) to the liquid phase change material 200L (lower part of FIG. 1), it absorbs the surrounding heat near the melting point and tries to maintain the temperature near the melting point. Conversely, when changing from the liquid phase change material ()200L (lower part of FIG. 1) to the solid phase change material 200S (upper part of FIG. 1), it releases heat to the surroundings near the freezing point and tries to maintain the temperature near the freezing point until it completely solidifies. That is, the heat storage body 1 stores heat by utilizing the absorption and release of latent heat accompanying the solidification and melting of the phase change material 200. In FIG. 1, the solid phase change material 200 is cross-hatched and denoted by the reference numeral 200S and the liquid phase change material 200 is dot-hatched and denoted by the reference numeral 200L.

[0016] [[ID= Figure 2 is a conceptual diagram illustrating the structure of the spherical silica porous body 100 of this embodiment. In Figure 2, as in Figure 1, a portion of the spherical silica porous body 100 is cut out to illustrate the shape and arrangement of the pores 10. The pores 10 are shown with hatching in the cross-section. As shown in the figure, the spherical silica porous body 100 of this embodiment has a plurality of substantially cylindrical pores 10, and the plurality of pores 10 are arranged radially from the center of the spherical silica porous body 100 toward the surface. The arrangement of the plurality of pores 10 can be confirmed by observing the heat storage body 1 with a TEM (Transmission Electron Microscope). Furthermore, by introducing a metal (for example, platinum) into the pores of the heat storage body 1 and observing it with a TEM, the arrangement of the plurality of pores can be confirmed more clearly.

[0017] Multiple pores 10 are arranged radially from the center toward the surface of the spherical silica porous body 100. Compared to, for example, the honeycomb-shaped silica porous body described in Non-Patent Literature 1, one end of the pores 10 is not open, thus suppressing leakage of the phase change material 200. Furthermore, because the shape of the pores 10 is approximately cylindrical, the phase change material 200 is held by capillary force, and even if it liquefies due to melting, leakage to the outside can be suppressed, and the stability of the holding can be maintained.

[0018] The pore diameters of the multiple pores 10 in the spherical silica porous body 100 are uniform. Here, uniform pore diameter means that the standard deviation of the pore diameter distribution curve in the range where the pore diameter is greater than 1 nm is within 25% of the central pore diameter. The central pore diameter refers to the pore diameter that shows a maximum peak in the range greater than 1 nm in the pore diameter distribution curve. In this way, capillary forces act uniformly, and the packing efficiency of the phase change material 200 can be improved, making it possible to create a heat storage body 1 with high heat storage capacity.

[0019] The spherical silica porous body 100 of this embodiment has a uniform pore diameter in its plurality of pores 10, and the plurality of pores 10 are arranged radially from the center toward the surface of the spherical silica porous body 100. Therefore, it can be said to be a "spherical silica porous body with highly regular pores." The pore diameter is not particularly limited.

[0020] The spherical silica porous body 100 can be synthesized by the method described in Japanese Patent No. 5480461. During synthesis, the diameter of the pores 10 can be adjusted by changing the type of surfactant. Furthermore, the pore diameter can be enlarged after synthesis by replacing the surfactant with another surfactant, introducing a swelling agent, or performing hydrothermal treatment under acidic conditions.

[0021] (2) Phase change materials In the heat storage body 1, a phase change material 200 is held within the pores 10 of the spherical silica porous body 100 (Figure 1). The phase change material 200 is not particularly limited, but sugar alcohols are preferred because they have a high heat storage density and can provide a heat storage body with good heat storage capacity. Paraffins are also preferred because they have a low degree of supercooling and can suppress a decrease in heat storage efficiency. Erythritol is preferred as the sugar alcohol, and linear paraffin is preferred as the paraffin. Other sugar alcohols such as mannitol, galactitol, xylitol, sorbitol, and ribitol, inorganic salts such as inorganic phosphates, branched paraffins, and inorganic hydrates can also be used as the phase change material 200. Furthermore, a mixture of multiple types of phase change materials may be used.

[0022] (3) Manufacturing method The heat storage body 1 melts when a predetermined amount of spherical silica porous material 100 is heated above its melting point. It can be synthesized by mixing 200L of a predetermined amount of dissolved liquid phase change material. The 200L of liquid phase change material is introduced into the pores 10 of the spherical silica porous body 100 by capillary force and held there.

[0023] In the heat storage body 1 of this embodiment, multiple pores 10 are arranged radially from the center toward the surface of the spherical silica porous body 100. Compared to, for example, the honeycomb-shaped silica porous body described in Non-Patent Literature 1, one end of the pores 10 is not open, thus suppressing leakage of the phase change material 200. Furthermore, because the shape of the pores 10 is substantially cylindrical, the phase change material 200 is held by capillary force, and even if it liquefies due to melting, leakage to the outside can be suppressed, improving the stability of retention.

