Method for heating ice and method for storing heat in ice

Abstract

At atmospheric pressure ice superheating method and ice heat storage method to it are provided. 【Solution means】 The superheating method of ice in the present invention is as follows: at atmospheric pressure ice is cooled to below the melting point in the first step, Sodium acetate aqueous solution is supercooled in the second step, Ice and the sodium acetate aqueous solution is submerged in it to form a crystal nucleus, Sodium acetate aqueous solution is crystallized, and ice around it Sodium acetate aqueous solution is covered with crystals of Covering and ice the surface of is made to disappear in the third step; Sodium acetate aqueous solution When freezes, the heat of solidification generated is utilized to ice is heated from its surroundings by heat conduction to a temperature exceeding the melting point, ice and the fourth step of making exist as a solid at a temperature exceeding the melting point are provided. By coating the surface of ice with crystals of a sodium acetate solution, the crystalline structure of water molecules on the ice surface can be made to resemble the hexagonal structure arranged in an orderly manner, similar to that inside the ice. This strengthens hydrogen bonding, thereby raising the temperature at which surface melting begins to exceed the melting point.

Description

Technical Field

[0001] The present invention relates to a method for superheating ice at atmospheric pressure and a method for storing heat in ice .

Background Art

[0002] Substances change their states to solids, liquids, or gases depending on pressure and temperature. At atmospheric pressure, water becomes ice (solid) below 0°C, water (liquid) between 0 and 100°C, and water vapor (gas) above 100°C. It is known that superheating occurs in liquids. When water is heated gently, it remains in a liquid state without boiling and reaches a superheated state exceeding the boiling point of 100°C. When an impact such as vibration is applied, film boiling occurs.

[0003] On the other hand, solids do not undergo superheating, and ice is considered to maintain its solid state and not exceed the melting point of 0°C. That is, ice cannot exist as a solid at a temperature exceeding the melting point unless the movement of water molecules is suppressed in a high-pressure environment (no superheating phenomenon is observed). The reason why superheating does not occur in solids containing ice is that solids have a surface and surface melting occurs. As a hypothesis for the reason why surface melting of ice occurs, it is said that "the crystal structure of the ice surface is disordered, and the density of hydrogen atoms is only about half that of the interior, so the force of hydrogen bonds is weak."

[0004] Examples of prior research on ice (state change of water) include the following. (1) In September 2009, the University of Oxford in the UK first produced "ice of XV phase" in a laboratory environment and demonstrated the existence of "ice of several hundred degrees" at ultra-high pressure. (2) In July 2016, the University of Tokyo, the Geochemical Experiment Facility, etc. succeeded in directly observing "ice of XV phase" existing under low temperature and high pressure. (3) In March 2018, the University of Nevada in the US discovered "ice of VII phase," which was thought to "not exist on Earth" because the pressure required for formation was too strong, from inside a diamond. (4) In September 2018, Toyama University succeeded in superheating from the isotopic ice surface by covering the surface of the ice with heavy water ice (freezing point 3.8°C), an isotope of water, thereby eliminating the ice surface that had been hindering superheating. (The following year, this was corrected to "the ice had changed into ice containing heavy water.") (5) On September 12, 2020, the University of Tokyo successfully observed the crystalline structure of water molecules on the surface of ice at the atomic scale using an atomic force microscope. They revealed that, unlike the interior of ice where hexagonal structures are neatly arranged, the positions of water molecules are not orderly and the crystalline structure is disordered (Non-Patent Literature 1). (6) In February 2021, the University of Tokyo, the Neutron Science Center, and others confirmed that the ice obtained by pressurizing room-temperature water and cooling the "phase VI ice" that first appears to the surface to about -150°C is "phase XIX ice".

[0005] Regarding (4) above, since heavy water is used in this experiment, I believe it will not work for the following reasons. Because the hydrogen bonds in heavy water are stronger than those in water, when an H2O molecule and a D2O molecule come into contact, the hydrogen bonds between the molecules instantly transform them into HDO molecules. The hydrogen bonds in heavy water are too strong compared to the intermolecular forces and thermal motion that govern the phase change (water-ice). • Heavy water has a high freezing point of 3.8°C, and because ice needs to be submerged in heavy water at 4°C or higher, the amount of heat instantly transferred to the surface of the ice is too great, causing the surface to melt. (Thermal motion due to the freezing point difference between water and heavy water (4°C) > Intermolecular forces that allow ice to exist) Toyama University stated that rapid freezing of heavy water is necessary, resulting in a heavy water ice shell containing countless air bubbles, making it impossible to observe the pure ice inside, for example, through a deflection device. They also suggested that the reason why stable ice superheating had not been achieved in the past was due to insufficient attention to the interfaces the ice was in contact with. They stated that if the surface of the ice is in direct contact with air or a solid surface, the ice will melt at 0°C.

