• 설비공학논문집
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• 제21권12호
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• pp.715-732
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• 2009

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2008. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends in thermal and fluid engineering have been surveyed in the categories of general fluid flow, fluid machinery and piping, new and renewable energy, and fire. Well-developed CFD technologies were widely applied in developing facilities and their systems. New research topics include fire, fuel cell, and solar energy. Research was mainly focused on flow distribution and optimization in the fields of fluid machinery and piping. Topics related to the development of fans and compressors had been popular, but were no longer investigated widely. Research papers on micro heat exchangers using nanofluids and micro pumps were also not presented during this period. There were some studies on thermal reliability and performance in the fields of new and renewable energy. Numerical simulations of smoke ventilation and the spread of fire were the main topics in the field of fire. (2) Research works on heat transfer presented in 2008 have been reviewed in the categories of heat transfer characteristics, industrial heat exchangers, and ground heat exchangers. Research on heat transfer characteristics included thermal transport in cryogenic vessels, dish solar collectors, radiative thermal reflectors, variable conductance heat pipes, and flow condensation and evaporation of refrigerants. In the area of industrial heat exchangers, examined are research on micro-channel plate heat exchangers, liquid cooled cold plates, fin-tube heat exchangers, and frost behavior of heat exchanger fins. Measurements on ground thermal conductivity and on the thermal diffusion characteristics of ground heat exchangers were reported. (3) In the field of refrigeration, many studies were presented on simultaneous heating and cooling heat pump systems. Switching between various operation modes and optimizing the refrigerant charge were considered in this research. Studies of heat pump systems using unutilized energy sources such as sewage water and river water were reported. Evaporative cooling was studied both theoretically and experimentally as a potential alternative to the conventional methods. (4) Research papers on building facilities have been reviewed and divided into studies on heat and cold sources, air conditioning and air cleaning, ventilation, automatic control of heat sources with piping systems, and sound reduction in hydraulic turbine dynamo rooms. In particular, considered were efficient and effective uses of energy resulting in reduced environmental pollution and operating costs. (5) In the field of building environments, many studies focused on health and comfort. Ventilation. system performance was considered to be important in improving indoor air conditions. Due to high oil prices, various tests were planned to examine building energy consumption and to cut life cycle costs.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 2004년도 춘계학술발표논문집
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• pp.127-139
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• 2004

The process of papermaking involves water removal on the paper machine wire, in the press section and in the dryer section. In the dryer section, liquid water in the wet web is removed mainly by evaporation. In conventional machine this is achieved by passing the web over a number of steam heated dryer rolls. A drying process of paper on a heated cylinder roll calculated based on a 1-dimensional model which concerns unsteady heat and mass transfer in the direction of paper thickness. In this study, Prediction of moisture contents average paper sheet temperature and volume fraction along a series of cylinder. Independently, developed models is compared using the same reference data. The model is implemented in CFD code, FLUENT, using user-define-function(UDFs).

• 대한기계학회논문집
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• 제18권7호
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• pp.1833-1839
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• 1994

Experiments have been carried out to investigate the burning characteristics of waste tires in high temperature environments. The burning of waste tire chips consists of four stages ; evaporation of volatile matters, ignition, burning of volatile matters, and burning of solid carbon. Burning time of waste tire chips depends on the gas temperature and the initial weight of the chip. However, the environments. In the ceramic matrix burner with a ceramic radiation shield, the burning time of the waste tire chips becomes shorter than that without the shield. This is due to the increase in heat transfer to the tire chips by radiation.

