A general model for the transition to gas-liquid dispersed bubble flow is proposed in this paper, based on an assumption that dispersed bubble flow cannot exist unless the turbulent kinetic energy of the liquid phase is greater than the surface free energy of dispersed spherical bubbles. This model is capable of predicting the transition boundary to dispersed bubble flow in various closed channels over the whole range of inclination angles. It also yields a good prediction for the slug liquid holdup in gas-liquid slug how in conjunction with the Barnea-Brauner hypothesis (1985, Int. J. Multiphase Flow 11, 43-49).