• 대한기계학회논문집B
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• 제21권5호
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• pp.713-723
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• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• Nuclear Engineering and Technology
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• 제24권2호
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• pp.130-140
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• 1992

동방향 성층이상유동에서의 직접적촉 응축현상을 일차원 모델인 RELAP5/MOD2와 /MOD3를 이용하여 해석하였으며, 해석결과를 Northwestern의 실험결과와 비교·검토하였다. 해석결과 RELAP5의 공유열전달 모델은 동방향 성층이상유동에서 응축율을 비교적 잘 예측하고 있다. 그러나 공유접촉면에 파형이 생기는 경우는 물경계두께 및 국부 열전달계수는 유사한 범위로 일치할분 현상을 예측하는데 상당한 차이가 있다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1999년도 춘계학술발표회요약집
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• pp.107-107
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• 1999

Direct-contact condensation experiments of atmospheric steam and steam/air mixture on subcooled water flowing co-currently in a rectangular channel are carried out uszng an infrared thermal camera system to develop a temperature measurement method. The inframetrics Model 760 Infrared Thermal Imaging Radiometer is used for the measurement of the temperature field of the water film for various flow conditions. The local heat transfer coefficient is calculated using the bulk temperature gradient along the (low direction. It is also found that the temperature profiles can be used to understand the interfacial condensation heat transfer characteristics according to the flow conditions such as noncondensable gas effects, inclination effect, and flow rates.

• 설비공학논문집
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• 제18권8호
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• pp.613-619
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• 2006

The objectives of this paper are to study the characteristics of heat transfer for enhanced tubes (19.05 mm) used in the condenser with high saturation temperatures and to provide a guideline for optimum design of a condenser using HFC134a. Three different enhanced tubes are tested at a high saturation temperature of $59.8^{\circ}C$ (16 bar); a low-fin and three turbo-C tubes.. The refrigerant, HFC134a is condensed on the outside of the tube while the cooling water flows inside the tube. The film Reynolds number varies from 130 to 330. The wall subcooling temperature ranges from $2.7^{\circ}C$ to $9.7^{\circ}C$. This study provides experimental heat transfer coefficients for condensation on the enhanced tubes. It is found that the turbo-C(2) tube provides the highest heat transfer coefficient.

• Journal of Advanced Marine Engineering and Technology
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• 제32권1호
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• pp.50-56
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• 2008

Experimental results for forced convection condensation of Refrigerant-22 and ternary Refrigerant-407C(HFC-32/125/134a 23/25/52 wt%) which is being considered as a substitute R-22 inside a horizontal micro-fin tube are presented. The test section was horizontal double-tube counterflow condenser with a length 4,000 mm micro-fin tube, having 8.53 mm ID, 0.2 mm fin height and 60 fins. The range of parameters of mass velocity were varied from 102.1 to 301.0 kg/(m2.s) and inlet quality 1.0. At the given experimental conditions. the average heat transfer coefficients for R-407C were lower than that for R-22 at a micro-fin tube. Over the mass velocity range tested. the PF(penalty factor) for R-22, R-407C were lower than the increasing ratio of heat transfer area by fins, and the EF(enhancement factor) for R-22, R-407C were higher than the increasing ratio of heat transfer area by fins.

• 설비공학논문집
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• 제14권1호
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• pp.83-90
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• 2002

An experimental study on the performance evaluation of a brazed plate heat exchanger with 10USRT of normal cooling capacity has been carried out. In the present study, a brazed plate heat exchanger was tested at a chevron angle $25^{\circ}$with refrigerant R-22. Refrigerant mass flux was ranged from 23 to 58 kg/$m^2$s in condensation, and from 22 to 53 kg/$m^2$s in evaporation. The heat transfer coefficients and pressure drops are increased as the mass flux increases. The water side pressure drop is increased as the cooling water flow rate and chilled water flow rate increase, while mass flux has little effect. It is also shown that the system performance can be improved by enlarging condensation heat transfer area.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1102-1111
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• 2002

The study focuses on the heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having 50, 60, 70, 80, 90 internal grooves. Three different working fluids(distilled water, methanol, ethanol) are used with various volumetric liquid fill charge ratio from 10 to 40%. Additional experimental parameters such as operating temperature and inclination angle of zero to 90 degrees are used for the comparison of heat transfer performance of the thermosyphon. Condensation and boiling heat transfer coefficients, heat flux are obtained using experimental data for each case of specific parameter. The experimental results are assessed and compared with existing correlations. The results show that working fluids, liquid fill charge ratio, number of grooves and inclination angle are very important factors for the operation of thermosyphons. The relatively high rate of heat transfer is achieved when the thermosyphon with internal grooves is used compared to that with plain tube. The optimum liquid fill charge ratio for the best heat transfer performance lies between 25% and 30%. The range of the optimum inclination angle for this study is 20$^{\circ}$～30$^{\circ}$ from the horizontal position.

• 한국분무공학회지
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• 제23권3호
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• pp.149-153
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• 2018

The present study investigates the heat transfer characteristics of droplet growth during dropwise condensation on the hydrophobic copper surface. We use the copper specimen coated by the self-assembled layer and conduct the real-time measurement of droplet size and spatial distribution of condensates during condensation with the use of the K2 lens (long distance microscope lens) and CMOS camera. The temperatures are measured by three RTDs (resistance temperature detectors) that are located through the holes made in the specimen. The surface temperature is estimated by the measured temperatures with the use of the one-dimensional conduction equation. It is observed that the droplets on the surface are growing up and merging, causing larger droplets. The experimental results show that there are three distinct regimes; in the first regime, individual small droplets are created on the surface in the early stage of condensation, and they are getting larger owing to direct condensation and coalescence with other droplets. In the second and third regimes, the coalescence occurs mainly, and the droplets are detached from the surface. Also, the fall-off time becomes faster as the surface wettability decreases. In particular, the heat transfer coefficient increases substantially with the decrease in wettability because of faster removal of droplets on the surfaces for lower wettability.

• 설비공학논문집
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• 제11권1호
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• pp.10-17
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• 1999

The present work presents condensation heat transfer and pressure drop data for the flow of R-12 in flat extruded aluminum tubes with small hydraulic diameters. The tube outside dimensions are $18mm(width){\times}1.7mm(height)$. Three types of internal geometry with the same outside dimensions are tested : sample 1 (7 tube holes), sample 2 (13 tube holes) and sample 3 (7 tube holes, micro-fin). The overall heat transfer coefficient is obtained for air-to-refrigerant heat transfer, and the Wilson plot method is used to determine the heat transfer coefficient for refrigerant flow. The sample 2 and sample 3 show significantly higher performance than sample 1. The heat transfer rates for the sample 2 and sample 3 are 9% and 12% higher, respectively, than sample 1. The friction factors for the sample 2 and sample 3 are 11.9% and 2.4% higher, respectively, than sample 1.

• 대한기계학회논문집
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• 제12권4호
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• pp.833-846
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• 1988

본 연구에서는 후래시현상과 가열이 동시에 존재하면서 증발을 일으키는 수직 증발관내에서의 유동양식에 대해서, 우선 전기 프로우브를 이용하여 관내의 유동양식 에 따른 전기적 신호를 얻고, 시진실험 방법(photographic experimental method)을 통 하여 이를 확인한다. 또한, 전기 프로우브를 통하여 얻은 신호는 적절한 해석과정을 통해 수직 증발관내의 유동에 따른 기공률을 측정하는데 적용된다.