A Critical Review of Condensation Heat Transfer Predicting Models--Effects of Surface-tension Force

摘要

Condensation is defined as the transformation of vapor to its liquid state. Gravity and vapor shear are the two forces that drive the flow of the condensate film inside plain tubes. Traditional codnensation predicting models generally incldue the effects of these two forces. For finned tubes, the surface-tension force will also be important. This paper provides a critical review of existed predicting models to correlate condensation heat transfer coefficients. Gravity-forced domianted models, vapor-shear dominated models and the effects of surface-tension ofrce re all discussed. Three basic methods have been used to model the vapor-shear dominated annular liquid film. The fist model assumed that the vapor core could be replaced with an equivalent liquid flow that would yield the same value for the vapor shear. The second model assumed that the major resistance to heat tranfer was offered only by the laminar liquid sublayer. The third model assumed that the velocity in liquid film could be predicted using von Karman universal velocity profile.