DEVELOPMENT OF DEVICES FOR IN-LINE VISCOSITY MEASUREMENTS OF WASTES

In applications involving the transport and evaluation of Hanford wastes, performance of the pipeline and pumping systems depends upon the viscosity of the waste stream. These streams are typically heterogeneous and involve a multiphase mixture of solids, liquids and, often, gases. These slurries are opaque and it is usually difficult to take a representative sample that can be tested off line. The goal of this research has been to develop on line sensors for the measurement of slurry viscosity. The principle of the technique rests with the conservation of linear momentum for steady pressure driven flow in a tube. Here, the pressure drop in the tube determines the local shear stress. A simultaneous measurement of the velocity and a robust technique for differentiating it provides the local shear rate distribution. Evaluating the shear rate and the shear stress at points along the tube yields the shear stress shear rate relation, which is equivalent to the shear viscosity shear rate relation. The superiority of experimental techniques based upon this principle is that a single measurement of the velocity profile and the pressure drop provides the viscosity over a wide range of shear rates - up to two decades in practice. This permits the accurate characterization of complex liquids including slurries. Implementing this technique for slurries requires measurement methods that provide for the accurate velocity determination over the entire tube radius and that the system can work in the presence of particles and with opaque systems. We have developed two techniques: one based on magnetic resonance imaging (MRI) and the other based on ultrasonic Doppler velocimetry (UDV). For the MRI, we use phase encode imaging to directly measure the velocity profile. Measurements have been on a variety of non-Newtonian fluids, including those showing shear thinning at high shear rates and a Newtonian plateau at low shear rates. We have also examined a suspension that has a well-defined yield stress. The MRI technique provides excellent agreement with standard rheological measurements. We are able to identify design parameters that can be used to build an instrument and make a priori viscosity measurements without reference to a particular model of fluid behavior. For the UDV, we have developed an instrument that is capable of making measurements of velocity in tubes. We have shown that these measurements can reproduce the parabolic velocity profile found for Newtonian fluids. We have also been able to make accurate measurements of