Instruments for Shear Rheology

Over the years, researchers have constructed a variety of instruments to measure the flow behavior of complex fluids. These can be broadly characterized as instruments for shear rheology and instruments for extensional rheology. This chapter focuses on shearing flow, while extensional flow is considered in the seventh chapter. Both steady and oscillatory flow are examined, as these are not only easy to implement in the laboratory but they also provide information on different aspects of flow behavior of materials. Commercial instruments primarily employ Poiseuille flow, Couette flow, or torsional flow, and details of these instruments, including their capabilities and limitations, are presented. Also given are the key equations needed for data analysis. Other instruments that are likely to be encountered in industrial practice are described. Current research is directed at understanding and measuring structural changes resulting from subjecting a material to shearing deformations. Experimental observations are commonly represented using constitutive equations (or equations of state) which are then employed to model processing operations.