This paper aims to investigate both experimentally and analytically the heat transfer characteristics in a porous heat sink characterized by straight circular ducts. This kind of heat sink is appreciated in miniaturized heat dissipation applications owing to the low flow resistance in comparison with its bead-characterized counterparts. The test systems were established for air and water flows and the experiments were conducted with the cell Reynolds number Re ranging from 6.7 to 545 and 8.5 to 990, respectively. The theoretical modeling is conducted based on a two-equation model. The measured wall temperature rises and the Nusselt numbers are presented for both working fluids. In the air experiment, a Re-1.05 dependence is found for the Nusselt number, while in the water experiment, the Re dependence is logarithmic. The theoretical results are compared with the experimental measurements and the agreement is satisfactory. (C) 2001 Elsevier Science Ltd. All rights reserved.