Film Condensation Theory

When the temperature of a vapor is reduced below its saturation temperature, the vapor condensed. In engineering applications, the vapor is condensed by bringing it into contact with a cold surface. The steam condensers for power plants are typical examples of the application of condensing of steam. If the liquid wets the surface, the condensation occurs in the form of a smooth film, which flows down the surface under the action of the gravity. The presence of a liquid film over the surface constitutes a thermal resistance to heat flow. Therefore, numerous experimental and theoritical investigations have been conducted to determine the heat transfer coefficient for film condensation over surface. The first fundamental analysis leading to the determination of the heat transfer coefficient during filmwise condensation of pure vapors (i.e., without the presence of non-condensable gas) on a flat plate and a circular tube was given by Nusselt in 1916. Over the years, improvements have been made on Nusselt's theory of film condensation. But with the exception of the condensation of liquid metals, Nusselt's original theory has been succesful and still is widely used.