• 대한의용생체공학회:의공학회지
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• 제10권2호
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• pp.94-96
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• 1989

Explosive evaporative removal process of biological tissue by absorption of a CW laser has been simulated by using gelatin and a multimode Nd:YAG laser. Because the point of maximun temperature of laser-irradiated gelatin exists below the surface due to surface cooling, evaporation at the boiling temperature is made explosively from below the surface. The important parameters of this process are the conduction loss to laser power absorption (defined as the conduction-to-laser power parameter, Nk), the convection heat transfer at the surface to conduction loss (defined as Bi), dimensionless extinction coefficient (defined as Br.), and dimensionless irradiation time (defined as Fo). Dependence of Fo on Nk and Bi has been observed by experiment, and the results have been compared with the numerical results obtained by solving a 2-dimensional conduction equation. Fo and explosion depth (from the surface to the point of maximun temperature) are increased when Nk and Bi are increased.To find out the minimum laser power for explosive evaporative removal process, steady state analysis has been also made. The limit of Nk to induce evaporative removal, which is proportional to the inverse of the laser power, has been obtained.

• 설비공학논문집
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• 제2권1호
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• pp.27-36
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• 1990

An experimental investigation was made to study the performance characteristics of evaporator having different fin configurations and tube inner grooves. Three different types of fin such as super slitted fin, slitted fin, plain fin, and two types of tube such as inner grooved tube, and bare tube, are tested varying the air velocity, evaporation temperature and superheat of refrigerant. Results show that in the range of air side Reynolds number $3{\times}10^3\;-\;1.5{\times}10^4$ evaporator with super slitted fin and inner grooved tube shows best performance. It is 80% higher in overall heat transfer coefficient and 2.6 times higher in pressure loss compared to that with plain fin inner grooved tube. Friction factor is found to be almost independent of evaporating temperature and degree of superheat, while Colburn j factor varies with evaporating temperature.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2001년도 추계 학술발표회 논문집
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• pp.69-76
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• 2001

The coal gasification process of a slurry feed type, entrained-flow coal gasifier was numerically predicted in this paper. By divding the complicated coal gasification process into several simplified stages suh as slurry evaporation, coal devolitilisation and two-phase reactions coupled with turbulent flow and two-phase heat transfer, a comprehensive numerical model was constructed to simulate the coal gasification process. The k-$\varepsilon$turbulence model was used for the gas phase flow while the Random-trajectory model was applied to describe the behavior of the coal slurry particles. The unreacted-core shrinking model and modified Eddy Break-Up(EBU) model were used to simulate the heterogeneous and homogeneous reactions, respectively. The simulation results obtained the detailed informations about the flow field, temperature inside the gasifier. Meanwhile, the simulation results were compared with the experimental data as function of $O_2$/coal ratio. It illustrated that the calculated carbon conversions agreed with the measured ones and that the measurd quality of the atngas was better than the calculated one when the $O_2$/coal ratio increases. The result was related with the total heat loss through the gasifier and uncertain kinetics for the heterogeneous reactions.

• 한국기계가공학회지
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• 제19권3호
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• pp.51-56
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• 2020

Research into natural refrigerants that use CO₂, instead of chlorofluorocarbons and hydrofluorocarbons, has increased due to the environmental problems caused by ozone depletion. CO₂ refrigerants are more environmentally friendly than conventional refrigerants because they have better latent heat of evaporation and heat transfer efficiency properties. However, they have very low critical temperatures and require high design pressures; therefore, pressure control valves, which reduce the pressure of the CO₂ refrigerant to a safe level and apply it to the refrigerant air conditioning system, are necessary to secure stability against high pressure. In the present study, we evaluated the flow characteristics and valve performance of the pressure control valve using a CO₂ refrigerant by measuring the pressure, velocity, and flow coefficient. In addition, we examined the applied forces caused by the internal pressure from the highly pressurized CO₂ refrigerant and required thrust characteristics.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.700-710
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• 2008

A Bubble size distribution model has been developed for the numerical simulation of cryogenic high-speed cavitating flow of the turbo-pumps in the liquid fuel rocket engine. The new model is based on the previous one proposed by the authors, in which the bubble number density was solved as a function of bubble size at each grid point of the calculation domain by means of Eulerian framework with respect to the bubble size coordinate. In the previous model, the growth/decay of bubbles due to pressure difference between bubble and liquid was solved exactly based on Rayleigh-Plesset equation. However, the unsteady heat transfer between liquid and bubble, which controls the evaporation/condensation rate, was approximated by a theoretical solution of unsteady heat conduction under a constant temperature difference. In the present study, the unsteady temperature field in the liquid around a bubble is also solved exactly in order to establish an accurate and efficient numerical simulation code for cavitating flows. The growth/decay of a single bubble and growth of bubbles with nucleation were successfully simulated by the proposed model.

