Inception criteria for droplet entrainment in two‐phase concurrent film flow

Inception criteria for droplet entrainment in concurrent gas‐liquid film flow were developed from simple physical models. For film Reynolds number ≳ 160, an entrainment model based on the shearing off of roll‐wave crests was used. At lower film Reynolds numbers, a wave undercutting mechanism was introduced. Experimentally observed abrupt changes in the critical gas velocity corresponding to the onset of entrainment at a certain film Reynolds number have been explained by the shift in the entrainment mechanisms. An agreement of the present inception criteria with various experimental data is shown to be satisfactory, and significant improvements over the existing empirical correlations have been made.