• 한국해양공학회지
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• 제8권1호
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• pp.105-113
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• 1994

Double-diffusive convection induced by simultaneously-imposed lateral temperature and concentration gradients in a rectangular enclosure with aspect retio, 2.0 has been studied experimentally for adiabatic and isothermal horizontal boundary conditions. Visual observations show two distinct flow structures depending on the buoyancy ratio. The unicell flow structure is observed for a lower buoyancy ratio while the layered flow structure appears for a higher buoyancy ratio. There exists an unstable flow regime between two buoyancy ratios.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제11권1호
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• pp.71-83
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• 2007

The double diffusive convection of cold water in the vicinity of its density maximum in a rectangular partitioned enclosure of aspect ratio 5 with isothermal side walls and insulated top and bottom is studied numerically. A thin partition is attached to the hot wall. The species diffusivity of the fluid is assumed to vary linearly with concentration. The governing equations are solved by finite difference scheme. The effects of position and height of the partition, variable species diffusivity and enclosure width are analyzed for various hot wall temperatures. It has been found that adding partition on the hot wall reduces the heat transfer. The density inversion of the water has a great influence on the natural convection. When increasing species diffusivity parameter heat and mass transfer rate is decreased.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.282-289
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• 2000

Direct numerical solution for flow and heat transfer for Benard convection with a body is obtained using an accurate and efficient Fourier-Chebyshev collocation and multi-domain method. The flow and temperature fields are obtained fur different Rayleigh numbers and thermal boundary conditions of body. The body has adiabatic and constant temperature conditions. The existence of a body gives different flow and heat transfer fields in the system, compared to pure Benard convection. The flow and temperature fields are also affected by the thermal boundary condition of a body.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.45-50
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• 2000

A numerical investigation is made of three-dimensional buoyant convection of a Boussinesq-fluid in a vertical cylinder. The top and bottom endwalls are thermally insulated. Flow is driven by the substantial azimuthal variations in thermal boundary conditions. Comprehensive numerical solutions to the Navier-Stokes equations are obtained. The representative Rayleigh number is large, thus, the overall flow pattern is of boundary layer-type. Three-dimensional (low characteristics are described. Specially, the global flow and the heat transfer features are delineated when the severity of azimuthal variation of sidewall temperature n, is intensified. Temperature and velocity fields on the meridional planes and the planes of constant height are presented. The global flow weakens as n becomes large. The pattern of the local Nusselt number on the surface of cylinder is similar regardless of n. The convective gain in heat transfer activities is reduced as n increases.

• Korean Chemical Engineering Research
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• 제55권6호
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• pp.868-873
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• 2017

Natural convection is driven by the compositional buoyancy in solidification of a binary melt. The stabilities of convection in a growing mushy layer were analyzed here in the time-dependent solidification system of a near-eutectic melt cooled impulsively from below. The linear stability equations were transformed to self-similar forms by using the depth of the mushy layer as a length scale. In the liquid layer the stability equations are based on the propagation theory and the thermal buoyancy is neglected. The critical Rayleigh number for the mushy layer increases with decreasing the Stefan number and the Prandtl number. The critical conditions for solidification of aqueous ammonium chloride solution are discussed and compared with the results of the previous model for the liquid layer.

• 설비공학논문집
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• 제13권9호
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• pp.845-852
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• 2001

The phenomena of energy separation in vortex tubes was investigated experimentally to see the effects of the conductivity of a tube and convective heat transfer on the outer surface of a tube. The experiment was carried out with different conductivity (pyrex, stainless steel and copper) of a tube and three kinds of convective heat transfer modes (adiabatic condition, natural convection (air) and forced convection (water) on the outer surface of a tube. the results were obtained that hot exit fluid temperature was highly affected by a change of conductivity of a tube when the outer surface was cooled by the forced convection of water. However, the cold exit temperature was little affected by heat transfer modes on the outer surface in vortex tubes.

• 설비공학논문집
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• 제13권2호
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• pp.88-95
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• 2001

Transition to chaotic convection is investigated for natural convection of a fluid with Pr=0.1 in a wide-gap horizontal annuls. The unsteady two-dimensional stream-function-vorticity equation is solved with finite difference method. As the Rayleigh number is increased, the steady 'downward flow' bifurcates to a time-periodic flow with a fundamental frequency, and afterwards a period-doubling bifurcation occurs. As the Rayleigh number is increased further, the chaotic flow regime is reached after a sequence of successive Hopf bifurcation to quasi-periodic and chaotic flow regimes. The route to chaos shows the Ruelle-Takens-Newhouse scenario. The flow of chaotic regime displays complex coalescence and separation of eddies in the side and lower region of the annulus.

• 대한기계학회논문집B
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• 제35권1호
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• pp.43-51
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• 2011

수평관 외부에서 발생하는 자연대류 열전달 현상을 실험적으로 연구하였다. 연구의 목적은 구리 도금계를 채택한 유사성실험방법론이 적용가능한지 확인하는 것과 수평관의 지름과 각도에 따라 달라지는 국부열전달을 시각화하는 것이었다. 구리의 전기도금계를 사용하면 양극에서 생성된 구리이온은 대류와 확산을 통하여 음극으로 이동되어 환원되는데 이는 열전달을 모사하게 된다. 구리와 색깔이 다른 알루미늄을 음극으로 채택함으로써 각도에 따라 환원되어 석출된 구리의 양을 시각화 할 수 있었다. 수평관의 직경은 0.01m에서 0.15m이었고 이는 $Ra_D\;=\;1.73{\times}10^7\;{\sim}\;5.69{\times}10^{11}$에 해당한다. 실험결과는 기존에 알려진 열전달 상관식과 일치하였다. 알루미늄 음극에 도금된 구리의 패턴은 Kitamura에 의해 액체결정온도측정법으로 시각화한 결과와 매우 잘 일치 하였다.

• 대한기계학회논문집
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• 제17권2호
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• pp.438-444
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• 1993

The circuit board of an electronic equipment were simulated with a vertical channel which had thermal blocks protruded from one of the channel walls. A rought front plate was made of a circuit board attached with short wires to simulate the back side of a printed circuit board. Natural convection experiments were carried out to study the effects of channel space and rough front plate and to find the suitable characteristic value after the fourth row. The effect of a rough front plate was negligble. There were negligible effects of the channel space on the first and second heaters. Heat transfer coefficients after the third row decreased as the channel space decreased. Heat transfer coefficients were almost constant for larger than 20 mm channel space. A characteristic length was suggested to non-dimensionalize Nu and Ra numbers in a vertical channel with protruded heaters. A correlation was obtained using the new characteristic lengths.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1657-1662
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• 2003

In this study, to research characteristics of heat flow of magnetic fluid, it's studied about numerical and experimental method of natural convections change and characteristics of heat transfer in Concentric double pipe annuli as analysis model. In the result, natural convection of magnetic fluid is controlled by direction and strength of the impressed magnetic field. Especially, according to average Nusselt number, heat transfer is the smallest on the balancing point between body force and buoyancy.