[0024] Furthermore, since the heat storage body 1 has a uniform pore diameter in the approximately cylindrical pores 10 of the spherical silica porous body 100, and the particle size of the spherical silica porous body 100 is also uniform, there is no distribution in the pore capacity or pore length of each particle, and the phase change material can be introduced uniformly. Therefore, the stability of heat storage can be improved.

[0025] The heat storage body 1 of this embodiment has a spherical silica porous body 100 having highly regular pores 10. Silica has better thermal conductivity than the phase change material, and heat is easily transferred from the porous spherical silica body 100 to the phase change material. Because the spherical silica porous body 100 has highly regular pores 10, the phase change material can be introduced uniformly, and the thermal conductivity from silica to the phase change material can be improved. As a result, the degree of supercooling of the phase change material can be reduced, and the decrease in the amount of heat stored can be suppressed.

[0026] The particle size of the heat storage body 1 in this embodiment is not particularly limited, but it is preferably on the order of several hundred nanometers. For example, the latent heat storage capsule described in Patent Document 1 is large, on the order of several tens of millimeters or more. In contrast, by setting the particle size of the heat storage body 1 in this embodiment to several hundred nanometers, the packing efficiency and dispersibility can be improved compared to the latent heat storage capsule described in Patent Document 1.

[0027] The heat storage body 1 of this embodiment can be used, for example, to regulate the temperature of clothing, building materials, and automotive components. For example, in electric vehicles, the heat storage body 1 can be used to cool the battery by filling the area around the battery pack. [Examples]

[0028] The present invention will be described in more detail by examples and comparative examples, but the present invention is not limited to the following examples. Both the examples and comparative examples are heat storage bodies in which a phase change material is filled into the pores of a porous silica body. The examples use the spherical porous silica body described in the above embodiment (Figure 2), while the comparative examples use a non-spherical porous silica body. Example 1 and Comparative Example 1 use erythritol as the phase change material, while Example 2 and Comparative Example 2 use linear paraffin (RT90HC, supplier: Rubitherm GmbH) as the phase change material.

[0029] Figure 3 is a conceptual diagram illustrating the manufacturing method of the spherical silica porous body 100B used in the embodiment. Similar to Figure 1, Figure 3 shows the internal structure of the spherical silica porous body with a portion cut out.

[0030] The spherical silica porous body 100B of the example was obtained by expanding the pore size of the base spherical silica porous body 100A by performing a treatment with reference to JP 2011-111332 and JP 2007-45701. The spherical silica porous body 100A was obtained by changing the surfactant from hexadecyltrimethylammonium chloride (C16Cl) to octadecyltrimethylammonium chloride (C18Cl) in the method described in Japanese Patent No. 5480461. It was synthesized using the same method. Surfactant 12A remains in the pores 10A of the spherical silica porous material 100A, and surfactant 12A is C18Cl. The central pore diameter of the pores of the spherical silica porous material 100A is 2.0 nm.

[0031] As shown in Figure 3, the spherical silica porous material 100B used in the example was formed by treating the spherical silica porous material 100A to enlarge the diameter of the pores 10A and create pores 10B. Specifically, 1.0 g of spherical silica porous material 100A was treated with a surfactant (C22(behenic acid) TMACl(Tetramethylammonium)). 3.03 g of chloride, 30 cc of ethanol, and 30 cc of pure water were mixed / dispersed and held at 80°C for one week. The pore size expanded to 3.5 nm by the substitution of surfactant 12C (C22 TMACl) with surfactant 12A (C18Cl). After the pore size was expanded, surfactant 12C was removed by calcination at 550°C for 8 hours, and then a phase change material was introduced.

[0032] Figure 4 shows a Scanning Electron Microscope (SEM) image of the spherical porous silica material 100B. The average particle diameter of the spherical porous silica material 100B is 0.918 μm, and the monodispersity is 8.5%. In this embodiment, the average particle diameter was determined by measuring the diameters of 200 particles using the SEM image shown in Figure 4, and using the arithmetic mean. The monodispersity [%] is calculated by dividing the standard deviation by the average particle diameter. The spherical porous silica material 100B used in this example has a monodispersity of 8.5% and is a uniform particle. Note that the average particle diameter and monodispersity of the spherical porous silica material are not limited to this embodiment, but it is preferable to have them on the order of several hundred nanometers because it can improve the packing efficiency and dispersibility of the heat storage material.

