ABSTRACT
Dropwise condensation involves a combination of several processes. Bare surface is continually exposed to vapor by coalescences between drops and by the sweeping action of the departing drops as they are removed from the surface by gravity or vapor shear stress. "Primary" drops are formed at nucleation sites on the exposed surface. Clean metal surfaces are wetted by non-metallic liquids, and film condensation is the mode that normally occurs in practice. Non-wetting agents, known as promoters, are needed to promote dropwise condensation. The heat-transfer coefficient of dropwise condensation of steam at a pressure near 1 atm has been measured by many researchers. Taken together, these show a considerable scatter due to the effect of noncondensing gas and the accuracy of measuring method. Several sets of results are available for dropwise condensation of steam on copper condensing surfaces at pressures below 1 atm.
