A method has been employed to augment the forced convection to ambient air from a horizontal rectangular plate with its upper surface mounted with transverse (to the mean air-flow) rectangular ribs, which are uniformly spaced and heated. The enhancement has been achieved by drilling uniformly-spaced holes in the base plate between consecutive ribs. The steady-state effects of varying the penetration ratio, beta, (i.e. of the total cross-sectional areas of the holes to the whole base-plate area between consecutive ribs), diameter of the hole, d, ratio of channel＇s height to rib＇s common height, H/B, and Reynolds number, Re,, of the air-Sow on the rate of forced convection from the rectangular prate were investigated experimentally for both laminar and turbulent flows over the ribs. Heat-transfer measurements were obtained for the ranges: 500 less than or equal to Re-c less than or equal to 19,000; 4 less than or equal to H/B less than or equal to 10 and 0.05 less than or equal to beta less than or equal to 0.20. The following correlation applied for the prediction of the average heat-transfer coefficient for this heat-transfer system (i.e. as contained in the wind-tunnel): Nu(C) = 0.39Re(C)(0.50)(H/B)(0.76)beta(0.24) To achieve the maximum heat-transfer performance with this type of heat exchanger-for a specified application in which the degree of inhibition experienced by the air in flowing through the holes is known-optimised choices of the location, diameter and number of holes, as well as for the materials of the ribs and base, have to be made.