• 대한설비공학회지:설비저널
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• 제17권3호
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• pp.230-237
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• 1988

An experiment was carried out to study the condensation heat transfer enhancement of horizontal circular cylinders with varying outside surface configurations. The refrigerant used is Freon-22 and the test condensing temperature is 34.1C. Pin-finned tube shows about 2.5-3.5 times higher overall heat transfer coefficient compared to that of smooth surface tube, thus has larger encomic benifit for condenser design. The condensation heat transfer coefficient was shown to increase as the fin-pitch of the pin-finned tube decreases for film Reynolds number larger than 100.

• 대한기계학회논문집
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• 제18권8호
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• pp.2177-2183
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• 1994

The rapid expansion or condensible gas such as moist air of steam gives rise to nonequilibrium condensation. As a result of irreversibility of condensation process in the supersonic cascade flow of low pressure steam turbine, the entropy of the flow is increased, and the efficiency of the turbine is decreased. In the present study, to investigate the flow of moist air in 2-dimensional cascade made as the configuration of the tip section of the last actual steam turbine moving blade, the static pressure at both sides of pressure and suction of blade are measured by static pressure taps and the distribution of Mach number on both surfaces of the blade are obtained by using the measured static pressure. Also, the flow field is visualized by a schlieren system. From the experimental results, the effects of the stagnation temperature and specific humidity on the flow properties in a 2-dimensional stationary cascade of a practical steam turbine blade are clearly identified.

• 수산해양기술연구
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• 제42권4호
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• pp.259-266
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• 2006

In this study, the 2-way condensation system was designed applying air-to-air heat pump to dry a marine product such as squid in the winter. And to be made the drying apparatuses by this system, there are two kinds of type, A type, was set a compressor outside of the drying apparatus, B type, was set a compressor in the drying room. And then the variations of temperature in drying room were measured to compare the heating performance of the drying apparatuses between A type and B type at $-6.5^{\circ}C$, outdoor temperature. The temperature of the drying room for B type was increased to $36^{\circ}C$ but the temperature of the drying room for A type was not increased to $36^{\circ}C$, to be increased to $20^{\circ}C$.

• 설비공학논문집
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• 제13권3호
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• pp.174-183
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• 2001

Experimental study has been carried out on the characteristics of pressure drop and heat transfer of brazed plate heat exchangers using R-404A. Data are presented for the following range of variables: the mass flux ($20~80kg/m^2s$), chevron angle($20^{circ}C,\;35^{circ}C,\;45^{circ}C$) and inlet pressure of he refrigerant (1.4 and 1.6 MPa). for both subcooled and tow-phase flow, as chevron angle increases, pressure drop and heat transfer coefficient decrease. Condensation hat transfer coefficient and pressure drop was compared with the previously proposed correlations. Among them, Traviss correlation agreed with experimental results within -35~82% for heat transfer coefficient and -73~93% for pressure drop.

• 설비공학논문집
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• 제13권4호
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• pp.295-303
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• 2001

Condensation of vapor on solid inherently accompanies generation of liquid drops on the solid surface. However, these drops prevent the solid surface from directly contacting the saturated vapor, thus causing thermal resistance. This work investigates a novel mechanism for enhancing the condensation process, in which the condensed drops are rapidly removed from a solid surface by imposing vibration on them. In the experiments, a water drop pendant from a solid surface is vibrated at a fixed frequency while increasing the vibration amplitude. Upon repeating the experiments using various frequencies, it is revealed that there exist resonant frequencies at which the minimum vibration amplitudes inducing a fall-off of the pendant drops are remarkably less than those at neighboring frequencies. These frequencies are supposed to correspond to the resonant frequencies for different modes of drop shape oscillations. They are compared with the resonant frequencies predicted by relatively simple analyses, and the factors causing discrepancy between then are discussed.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권3호
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• pp.1-9
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• 2001

In this study, condensation heat transfer coefficients (HTCs) of nonazeotropic refrigerant mixtures of HFC32/HFC 134a and HCFC123 at various compositions were measured on a horizontal smooth tube. All data were taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling of 3~8K. Test results showed that HTCs of tested mixtures were 11.0~85.0% lowed than the ideal values calculated by the mass fraction weighting of the HTCs of the pure components. Thermal resistance due to the diffusion vapor film was partly responsible for the significant reduction of HTCs with these nonazeotropic mixtures. The measured data were compared against thc predicted ones by Colburn and Drew's film model and a good agreement was observed within a deviation of 15%.

