reflux condensation heat transfer characteristics of countercurrent vapor-liquid flows on a vertical surface

the phenomenon of reflux condensation in vertical tubes occurs in nuclear power reactor u-tube steam generator during a loss of coolant accident. this phenomenon is considered and studied as it is related reactor safety. in the present work, a combined analytical and experimental study of reflux condensation heat transfer characteristics are conducted. the analytical model is developed to study the effect of surface waves, interfacial shear stress and convection on the condensate film thickness, Reynolds number and Nusselt number inside a vertical tube. this analytical study is conducted in both constant temperature and constant heat flux at tube inner wall. the analytical results of that model are compared with Nusselt and Gung's solutions, this comparison indicates that, the increase of surface waves and interfacial shear stress causes retardation of the condensate flow and the dimensionless film thickness to increase during reflux condensation in a vertical tube. this retardation in turn affects the heat transfer characteristics i.e.(Re,Nu)