Description

SUPERCOOLING APPARATUS

Technical Field

[1] The present invention relates to a supercooling apparatus, and more particularly, to a supercooling apparatus featuring a reduced possibility of release of the supercooled state. Background Art

[2] A term "supercooling" describes a phenomenon that melt or solid does not change even after it is cooled down to a temperature lower than the phase transition temperature at equilibrium state. In general, every material has its own stable state at a given temperature, so if temperature changes gradually, atoms of the substance keep abreast with the changes of temperature while maintaining its stable state at each temperature. However, if temperature changes abruptly, there is not enough time for the atoms to get into a stable state corresponding to each temperature. What happens then is the atoms either keep the stable state at a start temperature, or partially change to a state at a predetermined end temperature then stop.

[3] For example, when water is cooled slowly, it does not freeze for some time even though the temperature is below 0 ⁰ C. However, when an object becomes a supercooled state, it is a sort of metastable state where the unstable equilibrium state breaks easily even by a very small stimulus or minor external disturbance, so the object easily transits to a more stable state. That is to say, if a small piece of the material is put into a supercooled liquid, or if the liquid is subject to impact on a sudden, it starts being solidified immediately and temperature of the liquid is raised to a freezing point, maintaining a stable equilibrium state at the temperature.

[4] Normally, foods like vegetables, fruits, meats, or beverages are kept either refrigerated or frozen to retain freshness. Those foods contain liquid such as water. When the liquid is cooled below the phase transition temperature, it transits to a solid phase at one point.

[5] Although a certain stored item like water can be kept in a supercooled state for a short period of time, there are increasing demands nowadays for keeping foods in a supercooled state for an extended period of time.

[6] There are, however, several factors that release a supercooled state, and among them are external disturbance and freezing nucleus production. External disturbance occurs at the surface (free surface) where a supercooled liquid moves freely amongst another liquid to result in the release of a supercooled state. Meanwhile, a freezing nucleus is produced mainly in a liquid and at an upper part of a storage compartment storing the

liquid, and a contact face between liquid and a container. Once a freezing nucleus is produced, it spreads all over, eventually resulting in the release of a supercooled state and the phase transition. Disclosure of Invention

Technical Problem

[7] An object of the present invention is to provide a supercooling apparatus that is capable of maintaining the supercooled state of a stored item stably for a long period of time.

[8] Another object of the present invention is to provide a supercooling apparatus that is capable of maintaining the supercooled state of a stored item stably at a lowest possible temperature.

[9] A further object of the present invention is to provide a supercooling apparatus using a liquid container with improved shape to reduce external disturbance causing the release of a supercooled state, so that the supercooled state can be maintained stably for an extended period of time.

[10] A still further object of the present invention is to provide a supercooling apparatus using a blocking member on liquid to reduce the freezing nucleus causing the release of a supercooled state, so that the supercooled state can be maintained stably for an extended period of time, and at a lowest possible temperature. Technical Solution

[11] In order to achieve the above-described objects of the invention, there is provided a supercooling apparatus, comprising: a container for containing liquid; a contact- limiting unit formed inside or outside the container to reduce a contact area between the contained liquid and air; and a non-freezing operation unit for housing the container and maintaining the liquid in a non-frozen state at a phase transition temperature or below.

[12] In an exemplary embodiment, the contact- limiting unit is a liquid inlet of the container, and the liquid inlet is smaller than a liquid storage portion of the container in diameter.

[13] Preferably, the contact- limiting unit is a blocking member that floats on the liquid.

[14] Another aspect of the present invention provides a supercooling apparatus, comprising: a container for containing liquid; a non-freezing operation unit for housing the container and maintaining the liquid in a non-frozen state at a phase transition temperature or below; and a flow-control unit for reducing flow of the liquid.

[15] Preferably, the flow-control unit is a blocking member that floats on the liquid.

[16] Moreover, the flow-control unit is a liquid inlet of the container, and the liquid inlet is smaller than a liquid storage portion of the container in diameter.

