Flow Induced by Dual-Turbine of Different Diameters in a Gas-Liquid Agitation System: the Agitation and Turbulence Indices

Abstract

Flow induced by a dual turbine stirred tank was characterized measuring local velocities with a LDV and drawing the main velocity fields and the maps of turbulence intensities. The hydrodynamic regime studied in all the experiments was the so-called merging flow regime. Two impeller configurations were studied. In the first one, two disk style turbine of the same dimensions (configuration A) were used, while in the second one, the dimensions of the upper turbine were 20 % proportionally smaller than those of the lower turbine (configuration B). The agitation and turbulence indices were used to evaluate, as a first order approximation, the power consumption distribution between convective and turbulent flows. The comparison of the two-phase agitation systems studied showed that configuration B seems to be more efficient than configuration A, since both induce a similar global convective flow, but the first one assures a significant reduction of power consumption. The distribution of power consumption between convective and turbulent flows was evaluated using the agitation index and a new global parameter: turbulence index.

Two-Phase Flow and Bubble Size Distribution in Air-Sparged and Surface-Aerated Vessels Stirred by a Dual Impeller

“…In recent years the features of two-phase flow have been studied with advanced experimental techniques, primarily laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). For sparged vessels of standard geometry mainly the behavior of the liquid phase has been investigated, − while limited data are available on bubble velocities and on the turbulent features of the gas phase. − Similar information for more complex geometric configurations (such as dual or multiple impellers, surface aerators, self-inducing aerators, jet-loop systems, etc.) is even less available and is restricted to the liquid phase .…”