Rheology capillary viscometry

Equation 4-3b may be regarded as the basic equation of capillary viscometry. The properties of the liquid enter the equation by way of the rheological function which expresses the relation between rate of shear and shear stress. For Newtonian flow from Eqn 4-2 we get... 

Plotnikova, E. P, Kuhchihin, E. R, Mihailova, I. M., Kerber, M. L. (1996). Rotational and Capillary Viscometry of Melts of Mixes of Traditional and Liquid-Crystalline Thermoplasts. In Abstracts of the 18-th Symposium on Rheology. Karacharovo, 117. [in Russian]. 

There are numerous other GNF models, such as the Casson model (used in food rheology), the Ellis, the Powell-Eyring model, and the Reiner-Pillippoff model. These are reviewed in the literature. In Appendix A we list the parameters of the Power Law, the Carreau, and the Cross constitutive equations for common polymers evaluated using oscillatory and capillary flow viscometry. 

The homogeneous non-Newtonian capillary tube-power law model has a number of limitations. The models assume a power law relationship for the emulsion, and any deviations from this rheological behavior will lead to errors. The power law constants n and K are obtained by using viscometry, and their validity in porous media is questionable. No transient permeability reduction (assumption 4) is predicted, even though experimental evidence suggests otherwise. This model is seen to have validity only for high-quality emulsions that approach steady state quickly and have small droplet-size to pore-size ratios. 

The yield stress can be obtained by the rotational viscometry technique as shown in Chapter 4. Thus from two sets of rheological determinations, one the capillary flow technique and the other rotational viscometry, enough information can be obtained to treat the problems associated with the flow of grease in pipes. 

Rheological measurements on the slurry have been performed by Bohlin rheometer model VOR and constant stress rheometer C.. These two units combined are powerful enough to analyze slurries completely in viscometry, oscillatory and relaxation tests. Injection molding compound is fully characterized rheologically using capillary rheometer. 

---