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전단박화유체의 수직상향 난류유동시 저항감소에 관한 연구
차경옥,김봉각,김재근,Cha, Kyong-Ok,Kim, Bong-gag,Kim, Jea-Geun 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.12
The drag reduction is the phenomenon that occurs only when the shear stress from the wall of pipe is beyond the critical point. The drag reduction increase as the molecular weight, concentration of the polymer and Reynolds number increase, but it is limited by Virk's maximum drag reduction asymptote. Because of the strong shear force for the polymer on the turbulent flow, the molecular weight and the drag reduction do not decrease. Such mechanical degradation of the polymer occurs in all polymer solvent systems. This paper is to identify and develop high performance polymer additives for fluid transportations with the benefits of turbulent drag reduction. In addition, drag reduction in vertical flow by measuring the pressure drop and local void fraction on vertical-up flow of close system is evaluated.
차경옥,김재근,Cha, Gyeong-Ok,Kim, Jae-Geun 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.4
The phenomena of drag reduction using small quantities of a linear macromolecules has attracted the attention of experimental investigations. It is well known that drag reduction in single phase liquid flow is affected by polymer materials, molecular weight, polymer concentration, pipe diameter and flow velocity. But the research on drag reduction in two phase flow has not intensively investigated. Drag reduction can be applied to phase change system such as chemical reactor, pool and boiling flow, and to flow with cavitation which occurs pump impellers. The purpose of the present work is to evaluate the drag reduction by measuring pressure drop, mean liquid velocity, and turbulent intensity and determine the effects of polymer additives on drag reduction in horizontal two phase flow. Experimental results show higher drag reduction using co-polymer comparing with using polyacrylamide. Mean liquid velocities increase as adding more polymer, and turbulent intensities decrease as the distance for the wall in inversed.
방형파펄즈가열법에 의한 세라믹스의 열물성 측정에 관한 연구
차경옥,이경희,임굉,Cha, K.O.,Lee, K.H.,Yim, Going 한국결정성장학회 1999 韓國結晶成長學會誌 Vol.9 No.6
본 연구에서는 방형파 펄즈 가열법을 이용하여 세라믹 고유전체 열물성치의 측정에 활용하는 것에 대한 가능성을 검토하였다. 여기서 측정의 이론을 설정하고 측정의 자동화를 시도함으로써 매우 짧은 시간내 시료의 열확산계수, 비열 및 열전도율을 얻을 수 있었다. 또한 시료는 실온으로부터 약 1300 K 온도 범위까지 측정하였다. Thermophysical properties of the high-dielectric ceramics were measured by a single rectangular pulse heating method. The values of thermal diffusivities, specific heats, and thermal conductivities were measured as a function of temperature ranging from room temperature to 1300 K.
발작성심실성빈박을 수반한 Wolff - Parkinson - White 증후군 2 예
차경옥 ( Kyung Ok Cha ),권경민 ( Kyung Min Kwon ),박순일 ( Soon Il Park ),한원주 ( On Joo Han ) 대한내과학회 1969 대한내과학회지 Vol.12 No.11
Two cases of Wolff-Parkinson-White syndrome associated with paroxysmal ventricular tachycardia were reported. Case l. 19 years old male who had history of paroxysmal tachycardia for g years was admitted to Seoul Sanitarium and Hospital with complaints of d
[論文] 方形波 펄스 加熱에 의한 BaOTiO₂,SrOTiO₂,MgOTiO₂系列의 熱物性値 測定에 관한 硏究
차경옥(K. O. Cha),장희석(H. S. Chang),이흥주(H. J. Lee) 한국자동차공학회 1991 오토저널 Vol.13 No.2
In this study, thermophysical properties of the ceramic dielectrics such as BaOTi0₂, SrOTi0₂, MgOTi0₂, were measured by a single rectangular pulse heating method.The values of thermal diffusivities, specific heats, and thermal conductivities were measured as a function of temperature range from room temperature to 1300k. The measured thermal properties of one group of ceramic material were compared with those of other group and discussed in detail in connection with the chemical composition. Thus, some criteria for thermal design with the electric-electronic ceramic material were proposed.