Hydrodynamic Characteristics of Mixing in a Non-Newtonian Liquid-Gas-Solid System

This work presents the study of mixing a three phase non-Newtonian system in a QVF gas sparged vessel. The three phase system consists of air-non Newtonian liquid (polyacrylamide solution)-solid (alumina catalyst). The critical gas velocity for complete suspension of solid particles, mixing time, and bubble characteristics (bubble rise velocity, bubble diameter, bubble frequency, gas hold up, and number of bubbles) was studied with different polyacrylamid (PAA) concentrations (0.01, 0.03,0.05, 0.07) wt%, different particle diameters of alumina (63-500)mu m, and different solid loading of alumina (0.5, 1.0, 1.5, 2.0)Kg. The critical gas velocity was found to increase with increasing apparent viscosity, solid loading, and particle diameter. Mixing time increases with increasing apparent viscosity, and decreases with increasing solid loading, and particle diameter. Bubble characteristics were measured axially and radially using a modified electroconductivity probe consisting of four tips, an interface, a visual basic program, and a personal computer. The results showed that increasing apparent viscosity and particle diameter caused an increase of bubble coalescence and hence, an increase in bubble diameter and bubble rise velocity and a decrease in gas hold up.