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SWNT 투명박막히터의 열성능 평가를 위한 자유대류 열전달 해석
곽호상(H.S. Kwak),이성은(S.E. Lee),박경석(K.S. Park),김경진(K. Kim) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.4
A computational investigation is conducted on free convection from a thin plate having a surface heat source. The thermal configuration simulates the recently-proposed transparent film heater made of a single-walled carbon nanotube film on a glass substrate. The Navier-Stokes computations are carried out to study laminar free convection from the heater. Parallel numerical experiments are performed by using a simplified design analysis model which solve the conduction equation with the boundary conditions utilizing several existing correlations for convective heat transfer coefficient. Comparison leads to the most suitable boundary condition for the thermal model to evaluate the performance evaluation of a transparent thin-film heater.
주기적인 측벽가열에 반응하는 사각공동내의 이중확산 대류
곽호상(H.S. Kwak) 한국전산유체공학회 2001 한국전산유체공학회 학술대회논문집 Vol.2001 No.-
A numerical investigation is made of unsteady double-diffusive convection of a Boussinesq fluid in a rectangular cavity subject to time-periodic thermal excitations. The fluid is initially stratified between the top endwall of low solute concentration and the bottom endwall of high solute concentration. A time-dependent heat flux varying in a square wave fashion, is applied on one sidewall to induce buoyant convection. The influences of the imposed periodicity on double-diffusive convection are scrutinized. A special concern is on the occurrence of resonance that the fluctuations of flow and attendant heat and mass transfers are mostly amplified at certain eigenmodes of the fluid system. Numerical solutions are analyzed to illustrate the characteristic features of resonant convection.
회전식 화학증착 장치 내부의 유동해석을 통한 최적 유량 평가
곽호상(H.S. Kwak) 한국전산유체공학회 2012 한국전산유체공학회지 Vol.17 No.1
A numerical investigation is conducted to search for the optimal flow rate for a rotating-disk chemical vapor decomposition reactor operating at a high temperature and a low pressure. The flow of a gas mixture supplied into the reactor is modeled by a laminar flow of an ideal gas obeying the kinetic theory. The axisymmetric two-dimensional flow in the reactor is simulated by employing a CFD package FLUENT. With operating pressure and temperature fixed, numerical computations are performed by varying rotation rate and flow rate. Examination of the structures of flow and thermal fields leads to a flow regime diagram illustrating that there are a stable plug-like flow regime and a few unfavorable flow regimes induced by mass unbalance or buoyancy. The criterion for sustaining a plug-like flow regime is discussed based on a theoretical scaling argument. Interpretation of the flow regime map suggests that a favorable flow is attainable with a minimum flow rate at the smallest rotation rate guaranteeing the dominance of rotation effects over buoyancy.
곽호상(H. S. Kwak) 한국전산유체공학회 2002 한국전산유체공학회지 Vol.7 No.1
A numerical investigation is made of unsteady double-diffusive convection of a Boussinesq fluid in a rectangular cavity subject to time-periodic thermal excitations. The fluid is initially stratified between the top end wall of low solute concentration and the bottom end wall of high solute concentration. A time-dependent heat flux varying in a square wave fashion, is applied on one sidewall to induce buoyant convection. The influences of the imposed periodicity on double-diffusive convection are examined. A special concern is on the occurrence of resonance that the fluctuations of flow and attendant heat and mass transfers are mostly amplified at certain eigenmodes of the fluid system. Numerical solutions illustrate that resonant convection results in a conspicuous enhancement of time-mean mass transfer rate.
이상현(S. H. Lee),곽호상(H. S. Kwak),한창수(C. S. Han),류도현(D. H. Ryu) 한국전산유체공학회 2003 한국전산유체공학회지 Vol.8 No.4
This study presents a numerical model to analyze dynamic thennal behavior of a hot chuck designed for flip-chip bonders. The hot chuck of concern is a heater which has been specifically developed for accomplishing high-speed and ultra-precision soldering. The characteristic features are radiative heat source and the heating tool made of a material of high thermal diffusivity. A physical modeling has been conducted for the network of heat transport. A simplified finite volume model is deviced to simulate time-dependent thermal behavior of the heating too on which soldering is achieved. The reliability of the proposed numerical model is verified experimentally. A series of numerical tests illustrate the usefulness of the numerical model in design analysis.
노즐 축소부 수렴각이 고속 광섬유 피복유동에 미치는 영향
박신(S. Park),김경진(K. Kim),곽호상(H.S. Kwak) 한국전산유체공학회 2016 한국전산유체공학회지 Vol.21 No.4
A numerical study is conducted on the optical fiber coating flow in a primary coating nozzle consisting of three major parts: a resin chamber, a contraction and a coating die of small diameter. The flow is driven by the optical fiber penetrating the center of the nozzle at a high speed. The axisymmetric two-dimensional flow and heat transfer induced by viscous heating are examined based on the laminar flow assumption. Numerical experiments are performed with varying the convergent angle of nozzle contraction and the optical fiber drawing speed. The numerical results show that for high drawing speed greater than 30 m/s, there is a transition in the essential flow features depending on the convergent angle. For a large convergent angle greater than 30°, unfavorable multicellular flow structures are monitored, which could be associated with wall boundary-layer separation. In the regime of small convergent angle, as the angle increases, the highest resin temperature at the exit of die and the coating thickness decrease but the sensitivity of coating thickness on drawing speed and the maximum shear strain of resin on the optical fiber increase. The effects of the convergent angle are discussed in view of compromise searching for an appropriate angle for high-speed optical fiber coating.
차량용 납전지 전극 제조 금형의 유로 설계를 위한 수치 연구
홍성근(S.G. Hong),김태겸(T.G. Kim),곽호상(H.S. Kwak) 한국전산유체공학회 2022 한국전산유체공학회지 Vol.27 No.1
A numerical study is conducted on a die-casting process to produce the lead electrodes employed in car batteries. The primary concern is to reduce the processing time by enhancing cooling performance. The proposal is to employ a recursive cooling passage characterized by dual spiral channels, which overcomes the spatial restriction in the mold. A three-dimensional CFD model based on the ANSYS package is constructed to simulate the transient cool-down process from the molten-state lead to a solid product, in which the solidification process is included. The turbulent flow of water in the cooling channel and the conjugate heat transfer in the mold are examined. The preliminary computations for the mold with the conventional straight cooling channels illustrate that the required cool-down performance is hardly attainable even for high flow rate of water. The computations for the mold with spiral channels show that the spiral passage provides an augmentation of cooling performance even for a moderate flow rate. The cooling performance increases and the temperature uniformity decreases as the inclination angle of the spiral cooling passage. This suggests that an optimal selection of the inclination is needed to satisfy the both requirements for processing time and temperature uniformity.