Flow pattern criteria for vapor condensation inside a downward inclined tube

Vapor condensation in inclined tubes is a widely used process in various industries, but currently there is no verified map available for predicting flow patterns during condensation. This study aimed to develop a method to predict flow patterns during condensation in downward inclined tubes. The literature on condensation flow patterns in downward inclined tubes was thoroughly investigated, and this paper presented a summary of experimental data on condensation in downward inclined tubes, covering inclination angles from 7 degrees to 75 degrees (downward flow), tube diameters from 5.79 to 25.0 mm, pressures from 0.1 to 1.0166 MPa, mass fluxes from 8.1 to 705 kg/m2s, and three fluids including water and refrigerants. By comparing the existing flow pattern maps with the data, it was found that the existing flow pattern maps were deficient and did not predict the conden-sation flow pattern well. Based on extensive condensation flow pattern data, a set of criteria for predicting the flow pattern during condensation, using the modified Froude number F and the Lockhart-Martinelli parameter X as map coordinates, was proposed. The results showed good prediction accuracy for inclined in-tube conden-sation flow patterns.