• Journal of Industrial Technology
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• v.21 no.A
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• pp.33-40
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• 2001

Heat loss from the trapezoidal fins haying different upper side slope and that from a rectangular fin are investigated by the three dimensional analytic method. It is shown that the trapezoidal fins having different upper side slope become an approximate rectangular fin by inst adjusting the slope factor. The comparison of the heat loss between a rectangular fin and an approximate rectangular fin is represented as a function of the non-dimensional fin length, fin width and Biot number to make sure that the analysis on the trapezoidal fins having different upper side slope is countable. One of the results is that the relative value of heat loss between a rectangular fin and an approximate rectangular fin is less than 1.5% for given ranges of non-dimensional length and width in case of Bi = 0.1.

• Journal of Energy Engineering
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• v.26 no.3
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• pp.71-77
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• 2017

In the event of loss of coolant accident (LOCA) and station black out (SBO) in the primary system of a nuclear reactor, the coolant water should be injected to reactor coolant system (RCS) without any intervention of operators or active components. To satisfy the requirements, hybrid safety injection tank (Hybrid SIT) was suggested by Korea Atomic Energy Research Institute (KAERI). The pressure equalizing time of Hybrid SIT is an important parameter to determine the timing of coolant injection. To predict the pressure equalizing time of the Hybrid SIT, a separate effect test facility was constructed and sensitivity tests were conducted in various conditions. The main parameter determining the pressure equalizing time was obtained from separate effect test (SET) results. The wall of condensation on the inner wall of SIT and direct contact condensation on the water surface affected to the pressure equalizing time very much. In this study, the effect of each condensation phenomena on pressure equalizing time was quantitatively analyzed from results of SET and a prediction method of pressure equalizing time was proposed.

• Bulletin of Food Technology
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• v.15 no.2
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• pp.107-111
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• 2002

초고압 가공처리는 별동의 화학 보존제를 사용하지 않고도 저온에서 식품유래 미생물을 사멸시킬 수 있기 때문에 식품분야에서 주목받는 새로운 가공기술이다. 이러한 초고압 처리의 장점 덕분에 관능적 특성이 우수하고 영양성분이 그대로 보존되는 고품질 식품의 제조도 가능하다. 고압 조건에서의 미생물 사멸정도를 측정하기 위해서는 흔히 실험실 규모의 장비(그림 1)을 사용하여 소량의 미생물 접종액을 처리함으로서 대량 처리시(그림 2)의 양상을 예측할 수 있다. 초기에 개발된 실험실 귬의 초고압 처리장비에는 일반적으로 고압용기 내부에 온도감지 장치가 부착되어 있지 않아, 압력 조건 하에서의 압축발열 및 순간 감압냉각 효과가 제대로 보고되지 않았다. 그러나 가열효과를 고려하지 않으면 초고압 처리기 특유의 가압 특성 대문에 실험 결과의 재현성을 얻기가 힘들고, 특히 대용량 생산설비의 경우 더욱 그러하다. 이론적으로 초고압 처리는 매우 예측 가능한 공정이다. 즉 고압요기 내부에서는 어느 지점이던 간에 압력이 고르게 분포되고, 가열 확산에 근거한 처리공정과는 달리 압력이 모든 지점에 순간적으로 공정상 불균일이 야기될 소지가 있는 부분은 오직 압축에 다른 발열과 열 전달에 의한 온도 편차에 기인한다. 실제로 처리 대상 제품과 압력 전달매체의 압축시 발열정도 차이와 시료, 매체, 고압용기 간의 열 손실 또는 열 흡수 대문에 고압처리 공정에서 온도가 일정하지 않을 수 있다.

• Solar Energy
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• v.18 no.3
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• pp.63-69
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• 1998

The heat conduction and the water vapour diffusion flow through heat insulators between hygroscopical moist building materials were measured by means of the plate method. It was found that the heat transport increases with a moisture motion occuring in the temperature drop. On his basis of simplified assumptions, the increase in the thermal conductivity was calculated from the rate of diffusion flow per unit area, which generally resulted in values inferior to the measured values. The Increase in the heat transport due to water vapour diffusion measured at a large-scale wall specimen was inferior to the one measured by means of the plate method by using a comparable arrangement of layers. The overall heat transfer caused by moisture motion is not a characteristic value of the material, but a property of the whole wall structure

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.5
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• pp.305-310
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• 2009

