• International Journal of Air-Conditioning and Refrigeration
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• 제14권4호
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• pp.131-137
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• 2006

The absorber in which heat and mass transfer phenomena occur simultaneously is one of the most critical components in the absorption system. It has the most significant influence on the performance and the size of the absorption system. During the absorption process, heat and mass transfer resistances exist in both liquid and vapor regions, so that the heat transfer mode should be carefully selected to reduce them. The objective of this paper is to review the previous papers analysing mathematical models of simultaneous heat and mass transfer phenomena during the absorption process. The most conventional working fluids ($H_2O$LiBr and $NH_3/H_2O$) are considered and the most common absorption modes (falling film and bubble mode) are dealt with in this review.

• 한국분무공학회지
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• 제22권1호
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• pp.36-41
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• 2017

The present study investigates the evaporation heat transfer characteristics of nanofluid droplet for different nanoparticle sizes. Also, the heat transfer coefficient was measured at different nanoparticle concentrations during evaporation. From the experimental results, it is found that the evaporation behavior of sessile droplet can be considered as constant radius mode due to pinning effect. The total evaporation time of sessile droplet decreases with nanoparticle size up to 7.9% for 0.10 vol% nanofluid droplet. As nanoparticle concentration increases, the clear difference in heat transfer coefficient is observed, showing that the size effect should be examined. This result would be helpful in designing the correlation between the nanoparticle size and the heat transfer characteristics for various applications.

• 한국물환경학회지
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• 제26권1호
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• pp.81-88
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• 2010

This study was conducted to find the capability of comparison of overall oxygen transfer coefficient in the membrane coupled high performance reactor (MPHCR) in treating high organic loading wastewater. Effluent quality had been analyzed while the influent organic loading rate was changed from 2 to $7kg\;COD/m^3{\cdot}day$. The oxygen transfer coefficients had been investigated using two-phase nozzle for operating variables which were internal circulation flowrate (5~8 L/min), air flow rate (0.0125~0.2 L/min), liquid temperature ($10{\sim}20^{\circ}C$), and pure-oxygen flow rate (0.0125~0.2 L/min). The overall oxygen transfer coefficient was increased with flowrate of internal circulation and air and high temperature. Especially, internal circulation flow rate showed distinct effect on overall oxygen transfer coefficient due to an increase of gas holdup and air-liquid contract area by two-phase nozzle. In the high range of organic loading rate from 4 to $7kg\;COD/m^3{\cdot}day$, the removable efficiency of COD was 91%. Conventional activated sludge process usually treat organic loading from 0.32 to $0.64kg\;COD/m^3{\cdot}day$ however, the MPHCR can treat 10 to 20 times higher if it would be compared to the conventional activated sludge process. Foaming problem often happened and caused biomass wash out of the reactor, therefore, the foaming should be controlled for the enhanced operation.

• Nuclear Engineering and Technology
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• 제48권5호
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• pp.1154-1161
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• 2016

The heat transfer characteristics between liquid lead bismuth eutectic (LBE) and helium are of great significance for the two-loop cooling system based on an accelerator-driven system (ADS). This paper presents an experimental study on the resistance characteristics and heat transfer performance in a LBE-helium experimental loop of ADS. Pressure drops in the LBE loop, the main heat transfer, and the coupled heat transfer characteristics between LBE and helium are investigated experimentally. The temperature of LBE has a significant effect on the LBE thermo-physical properties, and is therefore considered in the prediction of pressure drops. The results show that the overall heat transfer coefficient increases with the increasing helium flow rate and the decreasing inlet temperature of helium. Increasing the LBE Reynolds number and LBE inlet temperature promotes the heat transfer performance of main heat transfer and thus the overall heat transfer coefficient. The experimental results give an insight into the flow and heat transfer properties in a LBE-helium heat exchanger and are helpful for the optimization of an ADS system design.

• 설비공학논문집
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• 제18권11호
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• pp.867-873
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• 2006

Vertical falling liquid film is extensively used in heat and mass transfer processes of many applications, such as evaporative coolers, cooling towers, and absorption chillers. In such cases, it is required that the falling film spreads widely in the surface forming thin liquid film to enlarge contact surface. An addition of surface active agent to a falling liquid film or hydrophilic surface treatment affects the fluid physical properties of the film. Surfactant addition not only decreases contact angle between the liquid and solid surface but also changes the surface from hydrophobicity to hydrophilicity. In this study, the effects of contact angle on falling film characteristics over a vertical surface have been investigated experimentally. The contact angle is varied either by an addition of surfactant to the liquid or by hydrophilic surface treatment. It is found that the wetted area is increased and film thickness is decreased by the hydrophilic treatment as compared with those of other surfaces. With this hydrophilic treatment, the falling liquid film spreads out widely in the surface. As surfactant concentration is increased, wetted area is also increased and the film thickness is substantially decreased.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1864-1869
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• 2007

