• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.57-61
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• 2015

A Superconducting Fault Current Limiter is an electric power device which limits the fault current immediately in a power grid. The SFCL must be cooled to below the critical temperature of high temperature superconductor modules. In general, they are submerged in sub-cooled liquid nitrogen for their stable thermal characteristics. To cool and maintain the target temperature and pressure of the sub-cooled liquid nitrogen, the cryogenic cooling system should be designed well with a cryocooler and coolant circulation devices. The pressure of the cryostat for the SFCL should be pressurized to suppress the generation of nitrogen bubbles in quench mode of the SFCL. In this study, we tested the performance of the cooling system for the prototype 154 kV SFCL, which consist of a Stirling cryocooler, a subcooling cryostat, a pressure builder and a main cryostat for the SFCL module, to verify the design of the cooling system and the electric performance of the SFCL. The normal operation condition of the main cryostat is 71 K and 500 kPa. This paper presents tests results of the overall cooling system.

• 동력기계공학회지
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• 제8권1호
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• pp.41-47
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• 2004

Cooling towers are widely used not only for cooling products and equipment in manufacturing process but HVAC(Heating, Ventilation and Air Conditioning) system. As a cooling tower is the terminal apparatus which discharges heat from industrial process, the efficiency of heat exchange in the cooling tower greatly affects to the overall performance of a thermal system. In this paper, we constituted a new water cooling system by using a Latent heat of evaporation in an enclosed tank, and this system is consisted of an enclosed vacuum tank and water driven ejector system. Several experimental cases were carried out for improvement methods of high vacuum pressure and water cooling characteristics. The ejector performance was tested in case of water temperature variations that flows into the ejector. Based on the vacuum pressure by water driven ejector, the water cooling characteristics were investigated for the vaporized air condensing effects.

• International Journal of Aerospace System Engineering
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• 제1권1호
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• pp.1-9
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• 2014

In this paper, the effects of the anti-vortex hole angle and blowing ratio on the flat plate film cooling effectiveness were experimentally investigated. For the film cooling effectiveness measurement, pressure sensitive paint technique was applied. The experiments were conducted for cylindrical and anti-vortex film cooling holes, and three blowing ratios of 0.25, 0.5, and 1.0 were tested. Two anti-vortex hole angles of 0 and 15 degree with respect to the flow direction were considered. For the cylindrical hole case, the film cooling effectiveness decreased as the blowing ratio increased because of the coolant lift-off. For the angle anti-vortex hole cases, however, higher blowing ratio resulted in higher film cooling effectiveness due to the reduced actual blowing ratio and diminished kidney vortex. For all blowing ratio, the angled anti-vortex hole case showed the highest film cooling effectiveness.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2907-2912
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• 2007

The cooling water system for the PEFP 20 MeV proton accelerator was established and tested to obtain the precise resonance frequency of DTL through the temperature control of cooling water. The water temperature in the main flow loop was manipulated by adjusting the proportion of hot water returning from the DTL structures through the heat exchanger loop. Due to low duty factor operation and insufficient cooling loop installation of the DTL tanks, the manual mode operation was applied to maintain the DTL temperatures close to their resonance temperatures. The optimized process conditions with flow balancing and pressure drop in the DTL cooling systems are reported.

• 설비공학논문집
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• 제1권2호
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• pp.116-127
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• 1989

Research on reheating cooling cycle and its practical application have been made to prevent unequalized distribution of temperature and humidity of room due to lack of supply air volume and dewdrops on supply diffusers to be taken place as a result of lower temperature of supply air than that of dew point of room air in cooling cycle of constant air volume, single duct, single zone and draw-through fan type. In view of the fact that human body is insensitive to humidity, it is possible not only to construct the complete non-reheating cooling cycle by increasing the humidity point allowable with the deduction of occupant's sense of pleasantness minimizing, but also to get cooling cycle decreasing the reheating quantity if the humidity exceeds the point allowable. In addition, it is possible to save maximum 8% in electric energy for cooling in cooling system by constructing non-reheating cooling cycle instead of reheating cooling cycle and by increasing the relative humidity of room from 50% to 65% in case efficiency and air pressure of cooling system are low. It is also possible to get an optimum cooling cycle by determining the room humidity in consideration of pleasantness of occupants and conservation rate of electric energy if the cooling capacity, efficiency and total pressure of cooling equipment are fixed.

• 생물환경조절학회지
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• 제20권1호
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• pp.1-7
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• 2011

