Hydrodynamics in a bubble column at elevated pressures and turbulence energy distribution in bubbling gas-liquid and gas-liquid-solid flow systems

In this study, the hydrodynamics in a high pressure bubble column is experimentally investigated. The turbulence energy distributions in the gas-liquid bubble column system and the effect of solids on the turbulence are investigated using the LDV and the PIV (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. The energy containing ranges for the bubble-induced turbulence and the shear-induced turbulence are determined from the liquid phase power spectra. Experimental results indicate that the bubble-induced turbulence dominates over the liquid shear-induced turbulence 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 power spectra indicates that the bubble-induced turbulence includes the turbulence from eddies in the bubble wake and that from the drift velocity change due to rising bubbles. The interaction between two turbulence fields is studied with a two-orifice gas distributor. The interaction can only be observed when the turbulence in both fields is strong and the interaction tends to enhance the turbulence in both fields. Furthermore, the effect of the solid particles on the liquid phase turbulence is studied. 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. The liquid phase turbulence is enhanced in the presence of particles at high superficial gas velocities while it is attenuated under low superficial gas velocity conditions. A criterion based on the variation of a parameter defined by Ug( r)/umf 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.; The behavior of a 6 mm mesobubble in an acoustic standing wave field is examined both experimentally and numerically. The acoustic standing waves at 16 kHz and 20 kHz are generated using two Nickel magnetostrictive transducers located at the top and bottom of the column. Experimental studies of the rise velocity of a mesobubble in the acoustic field indicate an axial wavy rising pattern of the bubble synchronized with that of the standing wave. The bubble rise velocity is significantly lower than that in the absence of an acoustic field. The behavior of bubble volume contraction and expansion can be accounted for by a 3-D direct numerical simulation of the bubble dynamics and flow field based on the compressible N-S equations coupled with the level-set method. (Abstract shortened by UMI.)...