• KIEAE Journal
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• 제16권6호
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• pp.109-114
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• 2016

Purpose: The underground air is the warm air discharged from the porous volcano bedrock 30-50m underground in Jeju, including excessive humidity. The temperature of the underground air is $15-20^{\circ}C$ throughout the year. In Jeju, the underground air was used for heating greenhouses by supplying into greenhouses directly. This heating method by supplying the underground air into greenhouses directly had several problems. The study was conducted to develop the heat pump system using underground air as heat source for resolving excessive humidity problem of the underground air, adopting the underground air as a farm supporting project by Ministry of Agriculture, Food and Rural Affairs(MAFRA) and saving heating cost for agricultural facilities. Method: 35kW scale(10 RT) heat pump system using underground air installed in a greenhouse of area $330m^2$ in Jeju-Special Self-Governing Province Agricultural Research & Extension Services, Seogwipo-si, Jeju. The inlet and outlet water temperature of the condenser, the evaporator and the thermal storage tank and the underground air temperature and the air temperature in the greenhouse were measured by T type thermocouples. The data were collected and saved in a data logger(MV200, Yokogawa, Japan). Flow rates of water flowing in the condenser, the evaporator and the thermal storage tank were measured by an ultrasonic flow meter(PT868, Panametrics, Norway). The total electric power that consumed by the system was measured by a wattmeter(CW240, Yokogawa, Japan). Heating COP, rejection heat of condenser, extraction heat of evaporator and heating cost were analyzed. Result: The underground air in Jeju was adopted as a farm supporting project by Ministry of Agriculture, Food and Rural Affairs(MAFRA) in 2010. From 2011, the heat pump systems using underground air as a heat source were installed in 12 farms(16.3ha) in Jeju.

• Journal of Advanced Marine Engineering and Technology
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• 제10권2호
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• pp.156-164
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• 1986

In the case of boiling on high temperature wall, vapor film covers fully or parcially the surface. This phenomenon, film boiling or transition boiling, is very important in the surface heat treatment of metal, design of cryogenic heat exchanger and emergency cooling of nuclear reactor. Mainly supposed hydraulic-thermal accidents in nuclear reactor are LCCA (Loss of Coolant Accident) and PCM (Power-Cooling Mismatch). Recently, world-wide studies on reflooding of high temperature rod bundles after the occurrence of the above accidents focus attention on wall temperature history and required time in transient cooling process, wall superheat at rewet point, heat flux-wall superheat relationship beyond the transition boiling region, and two-phase flow state near the surface. It is considered that the further systematical study in this field will be in need in spite of the previous results in ref. (2), (3), (4). The paper is the study about the fast transient cooling process following the wall temperature excursion under the CHF (Critical Heat Flux) condition in a forced convective subcooled boiling system. The test section is a vertically arranged concentric annulus of 800 mm long and 10 mm hydraulic diameter. The inner tube, SUS 304 of 400 mm long, 8 mm I.D, and 7 mm O.D., is heated uniformly by the low voltage AC power. The wall temperature measurements were performed at the axial distance from the inlet of the heating tube, z=390 mm. 6 chromel- alumel thermocouples of 76 .mu.m were press fitted to the inner surface of the heating tube periphery. To investigate the heat transfer characteristics during the fast transient cooling process, the outer surface (fluid side) temperature and the surface heat flux are computed from the measured inner surface temperature history by means of a numerical method for inverse problems of transient heat conduction. Present cooling (boiling) curve is sufficiently compared with the previous results.

• 한국추진공학회지
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• 제15권6호
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• pp.56-62
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• 2011

본 연구에서는 과산화수소와 케로신을 사용하는 소형 이원추진제 액체로켓엔진의 점화원으로서, 과산화수소의 촉매 반응에 의한 고온의 분해 가스와 케로신의 자연 발화를 이용하는 촉매형 점화기에 대한 연구를 수행하였다. 먼저 점화기를 설계하기 위해 열역학적 상용코드프로그램인 CEA를 사용하여 점화기 유량 및 혼합비를 선정하고 촉매형 점화기를 설계/제작하였으며, 점화 성공 및 지연 등을 판단하기 위한 가시화창과 분해 가스의 온도 분포를 파악하기 위한 열전대 장착이 가능한 연소실을 설계제작하였다. 분해 가스 유속을 결정하는 고정링(fixed ring)의 출구 면적 변화와 혼합비 변화에 따른 점화 성능 시험을 수행하였다. 결과적으로 쵸킹 면적보다 큰 출구 면적에서와 혼합비 6~8 사이에서 안정적인 점화 성능을 보임을 확인하였다.

