Industrial & Engineering Chemistry Research, Vol.44, No.5, 1150-1159, 2005
Energy spectra for interactive turbulence fields in a bubble column
The turbulent energy distributions in the gas-liquid bubble-column system and the effect of solids on the liquid-phase turbulence are investigated using laser Doppler and particle image velocimetries. 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 and liquid shear are examined. The energy containing ranges for the bubble- and shear-induced turbulence is determined from the liquid-phase power spectra. Experimental results indicate that the bubble-induced turbulence is the governing factor in the liquid-phase turbulence in bubbly flows. 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. The effect of solid particles on the liquid-phase turbulence is studied for different gas distributors. 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.