Use of the parallel-plate plastometer for the characterisation of viscous fluids with a yield stress

Abstract

The rheometry of highly viscous non-Newtonian fluids, especially those with the yield stress, currently requires sophisticated equipment. However, the parallel-plate plastometer, which can be made cheaply, has been found to be suitable for this application. At present there is no satisfactory theory for the behaviour of material in the instrument except for the Newtonian and power-law fluids. This paper reports the result of theoretical and experimental investigations into the behaviour in the instrument of some inelastic incompressible fluids. the yields stress can be derived from the limiting height measurement, thus providing a simple technique for measuring this fundamental fluid property. For Bingham and Herschel−Bulkley fluids, the rheological constant can be derived from the dynamic data. Experimental verification for Herschel−Bulkley fluids was carried out and good agreement was found with the theory.