Non-Newtonian Fluids

Abstract

Fluids give and flow under stress. Newtonians are the simplest of fluids, and they are characterized by the property that the velocity gradient at a point is proportional to the shear stress at that point, thus $$({\rm{Shear\;rate}})\alpha ({\rm{shear\;stress}})\;\;{\rm{or}}\;\;{{du} \over {dy}}\alpha \tau$$All other fluids are called non-Newtonians. Air, water, steam, all gases, and most fluids consisting of simple molecules are Newtonians. Dense suspensions, slurries, emulsions, solutions of long-chain polymers, biological fluids,Fig. 5.1Stress vs. shear rate for various kinds of time-independent non-Newtonians.liquid foods, paints, clay suspensions, and concrete mix are, as a rule, non-Newtonian.