• Membrane and Water Treatment
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• 제2권3호
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• pp.159-173
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• 2011

The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 ${\mu}m$. A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers' heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers' heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

• 수산해양교육연구
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• 제26권6호
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• pp.1352-1357
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• 2014

In the present study, the heat transfer performance on the heat recovery ventilator with rotary disk were experimentally investigated. The temperature of entrance and exit of the heat recovery ventilator, air flow distribution of high temperature air and low temperature air, heat flux and the overall heat transfer coefficients are estimated from the experimental results. As the number of revolution of rotary disk, the air flow distribution increase, heat flux and overall heat transfer coefficients increase.

• 한국추진공학회지
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• 제3권2호
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• pp.66-74
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• 1999

본 연구에서는 송풍기의 출력이 일정한 상태에서 열전달 계수의 증가를 가져오기 위한 방법으로 다공판을 이용하였다. 이 방법은 다공판에 의한 운동량 감소 등의 몇 가지 단점이 있지만 특정한 조건에서 사용될 때, 정체 유동 영역에서 다공판이 없는 경우보다 최고 2배 이상 열전달 계수가 증가하였다. 본 연구에서는 정확하고 간편한 실험을 위하여 액정을 온도 지시계로 사용하였으며, 액정을 이용하면 열전대 등을 온도 지시계로 이용하는 실험보다 훨씬 간단하고 정확한 실험이 가능하다는 것을 알 수 있었다.

• 설비공학논문집
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• 제12권12호
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• pp.1081-1089
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• 2000

Evaporating heat transfer coefficients of R-22 and R-134a were measured in smooth horizontal copper tubes with inner diameters of 1.77, 3.36 and 5.35mm, respectively. The experiments were conducted in a closed loop, which was driven by a magnetic gear pump. Experiments were performed for the following range of variables: mass velocity (200 to 400 kg/$m^2$.s), saturation temperature($0^{circ}C,; 5^{\circ}C$) and quality(0 to 1.0). Main results obtained are as follows: evaporating heat transfer coefficients in the small diameter tubes (ID<7mm) were observed to be strongly affected by various diameters and to differ from those in the large diameter tubers. The heat transfer coefficients of the small diameter tubes were higher than those of the large diameter tubs. And it was very difficult to apply some well-known previous predictions (Shah`s, Gungor-Winterton`s and Kandlikar`s correlation) to small diameter tubes.

• Nuclear Engineering and Technology
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• 제45권7호
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• pp.911-920
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• 2013

Experimental studies on both subcooled and saturated pool boiling of water were performed to obtain local heat transfer coefficients on a $3^{\circ}$ inclined tube of 50.8 mm diameter at atmospheric pressure. The local values were determined at every $45^{\circ}$ from the very bottom to the uppermost of the tube periphery. The maximum and minimum local coefficients were observed at the azimuthal angles of $0^{\circ}$ and $180^{\circ}$, respectively, in saturated water. The locations of the maxima and the minima were dependent on the inclination angle of the tube as well as the degree of subcooling. The major heat transfer mechanisms were considered to be liquid agitation generated by the sliding bubbles and the creation of big size bubbles through bubble coalescence. As a way of quantifying the heat transfer coefficients, an empirical correlation was suggested.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.783-786
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• 1996

In the temperature analysis, the heat transfer between the workpiece and the die has an important influence upon the temperature distribution. The accuracy of thermal analysis depends on the proper description of boundafy conditions. A t the contact surface of two materials with different temperature, this requires the knowledge of overall heat transfer coefficients. In order to evaluate the overall heat transfer coefficients, a technique is developed. This technique involves temperature measurement at the contact surface during hot upsetting operations and finite element computation to calcualte the overall heat transfer coefficient.

• Journal of Advanced Marine Engineering and Technology
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• 제22권3호
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• pp.285-293
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• 1998

This paper presents an experimental study on condensing heat transfer characteristics of R-22 alternative refrigerants, R-290 and R-410a on water sources heat pump. The apparatus mainly consisted of vapor pump condenser used to the test section evaporator manual expansion valve and measuring device. Test section constructed a smoothed tube of 10.07 mm ID and 12.7mm OD with a total length 6,300 mm was horizontal double pipe counterflow condenser. The refrigerants R-22, R-290 and R-410a were cooled by a coolant circulated in a surrounding annulus. Experimental range of mass velocities was changed from about 100 to 300 kg/($m^2$.s) and inlet quality 1.0 The credibility of experimental apparatus was 6 percent between heating capacity and cooling capacity added to compressor shaft power. The condensing heat transfer coefficients were increased with increasing mass velocity. However in case of R-290 they were more increasing than those of R-410a and R-22 Comparing the heat transfer coefficient between the experimental data and other's data the Cavallini-Zecchin's data was revealed to more similar prediction of author's experimental results on the average heat transfer coefficients.

• Journal of Mechanical Science and Technology
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• 제15권8호
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• pp.1156-1164
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• 2001

Evaporation heat transfer coefficients and pressure drops were measured for smooth and micro-fin tubes with R-22 and R-410A. Heat transfer measurements were performed for 3.0m long horizontal tubes with nominal outside diameters of 9.52 and 7.0mm over an evaporating temperature range of -15 to 5$\^{C}$, a mass flux range of 68 to 211kg/㎡s, and a heat flux range of 5 to 15kW/㎡. It was observed that the heat transfer coefficient increased with mass flux. Evaporation heat transfer coefficients of R-22 and R-410A increased as the evaporating temperature dropped at a lower heat flux. Generally, R-420A showed the higher heat transfer coefficients than R-22 in the range of low mass flux, high heat flux and high evaporating temperature. Pressure drop increased with a decrease of evaporating temperature and a rise of mass flux. Pressure drop of R-22 was higher than that of R-410A at the same mass flux.

• 설비공학논문집
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• 제18권10호
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• pp.842-849
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• 2006

In this study, the effect of carbon nanotubes (CNTs) on boiling heat transfer is investigated. Three refrigerants of R22, R123, R134a, and water are used as base working fluids and 1% of CNTs by volume is added to the base fluids to study the effect of CNTs. All data are obtained at the pool temperature of $7^{\circ}C$ for all refrigerants and $100^{\circ}C$ for water in the heat flux range of $10{\sim}80\;kW/m^2$. Test results show that CNTs increase the boiling heat transfer coefficients for all fluids. Especially, large enhancement was observed at low heat flutes. With increasing heat flux, however, the enhancement was suppressed due to vigorous bubble generations. Fouling was not observed during the course of this study. Optimum quantity and type of CNTs and their dispersion should be examined for their application in pool boiling heat transfer.

• 설비공학논문집
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• 제10권1호
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• pp.22-32
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• 1998

Separate type thermosyphon has larger critical heat flux than non-loop type thermosyphon, because the flooding phenomenon of vapor and liquid occurring in non-loop one does not occur. The experimental study has been carried out separate type thermosyphon with single tube. An investigation of heat transfer characteristics in separate type thermosyphon is performed experimentally. Heat transfer coefficients in an evaporator and condenser were measured experimentally. The effects of liquid filling ratio, height difference, cooling temperature and heat flux on the heat transfer coefficients were examined. As a result, the reasonable range of the liquid filling ratio and the dependence of heat transfer on vapor temperature and heat flux are obtained.