Mixing Mechanisms of High Viscosity Materials
Introduction to Mixing of High Viscosity Materials
Mixing is the process wherein the non-uniformity within the mixture is reduced.
Materials such as polymer, putties, pastes, grease, chewing gum, solid propellant have viscosities exceeding 10 Pa-s (10,000 centipoise) and are categorized as viscous materials.
The viscosities of materials to be processed are constantly on the rise, as there is an urgent need to cut levels of volatile organic compounds in most parts of the chemical process industry. As viscosity rises, we cross a threshold into a different realm of mixing technology.
Viscous materials generally exhibit characteristics such as resistance to flow, non-Newtonian behaviour and elasticity. Unlike liquid mixing where mixing takes place due to generation of flow currents; in viscous materials there are no turbulent eddies, or flow currents to help distribute the components. Mixing in viscous systems can therefore be achieved only by mechanical action or by the forced shear or by elongation flow of the matrix .
Mixing Mechanisms for High Viscosity Materials
Mixing of viscous material requires deformation of the mixture ensuring both lateral and transverse motion of material. The geometry of the mixing vessel and the design of the mixing element have significant impact on the mixing process. The relative motion between mixing element and the internal walls of the mixing vessel creates both shear and bulk motion. The shear effectively creates thinner layers of non-uniform material, which diminishes striations or breaks agglomerates to increase homogeneity. Bulk motion redistributes the effects of the stretching processes throughout the mixing vessel.
Mixing of viscous material necessitates dispersive mixing, distributive mixing and convective mixing mechanisms to occur in a system.
Dispersive mixing: Dispersive mixing is defined as the breakup of agglomerates or lumps to the desired ultimate grain size of the solid particulates or the domain size (drops) of other immiscible fluids [Paul et al, 2001].
Distributive mixing: Distributive mixing is defined as providing spatial uniformity of all the components and is determined by the history of deformation imparted to the material [Tekchandaney, 2012].
Convective mixing: Convective mixing in the laminar regime is effected by shear, kneading and stretching of material and results in reorientation of the dispersed elements [Tekchandaney, 2012].
These mechanisms are to be facilitated by the mixing equipment.
- Tekchandaney, J.R. (Author), Holloway, M.D., Nwaoha, C., Onyeweuenyi, O.A. (Editors), (2012), Process Plant Equipment, Wiley.
- Paul, E. L., Atiemo-Obeng, V. A., and Kresta, S. M. (Editors), (2004), Handbook of Industrial Mixing, Wiley.
Unique Mixers & Furnaces Pvt Ltd
Contact Person: Mr Jayesh R Tekchandaney
Phone – +91-22-25801214/25822385
Website - www.uniquemixer.com