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 (epsilong), residence time distribution (RTD) and liquid mixing time (t,rJ have been carried out in an air-water system in a 17 lit bubble column with an 11 em diameter, over a wide range ofsuperficial gas velocity (0.14-1.46 ms ) 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 U(sg)) indicated the transition point from homogeneous to heterogeneous regime at U(sg)= 0.7-0.9 ms-l . Besides, the experiments illustrated that HID 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 (DmJ Moreover, fitting results of the model and experimental RTD curves achievedfrom tracer injection method attained the model parameter, Dax , in three HID ratios of 4.73, 6.36 and 8.84. Results showed that an elevation in HID ratio, caused a rise in Dax . On the other hand, the mixing time data declined with an increase in U(sg); however enhancement of HID ratio caused an increase in t(m)