Developing combined free and forced laminar convection between vertical parallel plates with constant wall temperature.

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A theoretical study is presented on the transfer problem subject to developing flow of mixed convection between vertical parallel plates. Present analysis aims to make clear the transfer mechanism for aiding and opposing flow, based upon and developing Leveque''s solution. Average mass transfer measurements were obtained for both aiding and opposing flow in a vertical annulus by using the electrochemical method, i.e. the reduction of ferricyanide at the cathode in a solution of K4Fe(CN)6-K3Fe(CN)6-NaOH. Both theoretical and experimental results show that the parameter Grh/Reh is able to express the effect of the buoyancy force in aiding and opposing flows. With increasing Grh/Reh in the case of aiding flow, Nusselt numbers increase, being proportional to (RehPrDh/L)n, and the exponent n decreases. As to opposing flow, the buoyancy effect is more remarkable than in the case of aiding flow. It reduces the velocity in the thermal-boundary layer and promotes rapid transition to turbulent state owing to flow instability.
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