Comparative numerical and experimental investigation of process viscometry for flows in an agitator with a flat blade turbine impeller

Abstract

This paper presents a method for measuring the viscosity of generalized Newtonian fluid directly in flows generated by flat-blade turbine impellers, which are commonly used for moderate mixing and dispersion. A flat-blade turbine with four blades is defined as a model system and analyzed through numerical simulations with experimental verification. Carbopol 940 solution, a high viscosity non-Newtonian fluid with a yield stress, and a bentonite based drilling mud solution were selected as test fluids. Numerical simulation techniques for flow in agitators with a yield stress was established using the rotating coordinate system and flow solutions were validated with experiments by comparing the torque on the impeller shaft. The Metzner-Otto constant and the energy dissipation rate constant were predicted by numerical simulations using the Metzner-Otto correlation and validated via experiments. The effective viscosity that reproduces total energy dissipation rate identical to that of a Newtonian fluid was obtained from both numerical and experimental methods at different impeller speeds, from which the material viscosity curve was established as a function of the shear rate. The accuracy of viscosity prediction was compared with a rheological measurement and the average relative error was below 12% and 7% in the experiment and simulation, respectively. This method has the advantage of being able to measure the in-situ viscosity, where a drilling mud needs to transport more and heavier cuttings and careful preparation of the mud is key issue to a successful drilling process.