Effects of Height to Diameter Ratio and Aeration rate on Liquid Mixing and Hydrodynamic Properties in a Bubble Column
Experimental measurements of overall gas holdup (eg), residence time distribution (RTD) and liquid mixing time (tm) have been carried out in an air-water system in a 17 lit bubble column with an 11 cm diameter, over a wide range of superficial gas velocity (0.14-1.46 ms -1 ) and height to diameter ratio (1.36-8.84). The bed expansion method was used to obtain holdup values and the change of slope related to eg versus superficial gas velocity (Usg) indicated the transition point from homogeneous to heterogeneous regime at Usg= 0.7-0.9 ms -1 . Besides, the experiments illustrated that H/D ratio had no effect on holdup values. The axial dispersion model was used with semi-closed boundary conditions for prediction of RTD, and hence, the axial dispersion coefficients (Dax). Moreover, fitting results of the model and experimental RTD curves achieved from tracer injection method attained the model parameter, Dax , in three H/D ratios of 4.73, 6.36 and 8.84. Results showed that an elevation in H/D ratio, caused a rise in Dax. On the other hand, the mixing time data declined with an increase in Usg; however enhancement of H/D ratio caused an increase in tm.
Effects of Equipment Dimensions on Liquid Mixing Time of Bubble Column with Draft Tube
The liquid mixing time of a bubble column with a draft tube is experimentally studied. The diameter and height of the column, the diameter and length of the draft tube, and the mode of sparging gas were changed and the liquid mixing time was measured.The lengths of bottom and top clearances have significant effects on the liquid mixing time. The liquid mixing time increases with increasing column aspect ratio of height to diameter. The liquid mixing time of the bubble column with a draft tube is longer than that of a standard bubble column when the column aspect ratio is relatively high. The liquid mixing time has a minimum when the diameter ratio of draft tube to column is 0.5 to 0.6. These effects of equipment dimensions are expressed by an equation. In the experiment using different solutions, the liquid mixing time becomes shorter with increasing liquid surface tension, or with increasing liquid viscosity.
Liquid-phase mixing in bubble columns: Effect of liquid properties
Abstract Experimental data on the liquid-phase mixing in bubble columns were obtained with air and various liquids by using a transient-state measurement technique. The effect of the liquid physical properties on the liquid-phase longitudinal dispersion coefficient was studied. The liquid-phase dispersion coefficient was found to vary with the viscosity of the liquid, the superficial gas velocity and the column diameter. A new correlation for the liquid-phase dispersion coefficient is presented and shown to correlate the experimental data with an average deviation of 3.07%.