The settling of particles within fluids is not merely a physical curiosity but is instead fundamental to numerous natural phenomena and industrial applications. A new study reveals how particles behave when suspended in shear-thinning, viscoelastic fluids, challenging traditional assumptions about their settling dynamics.
Conducted by researchers from UK Research and Innovation, the investigation focuses on the interactions of solid particles as they fall through non-Newtonian fluids, particularly under conditions influenced by the walls of the container. These fluids exhibit properties contrary to Newtonian fluids, making the predictive models based on Stokes' Law insufficient without modifications.
Historically, Stokes' Law has provided the basis for calculating the terminal velocity of spherical particles falling through fluids. This law, first articulated by George Stokes in 1851, assumes particles move through unbounded fluids. Yet, the presence of walls alters this simple dynamic and has been extensively documented for traditional Newtonian fluids. The new research explores these effects under shear-thinning and viscoelastic conditions for the first time, contributing significant findings to the body of knowledge.
Through systematic experimentation using both Newtonian (golden syrup) and non-Newtonian (hydroxyethyl cellulose, HEC) fluids, the study presents experimental data on particle settling. The researchers measured how variables such as the sphere-to-tube diameter ratio affected settling velocities when particles were subjected to wall influences.
Interestingly, the study reveals notable deviations from traditional predictions. The researchers discovered shear-thinning properties reduced wall effects on particle settling, demonstrating how the distance between the walls and particles significantly affects their terminal velocities. The findings indicate particles settle faster due to the reduced localized region of fluid being sheared, which decreases the apparent viscosity of the fluid being displaced by the settling particle.
The quantitative analysis reveals the impact of viscoelasticity, particularly under higher Weissenberg numbers, where increased drag forces can slow down settling velocities. Researchers noted, "Viscoelastic properties, particularly at high Weissenberg number regimes, can increase the drag on particles and reduce settling velocities." This dual influence highlights the complexity of non-Newtonian behavior during settling processes.
By applying both shear-thinning and viscoelastic corrections to the predictions, the researchers significantly improved the accuracy of the settling velocity calculations. This new approach addresses the limitations of conventional models and provides precision necessary for various applications where particle settling is relevant, such as mineral processing and waste treatment.
Overall, the study advances our comprehension of fluid mechanics and offers potential for greater efficiency and accuracy in industries reliant on fluid dynamics. The findings are not just relevant for theoretical physics, but have practical applications ranging from the geological processes involved in sediment transport to the engineering of more effective industrial processes.
Looking forward, the research emphasizes the need for additional studies to explore the nuanced behaviors of non-Newtonian fluids and their interactions with solid particulates under varied conditions. Therefore, this exploration of particle settling dynamics opens new pathways for advancements both scientifically and industrially.