Drop breakage in stirred tanks with Newtonian and non-Newtonian fluid systems

Drop size distributions were measured in agitated non-Newtonian fluid syste ms using a 0.09 m diameter mechanically stirred tank. The dispersion proces s was carried out in the absence of coalescence by keeping the dispersed ph ase volume fraction at less than 0.005. Aqueous solutions of carboxymethyl cellulose and xanthan gum were used as the continuous phase with palm oil f orming the dispersed phase. Additionally, agar solutions were used as the d ispersed phase with salad oil as the continuous phase, which is weakly non- Newtonian. It was experimentally found that the non-Newtonian characteristi cs of the continuous phase caused an increase in the maximum drop size, par ticularly at low impeller speeds and wide drop size distributions, The Saut er drop diameter was proportional to the maximum drop diameter in non-Newto nian and Newtonian fluid systems. Models for drop breakage in a stirred tan k have been developed to account for the effect of non-Newtonian flow behav iour. The boundary-layer sheer force concept was applied to discuss the: in fluence of non-Newtonian flow behaviour on the shear stress acting on the d rop and drop break-up in a stirred tank. It was found that the experimental data correspond to the boundary-layer shear force models in non-coalescing systems. (C) 1999 Elsevier Science S.A. All rights reserved.