Graduate Thesis Or Dissertation
 

Natural convection and conduction in a vertical annulus with a concentric baffle : a numerical study

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  • Analytical and numerical study of steady-state laminar natural convection and conduction has been performed for an enclosure between concentric vertical cylinders. The inner and outer cylinders were isothermal, and the connecting top and bottom walls were adiabatic. A concentric baffle was included in the annulus, and the flow field and local heat transfer were investigated. The parameters of most interest in this study were the relative conductivity of the baffle and the properties of the fluid. A wide range of relative conductivities, Prandtl numbers, and Rayleigh numbers was investigated, assuming a particular cavity geometry with and without the baffle. The effect of a finite conductivity wall on the outside of the vertical annulus as well as the effect of high aspect ratio were also studied for low Prandtl number fluids (liquid metals). Results show that the relative conductivity of the concentric baffle affects the structure of the flow and the local Nusselt numbers. With increasing Rayleigh number, this effect diminishes. Multicellular flow is observed in each of the annular channels with increasing baffle conductivity ratio. A relatively low conductivity baffle promotes uniform channel flow in the annuli at lower Rayleigh numbers. The heat transfer results show that the baffle has an insulating effect at high Rayleigh numbers regardless of its conductivity. For the annulus with an outside wall of finite conductivity, results show that the relative conductivity of the wall is an important variable in determining the temperature of the rest of the domain. However, the conductivity of the outer wall had little effect on the structure of the flow field or the maximum velocities. For a higher aspect ratio cavity without an outside wall, the maximum velocities are higher while the overall heat transfer rates are found to be lower. This can be attributed to cavity geometry and the mechanisms for heat transfer above and below the baffle.
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