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권화길(Hwa-kil Kwon),유성연(Seong-Yeon Yoo) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
For the successful design of heat exchangers, it is very important to understand local heat transfer phenomena. Because complex flow phenomena affect heat transfer in the cross flow heat exchanger, it is difficult to measure local heat transfer coefficients by conventional methods of heat transfer measurements. In the present study, a naphthalene sublimation technique is employed to measure the local heat transfer coefficients for the cross flow heat exchanger and the experiments are performed for the staggered array of circular tubes. Local and average Nusselt numbers for various air velocities and distances between tubes are investigated, and empirical correlations are obtained using these data.
5 kW급 SOFC 시스템의 연료 개질기를 위한 2-유체 노즐과 3-유체 노즐의 검토
권화길 ( Hwa Kil Kwon ),이치영 ( Chi Young Lee ),이상용 ( Sang Yong Lee ) 한국액체미립화학회 2008 한국액체미립화학회지 Vol.13 No.1
In the present study, the 2-fluid nozzle and 3-fluid nozzle to atomize the diesel and water with air for the fuel reformer of SOFC system were experimentally examined. In the 2-fluid nozzle, the diesel and water were alternately atomized due to bislug flow pattern, and it implies that the mixing of both liquids strongly affects the atomization pattern. On the other hand, in the 3-fluid nozzle, the diesel and water were atomized simultaneously due to the separated injection channels without mixing problem. Therefore, compared to the 2-fluid nozzle, the 3-fluid nozzle is suitable for the stable operation of the fuel reformer. In case of the 3-fluid nozzle, Type A where the air was supplied through the central channel was the most efficient.
1 ㎾급 SOFC 시스템의 연료 개질기용 2-유체 분무 노즐의 미립화 특성에 관한 사전 연구
권화길(Hwa-Kil Kwon),이치영(Chi Young Lee),이상용(Sang Yong Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
In the present study, the atomization characteristics of a twin-fluid nozzle, which will be the component of a fuel reformer in 1 ㎾ SOFC system, were preliminarily investigated. Diesel and air were used as the test fluids. With two air cap sizes(1.6 and 4.5 ㎜) of the nozzle, the atomization of diesel fuel was visualized, and the approximate spray angle, the diesel flow rate and the average droplet size(SMD) of diesel were examined with the air flow rate and the difference of height(between nozzle and diesel level in diesel container). As the air flow rate and the difference of height were increased, the diesel flow rate sprayed from the nozzle was increased. For the air cap sizes of 1.6 and 4.5 ㎜, the average droplet sizes ranged from 20 to 80㎛, and from 50 to 250㎛, respectively. From this study, it was confirmed that the twin-fluid nozzle could be applied in the 1 ㎾ fuel reformer.
유성연(Seong-Yeon Yoo),권화길(Hwa-Kil Kwon),이상섭(Sang-Sub Lee),김병채(Byeong-Chae Kim),박동성(Dong-Seong Park) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
Fouling is very serious problem in heat exchanger because it rapidly deteriorates the performance of<br/> heat exchanger. Cross-flow heat exchanger with vortex generators is developed, which enhance heat<br/> transfer and reduce fouling. In the present heat exchanger, shell and baffle are removed from the<br/> conventional shell-and-tube heat exchanger. The naphthalene sublimation technique is employed to<br/> measure the local heat transfer coefficients. The experiments are performed for single circular tube,<br/> staggered array tube bank and in-line array tube bank with and without vortex generators. Local and<br/> average Nusselt numbers of single tube and tube bank with vortex generator are investigated and<br/> compared to those of without vortex generator.
정렬배열 직교류 열교환기에서 국소열전달 특성에 관한 연구
유성연(Seong-Yeon Yoo),권화길(Hwa-Kil Kwon),장광일(Kwang-Il Jang),박준택(Jun-Taek Park) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
For the successful design of heat exchangers, it is very important to understand local heat transfer characteristics on the circular cylinder of the cross flow heat exchangers. In the present study, a naphthalene sublimation technique is employed to measure the local heat transfer coefficients, and the experiments are performed for the in-line arrangement of circular tube banks. Local and average Nusselt numbers are investigated for various parameters such as cylinder spacing, cylinder location and Reynolds number. The empirical correlations are obtained from these results and they are also compared with conventional heat transfer results.
Y-자형 합류지점에서 공기-물 플러그 생성에 관한 사전 연구
이치영(Chi Young Lee),권화길(Hwa-Kil Kwon),이상용(Sang Yong Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
In the present study, the formation of air-water plugs at a merging Y-junction was investigated. The generation rates and lengths of gas and liquid plugs were checked for various gas and liquid superficial velocities. For the present experimental range, the generation rates of plugs were increased with increasing gas or liquid superficial velocity, and the effect of the liquid superficial velocity was predominant compared to the gas superficial velocity. The length of gas plugs became longer either by decreasing liquid superficial velocity or by increasing gas superficial velocity. On the other hand, the length of liquid plugs became slightly longer with increasing liquid superficial velocity in the low gas superficial velocity region, and independent of the liquid superficial velocity in the higher gas superficial velocity region. Through the comparison with the previous results of plug formation, the physical interpretations on the present results were provided.