Stability of stratified two-phase flows in inclined channels

Abstract

Linear stability of stratified gas-liquid and liquid-liquid plane-parallel flows in inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict parameter regions in which stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid

Stability of stratified two-phase channel flows of Newtonian/non-Newtonian shear-thinning fluids

“…4). This is in contrast to the results obtained for less viscous air-water system, where an increase of inclination has a destabilizing effect (Barmak et al, 2016b). In fact, for such conditions the flow destabilization is dominated by the liquid inertia.…”

“…, at near critical conditions), whose growth is still close to zero, and the shape of streamlines and disturbed interface are similar to those of longer wave perturbations (see details in Barmak et al, 2016b). It is important to mention that the flow is not steady with respect to the stationary frame of reference (which is used in the present study), and the (moving) interface at a particular moment of time may not coincide with a streamline (Figures 7(b), (d), (f), see details in Barmak et al, 2016b). Figures 7(a), (c), (e), the perturbations are represented by pairs of antisymmetric vortices (of /2 wave l width) with their core, i.e., the maximum of the stream function perturbations, located in the bulk of air layer (A and C) or at the interface (B).…”

“…Due to competition between gravity and shear forces multiple base-flow configurations (i.e., up to three solutions for the holdup) can be encountered in downward inclined gas/shear-thinning liquid flows (Picchi et al, 2016a(Picchi et al, , 2017. , at near critical conditions), whose growth is still close to zero, and the shape of streamlines and disturbed interface are similar to those of longer wave perturbations (see details in Barmak et al, 2016b). It is important to mention that the flow is not steady with respect to the stationary frame of reference (which is used in the present study), and the (moving) interface at a particular moment of time may not coincide with a streamline (Figures 7(b), (d), (f), see details in Barmak et al, 2016b).…”

Non-modal stability analysis of stratified two-phase channel flows

“…In slightly upward inclined flows ( 0.1 (Barmak et al, 2016b). This is a region of operating conditions of particular interest, since in upward inclined flows this is the only region where stratified flow was experimentally observed (e.g., Barnea et al, 1980).…”

“…The feasibility of obtaining multiple holdups in inclined channels was validated experimentally (Ullmann et al, 2003a, b). Moreover, at least two distinct solutions were found to be 20 stable in a range of superficial velocities in upward inclined concurrent and counter-current flow (Barmak et al, 2016b). of the corresponding optimal perturbations for point B (Fig.…”