Based on their correlation, given the regime transition properties between bubbly flow and churn-turbulent flow, namely the transition superficial velocity, Vg,trans and transition (critical) holdup Vg,trans, the small and large bubble velocities and holdup contributions can be estimated. Researches on bubble size distributions and factors affecting bubble sizes such as gas density, liquid viscosity, surface tension and operating conditions (pressure, temperature) are widely reported in literature [15].