To reveal the condensate film spatial distribution in flat tube is the basis of anti-freezing operation of air-cooled condensers in winter.Thus

a reflux condensation flow and heat transfer theoretical model was built up for finned flat tube widely applied in air-cooled condensers

including condensate bath development sub-model and condensate film development sub-model on the other wall.Considering the opposite interfacial shear stress from condensate water discharging direction for reflux condensation

the condensate liquid spatial distribution and condensation flow and heat transfer characteristics were investigated.Moreover

this model was applied in five condition cases in winter with low environmental temperature

and the variation characteristics or variation rules of condensation film thickness

condensation heat transfer coefficient and pressure drop along the axial direction were obtained.The results indicate that only a really thin film was formed on the vertical wall of the flat tube

most of the condensate water concentrated toward the bottom of the flat tube to form a condensate water bath.The bath locates at the region with the lowest temperature of the coolant

thus it has high risk of being frozen in winner.The condensation heat transfer coefficient decreases with the increasing axial distance.In the entrance region with high vapor velocity and very thin film

the condensate film backflow occurs due to the over large interfacial shear stress between the gas and liquid phase.Therefore

we can distinguish whether the frozen will occur in an area in winter by the distribution of condensate film inside the tubes.