Understanding how cavities collapse in non-Newtonian fluids

Non-Newtonian fluids are commonplace in food technology and biology, but even though the dynamic evolution of bubbles in Newtonian fluids are well understood, non-Newtonian fluids are more complex. In a new paper, Lu et al. modeled the evolution of small cavities in a shear-thinning fluid.

The authors found the behavior of small cavities in a shear-thinning fluid to be very different from that of a Newtonian fluid. The dynamics of the cavity are dominated by shear-thinning effects: The fluid viscosity near the contraction decreases, which accelerates the collapse of the cavity. The feedback mechanism causes the cavities to contract at an ever-increasing velocity, much faster than those in Newtonian fluids.

To further understand this behavior, the researchers modeled an initially dormant fluid and solved the Navier-Stokes equations for fluid velocity and pressure as the cavities contract. Because the fluid is shear-thinning, its viscosity decreases as the shrinking cavities cause an increase in flow.

This work is a starting point for the study of cavity collapse in non-Newtonian fluids. For a more realistic simulation for applications ranging from food to cleaning, additional parameters must be included, such as the effects of inertia during collapse.

“The findings have implications for the integrity of thin, perforated fluid films, such as bubble films, and therefore the stability of bubbles, food foams and foams in the food industry,” said author Jiakai Lu. “A more complete understanding of the shear-thinning physics will enable better predictions and ultimately control of relevant food applications.”

Source: “Contraction of a shear-thinning axisymmetric cavity,” by Jiakai Lu, Michele Ferri, Sebastian Ubal, Osvaldo Campanella, and Carlos M. Corvalan, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5126475 .