[0006] Regarding (5) above, at the surface of ice, the number of adjacent water molecules decreases compared to the inside of the crystal. As a result, some of the hydrogen atoms that make up the water molecules protrude from the surface regardless of hydrogen bonding. In atomic force microscope images, each of these protruding hydrogen atoms is visualized as an individual round dot, and when the density of these hydrogen atoms was counted, it was found to be 1.5 per 1 nm square. The number of hydrogen atoms per 1 nm square is expected to be 2.8 from the internal crystal structure, so it was found that there are only about half that number. These facts suggest that the hydrogen bonding is weaker at the surface of ice compared to the inside, making it a weak point for melting. [Prior art documents] [Patent Documents]

[0007] [Non-Patent Document 1] Intrinsic reconstruction of ice-I surfaces, Volume: 6, Issue: 37, DOI: (10.1126 / sciadv.abb7986) [Overview of the project] [Problems that the invention aims to solve]

[0008] Methods for controlling surface melting by adjusting the crystalline structure of ice surfaces, as well as methods for superheating solids, have not yet been elucidated. If superheating solids or heat storage in solids becomes possible, it could contribute to reducing the storage and transportation costs of frozen foods and other products, as well as to combating global warming.

[0009] Considering these problems, the present invention provides a solution for atmospheric pressure ice The method of heating and ice The objective is to provide a method for storing heat in a [unspecified area]. [Means for solving the problem]

[0010] The ice heating method of the present invention is performed under atmospheric pressure. ice The first step is to cool it to below its melting point, Sodium acetate aqueous solutionA second step of supercooling; The ice is the sodium acetate aqueous solution submerging it to form crystal nuclei, The aforementioned sodium acetate aqueous solution and crystallizing it, the ice surrounding The aforementioned sodium acetate aqueous solution with crystals of Covering and the ice a third step of causing the surface of The aforementioned sodium acetate aqueous solution to disappear; and the ice using the heat of solidification generated when the ice freezes to heat from its surroundings to a temperature above the melting point by heat conduction,

[0011] The heat storage method for ice according to the present invention includes at least: a first step of cooling ice to a temperature below the melting point under atmospheric pressure, Sodium acetate aqueous solution a second step of supercooling The ice is the sodium acetate aqueous solution submerging it to form crystal nuclei, The aforementioned sodium acetate aqueous solution and crystallizing it, the ice surrounding The aforementioned sodium acetate aqueous solution with crystals of Covering and the ice a third step of causing the surface of The aforementioned sodium acetate aqueous solution to disappear; and the ice using the heat of solidification generated when the ice freezes to heat from its surroundings to a temperature above the melting point by heat conduction,

Advantages of the Invention

[0012] The present invention focuses on the fact that an aqueous solution of sodium acetate crystallizes at a temperature above 0°C, can remain liquid even in a supercooled state below 0°C, and can heat ice from its surroundings using the heat of solidification generated when it freezes. In this invention, by coating the surface of ice with crystals of an aqueous sodium acetate solution (sodium acetate trihydrate), the crystalline structure of water molecules on the ice surface is made to resemble the crystalline structure in which hexagonal structures are neatly arranged, similar to the structure inside the ice. By strengthening hydrogen bonds, the temperature at which surface melting of ice begins can be raised to a temperature above the melting point. The concentration of the sodium acetate aqueous solution should preferably be around 40-50%. If the concentration of the sodium acetate aqueous solution is significantly higher than 50%, there is a risk that it will not be able to maintain a supercooled state below 0°C in a liquid state. If the concentration is significantly lower than 40%, there is a risk that ice will not crystallize even when submerged, and the ice will melt even below 0°C due to freezing point depression. By applying this method of heating ice, it becomes possible to heat a wide range of solids and store heat in solids. [Brief explanation of the drawing]

[0013] [Figure 1] Figures (a) and (b) show the experimental procedure for overheating ice. [Figure 2] A graph showing the change in the core temperature of the ice over time. [Figure 3] A graph showing the change in the core temperature of the ice over time. [Modes for carrying out the invention]