[17]

Advantageous Effects

[18] The present invention with the above-described configuration takes energy out of an item by a cooling operation yet supplies energy in another way to let molecules in a target liquid to be supercooled to do at least one of rotation, vibration, and translation movements, preventing the occurrence of phase transition. Therefore, a stored item can be kept in a supercooled state stably for an extended period of time at a lowest possible temperature.

[19] Moreover, the present invention suppresses external disturbances, one factor causing the release of a supercooled state, so that a supercooled state can be maintained stably for an extended period of time at a lowest possible temperature.

[20] Further, the present invention suppresses the production of freezing nucleuses, another factor causing the release of a supercooled state, so that a supercooled state can be maintained stably for an extended period of time at a lowest possible temperature. Brief Description of the Drawings

[21] FIG. 1 is a schematic view of the electrode structure of a supercooling apparatus to maintain a supercooled state;

[22] FIG. 2 is a graph reflecting a supercooling phenomenon that occurs in the supercooling apparatus based on FIG. 1 ;

[23] FIG. 3 shows one embodiment of the supercooling apparatus based on FIG. 1;

[24] FIG. 4 diagrammatically explains a cause of the release of a supercooling state;

[25] FIGs. 5 and 6 show examples of a storage unit;

[26] FIG. 7 shows one embodiment of a supercooling apparatus in which FIG. 5 and FIG.

6 are incorporated; and

[27] FIGs. 8 and 9 are schematic view of a storage unit provided with a blocking member.

[28]

Mode for the Invention

[29] Hereinafter, preferred embodiments of a supercooling apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

[30]

[31] When liquid such as water is cooled slowly, it does not freeze for some time even though the temperature is below 0 ⁰ C. However, when an object becomes a supercooled state, it is a sort of metastable state where the unstable equilibrium state breaks easily even by a very small stimulus or minor external disturbance, so the object easily transits to a more stable state. That is to say, if a small piece of the material is put into a supercooled liquid, or if the liquid is subject to impact on a sudden, it starts being so-

lidified immediately and temperature of the liquid is raised to a freezing point, maintaining a stable equilibrium state at the temperature.

[32] Even if the temperature is lower than the phase transition temperature at this time, the supercooled state can be maintained continuously as long as molecules are allowed to do at least one of the following: rotation, vibration, and translation constantly. In other words, if energy is supplied at the same time with the liquid cooling process (i.e. offsetting the energy absorbed during the cooling process) and to inhibit phase transition from liquid to solid, the liquid phase can be maintained stably for an extended period of time even at temperature lower than the phase transition temperature.

[33] FIG. 1 is a schematic view of the electrode structure of a supercooling apparatus to maintain a normal supercooled state.

[34] Referring to FIG. 1, a casing 1 includes two built-in electrodes 10a and 10b in opposite directions to each other with respect to a storage space Sl of the casing 1. A power supply 2 is also provided to apply high- voltage AC to the electrodes 10a and 10b. When high- voltage AC from the power supply 2 is impressed to the electrodes 10a and 10b, an electric field is created in the storage space Sl between the electrodes 10a and 10b, supplying energy to the storage space Sl.

[35] As a cooling operation takes place in the receiving place(or storage space) Sl according to a cooling cycle (not shown), heat energy is taken out of the receiving place(or storage space) Sl and another kind of energy (i.e. electric field energy) can be supplied instead. This explains how water or moisture-containing food can be kept in the storage space Sl for a long period of time in a stable, cooled state without being solidified or frozen even under the phase transition temperature.

[36] FIG. 2 is a temperature-time graph showing how temperature changes as water gets cooled down in the supercooling apparatus of FIG. 1.

[37] Normally, phase transition occurs if water is cooled down below its phase transition temperature.

[38] For the experiment, O.ll(liter) of distilled water was put into the storage space Sl of the casing 1 shown in FIG. 1, and the electrodes 10a and 10b having a wider surface than the receiving space Sl are arranged on opposite sides of the receiving space Sl. The gap between the electrodes 10a and 10b is 20mm. The casing 1 is made out of an acrylic material, and slid into and cooled down in a refrigerating space (a refrigerating apparatus having no supplementary electric field generator besides the electrodes 10a and 10b) to which chilled air is uniformly dispersed.

