Chaedong Kang

Ice storage system with water–oil mixture: formation of suspension with high IPF

Abstract A new method of forming ice, which is one of the dynamic types of ice storage system, is studied. In the method a water-oil emulsion is cooled with stirring in a vessel and changed into an ice-oil and water suspension. A mixture of 10 vol% silicone-oil and 90 vol% water is emulsified with a small amount of an additive. Silane-couplers are tested as the additive and effects of the additive on ice formation process are investigated. Cooling rate is changed and vessels made of various materials are tested. It is proved that the present method has the following characteristics. Ice–oil and water suspension (slush ice) which has a good fluidity is able to be formed without adhering to the cooling surface. Ice in the suspension is granular and dispersed state and the suspension with more than 70% of ice packing factor (IPF) is also able to be formed. The suspension with the high IPF can be preserved for a long time in the granular state.A new method of forming ice, which is one of the dynamic types of ice storage system, is studied. In the method a water-oil emulsion is cooled with stirring in a vessel and changed into an ice-oil and water suspension. A mixture of 10 vol% silicone-oil and 90 vol% water is emulsified with a small amount of an additive. Silane-couplers are tested as the additive and effects of the additive on ice formation process are investigated. Cooling rate is changed and vessels made of various materials are tested. It is proved that the present method has the following characteristics. Ice–oil and water suspension (slush ice) which has a good fluidity is able to be formed without adhering to the cooling surface. Ice in the suspension is granular and dispersed state and the suspension with more than 70% of ice packing factor (IPF) is also able to be formed. The suspension with the high IPF can be preserved for a long time in the granular state.

Ice storage system with water–oil mixture: formation of suspension with high IPFAccumulation thermique de glace utilisant un mélange d'huile et d'eauavec formation d'une suspension à facteur de compacité élevé

Abstract A new method of forming ice, which is one of the dynamic types of ice storage system, is studied. In the method a water-oil emulsion is cooled with stirring in a vessel and changed into an ice-oil and water suspension. A mixture of 10 vol% silicone-oil and 90 vol% water is emulsified with a small amount of an additive. Silane-couplers are tested as the additive and effects of the additive on ice formation process are investigated. Cooling rate is changed and vessels made of various materials are tested. It is proved that the present method has the following characteristics. Ice–oil and water suspension (slush ice) which has a good fluidity is able to be formed without adhering to the cooling surface. Ice in the suspension is granular and dispersed state and the suspension with more than 70% of ice packing factor (IPF) is also able to be formed. The suspension with the high IPF can be preserved for a long time in the granular state.A new method of forming ice, which is one of the dynamic types of ice storage system, is studied. In the method a water-oil emulsion is cooled with stirring in a vessel and changed into an ice-oil and water suspension. A mixture of 10 vol% silicone-oil and 90 vol% water is emulsified with a small amount of an additive. Silane-couplers are tested as the additive and effects of the additive on ice formation process are investigated. Cooling rate is changed and vessels made of various materials are tested. It is proved that the present method has the following characteristics. Ice–oil and water suspension (slush ice) which has a good fluidity is able to be formed without adhering to the cooling surface. Ice in the suspension is granular and dispersed state and the suspension with more than 70% of ice packing factor (IPF) is also able to be formed. The suspension with the high IPF can be preserved for a long time in the granular state.

Ice storage system using water-oil mixture: Discussion about influence of additive on ice formation process

Ice storage is one technique for effective use of thermal energy. So, many studies on slush ice as a thermal storage material have been done. We have also been studying a suspension (slush ice) made from an oil-water mixture by cooling and stirring. From our study results, it was found that an additive having both an amino group (-NH2) and a silanol group (-SiOH) was essential to form a suspension with high IPF without adhesion of ice to the cooling wall. Moreover, ice particles formed in the suspension were dispersed and granular, and did not stick to each other. In the present paper, we carried out experiments to clarify the characteristics of the suspension formation process. From a thermal analysis of the substance formed in the suspension by difference scanning calorimeter (DSC), it was found that the substance was not ice but a compound of ice and additive. Then, at a very small depression of freezing point (about 7°C) all water in the mixture could be frozen by using the additive.

Natural convection of water–fine particle suspension in a rectangular vessel heated and cooled from opposing vertical walls (classification of the natural convection in the case of suspension with a narrow-size distribution)

Abstract The water–fine SiO2 particle suspension with a narrow-size distribution (mean diameter of 2.97 μm , standard deviation of 0.03 μm ) was heated in a rectangular vessel from a vertical wall and cooled from the opposing vertical wall. Temperature distribution and local particle concentration of the suspension were measured under various temperature differences between the opposing vertical walls. It was found that behaviors of natural convection in the suspension were classified into five patterns. The critical wall temperature difference that would give rise to change of the natural convection pattern decreased as the initial particle concentration decreased.

Continuous ice slurry formation using a functional fluid for ice storage

Abstract A functional fluid composed of an oil–water mixture with an additive is transformed into an ice slurry by cooling while stirring. This paper describes a new continuous ice slurry formation method. Experiments were carried out by varying conditions such as the supply time of functional fluid, the stirrer torque, brine temperature and degree of supercooling. As a result, the characteristics of the ice formation and recovery processes were clarified. It was found that the ice particles gradually became uniform in size and spherical, and grew to 3.5 mm in diameter during about 10 h. The factors influencing the size of formed ice particles were discussed because the larger ice particles were expected to melt more rapidly. The ice particle size was found to increase with decreasing degree of supercooling and cooling rate, and with increasing stirrer wing diameter.

