ABSTRACT

Condensation of a vapor from an air stream can take place as a film of the condensed material on the wall of the condenser tube or as a series of drops that form at various points on the surface. Film-type condensation is the more common mechanism encountered in a condenser. The film uniformly coats the surface, and the thickness of the film increases with the extent of the surface. In dropwise condensation, the surface is not uniformly covered. The individual drops form and grow on the surface and tend to coalesce with neighboring drops. Adhesion of the drops is then overcome by gravitational forces, and the coalesced drops run off the surface. Impurities in the vapor stream promote dropwise condensation, which results in higher heat transfer coefficients. Unfortunately, there is not much information available on dropwise condensation. Therefore, design methods are limited to the film-type case.