In the present work, the heat transfer and friction loss characteristics were investigated experimentally, employing a finned heating surface kept at a constant temperature of 45 degreesC in a rectangular channel through which air was passed as working fluid. The position of the cylindrical fins attached on the surface was arranged either in-line or staggered. The parameters for the study were chosen as Reynolds number (3700-30 000), depending on hydraulic diameter, the distance between fins in the flow direction (S-y/D = 1.96-4.41) and fin arrangement. The variation of Nusselt number with these parameters was determined and presented graphically. For both fin arrangements, it was found that increasing Reynolds number increased Nusselt number, and maximum heat transfer occurred at S-y/D = 2.94. Correlations for Nusselt number and friction factor were developed for both fin arrangements and smooth channel, and the thermal performances of the arrangements were also determined and compared with respect to heat transfer from the same surface without fins. With the staggered array, a heat transfer enhancement up to 33% at constant pumping power was achieved. (C) 2001 Elsevier Science Ltd. All rights reserved.