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나선 그루브를 가진 열사이폰 열교환기의 비등열전달 특성
한규일(Kyuil Han),조동현(Dong-Hyun Cho),임태우(Tae-Woo Lim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
This study concerns the characteristics of boiling heat transfer in thermosyphon exchangers with helical grooves. Distilled water, methanol, ethanol have been used as the working fluid. The type of working fluid, the saturation pressure of working fluids and the numbers of helical grooves of the thermosyphon exchangers with helical grooves have been assessed and compared with a mathematical model. The results show that the type of working fluid, the saturation pressure of working fluids and the numbers of helical grooves are very important factors for the operation of thermosyphon exchangers.
곡률비가 다양한 코일 튜브에서의 열전달현상에 관한 연구
한규일,박종운,Han, Kyuil,Park, Jong-Un 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.11
An experiment was carried out for the fully developed turbulent flow of water in tube coils on the condition of uniform heat flux. The present work was conducted for various ranges for Dean number(1794~1321), Prandtl number (2.5~4.5), curvature ratio parameters (22~60). Heat transfer to steady viscous flow in coiled tubes of circular cross section was studied for fully developed velocity and temperature fields under the thermal boundary condition of uniform heat flux. The peripherally local Nusselt number correlated as a function of Dean and Prandtl numbers. We studied the flow in heat coiled tubes under the influence of both centrifugal and buoyancy forces in order to gain insight into the flow pattern. In the present study, we obtained three emperical formulas, $Nu_v=0.0231Re^{0.84}Pr^{0.4}(a/R)^{0.13}$ (vertical) $Nu_c=0.0241Re^{0.86}Pr^{0.4}(a/R)^{0.08}$ (corrugated) $Nu_h=0.0227Re^{0.84}Pr^{0.4}(a/R)^{0.09}$ (horizontal).
마이크로 노즐 내부 표면개질을 통한 유동제어의 실험적 연구
변도영(Doyoung Byun),김지훈(Jihoon Kim),엄성환(Seonghwan Eom),한규일(Kyuil Han),고한서(Hanseo Ko) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
Recently, the research of microfluidics has been widely studied by many researchers, because the microfluidics system has been used in several fields such as lab-on-a-chip in medicine, colloid thruster in aerospace, microhydrodynamic in engineering, etc. The hydrophobic and hydrophilic internal surfaces are very important property to optimally design the microfluidic system. However, until now, no investigation is performed experimentally and theoretically to understand the flow instability and change of meniscus shape depending on the surface affinity in the microchannel. In this study, we visualized experimentally the flow characteristics in the microchannel whose surface is divided into hydrophilic and hydrophobic regions sequencially. For the hydrophilic and hydrophobic surfaces arrangement, when the meniscus reaches the interface region, the meniscus shape changes from concave to convex and the velocity near the centre increases.