Continuous formation of slurry ice by cooling water-oil emulsion in a tube

Abstract Water-silicone oil emulsion with an additive, (C 2 H 5 O) 3 SiC 3 H 6 NH 2 , was examined as a heat storage material. A spiral tube used as a heat exchanger was immersed in a low temperature bath and the emulsion was circulated in the tube to make ice continuously. Ice was separated from the ice–liquid suspension in an outlet tank. The amount of formed ice, the temperatures of the inlet and the outlet of the heat exchanger, and the temperatures in the tube wall were measured and the overall heat transfer coefficient and the heat flux through the tube were calculated. Experiments were carried out, varying the flow rate, the temperature of cooling brine, and the thickness of tube wall. The condition under which slurry ice was formed continuously without adhesion of ice to the cooling wall was clarified. Though decrease in the thermal resistance of the tube increased the rate of ice formation or raised the brine temperature, it narrowed the range of the flow rate and of the brine temperature in which slurry ice was formed continuously.

Ice formation process by cooling water–oil emulsion with stirring in a vessel

Abstract An emulsion, which was a mixture of silanol-aqueous solution and silicone oil, was investigated as a heat storage material for a dynamic type ice storage system. The emulsion was poured into a vessel, which was immersed into a constant temperature bath at a low temperature, and frozen with stirring. Using stainless steel vessels coated with PFA resin and PTFE vessels with different thickness, the experiments were carried out under various conditions of temperature. Measuring the temperature history in the vessel, overall heat transfer coefficients before the start of freezing and during the ice formation were obtained. The effects of the material of the cooling surface and the thermal resistance of the wall on the ice formation process were clarified. If the heat flux of the wall was less than a critical value, slurry ice was formed without adhesion to the cooling surface. The results obtained under the same condition of the thermal resistance proved that it was effective against ice adhesion to coat PFA resin inside the vessel. It was found by the experiments in which the PTFE vessels were used that the critical value of the heat flux was nearly constant regardless of the thermal resistance.

Non-uniform melting in packed beds of fine ice slurry

Abstract The melting process of packed beds of ice slurry consisting of aqueous solution and ice particles with a mean diameter of 0.2 mm, so-called liquid ice, was studied. The packed ice layer was melted with aqueous solution sprayed on top of it directly and indirectly. Experiments of the melting process were done by changing the mass of ice, the inlet temperature and the flow rate. The time history of the outlet temperature of the bed was measured and the melting phenomenon was observed. During the melting, it was found that passages through the ice layer were formed and the aqueous solution sprayed on the top of the ice layer hardly permeated the ice layer, but flowed through the passages. Assuming that the flow rate of the solution through the passages was known, the melting process was analyzed. In the case of direct spraying, the effects on the outlet temperature and the formation of passage were clarified by changing the initial mass of ice, the flow rate and the inlet temperature. When the solution was sprayed on top of the ice layer directly (direct spraying), the outlet temperature was kept constant because the heat exchange was enhanced by the mixing effects of spraying. On the contrary, when an obstacle was placed on top of the ice layer (indirect spraying), the outlet temperature was higher than that in the case of direct spraying and was not kept constant.

Performance Evaluation of a Defrosting System Using the Condensation Heat of a Refrigerator in Cold Storage

Abstract In a cold chain, the refrigerator is also employed for defrosting, by using an electric heater, which consumes 15%of the power for the system operation. In this study, the condensation heat of the refrigerant was suggested as the heat source of defrosting heat, instead of that from an electric defrost heater. The heat for defrosting was stored to a phasechange material (PCM, NMP ： 52 ℃ ) in thermal storage, and was periodically supplied to the evaporator by a circulationloop of brine. As a result, a defrost time by the PCM was obtained that was less than or equal to that by the electric heater. Moreover, power consumption during defrosting was saved by up to 99% of that of the electric heater. Key words Waste heat(폐열), Defrost(제상), PCM(상변화물질), Heat storage(축열), Cold storage(저온저장)†Corresponding author, E-mail: ckang@jbnu.ac.kr 기호설명 COP ： 성능계수 EHD ： 전기히터 제상(defrost by electric heater)방식 F ： 유량계 [LPM] P ： 압력 [kPa] NMP ： 정상융점(normal melting point)  ： 냉각열전달률 [kW] R COP ： COP 감소 비율

Numerical Study of Heat Transfer with Selective Phase Change in Two Different Phase Change Materials

Abstract A numerical analysis of solid-liquid phase change was performed on a heat transfer module which consisted ofcirculating water path (BRINE), heat transfer plate (HTP) and phase change material (PCM) layers, such as high temperature PCM (HPCM, 78~79°C) and low temperature PCM (LPCM, 28~29°C). There were five arrangements, consisting of BRINE,HTP, LPCM and HPCM layers in the heat transfer module. The time and heat transfer rate for melting/solidification wascompared to their arrangements, against each other. As results, the numerical time without convection was longer than the experimental one for melting/solidification. Moreover, the melting/solidification with the BRINE Ⅰ -LPCM-BRINE Ⅱ - HPCMarrangement was faster(10 hours) than the others; HPCM-BRINE-LPCM, BRINE Ⅰ -HPCM-LPCM-BRINE Ⅱ one. Key words Phase Change Material(PCM: 상변화물질), Solidification(응고), Melting(융해), Phase Change(상변화), Computational fluid dynamics(CFD:전산유체역학)†Corresponding author, E-mail: ckang@jbnu.ac.kr 기호설명 B