[0033] Figure 5 shows the pore size distribution curve of spherical silica porous material 100B. The pore size distribution curve shown in Figure 5 was estimated from measured nitrogen adsorption isotherms using the BJH (Barrett, Joyner, and Halenda) method. In spherical silica porous material 100B, the shape of the pores 10B is approximately cylindrical, and multiple pores 10B have a uniform pore size (diameter). The central pore diameter of spherical silica porous material 100B is 3.5 nm, and the standard deviation is 13%. That is, the standard deviation in the range of pore diameters greater than 1 nm in the pore size distribution curve is within 25% of the central pore diameter.

[0034] Figure 6 is an SEM image of the non-spherical silica porous material used in the comparative example heat storage body. Figure 7 is the pore size distribution curve of the non-spherical silica porous material used in the comparative example heat storage body.

[0035] As shown in Figure 6, the silica porous material used in the comparative example's heat storage body is mostly non-spherical. As shown in Figure 7, the non-spherical silica porous material used in the comparative example's heat storage body has a uniform pore size.

[0036] The comparative example of non-spherical silica porous material was synthesized by the synthesis method described in non-patent literature (D. Zhao et al., Journal of the American Chemical Society, 120, 6024-6036 (1998)). Specifically, it was synthesized by the following steps (1) to (4). (1) Add the surfactant Brij 76 (polyoxyl stearyl ester) to 10 g of pure water. (2) Mix 4.4g of TEOS (tetraethoxysilane), 40g of HCl (2mol / l), and the above (1) to dissolve the surfactant. (3) Heat-treat the reaction solution from (2) above (at 100°C for 20 hours). (4) Filter the liquid after the heat treatment described above and calcine it (at 550°C for 8 hours).

[0037] Figure 8 shows the physical properties of the phase change materials used in the examples and comparative examples. Figure 8 shows the physical property values ​​from the material manufacturers. As shown in the figure, erythritol has a high heat storage density but also a high degree of supercooling.

[0038] Figure 9 shows the pore parameters and the amount of phase change material in the heat storage bodies of the examples and comparative examples. Figure 10 shows the TGA curve of the phase change material. Figure 11 shows the DSC curve of the phase change material.

[0039] In the table in Figure 9, pore volume [ml / g] and specific surface area [m²] are shown. 2 [ / g] was estimated from BET (Brunauer, Emmett, and Teller) plots using measured nitrogen adsorption isotherms. The pore size distribution curve was estimated using the BJH method. Specific surface area [m²] 2 / m 3 ] is the specific surface area per unit pore volume, and the pore volume [ml / g] and specific surface area [m²] are related. 2 It is calculated from [ / g].

[0040] The packing efficiency represents the proportion of the total pore volume occupied by the introduced phase change material (hereinafter also referred to as "PCM"), and can be estimated from simultaneous thermogravimetric and differential thermal analysis (TG-DTA). In this example, the Thermoplus TG-8120 simultaneous thermogravimetric and differential thermal analysis device was used. Measurements were taken using a RIGAKU product.

[0041] Figure 10 shows the TGA (Thermogravimetric Analysis) curve of the phase change material. The weight loss between 150 and 700°C was used as the organic fraction derived from the PCM, and the PCM packing efficiency within the pores was calculated. Specifically, it was calculated using (Equation 1) below.

[0042] Packing density [vol%] = Organic fraction / PCM density / Pore volume × 100 … (Equation 1)

[0043] In a heat storage body, the PCM density of PCM held in the silica porous material can be measured, for example, by the following method: The PCM gas, which is evaporated by heating the heat storage body, can be calculated using mass information obtained by gas chromatography-mass spectrometry (GC / MS).

[0044] Figure 11 shows the DSC curves of phase-change materials. Figure 11(a) shows a typical differential scanning calorimetry (DSC) curve for erythritol, and Figure 11(b) shows a typical DSC curve for linear paraffin. As shown in the figure, the difference between the endothermic peak and the heat-releasing peak represents the degree of supercooling. Also, as shown in the figure, the peak area of ​​the endothermic curve (shown with hatching in the figure) corresponds to the amount of heat stored.

[0045] Effective heat storage material represents the proportion of PCM (polycrystalline polymer) occupying the pores that can generate latent heat through melting / solidification, and can be estimated by differential scanning calorimetry (DSC) (latent heat storage density [J / g]). In this example, differential scanning calorimetry was performed using a differential scanning calorimetry meter DSC Q1000 (manufactured by TA Instruments) under conditions of -20°C to 150°C with a heating / cooling rate of 10°C / min. On the other hand, ineffective heat storage material is the total PCM minus the effective heat storage material.

[0046] The effective heat storage material can be calculated using the following equations (2) and (3). Effective heat storage material [vol%] = Apparent latent heat / PCM latent heat × 100 … (Equation 2) Apparent latent heat = heat storage amount / PCM density / pore capacity … (Equation 3)

[0047] Furthermore, differential scanning calorimetry was performed as described above to determine the melting point and degree of supercooling of the phase-change material, as shown in Figure 11.

