PIV measurements and Eulerian-Lagrangian simulations of the unsteady gas-liquid flow in a needle sparger rectangular bubble column

In this work, we conducted a detailed experimental as well as a computational study for the hydrodynamic characterization of the flow in a needle sparger rectangular bubble column. Particle image velocimetry technique (PIV) was used to simultaneously capture the images of both bubbles and seeding polyamide tracers of 50 μm in diameter, the tracer particles were selected to provide sufficient contrast and were neutrally buoyant. A three-dimensional computational model based on an Euler-Lagrange (E-L) approach was performed to simulate the dynamic characteristics of the oscillating bubble plume. The continuous phase velocity field was obtained by solving the unsteady Reynolds averaged Navier-Stokes equations along with the k-ε turbulence model. Bubble tracking was achieved by solving the Newton equations of motion taking into account drag force, pressure, buoyancy and gravity. Two-way coupling between the liquid and gas phases are accounted for in the continuous phase momentum equation. The effect of gas flow rate on the dynamic and time-averaged flow properties were studied, the flow was found to have an unsteady structure with three vortices moving in the upward direction and the bubble plume between them oscillated. The simulated results were found to be in accordance with the PIV measurements for a gas flow rate up to 0.1 l/min. The simulated turbulent kinetic energy indicates that the stronger bubble plume velocity oscillations are located near the entrance zone and are caused by the addition of a shear induced turbulence produced by the presence of an oscillating bubble plume.