Experimental visualization of two-phase flow patterns and transition from stratified to slug flow

Abstract

The transition from stratified to slug flow generates oscillations in pressure and flowrates. Large liquid surges associated with slug flow are detrimental to the operation of process equipments involving two-phase flow. The characterization of two-phase flow regimes and their transition is thus an important area of research. In the present work, flow patterns for various regimes of air-water two-phase flow are captured experimentally. A flow pattern map is established based on the visualized images. The developed flow regime map is compared with that obtained by Ghajar and Tang. Slug frequency is recorded for a variety of superficial Reynolds number to show the instances of impact pressure. The development of slug and transition to slug flow from stratified flow are analysed using these captured images. It is observed that slug becomes highly chaotic with dispersion of air bubbles, when gas superficial Reynolds number is increased for a fixed value of liquid superficial Reynolds number. For lower gas superficial Reynolds number, the slug is observed to be very clear (without air entrainment). This is true for higher value of liquid superficial Reynolds number as well. The air entrainment increases with increasing gas superficial Reynolds number. This air entrainment might play a dominant role in deciding the flow and thermal characteristics of such two-phase flows.

Prediction of liquid height for onset of slug flow

“…The outlet zone is made by galvanised iron pipe of diameter 25.4 mm. Description of various other components of the experimental test rig along with experimental methodology is provided in earlier paper by the same authors (Vaze and Banerjee, 2011).…”

Numerical rebuilding of dynamic instabilities and forces in multiphase pipe bend flow

“…The class of interFoam solvers can handle compressible or incompressible two-phase flow problems by applying an interface capturing technique based on the volume of fluid method (VOF). Validation has been performed for a wide range of multiphase problems, recently also for different flow regimes in pipe flow including validation for liquid hold-up and pressure drop [5][6][7][8]. For the present study the compressibleInterfom solver of OpenFoam 2.3.0 was used which can handle compressible, non-isothermal immiscible liquid or gaseous phases.…”

“…Recently, some of the cases have been rebuilt successfully by commercial CFD codes [3,4]. The present work focusses on the prediction of the different flow topologies resolving Kelvin Helmholtz instabilities on the gas liquid interface [5] and an accurate estimation of the forces in the bends by an open source CFD code (OpenFoam). Special emphasis will be put on the level of detail which is required with respect to mesh resolution, geometrical features, inflow and initial conditions but also turbulence modelling to successfully model these kind of multiphase flows.…”

Onset of intermittent flow: Visualization of flow structures

“…The authors showed that there is no direct transition between stratified and plug flow in the proposed flow pattern map. These observations, were also made by Ghajar and Tang [28], Vaze and Banerjee [29] and Thaker and Banerjee [10], contradicting those reported by Hurlburt and Hanratty [20]. Bhagwat and Ghajar [30] proposed an empirical model for the transition from stratified to non-stratified flows.…”