• 에너지공학
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• 제18권4호
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• pp.213-220
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• 2009

수분의 함량이 높은 저품위탄을 건조시키기 위하여 유중 건조 방법에 대해 조사하였다. 최적의 건조 조건을 선정하기 위하여 최종온도, 석탄과 등유의 혼합비율, 석탄 또는 등유의 양, 혼합물의총량, 교반방법에 따른 석탄의 건조 특성을 관찰하였다. 최종온도가 $120^{\circ}C$ 이하일 때는 완전한 증발이 이루어지지 않았으며, $130^{\circ}C$ 이상인 경우에는 수분의 증발량에 큰 차이가 나타나지 않았다. 석탄과 등유의 혼합비율에서 석탄의 양이 증가 할수록 수분의 증발이 잘 이루어짐에 따라, 열에너지의 전달이 수분의 증발에 미치는 영향보다 증발한 수분이 등유 속에서 배출되기 위하여 필요한 에너지가 더 큰 것으로 나타났다. 혼합물의 총량이 많은 경우에는 건조후의 수분 함량이 더 낮아지지만 많은 시간이 소모되는 반면, 적은 경우에는 수분 함량을 일정한 수준 이하로 낮추기 어려운 반면에 짧은 시간에 일정한 함량까지 수분을 증발시킬 수 있는 것으로 나타났다. 따라서 등유와 석탄 혼합물의 유동성이 확보되는 한도 내에서 등유의 양을 가능한 줄이는 것이 석탄의 건조에 유리한 것으로 판단되었다. 한편, 질소를 이용한 교반과 진공을 개별적으로 적용한 경우에는 증발량이 향상되었다.

• 한국산학기술학회논문지
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• 제16권12호
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• pp.8165-8175
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• 2015

여름철이 무더운 대한민국에서는 냉방에 많은 전력을 소비한다. 이 경우 간접증발냉각을 동시에 적용하면 전기 사용을 줄일 수 있다. 본 연구에서는 알루미늄, 플라스틱, 플라스틱/종이 재질로 만들어진 간접증발소자에 대하여 건표면 및 습표면 실험을 수행하였다. 실험 결과 플라스틱/종이 소자의 간접증발효율은 38.5% ~ 51.4%로 알루미늄 소자의 값 (41.9% ~ 47.5%)과 유사하고 플라스틱 소자의 값 (29.0% ~ 37.4%)보다는 높게 나타났다. 이로부터 저가의 플라스틱/종이 재질의 간접증발소자가 고가의 알루미늄 재질 간접증발소자를 대체할 수 있으리라 판단된다. 하지만 종이 채널의 압력손실은 알루미늄 채널의 압력손실보다 92% ~ 106% 크다. 한편 종이와 알루미늄 건채널의 열전달계수는 플라스틱 건채널의 값보다 15% ~ 44%, 185% ~ 203% 크게 나타났다. 반면 종이 건채널의 압력손실은 알루미늄 건채널 보다 93% ~ 106%, 플라스틱 건채널보다 34% ~ 48% 크게 나타났다. 습표면 해석결과 알루미늄 습채널에서는 17% ~ 23%, 플라스틱 습채널에서는 30% ~ 37%가 건표면으로 나타났다. 반면 종이 습채널의 경우는 100% 습표면으로 나타났다. 이는 종이의 흡습성이 알루미늄이나 플라스틱보다 월등하기 때문이다.