• 대한기계학회논문집B
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• 제28권11호
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• pp.1424-1431
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• 2004

With traditional experimental methods such as the secondary fluid (e.g., water) calorimetric method, it is very difficult to accurately test the local condensation heat transfer inside mini-channels. Hence, there are large discrepancies between the results of previous studies. The experimental methods as well as unidentified sources of uncertainties could be reasons for such discrepancies. In this study, innovative experimental techniques were developed to measure the in-tube condensation heat transfer coefficient. With these techniques, very low heat dissipation rates such as several watts from the mini-channel could be estimated and low mass flow rates below the 0.1 ㎏/h could be measured with reasonable uncertainties. To the authors' knowledge, these techniques provide a unique experimental apparatus for measuring the condensation heat transfer coefficients inside the sub-millimeter hydraulic diameter single channels.

• 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.

• 수산해양교육연구
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• 제4권1호
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• pp.47-61
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• 1992

An experimental study was carried out to investigate the condensation performance for the horizontal cylindrical heat transfer tube with various fin attached using R-11 vapor. The heat transfer tube used in this study was supplied by SUNG HYUNG METAL CO., LTD. Four different types of heat transfer tubes (plain tube, SH-CYR tube, thermocor tube and thermoexcel tube) were used. Each tube was surrounded by circular acrylate tube, and R-11 gas heated by boiler flows into the acrylate tube. Cooling water counter-flows in heat transfer tubes. Heat transfer coefficient of the plain tube from measured data was compared with those of three other tubes. The results are summarized as follows: 1. As the cooling water temperature decreased, the liquid film of R-11 turned to droplet drop on the top surface of the horizontal tube. 2. Heat transfer coefficient calculated theoretically was higher than that obtained from the experimental data. 3. As far as the condensation concerns the thermocor tube is the highest, the SH-CYR tube is the second, and the thermoexcel tube is the third excluding the plain tube.

• 설비공학논문집
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• 제12권3호
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• pp.235-243
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• 2000

A theoretical model for laminar filmwise condensation along an isothermal vertical wall at constant pressure has been formulated on the basis of conservation laws and other fundamental physical principles. The model was applied to the prediction of the influences of variable thermophysical properties of liquid and vapor layers in the filmwise condensation of superheated vapor of Rl2, R134a, R142b and R152a. The dimensionless velocity component method was employed in the transformation of the governing equations and their boundary conditions, and the polynomial method was used for treating variable thermophysical properties of liquid and vapor. Physical quantities, such as the dimensionless thickness of the liquid layer, local heat transfer rate and mean heat transfer coefficient, were investigated for different values of the superheated temperature of the stagnant vapor far from the wall. It was found that the value of mean heat transfer coefficient of R134a was higher than other refrigerants for the change of the superheated temperature.

• 반도체디스플레이기술학회지
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• 제22권3호
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• pp.119-124
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• 2023

In this study, experimental approach of the measurement of condensation and evaporation heat transfer coefficients is discussed for mixed refrigerants using in the ultra low-temperature cooling system for semiconductor etching process. An experimental apparatus was described performing the condensation and evaporation heat transfer measurements for mixed refrigerants. The mixed refrigerant used in this study was composed of the optimal mixture determined in previous research, with a composition of Ar:R14:R23:R218 = 0.15:0.4:0.15:0.3. The experiments were conducted over a temperature range from -82℃ to 15℃ and at pressures ranging from 18.5 bar to 5 bar. The convection heat transfer coefficients of the mixed refrigerant were measured at flow rates corresponding to actual operating conditions. The condensation heat transfer coefficient ranged from approximately 0.7 to 0.9 kW/m2K, while the evaporation heat transfer coefficient ranged from 1.0 to 1.7 kW/m2K. The detailed discussion of the experimental methods, procedures, and results were described in this paper.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.125-133
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• 1998

Nine tubes with trapezoidal integral-fins having fin densities from 748 to 1654fpm and 10,30 grooves and finned tubes with caves of 0.55 and 0.64mm height respectively are tested. A plain tube having same diameter as the finned tubes is also tested for comparison. In case of condensation CFC-11 condensates at saturation state of 32$^{\circ}C$ on the outside surface cooled by inside cooling water flows. And in case of boiling the refrigerant evaporates at a saturation state of 1bar on the outside tube surface and heat is supplied by hot water which circulates inside of the tube. The tube having fin density of 1299fpm and 30grooves has the best condensation overall heat transfer coefficient. However, as far as boiling heat transfer coefficient concerns, fin tubes with cave show higher value than low fin tube having fin density of 1299fpm and 30 grooves.