[0014] The inventors of this invention believe that the reason why overheating is not observed in solids is that "solids have a surface, and heating occurs from the surface, resulting in surface melting." Therefore, they considered whether it would be possible to cover the surface of a solid with crystals of a mixed solution with a high melting point to eliminate the surface and prevent the formation of an interface between the solid and the crystals of the mixed solution (the intermolecular interactions of the mixed solution are due to the properties of each component molecule that makes up the mixture), and thus completed the present invention. Specifically, the present invention consists of a first step of cooling ice to below its melting point under atmospheric pressure, a second step of supercooling an aqueous sodium acetate solution, a third step of immersing the ice in the aqueous sodium acetate solution to create a crystal nucleus, causing the aqueous sodium acetate solution to crystallize, thereby coating the ice with crystals of the aqueous sodium acetate solution (sodium acetate trihydrate) and eliminating the surface of the ice, and a fourth step of using the heat of solidification generated when the aqueous sodium acetate solution freezes to heat the ice from the surrounding area by heat conduction to a temperature above its melting point. It is preferable to use a low concentration of sodium acetate aqueous solution, around 40-50%.

[0015] In the first step, the ice is cooled to below its melting point. In the second step, a low-concentration sodium acetate aqueous solution is supercooled. When a small amount of sodium acetate, such as sodium acetate trihydrate (CH3COONa·3H2O), is dissolved in water, the aqueous solution will freeze even at temperatures above 0°C. Generally, ordinary salt (NaCl) aqueous solutions undergo "freezing point depression" and freeze below 0°C, but sodium acetate trihydrate crystallizes as a hydrate, and therefore exhibits the property of crystallizing even at temperatures above 0°C. On the other hand, even if the temperature of an aqueous sodium acetate solution is lowered while it remains in liquid form, it will not freeze unless there are nuclei (crystal nuclei) that initiate crystallization. Therefore, the solution can remain liquid even when it reaches a supercooled state below 0°C. Furthermore, as explained in step 4, the heat of solidification generated when an aqueous sodium acetate solution freezes can be used to heat the ice from its surroundings. Thus, the most distinctive feature of the ice heating method of the present invention is the use of an aqueous sodium acetate solution.

[0016] In the third step, ice is submerged in a sodium acetate solution to create a crystal nucleus, and the sodium acetate solution crystallizes, coating the ice with crystals of the sodium acetate solution (sodium acetate trihydrate), causing the ice surface to disappear. When ice is submerged in a sodium acetate solution, the ice acts as a crystallization nucleus. In a low-temperature environment below 0°C, the sodium acetate solution begins to crystallize, and eventually the ice is covered with crystals of the sodium acetate solution (sodium acetate trihydrate). As a result, the surface of the ice disappears. Because the crystalline structure of sodium acetate trihydrate contains the same water molecules as ice, the hydrogen bonding force causes the water molecules on the ice surface to approach a crystalline structure in which hexagonal structures are neatly arranged, similar to the structure inside the ice, and strengthens the hydrogen bonds. As sodium acetate, anhydrous sodium acetate (CH3COONa), which does not contain water molecules, may be used. In "humid air," anhydrous sodium acetate absorbs water and becomes stable as a hydrated salt such as trihydrate, and the hydrate can be dehydrated by heating to about 120°C.

[0017] In the fourth step, the heat of solidification generated when the sodium acetate solution freezes is used to heat the ice from the surrounding area through heat conduction to a temperature above its melting point, so that the ice exists as a solid at a temperature above its melting point. When crystallization begins, water molecules in the sodium acetate solution arrange themselves in an ordered lattice. Since the crystals of the sodium acetate solution do not melt even at around 20°C, the heat of solidification that continues to be generated as the freezing (crystallization) progresses from the crystal nucleus to the surrounding area is transmitted through the inner crystals that have already frozen and solidified, and the ice is heated by heat conduction from the surface of the ice. In other words, heat conduction occurs from the solid phase (crystals of the sodium acetate solution (sodium acetate trihydrate)) to the solid phase (ice). As mentioned above, the University of Tokyo revealed that the surface of ice has a disordered crystalline structure and the density of hydrogen atoms is only about half that of the interior, resulting in weak hydrogen bonds. Therefore, ice begins to melt immediately from the surface at 0°C (surface melting). However, in the third step, by covering the surface of the ice with crystals of an aqueous sodium acetate solution (sodium acetate trihydrate), the crystalline structure of water molecules on the ice surface is made closer to a crystalline structure in which hexagonal structures are neatly arranged, similar to the interior of the ice. By strengthening the hydrogen bonds, in the fourth step, the temperature at which surface melting of ice begins can be raised to a temperature above the melting point.