• 태양에너지
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• 제17권1호
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• pp.3-15
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• 1997

본 연구는 R-12($CF_2Cl_2F$) 대체냉매인 R-134a($CF_3CH_2F$) 적용 태양열 열펌프시스템에 의하여 학교교실($20{\sim}25$평형)이나 학교 화장실($13{\sim}17$평형)의 난방에 관한 것으로서 대체냉매 적용할 때 시스템의 안정성과 성능에 관해 실험되어졌다. 학교교실 난방을 위한 방법 중에서 온풍난방을 택하여 실험하였는데 대체냉매 적용 실제와 모형시스템의 난방성능을 비교 해석하였다. 이 결과를 근거로 R-22($CHClF_2$)와 그 대체냉매들에 대한 성능을 예측하였다. 서울지방 봄 가을철, 겨울철의 외기 온도에서 실내온도가 $18{\sim}20^{\circ}C,\;23{\sim}25^{\circ}C$로 유지할 수 있도록 설계 제작되었다.

• 한국철도학회논문집
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• 제9권3호
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• pp.291-297
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• 2006

The present study investigated the effect of fire suppression using a mid-low pressure water mist in a carriage fire. The fire extinguishing time and temperature distributions below ceiling in the enclosed compartment of $2.9m{\times}2.8m{\times}5.0m$ were measured by stopwatch and k-type thermocouples for various fire positions. The numerical simulations were extensively performed using. Fire Dynamics Simulator(FDS, Ver. 4.0) code and the predictions were compared with experimental data. The prediction results showed good agreement with the measured maximum temperature in the all cases. Whereas the predicted temperature was about $40^{\circ}C$ higher than the measured one after operating of water mist. The predicted fire extinguishing times were compared with those of measured data. Fires are extinguished within 200 seconds at the experiment in Case 2 and Case 3. But in Case 1 fire was not extinguished in the numerical simulation. The reason of the discrepancy between predicted and measured data was that a simple suppression algorithm has been implemented in FDS. Also, various databases of fire properties for combustible materials and more elaborate model considering the water mist were required fur better predictions of the cooling and suffocation effect.

• 공업화학
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• 제19권6호
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• pp.680-684
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• 2008

Silica sand 내에서의 메탄 하이드레이트($CH_4$ hydrate)의 형성과 분해는 $7.0^{\circ}C$의 온도에서 실험되었다. Silica sand 내에서 형성되는 메탄 하이드레이트의 형성 및 분해 특성을 연구하기 위해 새로운 반응기를 제작하였다. Silica sand bed 내에서 메탄하이드레이트의 형성과 분해되는 동안의 온도변화에 대한 연구를 위해 반응기 내의 주입한 silica sand 높이에 따라 열전대의 위치를 다르게 설치하여 실험하였다. 반응기 내에 가해지는 압력과 온도는 메탄 하이드레이트의 형성과 분해를 발생시키는 요인이다. 메탄 하이드레이트 형성을 위한 가스 흡착곡선과 분해실험을 위한 가스 발생곡선은 실험데이터로부터 결정되었다. 8 MPa의 압력에서 $7.0^{\circ}C$의 온도에서 메탄 하이드레이트 형성 실험을 수행한 결과 70%의 메탄이 하이드레이트로 전환됨을 알 수 있었다. 형성된 메탄 하이드레이트의 분해에 의한 메탄의 회수율은 82%였다.

• Tribology and Lubricants
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• 제34권2호
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• pp.43-48
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• 2018

This paper presents the thermohydrodynamic analysis of tilting journal pad bearings supporting a power turbine rotor applied to a 250 kW super-critical $CO_2$ cycle. In the analysis, the generalized Reynolds equation and 3D energy equation are solved to predict oil film temperature and the 3D heat conduction equation is solved for pad temperature. The power turbine rotor is supported by two tilting pad bearings consisting of five pads with an oil supply block between the pads. Copper backing pads with higher thermal conductivity compared to steel backing pads are adopted to improve thermal management. The predicted maximum pad temperature is around $55^{\circ}C$ which is approximately $15^{\circ}C$ higher than oil supply temperature. In addition, the predicted minimum film thickness is 50 mm at a rotating speed of 5,000 rpm. These results indicate that there is no issue in the thermal behavior of the bearing. An operation test is performed with a power turbine module consisting of a power turbine, a reduction gear and a generator. Thermocouples are installed at the 75% position from the leading edge of the pad to monitor pad temperature. The power turbine uses compressed air at a temperature of $250^{\circ}C$ in its operation. The steady state pad temperatures measured in the test show good agreement with the predicted temperatures.

