• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.4 no.2
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• pp.9-14
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• 2008

400RT geothermal system which is consist with vertical-typed 112 geothermal heat exchangers is measured and evaluated in spring, 21st${\sim}$24th May 2008. As the results, the average temperature difference between inlet and outlet of geothermal pipes is $1{\sim}2^{\circ}C$ and that of cool water supply is $2{\sim}6^{\circ}C$, when being normally operated. Despite temperature fluctuations by cooling loads, the average temperature difference between main pipes of inlet and outlet of geothermal heat exchangers is measured as $3^{\circ}C$. The geothermal system COPs are calcluated as 2.92${\sim}$3.92 in every 12 hours.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.11
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• pp.1323-1329
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• 2011

The purpose of study was to analyze how the visual information affects balance control of individuals during single leg stance. A total of 27 young normal people (20 males and 7 females, age: $13.7{\pm}2.6$, height: $162.3{\pm}13.2$ cm, weight: $53.9{\pm}13.9$ kg) was voluntarily involved in the experiment. The subjects were requested to maintain balance for 20 seconds with eyes both open and closed on a force plate and then foot ground reaction data were collected for that duration. Results showed that mean velocity of COP in closed eyes condition was larger 1.84 times than that of the open-eyes condition and range of vertical angle was increased approximately one degree in the closed eyes condition. To accomplish a balance, the frequency power in mediolateral and anteroposterior components of the foot-ground reaction force was increased by 1.3~1.4 times. Consequently, visual absence during single leg stance can result in critical loss of balance and lead to instability of body control.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.3
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• pp.465-473
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• 2002

Screw compressor type chiller is widely used in refrigeration for capacity over 30 RT. To enhance the chiller performance, an economizer which increases the cooling capacity and COP can be adopted. In this study the performance of an economizer is studied by using a simulation program. Simulation results are compared with experiment data to verify the validation of a simulation program. Maximum economizer injection pressure is estimated and the performance of an economizer for various evaporation and condensation temperatures is calculated. From the results, the performance enhancement of an economizer by using R22 and R407C is compared.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.10
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• pp.678-686
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• 2011

Simulation study on the operating characteristics in the solar hybrid R744 heat pump system for residential applications was carried out with heat pump operating temperature, outdoor temperature and solar radiation. As a result, collector operating time is decreased by 1.5 hours due to the increase of water temperature in the heat storage tank when the heat pump operating temperature rises. Heat pump operating time is reduced by 19.4% owing to the high temperature of a heat storage tank. Besides, indoor heating time is decreased from 10.3 to 5.5 hours as the indoor temperature increases from $3^{\circ}C$ to $11^{\circ}C$. In addition to, when the solar radiation rises from 10 to 20 MJ/$m^2$, the maximum outlet temperature of a solar collector is increased from $65^{\circ}C$ to $71^{\circ}C$.

• Journal of Bio-Environment Control
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• v.26 no.4
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• pp.353-360
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• 2017

In this study, the design and performance test of the air to water heat pump capable of producing hot water for greenhouse heating by using the surplus solar heat inside the greenhouse and the air heat outside greenhouse as the selective heat source were conducted. The heat storage operations using the surplus solar heat and the outside air heat were designed to be switched according to the setting temperature of the greenhouse in consideration of the optimum temperature range of the crop. In the developed system, it was possible to automatically control the switching of heat storage operation, heating and ventilation by setting 12 reference temperatures on the control panel. In the selective heat storage operation with the surplus solar heat and outside air heat, the temperature of thermal storage tank was controlled variably from $35^{\circ}C$ to $52^{\circ}C$ according to the heat storage rate and heating load. The heat storage operation times using the surplus solar heat and outside air heat were 23.1% and 30.7% of the experimental time respectively and the heat pump pause time was 46.2%. COP(coefficient of performance) of the heat pump of the heat storage operation using the surplus solar heat and outside air heat were 3.83 and 2.77 respectively and was 3.24 for whole selective heat storage operation. For the comparative experiment, the heat storage operation using the outside air heat only was performed under the condition that the temperature of the thermal storage tank was controlled constantly from 50 to $52^{\circ}C$, and COP was analyzed to be 2.33. As a result, it was confirmed that the COP of the heat storage operation using the surplus solar heat and outside air heat as selective heat source and the variable temperature control of the thermal storage tank was 39% higher than that of the general heat storage operation using the outside air heat only and the constant temperature control of the thermal storage tank.

