Turbulence energy distributions in bubbling gas–liquid and gas–liquid–solid flow systems

Abstract

The turbulence energy distributions in the gas–liquid bubble column system and the effect of solids on the turbulence are investigated using the laser Doppler velocimetry and the particle image velocimetry. The superficial gas velocity employed ranges from 0.025 to 7.5 cm/s , covering such bubble-flow conditions as single-bubble chain, bubbly flow and churn-turbulent flow. Turbulence induced by rising bubbles through bubble wakes is also examined. Experimental results indicate that the bubble-induced turbulence dominates over the liquid shear-induced turbulence in turbulence generation under the operating conditions of this study. The development of the flow field and the turbulence energy of the liquid-phase in the nozzle region are probed. Furthermore, a self-similarity phenomenon is observed in a two-phase flow system. The analysis of the power spectra in gas, liquid and solid phases indicates that the Kolmogorov −5/3 law is obeyed in the inertial range. The presence of solids reduces the transition frequency from the energy-containing range to the inertial range. The effect of the solids on the liquid-phase turbulence is complex. It depends on solids properties and flow field around particles. A criterion based on the variation of a parameter defined by U g ( r)/ u mf is proposed to account for the effect of the solids on the liquid-phase turbulence. The prediction based on this criterion matches well with the experimental results.