Mixed convection in a channel with porous multiblocks under imposed thermal modulation

Abstract

This study is made of an enhancement of a mixed-convection heat transfer in a channel containing multiple porous blocks heated from below. The heat flux from the most upstream heater varies in a sinusoidal form, while other heaters have a constant heat flux. The Brinkman-Forchheimer-extended Darcy model and two-equation energy model are adopted to characterize the flow and temperature fields inside porous regions. The explicit effect of thermal modulation at the upstream heater is examined by acquiring comprehensive numerical solutions. The heat transfer enhancement is pronounced at the far downstream heaters when resonance is realized. The resonance frequency is close to the characteristic frequency of the system, which scales with the time for the main stream to travel from a heater to a neighboring heater. The evolutions of flow and temperature fields are exemplified to provide physical interpretations. The effects of pore density and of porous block height are reported. The benefit of heat transfer augmentation, as opposed to the increased friction factor, is assessed to justify the use of thermal modulation in the upstream heater.