Non‐Newtonian Fluids

Abstract

This chapter aims at introducing and demonstrating the ubiquitous nature of non‐Newtonian flow characteristics in a broad spectrum of industrial settings. Beginning with the definitions of a viscous fluid and an elastic material and a Newtonian fluid, different kinds of non‐Newtonian flow characteristic are introduced and briefly discussed. Next, each of these is illustrated by presenting experimental data for polymer solutions, suspensions, and so on. Most such complex materials exhibit nonlinear viscosity (shear‐thinning, shear‐thickening, yield stress, visco‐elasticity, etc), time‐dependent, and extensional flow characteristics under appropriate conditions, which are of great interest from their processing, manufacturing and the end‐user stand point. This is followed by a discussion of a few constitutive models, some of which are purely empirical in nature, while others are based on different combinations of a dashpot (viscous) and a spring (elastic) elements to capture varying blends of fluid‐like and solid‐like non‐Newtonian characteristics. Next, a range of selected applications including the steady flow of such fluids in ducts of circular and noncircular cross‐sections, in packed columns and in unconsolidated porous media, and boundary layer‐type external flows over a sphere and a long cylinder are briefly discussed. The chapter is concluded by mentioning the other important aspects of this class of fluids and their processing in wide‐ranging settings for interested readers to gain further insights into the fascinating world of non‐Newtonian fluids.