Buoyancy-assisted mixed convection in a vertical channel with spatially periodic wall temperature

Abstract

The influence of a spatially periodic temperature boundary condition on the laminar mixed convection in an upward flow between two vertical parallel plates is numerically studied. A detailed assessment is presented of the effects of the Grashof and Reynolds numbers, the channel length, and the wavelength of the periodic temperature distribution at the colder wall on the flow and thermal characteristics. It is found that, above a critical ratio of Grashof-to-Reynolds numbers, the flow gradually changes into a multi-cellular regime, with periodic features that match the periodicity of the boundary temperature distribution. Local recirculating zones are formed near the colder wall with size and strength that are increased with increasing ratio of Grashof-to-Reynolds numbers, periodicity of the flow domain and/or wavelength of the spatially periodic wall temperature. The temperature field exhibits a variation in the vertical direction affecting the wall heat transfer with increasing Grashof and Reynolds numbers. The wall heat fluxes are initially decreased acquiring a local minimum value and are subsequently increased with increasing ratio of Grashof-to-Reynolds numbers, while they are reduced with increasing the channel length.