EXPERIMENTAL AND NUMERICAL INVESTIGATION OF INTERFACIAL DYNAMICS DURING SINGLE AND STRATIFIED LIQUID DRAINING

Abstract

Gravity-driven gas-liquid two-phase flow and gas-liquid-liquid three-phase flow are observed during liquid draining from a storage tank. It finds many applications like fuel feed systems, liquid rocket systems, bathtubs, kitchen sinks, nuclear reactors, etc. The presence of vortex formation in the tank hinders smooth drainage. A literature review reveals that flow physics inside a drain pipe for single liquid as well as stratified oil-water draining is less explored. The present work attempts to investigate the physics of flow through experimentation and numerical analysis. Experiments have been performed to study the flow physics during draining from a square acrylic tank fitted with a drainpipe at three different eccentric locations. Four different liquids are used for the experiments. Test liquids are water, kerosene and different mixtures of water and glycerol. Several flow regimes, such as bubbly, slug, churn, elongated slug, and annular flow, are observed inside the drain pipe. It is also noticed that bubble and slug never collide in the highly viscous liquid (60% glycerol) due to viscous force dominating. However, the collision occurs at the low viscous fluid (water, kerosene), which is inertia-dominating. Further experiments are performed with stratified oil-water draining to understand the flow physics of oil and water or air entrainment in the drainpipe. Two different oil-water stratifications are selected for the investigation of the influence of oil viscosity on the interfacial flow structure and air entrainment. In one case, the viscosity ratio of oil to water is 1.64 and 55 in other cases. An analytical correlation has been proposed for describing the condition of no air entrainment in the drainpipe in stratified draining. In addition, some interesting phenomena like liquid rope coiling in static and moving surfaces are noted. Different patterns are compared with silicone oil and epoxy resin. It is found that epoxy resin can have better control of pattern formation on a moving base. Further, attempts have been made to develop CFD models of liquid drainage. OpenFOAM software is used for the simulation. Simulations are performed to understand the interfacial dynamics at the extreme eccentric location of e 0.96, at which experiments could not be performed. Also, a scale-down model of the tank is simulated to study the effect of wall wettability. It is noticed that a hydrophobic tank wall is the best way to suppress the vortex, air entrainment and quick draining at extreme eccentricity.