• 설비공학논문집
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• 제14권2호
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• pp.143-152
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• 2002

It is critical for radiant floor cooling system using Ondol to cause condensation on a floor surface. To solve this problem, a radiant floor cooling system integrated with dehumidification was proposed and evaluated in terms of its applicability and prevention of condensation. Therresults show that the proposed system of radiant floor cooling integrated with dehumidification properly maintained the indoor setpoint temperatures and prevented the condensation on a floor surface. To achieve more stable indoor temperatures and humidity control, a further study for the operation of dehumidification panel will be needed.

• 설비공학논문집
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• 제13권6호
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• pp.490-496
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• 2001

An experimental study on the behavior of the water hold-up by condensation of a fin-and-tube heat exchanger with regard to the surface characteristics, i.e., contact angle, was conducted. The static and dynamic contact angles were measured, and condensation experiments were conducted. Flow patterns on the fins with different surface characteristics were visualized. Results showed that the static contact angle is proportional to the dynamic contact angle within the range of this study. The water hold-up of the heat exchanger increases as the static or dynamic contact angle of its surfaces increases. Existence of transition of flow patterns was found as the static or dynamic angle increase. Due to the transition in the flow patterns, changes in the gradient of the water hold-up is occurred around the static angle of 8$0^{\circ}C$.

• 설비공학논문집
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• 제12권12호
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• pp.1049-1056
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• 2000

In this study, condensation heat transfer coefficients(HTCs) of 2 nonazeotropic refrigerant mixtures of HFC32/HFC134a and HFC134a/HCFC123 at various compositions were measured on a horizontal smooth tube. All data were taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling of 3~8K. Test results showed that HTCs of tested mixtures were 11.0~85.0% lower than the ideal values calculated by the mass fraction weighting of the pure components HTCs. Thermal resistance due to the diffusion vapor film was partly responsible for the significant reduction of HTCs with these nonazeotropic mixtures. The measured data were compared against the predicted ones by Colburn and Drew\`s film model and a good agreement was observed.

• 한국항공우주학회지
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• 제31권6호
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• pp.23-29
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• 2003

얇은 익형 주위에 다양한 응축 과정을 수반하는 상대 습도가 100%인 포화 습공기 천음속 이상 유동에 대하여 연구하였다. 본 연구는 Rusak 과 Lee[11, 12]가 발전시킨 그리고 응축에 의한 열 증가의 효과를 포함하는 확장된 천음속 미 교란 모델을 사용하였고, 응축 과정은 서로 다른 두 가지 형태의 응축 과정을 고려한다. 먼저, 비 평형 균질 과정(nonequilibrium and homogeneous process)에서의 응축 질량비는 고전적 핵형성 이론과 작은 물방울 성장이론에 따라 계산되고, 평형과정(equilibrium process)에서의 응축 질량비는 등엔트로피 가정으로부터 계산된다. 유동 방정식과 응축 방정식들은 반복수치 계산법을 사용하여 그 해를 구하였다. 상류 유동 조건을 같게 하여 얻은 수치계산 결과들은 유동구조, 응축장, 그리고 익형 표면에서의 압력분포 등을 묘사한다. 유동특성, 즉 충격파의 위치와 강도 그리고 익형의 압력분포 등은 서로 다른 두 응축과정에서 각각 다른 유동특성을 나타냈다. 하지만, 각각의 응축과정에서 응축 결과로 생긴 열 증가는 유동거동에 상당한 변화를 야기 시키고 익형의 공력 성능에도 상당한 영향을 미친다.