In this study, we compare thermal performance between four different types of cold plates for humanoid robot cooling. Two commercially available cold plates made of copper have different dimensions and internal flow paths: One has $20{\times}20$ $mm^2$ base area with micro-channels and the other has $62.5{\times}62.5$ $mm^2$ base area with 85 round pin-fins. And two different types of cold plates of $20{\times}20$ $mm^2$ base area with 7 mm high are made of PC (polycarbonate), which aims to reduce the weight of cooling system. All cold plates are mounted on a $20{\times}20$ $mm^2$ copper block with two cartridge heaters of 30 $W/cm^2$. The overall heat transfer coefficient and thermal resistances for the liquid-cooled cold plates are obtained. The copper cold plate with micro-channels showed the best performance. Polycarbonate cold plates display fairly good thermal performance with more reduced system weight.

• 한국항공우주학회지
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• 제31권4호
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• pp.76-81
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• 2003

Kerosene/LOX를 추진제로 사용하는 액체로켓의 추력실에서 발생하는 열유속을 측정하기 위하여 calorimetric combustion chamber를 제작하여 연소실험을 수행하였다. 본 실험에 사용된 calorimetric combustion chamber는 연소실 및 노즐 부분이 각각 하나의 구역으로 제작되었으며, 각각의 구역에서 발생하는 열유속을 측정하기 위하여 냉각제의 출구에 열전대를 설치하였다. 실험은 O/F ratio 2.0에서 연소압 100psi에서 300psi까지 수행하였다. 본 실험에서 연소실에서 복사 열전달은 고려하지 않았다. 측정된 열유속은 연소압에 다라 거의 선형적인 변화를 보였다.

• 한국수정란이식학회지
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• 제15권3호
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• pp.237-245
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• 2000

This study was carried out to elucidate whether sperm contain a factor inducing second polar body extrusion and to search for an effective collection method of the sperm factor Thus, sperm extract, dialyzed sperm-extract or liquid chromatographic fractions of sperm extract was microinjected into ovulated oocytes. And the microinjected oocytes were incubated for 24 hours to investigate about the extrusion of second polar body. The results obtained were as follows; 1. Sperm extract significantly increased the second polar body extrusion. 2. Sperm extract showed five major fractions at retention volumes (RVs) 1.25, 1.37, 1.84, 2.10 and 2.67ml after separation with Superose 12 column. These sperm extract fractions did not significantly increase the second polar body extrusion. 3. Dialyzed sperm-extract significantly increased the second polar body extrusion 4. Dialyzed sperm-extract showed three maior fractions at RVs 1.88, 2.14 and 2.77ml after separation with Superose 12 column. Of these fractions, the fraction RV2.14 significantly increased the second polar body extrusion. In conclusion, sperm extract contained a factor inducing the second polar body extrusion and the factor was contained largely in fraction RV2.14 after dialysis and liquid chromatographic fractionation of sperm extract.

• Progress in Superconductivity
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• 제10권2호
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• pp.149-154
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• 2009

We measured and analyzed the quench development in coated conductor(CC) tapes. The CC was grown on hastelloy substrates and has an Ag protection layer. The tapes were subjected to simulated AC fault currents for quench development measurement. They were immersed in liquid nitrogen during the experiment. The quench resistance increased rapidly first, and the increase slowed down afterwards. It increased linearly with applied voltage at lower voltages, and depended less strongly on applied voltage at higher voltages. The resistance was compared with that of Au/YBCO films grown on sapphire substrates, and found to increase more monotonously than the latter. Data were analyzed quantitatively with the concept of heat transfer within the tape and the surrounding liquid nitrogen. A heat balance equation was derived and solved, taking into consideration temperature dependence of thermal parameters of the tapes. Solutions, together with values of thermal parameters taken from the literature, explained the data well. Cooling by liquid nitrogen affected the quench development considerably at lower applied voltages. Dependence on applied voltages could be also understood quantitatively.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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• pp.238-241
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• 2003

터보펌프식 기체 공급계의 액체산소 탱크는 저압이 유지됨에 따라 탱크 내에서 추진제의 기화가 활발히 이루어지게 되며, 이러한 경향은 가압 기체의 온도가 높아짐에 따라 커지게 된다. 가압헬륨의 충진량을 결정하기 위해서는 이에 대한 정밀한 해석이 필요하다. 본 연구에서는 탱크내의 유동현상을 이상유동(two phase flow) 형태로 모델링 하여 탱크 내에서의 액체산소의 증발현상에 대하여 고찰하고 가압기체 온도 및 표면 열전달 계수에 따른 필요 헬륨 가스량을 예측한다.