Low Reynolds number dynamics of viscoelastic drops

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" Low Reynolds number dynamics of viscoelastic drops "
Hongfei Wu H. B. Haj-Hariri, Ali

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	55702
Doc. No	:	TL25656
Call number	:	‭3294797‬
Main Entry	:	Hongfei Wu
Title & Author	:	Low Reynolds number dynamics of viscoelastic drops\ Hongfei Wu
College	:	University of Virginia
Date	:	2008
Degree	:	Ph.D.
student score	:	2008
Page No	:	159
Abstract	:	The effects of bulk elasticity on the behavior of drops translating in a Newtonian fluid at low Reynolds number are quantified, and contrasted with those of Newtonian drops. The non-Newtonian stresses in the drop phase are characterized by Oldroyd-B or FENE-CR models. Initially we examine the effect of viscoelasticity on the evolution of the shape of a viscoelastic drop translating in an immiscible, quiescent unbounded viscous fluid. Asymptotic analyses on small Deborah numbers (De) show that the effect of bulk elasticity is to render the drop shape into an oblate spheroid, and to favor formation of a depression at the rear stagnation point. In the limit of infinite capillary number (Ca), an unbounded indentation grows at the trailing end of the drop, whereas the leading end of the drop quickly returns to a hemispherical shape. Numeric simulations by a pseudo boundary integral on the stability of the shape of viscoelastic drops to finite perturbation at moderate De and Ca demonstrate that initially oblate viscoelastic drops are more stable, and initially prolate viscoelastic drops are less stable. This stabilizing or destabilizing effect of viscoelasticity results from the affine stretching of the polymeric molecules in alignment with the streamline of flow fields. We also examine the effect of drop phase elasticity on the axisymmetric pressure-driven motion of a drop in a tube. Compared to a Newtonian drop, a viscoelastic drop experiences smaller deformation, has larger mobility, and produces a smaller extra pressure loss in the tube. Drop phase elasticity delays the appearance of negative curvature at the trailing end of drops to larger capillary numbers. However, the critical capillary number for the onset of drop breakup through the re-entrant cavity mechanism appears to be slightly lower for viscoelastic drops. The observed difference is again attributed to the extension of polymer molecules along the streamlines of the flow field. Finally, numerical examinations on the effects of rheological properties on drop dynamics show that the polymer concentration has a strong influence on the stability of the shape of viscoelastic drops; but De and extensibility L, have relatively weak influences.
Subject	:	Applied sciences; Newtonian fluids; Reynolds number; Viscoelastic drops; Mechanics; Mechanical engineering; 0548:Mechanical engineering; 0346:Mechanics
Added Entry	:	H. B. Haj-Hariri, Ali
Added Entry	:	University of Virginia