On the prediction of the transition from stratified flow to roll waves and slug flow in horizontal pipes

A new theoretical model has been developed for determining flow regime transitions in two-phase gas-liquid flow in horizontal pipes. The theoretical model provides a physical explanation for the development of the perturbed interface of the stratified flow into a roll wave or slug flow. Transmission of kinetic energy from the gas phase to the liquid wave and the compressibility of the gas phase are considered. By tracking the interface – at the crest and at a reference point – the time required for the wave to develop into a slug and the time needed for the roll wave to be reached are calculated. The results represent a reasonable explanation for the discrepancy between theoretical predictions of slug stability theory and transition data for the critical superficial liquid velocity. In this paper we make use of the theoretical model and the slug stability model to improve the predictions of the transition to slug flow region for different pipe diameters. Besides the improved predictions the main contribution of this approach is the comprehensiveness that includes a mechanism for the initiation of roll waves. An important result is the prediction of critical superficial gas velocities at which roll waves start to initiate