Pressure gradient and holdup in horizontal two-phase gas–liquid flows with low liquid loading

Pressure gradient and holdup data are presented for air–water and air–oil flows in a horizontal, 0.079 m diameter pipe. Addition of a very small liquid flow was found to result in a considerable increase in the pressure gradient compared with single phase gas flow. The pressure gradient and the holdup data were compared with predictions of the ‘apparent rough surface’ (ARS) and the ‘double-circle’ models. The ARS model generally gave better predictions for the holdup over the experimental range. Both models predicted the pressure gradient for air–water flows at high gas flowrates reasonably well. However, the predictions of both methods were unsatisfactory for air–water experiments at low gas flowrates and for air–oil experiments. Overall the ARS model was judged to be the more robust.