The SIMPLE-C scheme is used to solve the mass, momentum, energy conservation equations and turbulent k-epsilon equations with a two-layer model near wall for a fluid past a reciprocating circular ribbed channel when changing Reynolds number (4250-10,000), Grashof number (0-400,000,000), pulsating number (0-9.3) and cooling mediums. The average time-mean Nusselt number for the reciprocating circular ribbed channel can be 45-182% larger than that for the equivalent stationary smooth channel. The heat transfer enhancement produced by buoyancy for the reciprocating circular ribbed channel decreases as the pulsating number increases. The oscillating amplitude of Nusselt number with crank angle in the oil-cooling is less than in the water-cooling. (c) 2005 Elsevier Ltd. All rights reserved.