Quantitative Representation of Flow Behavior

The traditional engineering model for purely viscous non-Newtonian flow is the so-called power law. 

This is a two-parameter model, the adjustable parameters being the consistency K and the flow index n. As written above, the dimensions of K depend on the 

FIGURE 14.6 Flow curves for polymer melts [9] (a) L-80 polyisobutylene and (b) low-density polyethylene. 

INTRODUCTION TO VISCOUS FLOW AND THE RHEOLOGICAL BEHAVIOR OF POLYMERS 

The parameter is a time constant or characteristic time, and tJo and tJqo represent the viscosity, rj, when(Ac-y) 1 and (Ac-y) 1, respectively. For mid-range values of (Acy), the equation generates a power-law region with a log-log slope of n— 1. This model has been quite successful in fitting data for polymer melts and solutions over at least three or four decades of shear rate. 

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