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

Abstract

This paper reports on the effect of impeller design on gas hold-up in high viscosity CMC (apparent viscosity, μ 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 modified designs (Concave bladed disc turbine, CBDT, and Scaba 6SRGT) have been used. The relative performance of these impellers is assessed by comparing the values of four key parameters: specific power dissipation (P G/ V), final total gas hold-up ( ε f), tiny bubble hold-up ( ε ft), and τ, a constant reflecting the time dependency of hold-up. It appears that DT demonstrates either superior to or at least comparable performance over its modified designs. In addition, gas hold-up and τ values in following solutions are compared: (i) pure CMC and PPG containing CMC solutions, (ii) PPG containing CMC and Castor oil. All the impellers produced higher gas hold-up and τ values in (i) PPG containing solution than pure CMC solution, whilst dissipating comparable or lower power and, (ii) Castor oil than PPG containing CMC solution. These observations have been explained by considering the differences between the physical and interfacial properties of these liquids and their effects on liquid flow.