Numerical Analysis of Enhanced Heat Transfer Using a Pair of Similar Porous Baffles in a Backward-Facing Step Flow

Baffles have long been known to be useful in enhancing heat transfer in channels with sudden expansions. However, their utility has been limited due to the increased differential pressure they incur in the flow. In this work, a pair of porous baffles is proposed to provide a solution to this problem. It is based on a finite-element numerical simulation of heat transfer and fluid flow through a two-dimensional channel with a backward-facing step. The baffles are modelled as matrices of two-dimensional rods arrayed downstream of the step, and on the top and bottom walls of the channel. Nondimensionalized parameters considered are the Reynolds number, Re (= 100 to 1000), normalized porous matrix location xp/S (= 0.5 to 6), normalized porous block length Lp/S (= 0.5 to 2.5), Darcy Number, Da (= 10-2 to 10-6), and normalized channel downstream length Ld/S (= 5 to 30). Results show that compared to the case of an unobstructed channel, the installation of porous baffles on both channel walls can generate up to 200% improvement in heat transfer. Optimal heat transfer effect with minimal differential power requirement is attained when the porous baffle length is half the step height S, and located 2S downstream from the step. Augmented heat transfer outcomes with minimal penalty of pressure drop are also reached at Re = 1000 and for Lu /H = 5. For such a case, for the same pressure drop requirement, convection to conduction heat transfer is 88% better when a pair of porous baffles are used, compared to an unobstructed flow.