• Journal of the Korean Solar Energy Society
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• v.25 no.4
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• pp.85-92
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• 2005

One of the most effective methods for utilizing solar energy is to combine thermal solar and optical energy simultaneously using a hybrid panel. Many systems using various kinds of photovoltaic panels have already been constructed. But utilizing solar energy by means of a hybrid panel with concentrator has not been to be attempted yet. Normally if sunlight is directed on the solar cell, and there is no increase in temperature, the absorption energy of each cell will increase per unit area. In a silicon solar cell. however, cell conversion efficiency decreases according to the increasing temperature. Therefore, to maintain cell conversion efficiency under normal condition, it is necessary to keep the cell at operating temperature. we design and make new hybrid panel with cooling system to prevent increasing of temperature on cell, collect effectively thermal energy. We compared performance of new hybrid panel with PV module and thermal panel. We also evaluated conversion efficiency, electric power and thermal capacity and confirmed cooling effect from thermal absorption efficiency.

• Journal of the Korean Solar Energy Society
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• v.22 no.4
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• pp.85-96
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• 2002

Recently the number of auditoriums such as theaters, assembly halls, and concert halls is increasing in Korea. Auditoriums have generally large space volume, have a high density of occupancy per unit floor area, compared to other buildings. Since they have relatively high ceilings, some heat may stratify above the occupied zone. The under floor air conditioning system, which is set under seats, is frequently selected in an auditorium, because typical air conditioning system where air is supplied from ceilings often causes drafts and unequal temperature distribution. Therefore, this study aims to suggest basic data for air conditioning system design of a middle-sized auditorium. Features and problems of air conditioning system of an auditorium which has about 500 seats are investigated as a case study. In addition, indoor thermal comfort and cooling energy consumption are analyzed with a CFD program and an energy analysis program.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.11
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• pp.874-880
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• 2006

The power density and heat dissipation rate per unit area of the telecommunication equipment have been increased with the technology development in the footprint of telecommunication hardware. A proper heat dissipation method from the PCB module is very important to allow reliable operation of its electronic component. In this study, a hybrid air-conditioner for the telecommunication equipment room was designed to save energy and obtain system reliability. For high outdoor temperatures, the hybrid system operates in the vapor compression cycle, while, for low outdoor temperatures, the hybrid system works in the secondary fluid cooling cycle with no operation of the compressor. The performance of the hybrid air-conditioner was measured by varying outdoor and indoor temperatures. The hybrid air-conditioner yielded 50% energy saving compared with the conventional refrigeration system when the mode switch temperature was $8.3^{\circ}C$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.11
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• pp.570-579
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• 2017

In this study, we examined the multi-stage piston-type air compressors typically used in a railroad vehicle, and the heat transfer efficiency was analyzed according to the design conditions of the heat exchanger (a compressor component module for cooling the compressed high temperature air). For the fin-tube heat exchanger used in the most air compressors, numerical analysis was performed to analyze heat transfer by defining the various rectangle tube sizes and the number of fin-per-unit area as design variables under the same flow rate of compressed air. Also, this analysis compared the temperature of the compressed air. Regarding environmental conditions for analysis, the flow rate of the external cooling air was measured and the mean value of the values was applied. And a "turbulence model" was considered in both the external flow of the cooling air and the internal flow inside the tube. From the results of analysis, it was found that the change of the aspect ratio value of the tube greatly influences the heat transfer efficiency of the compressed air, and influences if the fin density is relatively small. As a result, the optimum design specifications of the heat exchanger for air compressors were confirmed based on the analysis of the heat transfer efficiency, according to the design conditions of fin and tube by the operating temperature range of the compressed air.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6072-6081
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• 2013

In this study, experiments were performed on air heater samples with three different shapes (chevron, wave and dimple type) to reduce the plumes from cooling towers. The tests were conducted for a range of frontal air velocities of 1~3 m/s and water flow rate 0.19~0.33 kg/s. The results showed that the heat transfer rate increased with increasing air velocity or water flow rate. The air-side pressure drop also increased with increasing air velocity. At the same frontal air velocity, the highest heat transfer rate was obtained for the chevron sample (1.5~1.7 times compared to that of the plate sample), followed by the dimple, wave and plate samples. The heat transfer rate per unit power consumption was also 15% larger than that of the dimple sample. On the other hand, there was no noticeable difference between the other samples.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.5
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• pp.439-444
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• 2008

The heat capacity and pressure drop of $CO_2$ and coolant in a multi-tube type gas cooler were investigated experimentally. The main components of the refrigerant loop are a receiver, a $CO_2$ compressor, a mass flow meter, an evaporator and a multi-tube type gas cooler as a test section. The mass flowrate of $CO_2$ and coolant were varied from 0.06 to 0.075 [kg/s], respectively and the cooling pressure of gas cooler were from 8 to 10 [MPa]. The heat capacity of $CO_2$ in the test section is increased with the increment in mass flowrate of coolant, the cooling pressure and mass flowrate of $CO_2$. The pressure drop of $CO_2$ is decreased with the decrease in mass flowrate of coolant and $CO_2$, but decreased with increase in cooling pressure of $CO_2$. The heat capacity of $CO_2$ per unit heat transfer area of gas cooler is greatly high. Therefore, in case of the application of $CO_2$ at the multi-tube type gas cooler, it is expected to carry out the high-efficiency, high-performance and compactness of gas cooler.

