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충돌수분류(衝突水噴流)에 의한 원통내면(圓筒內面)에서의 열전달증진(熱傳達增進)에 관한 연구(硏究)
엄기찬,우창기,최국광,서정윤,Ohm, K.C.,Woo, C.K.,Choi, G.G.,Seo, J.Y. 대한설비공학회 1990 설비공학 논문집 Vol.2 No.4
An experimental study of the heat transfer characteristics between circular water jet and cylindrical inner surface is presented. The ratios of the semi-cylinder's inner diameter and the nozzle outlet diameter were varied parametrically, as were the Reynolds number and the supplementary water heights. The measurements showed that cirucmferential distribution of the heat transfer coefficient peaked at the stagnation point and, there occurred a kind of a secondary maximum of heat transfer that moved toward to stagnation point as the ratio d/D increased. The local heat transfer coefficient increases as the Reynolds number becomes larger, and the rate of increase is subjected to the influence of d/D & position of angle. Also, optimum heights of supplementary water which brings about the augmentation of heat transfer are S/D=1 for the stagnation point, the position of $15^{\circ}$ & $30^{\circ}$ angle, but for the positions of $45^{\circ}$ angle (d/D=10~11.67), $60^{\circ}$ & $75^{\circ}$ angle, the heat transfer coefficients in the case of using supplementary water are smaller than simple jet (S/D=0).
엄기찬,카시와기 타카오,서정윤,Ohm, K.C.,Kashiwagi, Takao,Seo, J.Y. 대한설비공학회 1994 설비공학 논문집 Vol.6 No.3
This paper deals with the correlation of absorption rate in absorber and evaporation rate in evaporator. The evaporator consists of a copper tube of 10mm dia, and 600mm long and chilled water flowing through the tube is fed by the chilled water circulator. The flowrate of LiBr-water solution in the absorber plays a significant role in determining the magnitude of the heat transfer rate from chilled water to refrigerant There exists a flowrate of solution which has a maximum value of heat transfer. It is interesting to note that the absorption rate of absorber increases with increasing the heat transfer rate of the evaporator. Also, absorption rate increases with evaportation rate, and the ratio(the former/the other) depends on the inlet temperature of LiBr-water solution in the absorber. The heating capacity in the absorber is higher than the refrigerating capacity in the evaporator.
수직관내(垂直管內)를 흘러내리는 액막식(液膜式) 흡수기(吸收器)의 흡수(吸收) 및 열전달특성(熱傳達特性)(제(第)2보(報) 열전달특성(熱傳達特性))
엄기찬,이동호,최국광,카시와기 타카오,서정윤,Ohm, K.C.,Rie, D.H.,Choi, G.G.,Kasiwagi, Takao,Seo, J.Y. 대한설비공학회 1993 설비공학 논문집 Vol.5 No.4
This is the second report of a three part study on the absorption and heat transfer characteristics of absorber, the correlation of refrigerating capacity and heating capacity. The 2nd report deals with the heat transfer characteristics of a vertical falling film type absorber of inner copper tube. The solute is LiBr-Water solution(60wt%) and the solvent is water vapor. The film Reynoles numbers are varied in the range of 35~130. The states of LiBr solution at the top of absorber are supercooled liquid and superheated liquid. The results are summarized as follows ; Heat transfer results reveal that for the absorption of falling film, the state of LiBr solution appears to be influential in determining the heat transfer. Thus, for the state of supercooled liquid, heat transfer coefficient decreases with increasing the film Reynolds number, but in the condition of superheated liquid, it increases conversely. The mass transfer coefficients that were presented in the 1st.report and heat transfer coefficients of this paper are presented as the dimensionless correlation. The optimum water flowrate which brings about maximum value of heat flux in the film exists, and that increases with increasing the cooling water temperature.
수직관내(垂直管內)를 흘러내리는 액막식(液膜式) 흡수기(吸收器)의 흡수(吸收) 및 열전달특성(熱傳達特性) (제(第) 1 보(報), 흡수특성(吸收特性))
엄기찬,백목 효부,서정윤,Ohm, K.C.,Kashiwagi, T.,Seo, J.Y. 대한설비공학회 1993 설비공학 논문집 Vol.5 No.1
Mass transfer coefficients were measured for water vapor absorption into a LiBr-Water solution of 60wt% flowing down an absorber of vertical tube type. The absorber is copper tube of 25mm inner diameter and 1000mm length. The film Reynolds number were varied in the range of 35~130. The solution is fed from the top of the pipe, and the conditions of solution are supercooled liquid and superheated liquid. As results, the flowrates of LiBr solution which takes peak value of average absorption mass flux exist. Mass transfer coefficients decrease with increasing the flowrate of LiBr solution, and the decrease rate in the case of supercooled liquid is large as compared with that in the case of superheated liquid. But the absorption rate of supercooled liquid is decidedly superior to that of superheated liquid.
