Analysis of Annular and Stratified Flows for Vapor Condensation Heat Transfer in Horizontal Tubes

The greater part of the horizontal condenser tube is occupied by the stratified and annular flows, which play important roles in condensation heat transfer coefficients. Both a volume of fluid (VOF) interface tracking method and k-e two equations model was applied to analyze the characteristics of the stratified and annular flows for horizontal tubes, obtaining distribution of velocity, contours of both temperature and local condensation heat transfer coefficients. The computation shows that an annular flow having thinner liquid film attached on the inner surface of tubes appears at the inlet of the horizontal condenser tube because vapor exerts a higher interfacial shear stress on the gas-liquid interface, therefore, there are a higher local condensation heat transfer coefficients there. Next, as vapor quality decreases and condensate gravity increases along the condenser tube length, the condensation flow pattern transforms from the annular flow into the stratified flow in which local condensation heat transfer coefficients decreases and distributes unevenly along the circumference as liquid film at the bottom of the condenser tube become thicker. In addition, in the stratified flow, a wave structure is formed in the middle of the condensate pool at the bottom of the condenser tube because condensate on the top of the condenser tube slides into the bottom of the condenser tube and collapse each other. The heat transfer rate calculated by the present method is compared to those predicted from a Shah correlation, the agreement is found to be good, and both errors is within 7%.