Heat Enhancement in a Short Air Channel with Solid and Permeable Baffles

Heat transfer enhancement to turbulent air flow in a short rectangular constant-wall temperature channel fitted with either solid or permeable baffles were numerically studied based on COMSOL (R) simulations. The number of used baffles (1 to 7), Reynolds number (10000, 20000, and 30000), and baffle permeability (1 x 10-11 to 1 x 10-6) were investigated. Operations under turbulent flow conditions were considered, which has not been extensively studied. The average temperature of air at the channel exit and the pressure drop along the channel were obtained via simulation for different cases. For solid baffles, the heat transfer enhancement parameter ranged from 0.30 to 0.35 due to the high friction, while for permeable baffles, it ranged from 1 to 35 as the permeability and number of baffles increased. This is due to the heat-transfer-area increase and pressure-drop reduction when the flow passes through the permeable baffles. For permeable baffles, a minimum heat exchanger temperature approach of 10 K was achieved with minimal pressure drop at a permeability of approximately 4 x 10-8 when using 4-6 permeable baffles. Accordingly, the results demonstrated that using four permeable baffles with a permeability of approximately 4 x 10-8 m2 is optimal from thermal, economical, and mechanical viewpoints.