The influence of liquid properties on flow structure, bubble dynamics and mass transfer in a laboratory bubble column: Experimental analysis versus numerical modelling and computation

Abstract

Based on detailed experiments with optical shadowgraphy in a bubble column, the influence of liquid viscosity on bubble behaviour was numerically computed with the Euler/Lagrange approach including mass transfer. Fluid flow and sub-grid-scale-turbulence (SGS) was obtained by Large Eddy Simulation (LES) including a k-transport equation. Bubbles were tracked by a point-mass approach, considering all relevant forces. For the lift coefficient a composite correlation was applied considering viscosity. An experimentally-based bubble dynamics model was considered, randomly generating eccentricity, motion angle and Sherwood numbers. SGS turbulence acting on bubble motion was modelled through a Langevin-type approach. Two-way coupling was considered in momentum and SGS turbulence. The bubble column (diameter 140 mm; height 710 mm) contained either pure water or water-glycerol mixtures. Bubbles were injected through 4 needles yielding a distribution with a mean diameter 3.6 mm. The numerical results demonstrated the enormous effect of accounting for bubble dynamics and the possibility to adapt this model for different liquid properties, although not yet generalised. Overall, good agreement between simulations and measurements was found for non-reactive and reactive cases. This concerns local properties, spatial distributions of the velocities of both phases and the temporal evolution of the pH-value when modelling bubble dynamics properly.