An experimental study was carried out to investigate enhancement of heat transfer in compact heat exchanger by keeping pressure drop constant in a given range. Two different test matrices, cylindrical and triangular, used to find the optimum ribs were compared with a smooth channel. The investigation was performed with both laminar and turbulent forced how for Reynolds numbers from 250 to 7000. The geometric parameters, in order to satisfied manufacturer demands, were fixed at p/e = 6.67 and the wall temperature was held constant at 50 degrees C. The technique of holographic interferometry was used to determine the temperature distribution in the test duct. Velocity distribution was measured using laser doppler anemometer techniques. For comparison the technique of global measurement was also used. The results revealed that cylindrical ribs are optimum heat transfer for conversion of pressure drop. An 8% experimental error was found in global measurement compared to holographic interferometry. (C) 1998 Elsevier Science Inc. All rights reserved.