Experimental Investigation of the Power Consumption and Metzner–Otto Constant for Highly Shear-Thinning Fluids with Different Impeller Geometries

Abstract

Common industrial non-Newtonian fluids are pseudoplastics with shear-thinning properties. During mixing, it is challenging to evaluate the power consumption for these fluids because the apparent viscosity (ηa), which is needed for the evaluation of the impeller Reynolds Number (Re), is a function of the shear rate, which itself is a function of the flow parameters.; the Metzner–Otto method is widely used to predict the ηa and average shear rate ([Formula: see text]) under these conditions. In this study, using polyglycerin and starch syrup as Newtonian fluids and hydroxyethyl cellulose as a non-Newtonian fluid, the power consumption and Metzner–Otto constant (Ks) were evaluated for different impeller geometries in the laminar regime. The power number decreased linearly with increasing Re in the laminar flow regime, and using the Metzner–Otto method, all power curves for the shear-thinning fluids coincide with those of the Newtonian fluids. Therefore, the power constant was dependent only on the geometrical parameters of the system. Furthermore, the [Formula: see text] varies linearly with the impeller rotational speed ; however, Ks between the [Formula: see text] and N was found to be a function of the flow behavior index (n) and the system geometrical parameters. This study established complete correlations between B and the impeller geometry, and between Ks and the impeller geometry and n through linear regression analysis to predict the power consumption of shear-thinning fluids under laminar flow.

Keywords

• Mixing
• Shear-thinning fluids
• Power consumption
• Metzner-Otto constant
• Laminar flow