Settling Properties of Particles in Non-Newtonian Fluids
Aqueous solutions of three polymers: a synthetic high molecular weight polymer, partially hydrolyzed polyacrylamide (PHPA); a xanthan type biopolymer (Xanvis), and a cellulose type polymer (HEC) were investigated. It was found that the steric arrangement of molecules or interactions between molecules can be detected by a systematically designed strain and frequency sweep measurement, and is reflected by the different relaxation times of the solutions. The degree of elasticity. can be quantified by .G'/IG*I. Results show that within the tested concentration ranges, PHP A solutions are highly elastic with moderate relaxation times that are strain and concentration · insensitive. Xanvis solutions are also highly elastic but with high relaxation times vu that are both strain and concentration sensitive, indicating a different mechanism of elasticity compared to PHPA solutions. HEC (cellulose derivatives ) are mostly viscous shear thinning fluids with weak elasticity and short relaxation times that are insensitive to strain but sensitive to concentration. A direct drag force measurement method was developed which makes it possible to study the settling process of particles in both transparent and opaque fluids. Calibration and verification tests in both Newtonian and non-Newtonian fluids showed that this method is accurate in a practical stand. A dimensionless treatment was proposed which takes into account the shear thinning effects of the fluids to normalize the measured drag force data. A wide range of particle Reynolds numbers (from 10-4 to 102) can be covered by this method and a profile of friction factor versus Reynolds number can be established by the dimensionless treatment. An algorithm for the prediction of settling of particles in non-Newtonian fluids was introduced. This algorithm can be implemented by a computer program. With experimental data obtained from rheological and drag force measurements, the settling velocities predicted by the computer model are very close to the measured ones ih both Newtonian and non-Newtonian fluids. This technique is helpful to the study of particle settling process in non-Newtonian fluids, especially in drilling, completion and fracturing fluids used in the oil industry .