[39] The power supply 2 applies 0.9IkV (6.76mA), 2OkHz AC to the electrodes 10a and

10b, and the inside temperature of a refrigerating space is about -7°C.

[40] As can be seen in FIG. 2, by supplying energy in form of the electric field, a su-

percooled state (non-frozen state) can be maintained stably for an extended period of time.

[41]

[42] FIG. 3 shows one embodiment of a supercooling apparatus based on FIG. 1. In particular, the supercooling apparatus of FIG. 3 is an indirect cooling (e.g., fan cooling) type apparatus with a cooling cycle.

[43] The supercooling apparatus is constituted of a casing 110 which has one open side and a storage space A being partially divided by a shelf 130, and a door 120 for opening or closing the open side of the casing 110. A refrigeration cycle 30 of the indirect cooling type super cooling apparatus includes a compressor 32 for compressing a refrigerant, an evaporator 33 for producing chilled air (indicated by arrows) to cool the storage space A or a stored item, a fan 34 for forcibly circulating the produced chilled air, an inlet(or suction) duct 36 for introducing the chilled air into the storage space A, and an outlet(or discharge) duct 38 for leading the chilled air having passed through the storage space A to the evaporator 33. Although not shown, the refrigeration cycle 30 can further include a condenser, a drier, an expansion unit, etc. For the supercooling apparatus, the refrigeration (or cooling) cycle can be embodied based on the direct cooling system as well as the indirect cooling system.

[44] Electrodes 50a and 50b are formed between inner faces 112a and 112c facing the storage space A and the outer faces of the casing 110. The electrodes 50a and 50b are arranged to face the storage space A from opposite sides, so that an electric field can be applied to the entire storage space A. The storage space A is formed between the electrodes 50a and 50b or at the center, being spaced apart from the ends of the electrodes 50a and 50b by a predetermined distance in the inward direction, such that a uniform electric field may be applied to the storage space A or the stored item. Moreover, there is a power supply (not shown) for generating and applying high voltage to each of the electrodes 50a and 50b.

[45] The inlet duct 36 and the outlet 38 are formed in the inner face 112b of the casing

110. In addition, surfaces of the inner faces 112a, 112b, and 112c of the casing 110 are made of a hydrophobic material such that water such as moisture are not frozen during a supercooling mode due to reduction of surface tension of it. Needless to say, the outer faces and the inner faces 112a, 112b, and 112c of the casing 110 are made of an insulating material to protect a user from the exposure to an electric shock generated from the electrodes 50a and 50b and at the same time, to prevent a stored item from coming into a direct electrical contact with the electrodes 50a and 50b via the inner faces 112a, 112b, and 112c. Although the indirect cooling type supercooling apparatus has been illustrated, it is evident that the present invention can be embodied in a direct cooling type supercooling apparatus as well.

[46] FIG. 4 diagrammatically explains a cause of the release of supercooling. A re- ceptacle(or container) 20 contains liquid 40, and sometimes there is a non-contact portion 20a if the receptacle (or container) 20 is not filled up completely with the liquid 40.

[47] The supercooled state is a very unstable state, meaning that the liquid in the supercooled state is subject to the phase transition even by a minor impact to the receptacle 20, entering a solid phase to be more stable even at a temperature below the phase transition temperature. Such impact from outside is called an external disturbance. To maintain the supercooled state, it is necessary to reduce the influence of external disturbances. External disturbances include not only vibration and impact on the liquid 40 being supercooled, but also a sharp change in ambient (or air) temperature. That is, the surface of the liquid 40 may experience a sharp change in temperature in result of the sharp temperature change in the ambient air in contact with the liquid 40, and this is led to the release of the supercooled state of the liquid 40.

