CFD analysis of viscous non-Newtonian flow under the influence of a superimposed rotational vibration

The effects of a superimposed sinusoidal rotational vibration on the flow of non-Newtonian fluids in a tube are studied numerically by computational fluid dynamics (CFD). Inelastic time-independent fluids of the power law, Herschel-Bulkley, Bingham plastic, and Newtonian types are investigated. Newtonian flow is unchanged by any superimposed oscillations but the flow of non-Newtonian fluids is greatly affected. The flow of shear-thinning fluids and viscoplastic fluids is enhanced, whilst the flow of shear-thickening fluids is retarded. The effects of the various rheological as well as vibration parameters are studied in detail. Flow is affected by both vibration frequency and amplitude, but different amplitude-frequency combinations which correspond to the same peak acceleration result in the same effect. Mechanical vibration in the sonic range generates substantial flow enhancements in low to moderately viscous fluids, but has limited scope for highly viscous fluids. Mechanical vibration in the ultrasound range, however, has a good potential for the processing of highly viscous materials, being able to generate orders of magnitude enhancement in flow. The extent of flow enhancement achieved is also dependent on the nature of the superimposed vibration: a rotational oscillation produces more flow enhancement than a transversal oscillation, but less than a longitudinal oscillation. (C) 2007 Elsevier Ltd. All rights reserved.