• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.3
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• pp.284-291
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• 1997

A hydrogen liquefaction equipment by direct cooling has been designed and built at KIST. Cool-down characteristics and liquefaction performance of the equipment have been investigated. The hydrogen liquefaction equipment consists of a GM refrigerator, a liquefaction velssel, a radiation shield and a cryostat. It is found that the hydrogen starts to be liquefied in the liquefaction vessel after 40~50 minutes of cool-down from the gas state of 270K. The effect of natural convection phenomena of charged gas in liquefaction vessel on the cool-down characteristics is evaluated by comparing with those in vacuum of liquefaction vessel. It is seen that the cool-down time of a liquefaction vessel is substantially increased in vacuum environment of liquefaction vessel. The experiments have been performed for 1~5 atm of hydrogen pressure to investigate the influence of hydrogen pressure on the liquefaction rate and figure of merit(FOM). It is found that both liquefaction rate and FOM are increased as the charged hydrogen pressure is increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.600-609
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• 1998

The experimental investigation of thermal response characteristics by the air flow through the porous media has been carried out. The packed spheres of steel or glass were considered as the porous media in the present study. Temperature distributions of the fluid in the porous media as well as pressure drops through the porous media were measured. The transient temperature variations in the porous media are compared favorably with the analytical results in the high Reynolds number ranges. However, in the low Reynolds number ranges, the experimental data deviate from the analytical results, due to the dominant heat conduction penetration to the upstream direction, which is not considered in the analytical model. The cool-down response of porous media is found to be dependent upon the specific dimensionless time considering the material property and air velocity. The heat discharge process is recommended to be operated until a certain time, considering the cost efficiency.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.100-107
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• 2002

Combustion characteristics of diesel engine depends on mixture formation process during Ignition delay and premixed flame region. Fuel and air mixture formation has a great influence on the exhaust emission. Therefore, the present study focused on the combustion mechanism of Homogeneous Charge Compression Ignition (HCCI) engine. This study was carried out to investigate the combustion characteristics of direct injection type HCCI engine using a visualization engine. To investigate the combustion characteristics, we measured cylinder pressure and calculated heat release rate. In addition, we investigated the flame development process by using visualization engine system. From the experimental result of HCCI engine, we observed that cool flame was always appeared in HCCI combustion and magnitude of cool flame was proportional to magnitude of hot flame. And we also found that fuel injection timing is more effective to increase lean homogeneous combustion performance than intake air temperature. Since increasing the intake air temperature improved fuel vaporization before the fuel atomizes, we concluded that increasing the temperature has disadvantage fur homogeneous premixed combustion.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.23 no.5
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• pp.361-377
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• 1994

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.860-865
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• 2006

The traditional Korean Ondol System that is a radiant floor heating system was made as warm floor and cool indoor temperature. Nowaday, Ondol is developed as the hydronic floor heating system. But unbalance of floor temperature and indoor temperature is occurred bocause strengthen thermal insulation and airtightness in building changes thermal performance. To solve these problems, we examine actual indoor environment of heating system methods in existing apartments and present the new method of floor heating system. The existing heating system made definite indoor temperatures but floor temperatures that is $22^{\circ}C-26^{\circ}C$ was maintained. To solve these problems, we adopted the differential heating system which made warm area and cool area. A differential heating system was made different pitches of heating pipe in single zone and ratio of warm area to cool area is 1 to 2. As a result of experiments, warm area temperature is $40.7^{\circ}C$, cool area temperature is $36.1^{\circ}C$. A difference of temperature between both area is 4K. A distribution of indoor vertical temperature is similar to both warm area and cool area.

• Korean Journal of Food Science and Technology
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• v.30 no.4
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• pp.877-882
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• 1998

To establish optimum drying methods for Korean yam, freeze drying, cool air drying and hot air drying methods were compared by determining some quality criteria. The native color, odor, taste and viscosity of raw yam were preserved by only freeze drying at less than $40^{\circ}C$. The native white color of yam changed to brown and odor and taste of yam decreased largely by cool air drying and hot air drying. Especially cooked and roasted flavor was developed in hot air dried yam. The viscosity of cool and hot air dried yam was about half than that of freeze dried yam. Conclusively freeze drying method was shown optimum to preserve quality properties of yam such as viscosity, color, odor and taste. The physical properties of yam powder such as dispersiveness and solubility was the best in $40{\sim}60{\;}mesh$ particle size.

• Journal of Environmental Science International
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• v.19 no.1
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• pp.81-87
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• 2010

Cool island intensity urban green space was investigated based in Dalsung Park, that is one of the largest parks in Daegu. Cool island intensity(CII), which is defined as the temperature difference between the green space and its surrounding built-up areas, shows time variations. A through-year measurement(2008-2009) of ground level air temperature revealed seasonal variation and relationship to the atmospheric condition of CII. The temperature variation in the park and the reference downtown Daegu was as same order as CII. The noontime CII is larger in summer than that in winter due to the leaf fall of the park trees. On the other hand, seasonal variation of nighttime CII is not so clear. The nighttime CII was larger under the stable atmosphere.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.499-504
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• 2008

Our government will make a plan regulating the cooling limit temperature of the summer season to 26 degree and the heating limit temperature of the winter season to 20 degree for energy saving. Where, the key point of this politic pursuit can be the charge system on heating and cooling cost. We have suggested new cost allocation methodology as a worth evaluation method in the precedent study, and preformed the worth evaluation and cost allocation on four kind of warm air produced from a heating system as an example. In this study, we applied the suggested method to four kind of cooling air as an example, and preformed the worth evaluation and cost allocation on each cooling air. As a result, similarly to the precedent study, the more energy a customer saved, the more heating unit cost decreased, and the more energy a customer consumed, the more heating unit cost increased. From this analysis, we hope that the suggested methodology can offer a theoretical basis to the politic pursuit of government, and induce the spontaneous energy saving of consumers.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.11
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• pp.1089-1096
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• 2001

The cool-down performance after soaking is very important in an automotive air-conditioning system and is considered as the key design variable. Therefore, understanding of the overall transient characteristics of the system is essential to the preliminary design as well as steady-state characteristics. The objective of this study is to develop a computer simulation model and estimate theoretical1y the transient performance of an automotive air-conditioning system. To accomplish this, a mathematical modelling of each component, such as compressor, condenser, expansion valve, and evaporator, is presented first of all. For a detailed calculation, condenser and evaporator are divided into many subsections. Each sub-section is an elemental volume for modelling. In models of expansion valve and compressor, dynamic behaviors are not considered in an attempt to simplify the ana1ysis, but the quasi-static ones are just considered, such as the relation between mass flow rate and pressure drop in expansion device, polytropic process in compressor, etc. The developed simulation model is validated with a comparison to laboratory test data of an automotive air-conditioning system. The overall time-tracing properties of each component agreed fairly well wish those of test data in this case.

• Horticultural Science & Technology
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• v.16 no.1
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• pp.15-17
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• 1998

In order to provide cool night to strawberry plant with cool air and water, an abandoned cool mine was utilized. It's effects on flower induction and fruit yield in 4 different cultivars were examined. After 70 days of transplanting, flowering frequency was below 65% and 100% in control and treatment of night cooling, respectively and regardless of cultivars. Number of flower buds and flower clusters were higher in treated plants compared with the control. Average time until flowering was much less in treated plants. In terms of yield weight and total yield, 'Suhong' was found to be the best cultivar, averaging 24.2g fruit. Cooling contributed to the 6-7 times of increase in total yield within the frame of harvesting times. The fruit were harvested at 80-97 days after transplanting.