Analysis of stratified/non-stratified transitional boundaries in inclined gas-liquid flows

Stability and well-posedness analyses are shown to yield complimentary predictive tools for the stability of stratified gas-liquid flow and the departure to other bounding flow patterns over a wide range of (upward and downward) inclination. The conditions for marginal stability and well-posedness are further shown to coincide with the conditions for stable kinematic and dynamic waves derived from wave theory. A complete stratified/non-stratified transitional boundary is proposed, which shows satisfactory agreement with experimental observations in horizontal and inclined conduits. The observed sensitivity of the departure from the stratified configuration to the flow inclination is well-elucidated, in view of the dramatic effects of inclination on the structure of the stability and well-posedness map. The effects of physical properties, liquid viscosity, phases densities and density differential on the stability and well-posedness map in inclined systems are also explored.