This paper reports the heat transfer enhancement and corresponding pressure drop over a flat surface equipped with circular cross section perforated pin fins in a rectangular channel. The channel had a cross section area of 100-250 mm(2). The experiments covered the following ranges: Reynolds number 13500-42,000, clearance ratio (C/H) 0, 0.33 and 1 and interfin spacing ratio (S-y/D) 1.208, 1.524, 1.944 and 3.417. Correlation equations were developed for the heat transfer, friction factor and enhancement efficiency. The experimental results showed that the use of circular cross section pin fins may lead to heat transfer enhancement. Enhancement efficiencies varied between 1.4 and 2.6 depending on clearance ratio and interfin spacing ratio. Using a Taguchi experimental design method, optimum design parameters and their levels were investigated. Nusselt number and friction factor were considered as performance parameters. An L-9(3(3)) orthogonal array was selected as an experimental plan. First of all, each goal was optimized separately. Then, all the goals were optimized together, considering the priority of the goals, and the optimum results were found to be Reynolds number of 42,000, fin height of 50 mm and streamwise distance between fins of 51 mm. (C) 2007 Elsevier Ltd. All rights reserved.