[0018] The method of the present invention is applicable to a wide range of solids, not just ice. Examples of solids that can be superheated using the method of the present invention include, in addition to ice, inorganic salt crystals such as sodium chloride and sodium sulfate, inorganic oxide crystals such as silicon dioxide and aluminum oxide, dry ice (solid carbon dioxide), organic crystals such as sucrose, urea, and naphthalene, phase change materials such as paraffin wax, crystalline polymer materials such as polyethylene and polypropylene, and metals such as aluminum, copper, and iron. Furthermore, the method of the present invention is not limited to aqueous solutions of sodium acetate; aqueous solutions of other substances can also be used. Examples of such substances include inorganic salts such as sodium sulfate, calcium chloride, and sodium borate; organic salts such as potassium acetate and ammonium acetate; and organic molecular compounds such as urea and sucrose. Polymers that are raw materials for adhesives used with metals, such as polyisoprene (natural rubber), nylon 66, and polytetrafluoroethylene (Teflon®), are particularly preferred.

[0019] In the present invention's method for heating solids, the surface of the solid is coated with crystals of a substance different from the solid, thereby bringing the crystalline structure of the molecules on the solid surface closer to a crystalline structure in which the structure is arranged in an orderly manner, similar to that inside the solid, and strengthening the bonds. This raises the temperature at which surface melting of the solid begins to a temperature above its melting point. From this perspective, when using a metal as the solid, it is preferable to use a polymer, which is commonly used as a metal adhesive, as the substance to be made into an aqueous solution.

[0020] Furthermore, the present invention is not limited to a liquid-derived crystalline layer, but may also be composed of a solid layer. In other words, instead of using an aqueous solution, the surface of a solid may be directly coated with a solid different from that solid. Specifically, the method for superheating a solid may include at least the following steps: a first step of cooling the first solid to below its melting point; a second step of covering the first solid with a second solid having a higher melting point than the first solid, thereby eliminating the surface of the first solid and strengthening the bonding force of the second solid to the first solid through interactions such as chemical bonding, intermolecular forces, or electrostatic adsorption; and a third step of heating the first solid from its surroundings to a temperature above its melting point by utilizing heat conduction from the second solid to the first solid by heating the second solid, thereby bringing the first solid into a state where it exists as a solid at a temperature above its melting point.

[0021] In this way, by covering the surface of the first solid with a second solid that has a higher melting point than the first solid, surface melting of the first solid can be suppressed. For the present invention to be valid, it is preferable that the following conditions are met. (1) In order to ensure thermal conductivity and interfacial stability, the interface between the first solid and the second solid should be close together (there should be interaction). (2) To prevent the interface from breaking down due to chemical reactions, the second solid is chemically stable and does not react easily with the first solid. (3) In order to efficiently conduct heat from the coating layer and easily create an overheated state, the higher the thermal conductivity of both solids, the better. For example, if the first solid is aluminum or copper, aluminum oxide or aluminum nitride can be used as the second solid. Also, if the first solid is a low-melting-point metal such as tin or lead, a high-melting-point metal such as copper, nickel, or aluminum can be used as the second solid. The present invention's method for superheating solids can be applied to methods for storing heat in solids. [Examples]

[0022] This document describes the experimental procedure and results regarding the overheating of ice. [Experimental Procedure] (1) Under atmospheric pressure and room temperature of -2°C to 0°C, a thermocouple (thermometer) was embedded in the center of the ice as shown in Figure 1(a) and cooled to -2°C. (2) A low-concentration (approximately 45%) aqueous solution of sodium acetate was supercooled to below 0°C. (3) As shown in Figure 1(b), the ice from (1) was submerged in the aqueous solution from (2) to serve as a crystal nucleus, and the crystallization of the aqueous solution began. (4) The ice was heated using the heat of solidification generated when the aqueous solution freezes. As shown in Figures 2 and 3, the core temperature of the ice was measured every 0.1 seconds. (5) The boundary between the ice and aqueous solution crystals was observed.

[0023] [result] (1) The temperature of the ice rose to +1°C due to the heat of reaction when the sodium acetate solution froze (Figure 2a). (2) No interface is formed at the boundary between the ice and the sodium acetate aqueous solution crystals (sodium acetate trihydrate) (Figure 2b). (3) The ice began to melt 37.2 seconds after its core temperature exceeded 0°C (Figure 2c). (4) The temperature decreased due to the heat of fusion of the ice (Figure 2d). (5) After all the ice had melted, crystals of sodium acetate solution (sodium acetate trihydrate) remained in the surrounding area (Figure 2e). If surface melting of the ice had occurred, a layer of water should have formed at the boundary between the ice and the crystals. However, since no layer of water formed, it can be inferred that the ice and crystals were directly connected. Visual observation confirmed that the ice was in a superheated state without melting. From the above, we were able to create warm ice that was superheated to +1°C at atmospheric pressure. When the surface of the ice was covered with crystals of sodium acetate aqueous solution (sodium acetate trihydrate), the crystalline structure of water molecules on the ice surface approached a crystalline structure in which hexagonal structures were neatly arranged, similar to the structure inside the ice, and it is thought that the hydrogen bonds were strengthened, thus raising the onset temperature of surface melting.

