Physical understanding of gas-liquid annular flow and its transition to dispersed droplets

Abstract

Transformation from annular to droplet flow is investigated for co-current, upward gas-liquid flow through a cylindrical tube using grid based volume of fluid framework. Three transitional routes, namely, orificing, rolling, and undercutting are observed for flow transformation at different range of relative velocities between the fluids. Physics behind these three exclusive phenomena is described using circulation patterns of gaseous phase in the vicinity of a liquid film which subsequently sheds drop leading towards transition. Orifice amplitude is found to grow exponentially towards the core whereas it propagates in axial direction in a parabolic path. Efforts have been made to fit the sinusoidal profile of wave structure with the numerical interface contour at early stages of orificing. Domination of gas inertia over liquid flow has been studied in detail at the later stages to understand the asymmetric shape of orifice, leading towards lamella formation and droplet generation. Away from comparative velocities, circulations in the dominant phase dislodge the drop by forming either a ligament (rolling) or a bag (undercut) like protrusion in liquid. Study of velocity patterns in the plane of droplet dislodge reveals the underlying physics behind the disintegration and its dynamics at the later stages. Using numerical phase distributions, rejoining of dislodged droplet with liquid film as post-rolling consequences has been also proposed. A flow pattern map showing the transitional boundaries based on the physical mechanism is constructed for air-water combination.

Dynamics of inner gas during the bursting of a bubble at the free surface

“…Grid adaptation based on the gradient of phase fraction (T) is considered to refine the interface locally. Earlier, Gerris has been used extensively to predict the complex interfacial phenomenon [12,18,[32][33][34][35].…”

Multiphasic Continuous‐Flow Reactors for Handling Gaseous Reagents in Organic Synthesis: Enhancing Efficiency and Safety in Chemical Processes

“…This results in a very thin liquid layer, leading to a high interfacial contact area and a short diffusion length, as well as relatively large availability of the gaseous reagent [4,41] . However, ideal annular flow is often very difficult to achieve since droplets can be dislodged from the liquid film due to the force of the gas phase [42] . The occurrence of these dispersed droplets can lead to a deviation from annular flow, and is commonly called misty flow (Figure 4E).…”

Experimental Investigation on the Pulse Flow Regime Transition of Gas–Liquid Concurrent Downward Flow through a Sieve Plate Packed Bed

“…A detailed process of the rolling breakup of the liquid disturbance wave 29 is presented in Figure 12. In the pulse flow regime, as G s increases, the amplitude of the disturbance wave increases (see Figures 12a and 12b), thereby enhancing the intensity of the pulse flow.…”

“…In the pulse flow regime, as G s increases, the amplitude of the disturbance wave increases (see Figures 12a and 12b), thereby enhancing the intensity of the pulse flow. Subsequently, folding of the liquid disturbance wave from the gas/liquid interface appears 29 (see Figures 12c and 12d). Finally, the liquid wave thins out to form lamella because of the intense disturbance of the gas phase, and these lamellae subsequently pinch off at the base, 29 as shown in Figures 12e and 12f.…”

“…Subsequently, folding of the liquid disturbance wave from the gas/liquid interface appears 29 (see Figures 12c and 12d). Finally, the liquid wave thins out to form lamella because of the intense disturbance of the gas phase, and these lamellae subsequently pinch off at the base, 29 as shown in Figures 12e and 12f. The breakup of the liquid waves broadens the flow path of the gas phase, thus leading to the disappearance of the pulse flow.…”