Turbulent pipe flow of thixotropic fluids

Abstract

In this work, aqueous suspensions of 1% and 1.5% by weight laponite and a blend of 0.5%/0.07% laponite/carboxymethil cellulose (CMC) are investigated in terms of their rheology and hydrodynamic behaviour in pipe flows. All fluids were shear-thinning, thixotropic and had an yield stress which was measured by direct and indirect methods. The oscillatory tests showed that the 1% laponite suspension was inelastic but the other two fluids exhibited some degree of elasticity. The turbulent pipe flow measurements showed a small amount of drag reduction for the pure laponite suspensions, which was basically accounted for by shear-thinning at Reynolds numbers in excess of 35,000, whereas for the polymer–clay blend the drag reduction was significantly more intense. This work confirmed findings in the literature that the equilibrium condition in the pipe flow was different from the equilibrium condition in the flow curve, which caused some difficulties in data interpretation. However, it found negligible drag reduction for the flow of pure 1.5% laponite suspensions at Reynolds numbers in excess of 60,000, in contradiction to previous findings.