[48] Besides the external disturbance, a freezing nucleus is another factor that influence the supercooled state. The freezing nucleus production begins with the development of a solid phase embryo from a melt solution (e.g., supercooled water). Since embroys are in metastable state, they are constantly developed and then destroyed, but some of them grow to a certain size and become stable (they are called crystal nucleuses or freezing nucleuses). A freezing nucleus or crystal nucleus is usually formed at an interface between water and a container. Once a crystal nucleus is formed, molecules of the melt solution bond to the crystal nucleus, making it grow, but this procedure is restricted by heat/mass transfer characteristics. When the crystal nucleus grows to a certain size or bigger, the supercooled melt solution adheres to the crystal nucleus, freezing all over.

[49] For instance, the liquid 40 may be vaporized to make the evaporated gas freeze at the portion 20a. Freezing at this portion 20a produces crystal nucleuses explained earlier, and the supercooled liquid state can be released by them. Therefore, it is important to suppress the formation of freezing nucleuses in order to prolong the supercooled liquid state.

[50] An effective way for preventing the release of a supercooled state caused by external disturbance or freezing nucleus production is to utilize a means that can meet such needs.

[51] FIGS. 5 and 6 are examples of a liquid receptacle. If receptacles (or container) 22 and

24 are provided with a cushioning device to reduce an impact thereto, external disturbance, which is known to cause the release of a non-frozen state, will occur mainly on the surface where liquid does not come in contact with the receptacles. In case of FIG. 5 and FIG. 6, liquid 40 in the receptacles has contact with the receptacles 22 and

24, or air at a liquid inlet area. As described above, if a supercooling apparatus is provided with a cushioning device to reduce impact to the receptacles 22 and 24, the external disturbance to release a non-frozen state will mainly occur at the surface area where the liquid 40 has no contact with the receptacles.

[52] FIG. 5 illustrates the receptacles 22, in which a liquid inlet 22b has a smaller diameter than that of a liquid storage portion 22a. In other words, if receptacles should contain the same volume of liquid, one with a smaller liquid inlet 22b than the liquid storage portion 22a in diameter is more desirable because an area exposed to the action of a possible external disturbance is small, and an area of the liquid 40 on contact with air is reduced. Moreover, an area for the liquid 40 to evaporate and freeze becomes smaller.

[53] FIG. 6 is another kind of the receptacles 24 that has a smaller liquid inlet 24b than a liquid storage portion 24a. In short, a contact area between the liquid and air is made smaller to reduce an area exposed to the action of a possible external disturbance.

[54] Shapes of the receptacles shown in FIGs. 5 and 6 are illustrative only, and receptacles of other shapes can also be used as long as the area exposed to the action of a possible external disturbance is designed small. Nevertheless, provided the same volume of liquid is poured, a round(ed) interior space of the receptacles 22 has a smaller contact area between the liquid and the receptacle, so it can reduce the influence of external disturbance better. As explained with reference to FIG. 5 and FIG. 6, the liquid inlets 22b and 24b narrower than the liquid storage portions 22a and 22b in diameter are advantageous to restrict the contact between air and liquid and to suppress the flow of liquid, thereby inhibiting the external disturbance and the freezing nucleus production.

[55] FIG. 7 shows an embodiment of a supercooling apparatus provided with one of re- ceptacles(or container) illustrated in FIGs. 5 and 6. In particular, FIG. 7 shows a direct cooling type refrigerator, which includes a container 1 for supercooling liquid. This container 1 corresponds to the receptacles 22 and 24 of FIGs. 5 and 6. The supercooling apparatus incorporates a cooling cycle is composed of a compressor 8 for compressing a refrigerant and an evaporator 9 for evaporating the refrigerant, and electrodes 7a and 7b connected to an AC power supply (not shown), at the top and bottom of a compartment, facing each other are included, so as to generate an electric field.

[56] The supercooling apparatus further includes a cover 5 for preventing evaporation of the liquid, a water supply pump 3, and a water supply valve 2. With this configuration, a means for taking energy out of a stored item and a means for supplying less energy than the lost energy to allow water molecules in the stored item to do one of rotation, vibration, and translation movements are able to keep the stored item in a liquid state

below the phase transition temperature. In addition, a shock-absorbing device (not shown) protects the container against vibration and reduces a contact area between air and the liquid, so that external disturbances are suppressed, the possibility of the release of a supercooled state decreases, a supercooled state can be maintained stably for a long period of time even at a lower temperature.