The amount of heat loss of a refrigerator through the gasket is nearly 30% of total refrigerator heat loss. In this paper, quantitative evaluation analysis of heat loss through gasket is established with numerical heat transfer analysis. Extending the gasket shape to protect the heat loss from the gasket, power consumption is measured by using real refrigerator in a temperature and humidity chamber and suggest the gasket shape to reduce the heat loss. From the present result of the numerical simulation of heat transfer and experiment with varying gasket shape, we are able to reduce the heat loss about 20-40% by using extended gasket and the power consumption can be reduced about 5%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.351-358
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• 2008

Extinction characteristics of hydrogen-air diffusion flames at various pressures are investigated numerically by adopting counterflow flame configuration as a model flamelet. Especially, effect of radiative heat loss on flame extinction is emphasized. Only gas-phase radiation is considered here and it is assumed that $H_2O$ is the only radiating species. Radiation term depends on flame thickness, temperature, $H_2O$ concentration, and pressure. From the calculated flame structures at various pressures, flame thickness decreases with pressure, but its gradient decreases at high pressure. Flame temperature and mole fraction of $H_2O$ increase slightly with pressure. Accordingly, as pressure increases, radiative heat loss becomes dominant. When radiative heat loss is considered, radiation-induced extinction is observed at low strain rate in addition to transport-induced extinction. As pressure increases, flammable region, where flame is sustained, shifts to the high-temperature region and then, shrunk to the point on the coordinate plane of flame temperature and strain rate. The present numerical results show that radiative heat loss can reduce the operating range of a combustor significantly.

• Journal of Energy Engineering
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• v.23 no.2
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• pp.207-216
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• 2014

The energy loss can be divided into the loss caused by heat transfer and the loss caused by air flow. Heat transfer is the loss resulting from the heat transmittance of external wall, roof, and floor, and represents one of the most vulnerable elements of existing buildings. To prevent such loss, it is necessary to increase the mean heat transmittance of entire external wall, including the window, to a level above the standard regional value and ensure the air-tightness of window. The old buildings have the structure which is prone to the loss of greater air flow due to the air infiltration through the exit/entrance door upward along the stairway by the stack effect and simultaneous suction of air from each floor, and becomes even vulnerable to the loss of heat insulation for each floor, although the external wall and windows are the most vulnerable parts. The improvement plans for each floor need to be submitted in tandem with the diagnosis of whole building, regarding the diagnosis plan and energy improvement measures based on the survey of site, rather than adhering to the misconception that the replacement of window alone will result in energy-savings.

• Solar Energy
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• v.15 no.3
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• pp.119-125
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• 1995

Since the using of heating energy associated with infiltration is significant in a building, the efforts to minimize the infiltration while ensuring minimum ventilation rates for various types of occupancy will be beneficial. In constrast to that many efforts have been made to reduce heat loss by improving thermal resistance of building envelope, little has been tried to reduce heat loss from infiltration. For achieving such an objective, measurement of air leakage rate will be pre-requisite as a diagnostic tool. A blower door system, a depressurization/pressurization method, was employed and it demonstrated a good potential for measuring airtightness performance of residential buildings. Based on the test results, annual energy savings for residential heating was estimated by reducing infiltration to a level of reasonably airtight or to a level of ASHRAE Standard 62-1989 for minimum ventilation.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.2 s.17
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• pp.32-40
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• 2004

In this paper, a simulation model for FLAS(Fixed Linear Arrays System) is presented and methods for effectiveness analysis are studied to analyze the valid target detection effectiveness of this system. The simulation model is constructed taking the FLAS operational specification into account, and thus the change in system specification is effectively reflected on the simulation results. The computational burden is reduced by using the pre-processed simulation parameters which are calculated from the real environmental database. Also, the cell effectiveness and TMOE(Total Measurement of Effectiveness) are computed. The target detection effectiveness of FLAS can be simulated under the multiple target interference simulation. It is shown that the presented algorithm is suitable for the underwater system which needs the simulation model for the optimum system design.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.1-7
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• 2017

The performance of a MEMS solid propellant thruster was predicted and analyzed through internal ballistics model and CFD analysis. The nozzle throat was $416{\mu}m$, and the area ratio of the nozzle was 1.85. As a result of the internal ballistics model, chamber pressure increased up to 197 bar and the maximum thrust was 3,836 mN. In CFD analysis, the chamber pressure of the internal ballistics model was applied as the operating pressure, and the CFD model was divided into an adiabatic and a heat loss model. As a result, the maximum thrust of the adiabatic model was 14.92% lower than that of the internal ballistics model, and the effect of heat loss was insignificant.