chapter  1
Overview of Processing Instabilities
BySavvas G. Hatzikiriakos, Kalman B. Migler
Pages 12

Hydrodynamic stability is one of the central problems of fluid dynamics. It is concerned with the breakdown of laminar flow and its subsequent development and transition to turbulent flow (1). The flow of polymeric liquids differs significantly from that of their low-viscosity counterparts in several ways and, consequently, the nature of flow instabilities is completely different. Most notably, whereas for low-viscosity fluids it is the inertial forces on the fluid that cause turbulence (as measured by the Reynolds number), for highviscosity polymers, it is the elasticity of the fluid that causes a breakdown in laminar fluid flow (asmeasured by theWeissenberg number). Additionally, the


high viscosity and the propensity for the molten fluid to slip against solid surfaces contribute to a rich and diverse set of phenomena, which this book aims to review.