The effect of surface tension on flow pattern, holdup and pressure drop during horizontal air—water pipe flow at atmospheric conditions

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Experimental data are reported for cocurrent air—water and air—surfactant solution two-phase flow in a pipe 0.0935 m in inside diameter. The surfactant solution reduced the surface tension of water from 0.072 to 0.046 kg s −2. The effect of surface tension reduction on observed flow pattern, holdup and pressure drop was investigated. The pressure drop was unaffected, but holdup increased by a maximum of 30% above that of water, between air flow rates of 0.02 and 0.07 m 3 s −1. The transition from smooth stratified to stratified and ripple flow was at higher air velocities and the onset of entrainment at reduced air velocities, for the surfactant solution. The observed experimental flow patterns were plotted on the flow maps of Baker, Weisman et al. and Andritsos. The entrainment criterion of Ishii was also investigated.