FLOW AND HEAT TRANSFER PAST A CYLINDER IN PROXIMITY OF A WALL
The wake dynamics past a circular cylinder at the vicinity
of a wall has gained immense attention over last decade.
Similar flow features can be observed during take-off and
landing of an aircraft or in shell tube heat exchangers where
the tube is near the shell. However, many interesting features
concerning the heat transfer characteristics are yet to be
resolved realistically. Objective of the present work is to
resolve the flow physics and thermal field for a cylinder in
proximity to a wall through numerical simulations. A detailed
parametric study for different G/D (gap to diameter ratio) and Prandtl numbers are performed to explore the induced
unsteady flow physics and heat transfer at a fixed small
Reynolds Number, ReD=200. Interaction between flat plate boundary layer and cylinder shear layer is found to be enhanced while decreasing gap to diameter ratio which is varied as G/D=1, 0.75, 0.5 and 0.25. This results in increased heat transfer due to convective mixing. However, there is drastic fall in heat transfer when the gap is below a certain critical gap ratio which can be attributed to the frozen vortices behind the cylinder. When variation of Prandtl number is considered for three commonly used fluid, namely air (Pr=0.71), water (Pr=3.24) and Ethylene Glycol 30% (Pr=7.5), decrease in convective mixing while increase in thermal diffusion can be observed for increasing Prandtl number of the fluid. Existence of optimum Prandtl number for maximum heat transfer at a particular gap ratio is one of the most interesting findings of the present study which may also lead to design optimization.