[57] FIGs. 8 and 9 show examples of a container having a blocking member.

[58] FIG. 8 and FIG. 9 are similar in that they are incorporated into a supercooling apparatus provided with electrodes 50a and 50b to generate an electric field therebetween as an energy supply. As discussed earlier, a freezing nucleus is usually produced at an interface between liquid and a container, or an interface between liquid and air. Making the contact area between liquid and air small as in FIG. 5 and FIG. 6 may be one way to suppress the freezing nucleus production, but liquid and air may not come into direct contact with each other at all regardless of the interface.

[59] FIG. 8 is a conceptual view of a supercooling apparatus provided with a blocking member 42 between liquid 40 and air. A container 26 containing liquid 40 includes a container casing 26a, an outlet 26b, and a blocking member 42 to cover the liquid 40 from the top.

[60] In general, when the liquid 40 comes in direct contact with air, its supercooled state can be released by external disturbance, and a temperature difference between liquid and air may produce freezing nucleuses. However, with the blocking member 42, the liquid 40 does not make direct contact with air, so it is less affected by external disturbance, and the freezing nucleus production is inhibited. As explained before, since external disturbance and freezing nucleus production may release a supercooled liquid state, suppressing these two factors makes it possible to prolong a supercooled state in a more stable manner and to maintain the supercooled state at a lower temperature. Apart from this, the outlet 26b, an exit of the liquid 40, permits only the liquid 40 to go out, with or without the blocking member 42 on the liquid.

[61] Preferably, the blocking member 42 has specific gravity lower than that of the liquid

40 to float in contact with the liquid 40. Moreover, the blocking member 42 is preferably made of an insulating material to intercept a sharp temperature change in air. Like the external disturbance, a rapid change in air temperature can release the supercooled liquid state, so it is desirable to make the blocking member 42 out of an insulating material such as styrofoam, and let it float on the liquid 40.

[62] FIG. 9 is a conceptual view of a supercooling apparatus provided with an oil layer 44 between liquid and air. A container 26 containing liquid 40 includes a container casing 26a, an outlet 26b, and an oil layer 44 to cover the liquid 40 from the top.

[63] A freezing nucleus causing the release of a supercooled state is usually produced at an interface between liquid and a container, or an interface between the liquid 40 and

air. If the liquid 40 is water, surface of water can be blocked by the oil layer 44. In this manner, it is possible to prevent the freezing nucleus production resulted from a temperature change between water and air, and thus a supercooled liquid state can be maintained more stably at a lower temperature.

[64] As used in the container of FIG. 8, an outlet 26b for example needs to be formed at a lower area of the container to let the liquid 40 flow out. The oil layer is provided as an example of liquid materials that do not mix with a liquid to be cooled, so other kinds of liquid materials can also be used to intercept the target liquid from air. In case of FIG. 8 or FIG. 9, the blocking member 42 or the oil layer 44 serves to restrict the contact between air and liquid and reduce heat transfer from the air, suppressing external disturbances and the freezing nucleus production. Accordingly, a supercooled liquid state can be maintained more stably at a lower temperature.

[65] It is evident to a person skilled in the art that a supercooling apparatus including the container 26 with the above-described configuration, a cooling cycle composed of a compressor 8 for compressing a refrigerant and an evaporator 9 for evaporating the refrigerant, electrodes 7a and 7b connected to an AC power supply (not shown), at the top and bottom of a compartment, facing each other, so as to generate an electric field, a cover 5 for preventing evaporation of the liquid; a water supply pump 3, and a water supply valve 2 can be advantageously used for the supercooling performance.

[66]

[67] The present invention has been described in detail with reference to the embodiments and the attached drawings. However, the scope of the present invention is not limited to the embodiments and the drawings, but defined by the appended claims.