The effect of impeller design on gas hold-up in surfactant containing highly viscous non-Newtonian agitated liquids

This paper reports on the effect of impeller design on gas hold-up in high viscosity CMC (apparent viscosity, mu (a) = 0.5-0.8 Pas) and CMC solutions containing polypropylene glycol as an interfacially active additive. Three disc type impellers, namely, flat bladed disc turbine (DT) and two of its m odified designs (Concave bladed disc turbine, CBDT, and Scaba 6SRGT) have b een used. The relative performance of these impellers is assessed by compar ing the values of four key parameters: specific power dissipation (P-G/V), final total gas hold-up (epsilon (f)), tiny bubble hold-up (epsilon (ft)), and tau a constant reflecting the time dependency of hold-up. It appears th at DT demonstrates either superior to or at least comparable performance ov er its modified designs. In addition, gas hold-up and tau values in followi ng solutions are compared: (i) pure CMC and PPG containing CMC solutions, ( ii) PPG containing CMC and Castor oil. All the impellers produced higher ga s hold-up and tau values in (i) PPG containing solution than pure CMC solut ion, whilst dissipating comparable or lower power and, (ii) Castor oil than PPG containing CMC solution. These observations have been explained by con sidering the differences between the physical and interfacial properties of these liquids and their effects on liquid flow. (C) 2002 Elsevier Science B.V.. All rights reserved.