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평판전열면(平板傳熱面)에 충돌(衝突)하는 2차원충돌분류계(二次元衝突噴流系)의 열전달특성(熱傳達特性)에 관(關)한 연구(硏究)
이용화,김상필,서정윤,Lee, Y.H.,Kim, S.P.,Seo, J.Y. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.1
The purpose of this study is to investigate the heat transfer characteristics and the flow structure in the case of rectangular air jet impinging vertically on the flat heating surface. The maximum value of Nusselt number at stagnation point is observed at H/B=10. It is found that this trend has been caused by the effect of stretching of large scale vortex in the stagnation region. For potential core region the Nusselt number distribution in the downstream of the stagnation point decreases gradually and begins to increase at about X/B=3. From the flow visualization it could be seen that small eddy produced from the nozzle edge grows in large scale and that large scale eddy disturbed the thermal boundary layer on the heating plate. The local average Nusselt number becomes maximum at X/B=0.5 regardless of H/B variation.
이용화(Y.H.Lee),이동호(D.H.Rie),카시와기타카오(T.Kashiwagi),서정윤(J.Y.Seo) 한국태양에너지학회 1995 한국태양에너지학회 논문집 Vol.15 No.1
본 연구는 H₂0/LiBr 과 NH₃/ H₂O계를 사용하는 2단2원 흡수식 사이클의 특성에 관한 연구이다. 이 사이클은 2개의 단효용 사이클로 이루어져 있으며, 저온단의 흡수기와 응축기에서 얻어진 열을 고온단의 증발기에서 이용하는 사이클로서 저온단의 증발기 및 응축기의 온도, 재생기 온도, 열교환 온도차를 파라메터로 하여 계산한 결과 다음과 같은 결론을 얻었다. 2단2원사이클의 성립범위를 확인하였으며 본 계산조건에서 50~70℃의 승온폭을 얻을 수 있었다. 또한 50℃의 난방온도를 얻기위한 최적재생온도는 105℃, 최대 COP를 얻기위한 저온측사이클의 응축압력은 16℃, 그리고 이 조건에서 저온측 사이클으 응축압력을 단효용 사이클의 경우보다 낮게 억제하는 것이 가능함을 알았다. This paper concerns the study of a two-stage binary absorption cycle employing the refrigerant/ absorbent combinations of LiBr / H₂0 and NH₃/ H₂O. This cycle consists of coupling two single-effect absorption cycles so that the first stage absorber and condenser produces heating water to evaporate refrigerant in the evaporator of the second stage. The effect of operating variables such as evaporator temperature, condenser and absorber temperature, and generator temperature on the coefficient of performance and temperature lift have been studied for two-stage binary absorption heat pump systems. It is found that this cycle has a large temperature lift at 105℃ of optimum generator temperature to obtain 50℃ of condenser temperature.
충돌분류계(衝突噴流系)에서 난류촉진체(亂流促進體)에 의한 방열효과(放熱效果)에 관(關)한 연구(硏究)
이용화,서정윤,Lee, Y.H.,Seo, J.Y. 대한설비공학회 1992 설비공학 논문집 Vol.4 No.1
The purpose of this study was to investigate the enhancement of heat transfer without additional external power in the case of rectangular air jet impinging vertically on the flat heating surface. In an attempt to enhance the heat transfer rate in two-dimensional impinging jet, the technique used in the present study was placement of square rod bundles as a turbluence promoter in front of the heat transfer surface. The effects of the clearance between the flat plate and square rod, and the nozzle exit velocity on the heat transfer characteristics have been investigated experimentally. The results obtained through this study were summerized as follows. High heat transfer enhancement was achived by means of flow acceleration and thinning of boundary layer by inserting rods in front of the heating flat plate. The smaller the clearance between rod and heating plate was, the larger heat transfer effect became. Average Nusselt number reached maximum at $Re=5.76{\times}10^4$ and C=1㎜ and the enhancement rate of heat transfer became maxium at this condition with the enhancement ratio as high as about 1.427 when normalized by the flat plate value. The correlating equation of average Nusselt number and Reynolds number was obtained, which is $\bar{N}uo=1.324{\cdot}Re^{0.459}{\cdot}(C/A)^{-0.034}$.
2차원(次元) 충돌분류(衝突噴流)의 열전달(熱傳達) 증진(增進)에 관(關)한 실험적(實驗的) 연구(硏究) (사각(四角) Rib폭(幅)의 효과(效果))
이용화,이관석,서정윤,Lee, Y.H.,Rhee, K.S.,Seo, J.Y. 대한설비공학회 1988 설비저널 Vol.17 No.4
The impinging air jet system is still being used in the various fields with its inherent merits, that is, the easiness in engineering application and high heat transfer coefficients at stagnation point. The purpose of this study is augmentation of heat transfer without additional power in the rectangular air jet which impinges vertically to the heating surface. As a method of passive heat transfer augmentation in a two-Dimensional impinging jet, the transverse-repeated surface roughness of square cross-section is used. This paper deals with the experimental study on the characteristics of heat transfer at the x-direction in between nozzle exit and heating surface of flat plate, and that of ribbed plate. And this study also investigates the effect of square rib widths. The integral average heat transfer coefficient of ribbed plate is about 2.2 times larger than that of flat plate.
이용화,Lee, Y.H. 대한설비공학회 1996 설비공학 논문집 Vol.8 No.2
The gas-fired absorption refrigeration system to utilize treated sewage is available for environmental protection and energy conservation. Simulation analysis on the double-effect absorption refrigeration cycles with parallel or series flow type has been performed. The working fluid is Lithium Bromide and water solution. The main purpose of this study is evaluating the possibilities of effective utilization of treated sewage as a cooling water for the absorber and condenser. The efficiency of a couple of cycles has been studied and simulation results show that higher coefficient of performance could be obtained for parallel flow type. The other purpose of the present study is to determine the optimum designs and operating conditions based on the operating constraints and the coefficent of performance in the paralledl flow type.
충돌판(衝突板) 근방(近傍)에 배열(配列)된 2차원(次元) rod가 충돌분류(衝突噴流) 열전달(熱傳達)에 미치는 영향(影響)[3] : rod직경변화(直徑燮化)에 대한효과(效果)
김동춘,이용화,서정윤,Kim, D.C.,Lee, Y.H.,Seo, J.H. 대한설비공학회 1990 설비공학 논문집 Vol.2 No.4
The purpose of this study is augmentation of heat transfer without additional power in two-dimensional impinging air jet. The technique of heat transfer augmentation used in this experiment is to place rod bundles in front of the flat heated surface. The effects of rod diameter, nozzle-to-target plate distance and the nozzle exit velocity on heat transfer have been investigated. The main conclusions obtained from this experiment are as follows. High heat transfer augmentation is achieved by means of flow acceleration and thinning of boundary layer by placing rod bundles in front of the flat plate. Average heat transfer coefficient becomes maximum in the case of H/B=10,D=4mm. For H/B=2,D=4mm, maximum heat transfer augmentation has been determined to be about 1.5 times larger than that of the flat plate. Heat transfer augmentation by placing the rod bundles at 12m/s is to be about 2 times more than increasing nozzle exit velocity from 12m/s to 18m/s.