Theoretical And Experimental Studies On Hydrodynamics In Bubble Columns

Bubble columns have been fully developed and widely used in chemical, petrochemical and biochemical processes as chemical reactors. The knowledge of hydrodynamics and the modelling of hydrodynamics are considered very important in the design, scale-up and optimal operation of bubble columns.However, most previous experimental investigations of bubble columns consisted only of the measurement of such global parameters as total pressure drop and void fraction. Some empirical and semiempirical correlations attained are restricted to specific flow and geometric condition.In order to study hydrodynamics quantitatively, in the present work bubble behavior and flow structure were determined in a wide range of operating conditions. The experiments were conducted in a plexiglass column of 290 mm ID and 4.5 m height. A five-point electric conductivity microprobe was used to measure radial distribution of gas hold-up, bubble size and bubble rise velocity. An ultrasonic doppler technique was used to determ(?)ne two components of bubble velocity and their spectra in axial, radial directions by means of changing the orientation of the probe. A hot film anemometer was used for determination of radial profiles of liquid velocity and turbulence intensity. Measurements were performed at 5 different heights above the gas distributor and 12 to 17 levels in radial direction.Based on a lot of experimental results and detailed theoretical analysis, the following conclusions can be drawn:1. At lower superficial gas velocity, Ugo, the bubble rise velocity, Ubz, shows a fairly uniformly radial distribution. However, at higher Ugo, Ubz increases and changes significantly along the radial direction.2. There are two peaks in a spectrum of radial component of bubble rise velocity. In the homogeneous flow regime, bubbles move with almost equal velocity in opposite radial direction. In heterogeneous flow regime, The radial velocities of bubbles migrating toward the center of the column are greater than those of the bubbles moving toward the wall. This phenomenon interprets well phase distribution mechanism.3. The average bubble diameter is almost uniform radially except in the region near the wall. The axial position and Ugo have slight effects on bubble size.