• Journal of the Korean Wood Science and Technology
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• v.42 no.3
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• pp.309-317
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• 2014

Harvested wood products (HWP) are known as products from the tree such as sawn wood, plywood, particle board, structural lumber, wooden interior material, wooden furniture, and paper products. Because carbon is locked up in the HWP until eventual end-use of HWP, HWP played a role as the carbon storage which has the effect of stabilizing the concentration of carbon dioxide in the atmosphere. For these reasons, the suggestion that it must admit the carbon storage effect of HWP has been constantly raised. In 2011, the 17th session of the Conference of the Parties (COP) to the United Nations Framework Convention on Climate Change (UNFCCC) which was held in Durban, South Africa, assigned "Production Approach" which targets only the HWP producted by using round wood of domestic forestry as a official method for carbon accounting. Therefore, it is necessary that each country has to determine the half-life of wood in order to correspond to the discussions and negotiations between countries in the future and to develop an inventory of product-specific domestic wood. In this study, some countries' examples of the methods and conditions for determining half-life of HWP were investigated, and it was tried to derive the factor and methodology to determine half-life span of domestic HWP appropriately.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.6
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• pp.702-708
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• 2006

This study shows the experimental characteristics of the double pipe inserted liquid pipe with small diameter in the gas pipe with large diameter for circulating of a liquid of high temperature, pressure and a gas of low temperature, pressure at the same time. So the functions of pipe and pipe's expansion and heat transfer are presented simultaneously. In the result, the temperature of gas refrigerant at the inlet of compressor increased about $5^{\circ}C$ by the heat transfer with liquid refrigerant in case of the double pipe. And liquid gas refrigerant which the temperature at the inlet of evaporator decreased about $3^{\circ}C$ comparing with the existing type flows into an evaporator COP of the double pipe increased about $7{\sim}10%$ comparing with that of the conventional pipe. And the noise of the double pipe at capillary tube is less than that of the conventional type about 3dB. Consequently. it is convinced the superiority of the double pipe in the heat loss and soundproofing aspect.

• The Journal of Korean Physical Therapy
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• v.29 no.3
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• pp.142-144
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• 2017

Purpose: Few studies have addressed the effect of diurnal circadian rhythms on postural stability, and thus the aim of the present study was to examine circadian effects on static and dynamic postural stability in young adults. Methods: Twenty-four subjects (9 men, 11 women: age=$22.20{\pm}1.77$, height=$167.20{\pm}10.47$, weight=$59.85{\pm}10.66$) from a university community volunteered for this study. Static and dynamic balance testing, which recorded using a Good Balance system (Good Balance, Metitur Ltd, Finland) was conducted at 9:00, 13:00, and 17:00 hours on two consecutive days, and the sequencing of static and dynamic balance tests were randomized. Results were analyzed using the non-parametric one-way repeated Friedman test in SPSS version 18.0 (SPSS Inc., Chicago, IL, USA), and variable found to be significant were subjected to Wilcoxon post hoc testing. Results: Static and dynamic balance showed significant difference at the three times assessments (test at 9:00, 13:00, and 17:00) during circadian. In the post hoc test of static (anteroposterior distance, mediolateral distance and COP (center of pressure) velocity) and dynamic balance (performance time), 13:00 was the longer and faster than 9:00. Conclusion: These results indicated that control of postural balance is influenced by diurnal circadian rhythms, and confirm that control of postural balance is more effective and better performance in the 09:00 hours than 13:00 hours or 17:00 hours.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.11
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• pp.621-628
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• 2009

The objectives of this study are to analyze the performance of a river water-source heat pump and to carry out economic assessment for the heat pump. The COP of the river water-source heat pump was 3-21% higher than that of the air-source heat pump because river water provides stable operating temperature compared with air temperature throughout the year. The economic analysis was carried out by comparing the initial and operating cost of the river water-source heat pump with those of the conventional air-source heat pump. The ratio of the life cycle operating cost to the life cycle cost increased with the increase of building capacity. The payback period was found to be less than 3.5 years when the capacity of the river water-source heat pump was larger than 10 RT.

• Journal of the Semiconductor & Display Technology
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• v.23 no.2
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• pp.6-11
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• 2024

This paper presents the design and experimental analysis of a cryogenic refrigeration system for -100 ℃, primarily intended for semiconductor etching process. The refrigeration system utilizes non-flammable mixed refrigerant Joule-Thomson refrigeration cycle, incorporating a precooling stage to enhance overall performance. The selected refrigerants for the system include R1234yf for the precooling stage, and Ar, R14, R23 and R218 for the main cooling stage of the Joule-Thomson refrigeration cycle. Design results according to the system constraints and experimental results are discussed, including lowest evaporation temperature, compressor isentropic efficiency and overall pressure tendencies. The achieved refrigerant fraction from optimal design is Ar: R14: R23: R218 = 0.15: 0.4: 0.15: 0.3, indicating COP of 0.1118 at the isentropic compressor efficiency of 50%. The experimental result shows the developed system reaches steady state in approximately 3 hours.