• Asian-Australasian Journal of Animal Sciences
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• 제12권6호
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• pp.886-890
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• 1999

From previous studies, there is a strong possibility in buffaloes that the marked increase in blood volume (BV) under hot conditions contributes to heat transportation from the rectum to the skin. The present study was done to clarify changes with environmental temperature on water-shift between blood and extracellular fluid (ECF), heat distribution between the rectum and the skin, and blood flow rates (BFR) at the hind legs (reflecting the skin surface). Four buffaloes and four Friesian cows were successively exposed to three different temperatures of $20^{\circ}C$, $30^{\circ}C$ and $35^{\circ}C$. BV and ECF volume were measured with Evans' blue and sodium-thiocyanate dilution methods, respectively. Rectal and subcutaneous (as the skin) temperatures were measured by copper-constantan thermocouples. BFR were measured by a supersonic blood flow meter. With an increase in environmental temperature, skin temperature in buffaloes increased significantly than cows, but rectal temperature was not significantly different between two species. BV, especially plasma compartment, increased significantly in only buffaloes, while ECF volume did not change in both species. BFR increased significantly in buffaloes, but not in cows. From these results, the increased of BV may be caused by water flowing from ECF compartment. The water-shift may induce the increase of BFR and skin temperature. It is suggested in the present study that internal changes of blood compartment in buffaloes contribute to transfer of heat to the skin surface.

• 한국음향학회지
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• 제14권6호
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• pp.13-20
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• 1995

본 논문에서는 열음향 냉장시스템을 실제로 설계, 제작하고 그 동작을 확인하였다. 제작된 시스템은 4인치의 중음부 스피커로 구동되며 스피커 하우징, 챔버, 스택하우징, 스택, 열교환기, 가는관, 그리고 공명구로 구성되었으며 내부에 10기압의 He을 채워 실험하였다. 실행 중 온도하강측정을 위하여 T 타입의 열전쌍을 열교환기에 부착하였고, 내부음압측정용 콘덴서 마이크로폰을 장착하였다. 스피커의 열손상을 막고 고온 열교환기를 냉각시키기 위하여 냉각수를 공급하였다. 실제 실험을 위하여 제작된 열음향기관의 전기적인 임피던스를 측정하여 공진특성을 파악하였는데, 실험 결과 설계치와는 약간 다르게 340Hz로 구동하는 것이 효율적이었다. 이러한 해석을 기초로 실제 냉장실험을 수행한 결과 $30^\circ{C}$의 조건하에서 340Hz, 50W로 구동하였을 때 $16^\circ{C}$의 냉장효과를 관찰하였다. 관찰된 냉각효과와 설계치의 차이를 규명하기 위하여 제작된 열음향기관의 미비점을 고찰하였는 바, 냉각부의 단열이 제일 중요한 문제임을 파악하였으며 그외의 보완이 필요한 사항은 이후의 진행될 연구의 과제로서 제시하였다.

• 대한기계학회논문집B
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• 제25권5호
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• pp.722-730
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• 2001

The local heat transfer of an axisymmetric submerged air jet impinging on a heated flat plate is investigated experimentally with the variation of mesh-screen solidity. The screen installed in front of the nozzle exit modifies the flow structure and local heat transfer characteristics. The mean velocity and turbulence intensity profiles of streamwise velocity component are measured using a hot-wire anemometry. The temperature distribution on the heated flat surface is measured with thermocouples. The smoke-wire flow visualization technique was employed to understand the near-field flow structure qualitatively for different mesh screens. Large-scale toroidal vortices and high turbulence intensity enhance the heat transfer rate in the stagnation region. For a higher solidity, turbulence intensity become higher which increases the local heat transfer at small nozzle-to-plate spacings such as L/D<6. The local and average Nusselt numbers of impinging jet from the $\sigma$(sub)s=0.83 screen at L/D=2 are about 5.6∼7.5% and 7.1% larger than those for the case of no screen, respectively. For the nozzle-to-plate spacings larger than 6, however, the turbulence intensities for all tested screens approach to an asymptotic curve and the mean velocity along the jet centerline decreases monotonically. As the nozzle-to-plat spacing increases for high solidity screens, the heat transfer rate decreases due to the reduction in turbulence intensity and jet momentum.