In this paper, results obtained using a phenomenological model which incorporates a correlation to calculate the fraction of the total liquid flow entrained as droplets at the onset of annular flow are presented. Both diabatic and adiabatic cases are studied. In the adiabatic case, comparisons are made with the experimental equilibrium entrained fraction. i.e.. that resulting from equal rates of droplet entrainment and deposition. In the diabatic situation, results are presented in terms of the heat transfer coefficient for forced convective boiling of binary and ternary hydrocarbon mixtures. In the air-water case, present results show better agreement with experimental data than previously used approaches and methods. In the flow boiling situation, the inclusion of the entrained fraction correlation provides the best agreement with the experimental data in only a few cases.