• Nuclear Engineering and Technology
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• v.40 no.6
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• pp.467-476
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• 2008

To keep the superconducting (SC) magnet coils of KSTAR at proper operating conditions, not only the coils but also other cold components, such as thermal shields (TS), magnet structures, SC bus-lines (BL), and current leads (CL) must be maintained at their respective cryogenic temperatures. A helium refrigeration system (RRS) with an exergetic equivalent cooling power of 9 kW at 4.5 K without liquid nitrogen ($LN_2$) pre-cooling has been manufactured and installed. The main components of the KST AR helium refrigeration system (HRS) can be classified into the warm compression system (WCS) and the cryogenic devices according to the operating temperature levels. The process helium is compressed from 1 bar to 22 bar passing through the WCS and is supplied to cryogenic devices. The main components of cryogenic devices are consist of cold box (C/B) and distribution box (D/B). The C/B cool-down and make the various cryogenic helium for the KSTAR Tokamak and the various cryogenic helium is distributed by the D/B as per the KSTAR requirement. In this proceeding, we will present the commissioning results of the KSTAR HRS. Circuits which can simulate the thermal loads and pressure drops corresponding to the cooling channels of each cold component of KSTAR have been integrated into the helium distribution system of the HRS. Using those circuits, the performance and the capability of the HRS, to fulfill the mission of establishing the appropriate operating condition for the KSTAR SC magnet coils, have been successfully demonstrated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.771-779
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• 1989

Numerical analysis by SIMPLE algorithm has been performed to predict the characteristics of flow and heat transfer in channels between the printed circuit boards of an electronic cabinet. It is assumed that the electronic parts release uniform heat flux per unit axial length to the cooling air. The air flow between channels is assumed fully developed laminar, incompressible, and mixed convective. In this study, the electronic parts are mounted on both sides of the prinked circuit boards by two kinds of configuration such as the zig-zag and the symmetric one. The Rayleigh numbers ranging from 0 to 10$^{6}$ are considered to predict the characteristics of the main flow and the secondary flow occurred by natural convection, the temperature distribution in channel, the heat transfer rate from heated electronic parts and the increase of friction factor by natural convection. As the results of numerical calculation, several conclusions are drawn as follows. The influence of natural convection on the flow characteristics appears strong when the Rayleigh number is above 10$^{4}$. The main axial flow rate decreases by a half or more at the Rayleigh number of 10$^{6}$ . Although the friction factor increases as Rayleigh number increases, the increasing rate of heat transfer is higher than that of the friction factor. The cooling efficiency of the zig-zig-configuration is superior to that of the symmetric configuration at same Rayleigh number.

• Journal of Chest Surgery
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• v.14 no.4
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• pp.381-387
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• 1981

Fourteen Infants with congenital cardiac anomalies underwent primary surgical Intervention within the first 12 months of life. There were eight patients with ventricular septal defect, two with total anomalous pulmonary venous return [TAPVR], and the remainders with tetralogy of Fallot, transposition of great arteries [d-TGA], Taussing-Bing malformation, and coronary A-V fistula. The age of the patients ranged from 5 to 12 months, with a mean age of 9.9 months. The mean weight was 6.7 Kg [3.8 to 9.5 KS]. Congestive heart failure persisting despite intensive medical treatment was present In 8 patients [56%], and was the most common indication for operation. Early operation was necessary in 5 of these patients [35%], because of failure to thrive and recurrent pulmonary infection. In one patient with TOF, frequent hypoxic spell prompted the necessity for early operation. In cases of VSD, TAP. VR, TOF, and coronary A-V fistula, Intracardiac repair was done with conventional cardiopulmonary bypass, chemical cold cardioplegia, and topical myocardial cooling. Deep hypothermic circulatory arrest with surface induced cooling, followed by core cooling and core rewarming, was employed .for better exposure in the cases of d-TGA and Taussing-Bing malformation. The results were however, not satisfactory. The overall mortality was 28 per cent. There were no deaths in the eight patients with VSD. The one with coronary A-V fistula survived. The other 5 cases all expired either on the table or immediately after operation. The non-fatal post-operative complications included low cardiac output, respiratory insufficiency, bleeding, and temporary A-V block. The causes of death were prolonged circulatory arrest time in d-TGA, complete A-V block and low cardiac output in TOF and Taussing-Bing malformation and prolonged bypass time and Inadequate correction in TAPVR.

• Journal of Chest Surgery
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• v.14 no.4
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• pp.388-398
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• 1981

Fourteen Infants with congenital cardiac anomalies underwent primary surgical Intervention within the first 12 months of life. There were eight patients with ventricular septal defect, two with total anomalous pulmonary venous return [TAPVR], and the remainders with tetralogy of Fallot, transposition of great arteries [d-TGA], Taussing-Bing malformation, and coronary A-V fistula. The age of the patients ranged from 5 to 12 months, with a mean age of 9.9 months. The mean weight was 6.7 Kg [3.8 to 9.5 KS]. Congestive heart failure persisting despite intensive medical treatment was present In 8 patients [56%], and was the most common indication for operation. Early operation was necessary in 5 of these patients [35%], because of failure to thrive and recurrent pulmonary infection. In one patient with TOF, frequent hypoxic spell prompted the necessity for early operation. In cases of VSD, TAP. VR, TOF, and coronary A-V fistula, Intracardiac repair was done with conventional cardiopulmonary bypass, chemical cold cardioplegia, and topical myocardial cooling. Deep hypothermic circulatory arrest with surface induced cooling, followed by core cooling and core rewarming, was employed .for better exposure in the cases of d-TGA and Taussing-Bing malformation. The results were however, not satisfactory. The overall mortality was 28 per cent. There were no deaths in the eight patients with VSD. The one with coronary A-V fistula survived. The other 5 cases all expired either on the table or immediately after operation. The non-fatal post-operative complications included low cardiac output, respiratory insufficiency, bleeding, and temporary A-V block. The causes of death were prolonged circulatory arrest time in d-TGA, complete A-V block and low cardiac output in TOF and Taussing-Bing malformation and prolonged bypass time and Inadequate correction in TAPVR.