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불응축가스량이 가변전열 히트파이프의열수송 특성에 미치는 영향
서정세,박영식,정경택 대한설비공학회 2006 설비공학 논문집 Vol.18 No.4
Numerical analysis and experimental study are performed to investigate the effect of heat load and operating temperature on the thermal performance of several variable conductance heat pipe(VCHP) with screen meshed wick. The heat pipe is designed in 200 screen meshes, 500mm length and 12.7mm outer diameter tube of copper, water(4.8g) is used as working fluid and nitrogen as non-condensible gas(NCG). Heat pipe used in this study has evaporator, condenser and adiabatic section, respectively. Analysis values and experimental data of wall temperature distribution along axial length are presented for heat transport capacity, condenser cooling water temperature change, degrees of an inclination angle and operating temperature. These analysis and experiment give the follow findings: For the same charging mass of working fluid, the operating temperature of heat pipe becomes to be high with the increasing of charging mass of NCG. When the heat flux at the evaporator section increases, the vapor pressure in the pipe rises and consequently compresses the NCG to the condenser end part and increases the active length of the condenser. From previous process, it is found out we can control the operating temperature effectively and also the analysis and experimental results are relatively coincided well.
서정세,박영식,정경택 대한설비공학회 2005 설비공학 논문집 Vol.17 No.12
This study has been performed to investigate the thermal performance of variable conductance heat pipe(VCHP) with meshed wick. The length of condenser portion in a VCHP is varied by the expansion of inert gas with the operation temperature, and the heat transport capacity is thus varied with the operating temperature. In this study, numerical evaluation of the VCHP is made for the thermal performance of VCHP, based on the diffusion model of inert gas. Water is used as a working fluid and nitrogen as a control inert gas in the copper tube. As a result, the thermal performance of VCHP has been compared with that of constant conductance heat pipe(CCHP) according to the variation of operation temperature. Maximum heat transport capacity of VCHP is mainly presented for operation temperature and the variation of operation temperature is also presented for heat transfer rate of VCHP.
서정세,Suh, J.S. 대한설비공학회 1995 설비공학 논문집 Vol.7 No.4
A numerical study is made on the melting process of an unconstrained ice inside an isothermal ice-ball capsule. The unmelted ice core is continuously ascending on account of buoyancy forces. Such a buoyancy-assisted melting is commonly characterized by the existence of a thin liquid film above the ice core. The present study is motivated to present a full-equation-based analysis of the influences of the initial subcooling and the natural convection on the fluid flow associated with the buoyancy-assisted melting. In the light of the solution strategy, the present study is substantially distinguished from the existing works in that the complete set of governing equations in both the melted and unmelted regions are resolved in one domain. Numerical results are obtained by varying the wall temperature and initial temperature. The present results reported the transition of the flow pattern in a spherical capsule, as the wall temperature was increased over the density inversion point. In addition, time wise variation of the shapes for the liquid film and the lower ice surface, the time rate of change in the melt volume fraction and the melting distance at symmetric line is analyzed and is presented.
서정세,노승탁,Ro, Sung Tack 대한기계학회 1995 대한기계학회논문집 Vol.19 No.10
Buoyancy-assisted melting of an unconstrained ice in an isothermally heated horizontal enclosure was numerically analyzed in a range of wall temperatures encompassing the density inversion point. The problem as posed here involves two physically distinct domains each of which has its own scales and respective heat transfer mode. These two domains join at the junction where the liquid squeezed out of the film region flushes into the lower melt pool. Both of these domains have been treated separately in the literature by a patching technique which invokes several, otherwise unnecessary, assumptions. The present study eliminates successfully such a superfluous procedure by treating the film and lower melt pool regions as a single domain. As a result of this efficient solution procedure, the interaction of the water stream ejected at the junction and the natural convection in the melt pool could be clarified for different wall temperatures. Though limited by two-dimensionality, the present results conformed indirectly the earlier reported transition of the flow pattern, as the wall temperature was increased over the density inversion point. The transient evolution of the melting surface, the time rate of change in melt volume fraction, the local and temporal variation of the heat transfer coefficients are analyzed and presented.
徐正世 慶尙大學校 工科大學 自動化및컴퓨터應用技術硏究所 1994 自動化 및 컴퓨터應用技術 Vol.1 No.1
Numerical analysis is made on the melting process of phase-change material inside a horizontal tube and a spherical enclosure which are usually used in the latent thermal storage system. The unmelt solid core is moving downward on account of gravity forces and melt by directly contacting with a heated wall. Such a gravity-assisted melting is characterized by the existence of a melt pool in a upper region and a thin liquid film region below the solid core. The present study is motivated to present a numerical analysis of the influences of the natural convection on the fluid flow and heat transfer characteristics in a horizontal tube and a spherical capsule. Numerical results are obtained by varing the Rayleigh numbers respectively. For the range of parameter examined, the melting process goes faster in a spherical capsule than a horizontal tube.