Measurements of the liquid film profile and pressure drop were made in tubes with grooves of varying angle (0degrees, 9degrees and 18degrees) as well as tubes with varying numbers of grooves at a common angle (18degrees). These data indicate that the grooves act to redistribute the liquid film on the inner wall perimeter and that only a relatively small number of grooves (12) is needed to do this. The grooves also affect the stability of the vapor-liquid interface and can generate lower average liquid film thickness. The pressure loss is directly related to the number of grooves for the tubes studied. (C) 2003 Elsevier Ltd..All rights reserved.