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

Drop size distributions were measured in agitated non-Newtonian fluid systems using a 0.09 m diameter mechanically stirred tank. The dispersion process was carried out in the absence of coalescence by keeping the dispersed phase volume fraction at less than 0.005. Aqueous solutions of carboxymethyl cellulose and xanthan gum were used as the continuous phase with palm oil forming the dispersed phase. Additionally, agar solutions were used as the dispersed phase with salad oil as the continuous phase, which is weakly non-Newtonian. It was experimentally found that the non-Newtonian characteristics of the continuous phase caused an increase in the maximum drop size, particularly at low impeller speeds and wide drop size distributions. The Sauter drop diameter was proportional to the maximum drop diameter in non-Newtonian and Newtonian fluid systems. Models for drop breakage in a stirred tank have been developed to account for the effect of non-Newtonian flow behaviour. The boundary-layer shear force concept was applied to discuss the influence of non-Newtonian flow behaviour on the shear stress acting on the drop 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.

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