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강병하(B.H.Kang),김도규(D.K.Kim),박경근(K.K.Park) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
The heat transfer enhancement by pulsating flow in a plate heat exchanger has been experimentally investigated in this study. The effect of the pulsating flow, such as pulsating frequency and flow rate, on the heat transfer as well as pressure drop in a plate heat exchanger has been studied in detail. Reynolds number in cold side of a plate heat exchanger is varied 100~530 while that of hot side is fixed at 620. The pulsating frequency is considered in the range of 5~30 Hz. The results of the pulsating flow are also compared with those of steady flow. It is found that the average heat transfer rate as well as pressure drop is increased as flow rate is increased for both steady flow and pulsating flow cases. When pulsating flow is applied to the plate heat exchanger, heat transfer could be substantially increased in particular ranges of pulsating frequency or Strouhal number; St=0.36~0.60 and pressure drop is also increased, compared with those of steady flow.
백종훈,강병하,장호명,Baik, J.H.,Kang, B.H.,Chang, H.M. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.3
A hydrogen liquefaction equipment by direct cooling has been designed and built at KIST. Cool-down characteristics and liquefaction performance of the equipment have been investigated. The hydrogen liquefaction equipment consists of a GM refrigerator, a liquefaction velssel, a radiation shield and a cryostat. It is found that the hydrogen starts to be liquefied in the liquefaction vessel after 40~50 minutes of cool-down from the gas state of 270K. The effect of natural convection phenomena of charged gas in liquefaction vessel on the cool-down characteristics is evaluated by comparing with those in vacuum of liquefaction vessel. It is seen that the cool-down time of a liquefaction vessel is substantially increased in vacuum environment of liquefaction vessel. The experiments have been performed for 1~5 atm of hydrogen pressure to investigate the influence of hydrogen pressure on the liquefaction rate and figure of merit(FOM). It is found that both liquefaction rate and FOM are increased as the charged hydrogen pressure is increased.
평판핀이 부착된 공냉형 암모니아 응축기의 열전달 성능에 대한 수치적 연구
김영일,강병하,Kim, Y.I.,Kang, B.H. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.3
Ammonia has been used as refrigerant for more than 100 years in absorption as well as in compression systems. Due to its poisonous and inflammable properties, however, its use has been mainly on heavy industrial plants in which regular maintenance are available. For these systems, condensers are generally water-cooled. This is suitable for large systems over 20 RT but is not suitable for small systems. In order to apply ammonia for a small system, it is important to adopt an air-cooled condenser. In this study, simple numerical analysis of an air-cooled condenser for an ammonia refrigeration system has been carried out. The condenser is designed as horizontal tubes with plate fins attached at the outer surface to enhance the air-side heat transfer rate. Effects of fin shape and arrangement are studied in detail. Since the local heat transfer coefficient is highest at the leading edge, heat flux is highest at the edge and decreases along the distance. Conditions of inlet air are also varied in the study and condenser length that is required for full condensation is calculated. The results show that it is important to enhance both the air-side and internal heat transfer coefficients.
재생기 및 냉각기가 VM열펌프의 냉방성능에 미치는 영향
이건태,강병하,유호선,이재헌,Lee, G.T.,Kang, B.H.,Yoo, H.,Lee, J.H. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.3
An experimental study has been carried out to investigate the effects of the combination of the different wire mesh number in a regenerator and the tube number in a cooler on the cooling performance of a Vuilleumier cycle heat pump. Effects of operating conditions, such as charging pressure, operating speed, and heat input, on the cooling performance are also studied. The experimental results obtained indicate that the cooling performance could be improved with the proper combination of different wire meshes in a regenerator. More tubes in a cooler are desirable for better cooling performance. It is also found that the cooling capacity is enhanced, whereas COP is reduced with an increase in the heater tube temperature and the revolution speed. Both the cooling capacity and COP are incereased with a higher charging pressure.
저온 폐열 회수를 위한 제1종 흡수식 열펌프의 컴퓨터 시뮬레이션
강상우,강병하,정시영,이춘식,Karng, S.W.,Kang, B.H.,Jeong, S.,Lee, C.S. 대한설비공학회 1996 설비공학 논문집 Vol.8 No.2
A computer program for thermal design analysis has been developed to predict the operating characteristics and performance of an absorption heat pump to recover $30{\sim}40^{\circ}C$ of waste hot water. The effects of heat transfer area of the system components, temperature and mass flow rate of heat transfer medium, and solution circulation rate on the system performance are investigated in detail. The results obtained indicate that the COP is increased with a decrease in the temperature of driving steam and with an increase in the temperature of waste hot water while the COP is little affected by the variation of a hot water temperature. It is also found that the heating output is increased with an increase in the temperature of waste hot water and driving steam as well as with a decrease in the temperature of hot water. The simulation results are also compared with the experimental results for a periodic operation of the system and obtained a satisfactory agreement.
가정용 열펌프 구동용 스터링 엔진의 시스템 설계 및 성능 예측
김웅태,강병하,이춘식,Kim, U.T.,Kang, B.H.,Lee, C.S. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.4
A design method has been developed for a Stirling engine with a tubular heater and cooler and a screen type regenerator. This paper provides a design procedure to determine the thermodynamic states and the geometric configurations of the Stirling engine for residential heat pumps. The major design is concerned with the working spaces, i.e. compression and expansion spaces and the heat exchangers such as the heater, the cooler and the regenerator. The Schmidt analysis has been employed to obtain the mass flow rates and heat transfer requirements of the system. The performance analysis of a model Stirling engine was performed by Martini-Weiss program to prove the validity of this design method. The results obtained indicate that this design method is valid for the Stirling engine conceptual design and performance analysis.