[0048] As shown in Figure 9, the heat storage body of the example has the same pore capacity and packing efficiency as the heat storage body of the comparative example, but it has a higher heat storage density and a higher proportion of effective heat storage material compared to the heat storage body of the comparative example. This is thought to be because the heat storage body of the example has a uniform pore diameter in the approximately cylindrical pores 10 of the spherical silica porous body 100, and the particle size of the spherical silica porous body 100 is also uniform, so there is no distribution in pore capacity or pore length for each particle, and the phase change material can be introduced uniformly.

[0049] Figure 12 shows the SDC endothermic peaks of the heat storage bodies for Example 1 and Comparative Example 1. Figure 13 shows the SDC endothermic peaks of the heat storage bodies for Example 2 and Comparative Example 2. Specifically, Figure 12 shows an example where the phase change material is erythritol, and Figure 13 shows an example where the phase change material is linear paraffin. Figures 12 and 13 show the results of differential scanning calorimetry performed using a differential scanning calorimeter DSC Q1000 (TA Instruments) under conditions of -20°C to 150°C with a heating / cooling rate of 10°C / min. In the illustrated examples, heating and cooling are considered as one set, and this is repeated 10 times. The endothermic curves for the first set (indicated as n=1 in the figure) and the tenth set (indicated as n=10 in the figure) are shown. Note that in the figures, the positions of each curve are shifted for ease of comparison and do not represent the absolute value of the heat flow.

[0050] As shown in Figure 12, the heat storage body of Example 1 shows a single endothermic peak for both the first set (n=1) and the tenth set (n=10). In contrast, the heat storage body of Comparative Example 1 shows a single endothermic peak for the first set (n=1), but the endothermic peak splits into two for the tenth set (n=10). Similarly, the heat storage body of Example 2 shows a single endothermic peak for both the first set (n=1) and the tenth set (n=10). In contrast, the heat storage body of Comparative Example 2 shows a single endothermic peak for the first set (n=1), but the endothermic peak splits into two for the tenth set (n=10) (Figure 13).

[0051] From these results, it is considered that in the comparative example's heat storage body (non-spherical silica porous material), the phase change material leaked out due to repeated heating and cooling. In the comparative example's endothermic peak for n=10, the high-temperature peak is higher than the melting point of the pure phase change material and is considered to be a peak originating from the leaked phase change material. In other words, the heat storage body of the example was able to suppress the leakage of the phase change material introduced into the pores compared to the heat storage body of the comparative example. As shown in Figure 7, the non-spherical silica porous material used in the comparative example's heat storage body has a uniform pore diameter, but as shown in Figure 6, the particle shape and size are non-uniform. Therefore, the pore length and the number of pores (inlets) per particle are non-uniform. In other words, in the non-spherical silica porous material used in the comparative example, the pore inlets are not uniformly arranged on the surface, making it difficult to uniformly introduce molten PCM (viscous liquid) into the pores when manufacturing the heat storage body, and it is considered that there is a large amount of PCM near the surface of the pores. Therefore, it is thought that PCM leakage occurred due to repeated heating and cooling. Furthermore, while the non-spherical silica porous material of the comparative example has a honeycomb structure with both ends of the pores being open, the pores of the spherical silica porous material of the example are arranged radially from the center toward the surface, and one end is not exposed to the surface, thus suppressing leakage of PCM introduced into the pores.

[0052] As explained above, the heat storage body of this embodiment has a spherical silica porous body and a high degree of regularity among its multiple pores, which suppresses leakage of the phase change material. As a result, stable heat storage can be achieved.

[0053] The present invention has been described above based on embodiments and examples, but the embodiments described above are for the purpose of facilitating understanding of the present invention and do not limit the present invention. The present invention may be modified and improved without departing from its spirit and claims, and equivalents thereof are included in the present invention. Furthermore, any technical features not described as essential in this specification may be appropriately deleted. For example, a heat storage body may be constructed using the spherical silica porous body 100A described in the above embodiment. [Explanation of symbols]

[0054] 1… Heat storage element 10…Pore 100, 100A, 100B... Spherical porous silica 200, 200L, 200S… Phase change materials

Claims

1. A heat storage body having a spherical silica porous body in which a plurality of substantially cylindrical pores are formed, The spherical silica porous body has a phase change material in the plurality of pores, In the aforementioned spherical silica porous body, The plurality of pores have a uniform pore diameter, are connected to the central hollow portion of the spherical silica porous body, and are arranged radially from the hollow portion toward the surface. Heat storage device.

2. A heat storage body according to claim 1, The phase change material is at least one of a sugar alcohol and paraffin. Heat storage device.

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