• Nuclear Engineering and Technology
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• 제45권6호
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• pp.759-766
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• 2013

As passive safety features for nuclear power plants receive increasing attention, various studies have been conducted to develop safety systems for 3rd-generation (GEN-III) nuclear power plants that are driven by passive systems. The Passive Auxiliary Feedwater System (PAFS) is one of several passive safety systems being designed for the Advanced Power Reactor Plus (APR+), and extensive studies are being conducted to complete its design and to verify its feasibility. Because the PAFS removes decay heat from the reactor core under transient and accident conditions, it is necessary to evaluate the heat removal capability of the PAFS under hypothetical accident conditions. The heat removal capability of the PAFS is strongly dependent on the heat transfer at the condensate tube in Passive Condensation Heat Exchanger (PCHX). To evaluate the model of heat transfer coefficient for condensation, the Multi-dimensional Analysis of Reactor Safety (MARS) code is used to simulate the experimental results from PAFS Condensing Heat Removal Assessment Loop (PASCAL). The Shah model, a default model for condensation heat transfer coefficient in the MARS code, under-predicts the experimental data from the PASCAL. To improve the calculation result, The Thome model and the new version of the Shah model are implemented and compared with the experimental data.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1470-1477
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• 2000

Due to the ozone depletion and global warming potentials, some refrigerants(CFx and HCFCs) have been rapidly substituted. R410A is considered as the alternative refrigerant of R22 for the air-conditioners used a home and in industry. Experiments on the condensation heat transfer characteristics inside a smooth or a micro-fin tube with R410A are performed in this study. The test tubes 7/9.52 mm in outer diameters and 3 m in length are used. Varying the mass flux of the refrigerant and the condensation temperatures, the average heat transfer coefficients and pressure drop are investigated. It is shown that the heat transfer is enhanced and the amount of pressure drops are larger in the microfin tube than the smooth tube. From the heat transfer enhancement coefficient and the pressure penalty factor, it is found that the high heat transfer enhancement coefficients are obtained in the range of small mass flux while the penalty factors are almost equal.

• 한국가스학회지
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• 제12권1호
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• pp.48-53
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• 2008

본 연구는 세관내 R-22와 R-410A의 응축 열전달 계수를 실험적으로 조사하였다. 냉매 순환루프의 주요 구성품은 수액기, 변속 액펌프, 질량유량계, 증발기(예열기), 응축기(시험부)로 구성된다. 시험부는 평활, 수평 동관으로 내관의 내경과 외경이 각각 1.77 mm와 3.38 mm이다. 냉매 질량유속은 $450{\sim}1050\;kg/(m^2s)$이고, 입출구 평균건도는 $0.05{\sim}0.095$이다. 주요 실험결과를 요약하면, 응축 열전달 계수는 질량유속과 건도이 증가할수록 증가하였고, R-410A의 응축 열전달 계수가 R-22에 비해 약간 높았다. 종래의 상관식과 비교한 결과, 저건도와 저질량유속을 제외하고는 실험값과 종래의 상관식으로 예측한 값의 차이가 큰 것으로 나타났다.

• 설비공학논문집
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• 제9권3호
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• pp.376-388
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• 1997

In this study, an experiment was performed to investigate the characteristics of pressure drop and heat transfer of multi-channel tubes for automotive condenser using HFC-134a as an alternative refrigerant. The mass flux and inlet saturation pressure of the refrigerant were controlled, respectively, in the range of 200 to $500kg/m^2s$ and 1.0 to 1.6MPa. Pressure drop and heat transfer coefficient were compared with the previously proposed correlations and new correlations based on Traviss' correlation were suggested. Prediction of pressure drop and heat transfer coefficient based on the new correlations agrees with experimental results within ${\pm}9%$ and -18~+11%, respectively.