Effect of perturbation wavelength on jets of complex fluids
Abstract
A liquid jet can become unstable and break up into drops as a result of undulations on its surface. The effect of these undulations on the breakup process, particularly on crucial features such as drop size and drop size distribution, is of broad scientific interest, and of particular interest to those studying spray and propulsion. Due to the widespread industrial use of complex fluids, which include polymeric and surfactant solutions, recent modeling studies focused on the breakup of non-Newtonian liquid jets or surfactant laden jets, but modeling of the two subjects proceeds more or less independently and little is known about their coupled effect. Specifically, the precise role of undulation wavelength on the drop size distribution resulting from the breakup of non-Newtonian surfactant laden jets remains an important open question. Results from this study demonstrate that the effect of perturbation wavelength on drop size distribution is profoundly altered by coupled surfactant and non-Newtonian effects. The results were obtained using Direct Numerical Simulation, that is by simultaneously solving the full system of three-dimensional axisymmetric partial differential equations governing the non-Newtonian capillary driven flow and the transport of surfactant in a continually deforming jet. Direct numerical simulations demonstrate that as the wavelength of the surface undulation is increased, a threshold wavelength is reached above which the system makes a sudden transition to a new, different dynamical behavior that leads to a much different drop size distribution. This threshold wavelength is associated with surface-tension-gradient driven flows (Marangoni flows) induced by uneven distribution of surfactant and enabled by non-Newtonian shear-thinning effects. Results from this study enhance our current scientific understanding of the physical process involved in the breakup of complex fluid jets and can have a significant impact on the rational design of polymer and surfactant additives for industrial spray and propulsion systems.
Degree
M.S.M.E.
Advisors
Sojka, Purdue University.
Subject Area
Mechanical engineering
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