[0024] For the following reasons, we believe that the coating method using an aqueous sodium acetate solution of the present invention has resolved the issues of the coating method using heavy water developed by Toyama University as described above. (1) Regarding the problem that when H2O molecules and D2O molecules come into contact, they instantly change into HDO molecules due to intermolecular hydrogen bonding, sodium acetate aqueous solution is a mixed solution with water, and freezing (crystallization) in a low-concentration supercooled state proceeds very gently and slowly over time. (2) Regarding the problem that the hydrogen bonds of heavy water are too strong compared to the intermolecular forces and thermal motion that govern the change of state (water-ice), the crystallization of sodium acetate aqueous solution is also due to the same intermolecular forces, and since it is a low-concentration aqueous solution, the force is not strong enough to break the intermolecular forces of ice. The intermolecular interactions of a mixed solution are due to the properties of each component molecule, so in a low-concentration aqueous solution, the intermolecular forces are almost the same as those of water. (3) Regarding the problem that heavy water has a high freezing point, causing the surface of ice to melt due to the excessive amount of heat instantly transferred to the surface when ice is submerged in heavy water, a low-concentration sodium acetate aqueous solution can be supercooled to temperatures below 0°C, and in low-temperature environments below 0°C, the sodium acetate aqueous solution can be frozen around the ice without melting the ice.

[0025] [Conclusion] (1) We were able to reveal the existence of superheating in solids, which had not been known until now. (2) By covering the ice with crystals of a low-concentration sodium acetate aqueous solution (sodium acetate trihydrate), we were able to create warm ice at +1°C at atmospheric pressure for the first time in the world. (3) We discovered a method of coating ice with an aqueous sodium acetate solution that can be easily heated and confirmed. (4) The fact that we were able to confirm superheating in a solid form of water, which shrinks when melted, is considered to be of great significance as it may serve as direct proof that superheating of solids exists. This is because, by successfully superheating the solid by covering the surface with crystals of a mixed solution with a high melting point and causing the surface to disappear, we found that in substances that expand when melted, unlike water, the pressure inside the solid increases and the melting point rises (melting is suppressed by pressure), so there is a high possibility that superheating can be achieved by applying the present invention. The following effects can be expected by applying and developing the solid heating method and the heat storage method for solids of the present invention. (1) Reduction of storage and transportation costs for ice, dry ice, frozen foods, etc. (2) Development of new heat storage materials for use in heating and cooling of houses and buildings (3) Measures to combat global warming by suppressing the surface melting of glaciers and ice in Antarctica and accumulating heat within the ice. (4) Applications in a wide range of fields, such as the overheating of other solid materials like metals. [Industrial applicability]

[0026] This invention relates to atmospheric pressure ice The method of heating and ice This is a method for storing heat and has industrial applicability.

Claims

1. The first step is to cool the ice below its melting point under atmospheric pressure, The second step involves supercooling the sodium acetate aqueous solution, A third step involves immersing the ice in the sodium acetate aqueous solution to create a crystal nucleus, causing the sodium acetate aqueous solution to crystallize, thereby coating the ice with crystals of the sodium acetate aqueous solution and eliminating the surface of the ice. A method for superheating ice, comprising at least a fourth step of using the heat of solidification generated when the sodium acetate aqueous solution freezes to heat the ice from its surroundings by heat conduction to a temperature above its melting point, thereby causing the ice to exist as a solid at a temperature above its melting point.

2. The method for heating ice according to claim 1, characterized in that the concentration of the aqueous sodium acetate solution is 40 to 50%.

3. The first step is to cool the ice below its melting point under atmospheric pressure, The second step involves supercooling the sodium acetate aqueous solution, A third step involves immersing the ice in the sodium acetate aqueous solution to create a crystal nucleus, causing the sodium acetate aqueous solution to crystallize, thereby coating the ice with crystals of the sodium acetate aqueous solution and eliminating the surface of the ice. A method for storing heat in ice, characterized by comprising at least a fourth step of using the heat of solidification generated when the sodium acetate aqueous solution freezes to heat the ice from its surroundings by heat conduction to a temperature above its melting point, thereby causing the ice to exist as a solid at a temperature above its melting point.

4. The method for storing heat in ice according to claim 3, characterized in that the concentration of the sodium acetate aqueous solution is 40 to 50%.

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