토마토 재배용 상엽용 온실의 여름철 냉방에 최근 국내에서 개발된 저압분무식 포그냉방시스템을 사용하기 위한 시스템 설치 및 관리기술을 규명하기 위하여 저압 포그시스템을 온실에 설치하여 실험을 통하여 그 적용 가능성을 분석하였으며 결과를 요약하면 다음과 같다. 포그를 분사한 온실이 분사하지 않은 온실보다 온도가 더 낮은 값을 보여 포그분사에 의한 냉방효과가 있음을 확인할 수 있었다. 그러나 전체적으로 상대습도가 비교적 낮게 나타나 냉각효과를 충분히 얻지 못한 것으로 판단되며, 포그노즐의 설치간격을 더 줄이거나 포그분사 시간을 더 늘리는 등의 조정을 통해서 충분한 냉방효과를 얻을 수 있을 것으로 판단되었다. 온실 전체의 시간에 따른 온도분포는 짧은 시간 동안에는 온도분포의 큰 변화는 없었으나 하루의 긴 시간 동안에는 온도분포의 변화가 다소 크게 나타났다. 이는 포그분사에 따른 온도편차의 발생은 크지 않으나 일사, 공기유동 등 다른 환경요인들에 의해 발생된 편차가 큰 것으로 판단된다. 특히 본 자료에는 나타내지 않았지만 온실 하부에서의 수평방향의 온도편차는 더 크게 나타나는 경향이 있었기 때문에 온도편차를 줄일 수 있는 포그시스템 관리방안에 대한 연구가 필요할 것으로 판단되었다. 앞으로 추가 실험을 통해 자연환기 토마토재배온실의 냉방을 위한 저압포그시스템 설치 및 관리기술을 제시하고자 한다.

• Journal of Biosystems Engineering
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• 제36권5호
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• pp.319-325
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• 2011

This study was conducted to figure out the diagnosis basis of cooling performance depending on water amount in the refrigerant of air conditioner, which can be estimated by the temperatures and pressures along the refrigerant circulation line. A car air conditioner of SONATA III (Hyundai motor Co., Korea) was tested at maximum cooling condition at the engine speed of 1500 rpm in the room controlled at 33~$35^{\circ}C$ air temperature and 55~57% relative humidity conditionally. Measured variables were temperature differences between inlet and outlet pipe surfaces of the compressor, condenser, receive drier and evaporator; and high pressure and low pressure in the refrigerant circulation line; and temperature difference between inlet and outlet air of the cooling vent of evaporator. In this study, changes of the water amount in the refrigerant were correlated to the temperatures and pressure changes and also water amount caused poor cooling performance. As water amount increased in the refrigerant in the air conditioner, the performance of the cooling or the heat transfer became worse. Temporal variations of the surface temperature of the evaporator outlet pipe and the low-side pressure showed various patterns that could estimate the water amount. When the water amount caused bad cooling performance, the patterns of the temperature of the evaporator outlet pipe indicated irregular fluctuation greater than $5^{\circ}C$. When the diagnosis system is using just external sensors of the low-side pressure and the temperatures of inlet and outlet air of cooling vent of the evaporator, the precise pattern of bad cooling performance caused by excess water amount in the cooling line was irregular pressure fluctuation, 25 kPa under 120 kPa, and temperature, $12^{\circ}C$ and less.

• 대한기계학회논문집B
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• 제28권4호
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• pp.415-424
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• 2004

Cooling the electronic equipment is one of the major focal points of the design process and the key to successful product launch. The two-phase loop thermosyphone which is a good candidate among many available options was investigated fur cooling of the high power amplifiers. The system is composed of evaporator which contains 6 parallel cold plates, fan cooled condenser, gas-liquid separator, and interconnecting tubes. Experiments were performed for several refrigerant charging values, hs and as a experiment result, the optimum charging value fur this system was proposed. In order to optimize the system design, the operating cycle pressure and inlet/outlet temperatures of evaporator and condenser are measured and analyzed. The effect of the three parameters such as flow rate and temperature of condenser cooling air, and thermal load on the evaporator are investigated. The lower the operating pressure and the cycle temperatures are also better to prevent the leakage of the system. The system invesigated in this paper can be directly used for cooling of a real unmanned wireless communication station.

• 설비공학논문집
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• 제12권3호
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• pp.251-257
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• 2000

District heating and cooling systems offer highly efficient energy utilization and maintenance by centralizing heat management. More pumping power, however, is required because the water has to travel long distance from heat source to the users. In the present study, a trace of drag reduction additives is added to the District Cooling system to achieve a significant drag reduction and save pumping power. Water-soluble polymers, surfactants, and environment-friendly degradable polymers are used as effective drag reducing additives. Time dependent percent drag reductions are compared for various additive solutions at 100 wppm concentration for different water velocity. Without as an anionic surfactant, copolymer was most effective in percent drag reduction. It is found that there exists an optimal condition when copolymer is mixed with SDS. An environment-friendly degradable polymer, xanthan gum, is found to be a significant drag reduction additive. Ice slurry systems, can give less pressure drops compared with chilled water system for certain condtions. Drag reduction additives were also effective for the ice slurry system.

• Journal of Biosystems Engineering
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• 제21권1호
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• pp.44-51
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• 1996

The purpose of this paper is to obtain the basic data for design of pressure cooling system. Static pressure drop, as a function of superficial velocity, was measured for different stacking methods and stacking heights of some fruits and vegetables. At given superficial velocity, sphericity and void fraction had a much greater influence on static pressure drop than average diameter of spherical fruits such as apple, peach, tomato and kiwi fruit. Among cylindrical vegetables such as cucumber, carrot, radish and chinese cabbage, cucumber showed different pattern of static pressure drop because of its bended shape, radish showed less static pressure drop than other vegetables because its large sizes of voids. When cucumber and spinach were stacked vertically and horizontally to air flow, a much greater static pressure drop was shown in vertical than in horizontal type, therefore static pressure drop was affected not only by void fraction but also by void shape. Also, in packed-beds of fruits and vegetables, static pressure drop could be estimated very well by Ramsins equation.