엄기찬(K.C.Ohm),이종수(J.S.Lee),서정윤(J.Y.Seo) 한국태양에너지학회 1994 한국태양에너지학회 논문집 Vol.14 No.1
본 연구에서는 내부곡선이 정현곡선형으로 된 노즐(출구형 : 6㎜)로부터 상향으로 반원통의 내면 및 외면(직경 : 각각 40㎜, 50㎜, 60㎜, 70㎜의 4종류)에 충돌시켜 그 열전달 특성을 구명하고, 동시에 보조수를 사용하여 열전달 촉진현상을 실험적으로 구명하였다. 그 결과 다음과 같은 결론을 얻었다.<br/> 반원통의 내외면 공히 국소열전달계수는 정체점으로부터 벽면을 따라 단순 감소하는데, 요면의 경우는 보조수를 사용하지 않는 경우에는 정체점으로부터 벽면을 따라 노즐직경의 10배 이후의 영역에서 거의 균일한 분포를 갖는다. 최대 열전달계수는 보조수층 높이가 노즐직경의 1배의 조건에서 나타나며, 凸面에 비하여 凹面의 경우에 열전달계수가 크다. 평균열전달계수는 전열면직경/노즐직경의 비가 작을수록 크게 나타나고 있다. Experiments are performed to study heat transfer processes over a convex and concave surface. A single water jet issuing from nozzle and a water jet accompanied by supplementary water impinge normally on the convex side or the concave side of a heated semi-cylindrical surface. The local heat transfer Nusselt number along the surface is measured. In the experiment, the Reynolds number ranges from 24000 to 54000, and the supplementary water height to nozzle diameter ratio S/D is from 0 to 3.<br/> The local heat transfer and the average heat transfer are maximum value in the condition of S/D=1 and them of concave surface are larger than those of convex surface. The average heat transfer increases with decreasing d/D. Correlations of both the stagnation point and the average Nusselt number over the curved surface, which account for the surface curvature effect, are presented.
충돌과냉수분류(衝突過冷水噴流)의 비등열전달(沸騰熱傳達)에 관한 연구(硏究)
이강진,이종수,엄기찬,조용철,서정윤,Lee, G.J.,Lee, J.S.,Ohm, K.C.,Cho, Y.C.,Seo, J.Y. 대한설비공학회 1993 설비공학 논문집 Vol.5 No.1
This paper describes the boiling heat transfer phenomena to be divided into three regions, nonboiling, nucleate boiling and burn-out in the impinging subcooled water jet system. In the nonboiling region, Nusselt number is a function of Prandtl number, Reynolds number and ${\Delta}T_{sub}/T_{ast}$ In the nucleate boiling region, the heat flux increases with increment of the nozzle exit velocity. But the degree of liquid subcooling does not affect the shape of the nucleate boilng curve. The dimensionless correlations can be expressed in the form of $q{\ell}/K_f{\Delta}T_{ast}=C(Bo{\cdot}C_p{\cdot}{\Delta}T_{sat}/Vo^2)^m{\cdot}(Re/We)^n$. The burn-out heat flux increases linearly with increment of the nozzle exit velocity, but independs of degree of subcooling and the supplementary water height.
연직상향(鉛直上向) 사각충돌수분류(四角衝突水噴流)의 포화비등 열전달에 관한 연구
이종수,엄기찬,서정윤,Lee, J.S.,Ohm, K.C.,Seo, J.Y. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.5
The purpose of this investigation was to characterize nucleate boiling and burn-out heat flux for rectangular free jet with saturated water impinging perpendicularly and upward against a flat uniform heat flux surface. Heat flux measured for Reynolds number based on rectangular nozzle width and for aspect ratio. The result of nucleate boiling heat transfer was presented nondimensional experimental equation including Nusselt, Boiling, Subcooling, Reynolds and Weber number. The effect of aspect ratio of heated surface in the burn-out heat flux had not appeared distinctly. But for the same aspect ratio, burn-out heat flux increased linearly with increment of nozzle exit velocity.