The processes of dropwise condensation of steam on various copper alloy surfaces were recorded by high speed photography.The obtained negatives were analyzed by digital image processing. The results of drop-size distributions

drop growth rates and drop departure diameters under different conditions were derived

and analyzed. The drop size distribution can be expressed as N(D) = AD-B. It was mainly affected by surface properties and was little affected by operation conditions. The growth rate of a small drop was controlled by steam condensing rate

and coalescence among drops was the dominant reason of big drop growth. The drop departure diameter was determined by condensation surface properties. Operation conditions has little influence on drop departure diameter but had obvious effect on drop growth rate.