Dispersion visualization of model fluids in a transparent Couette flow cell

Vananroye

Puyvelde

et al. 2011

Macro Materials & Eng

The breakup of confined droplets was studied systematically for systems with either interfacial or component viscoelasticity. The former was obtained by adding a compatibilizer, the latter by using a viscoelastic fluid as the droplet or as the matrix phase. The critical capillary numbers of Newtonian and compatibilized droplets showed a similar increase with increasing confinement ratio. However, a decrease in breakup length was observed in the compatibilized case, caused by the viscoelastic interface. Viscoelastic droplets experienced more stabilization by confinement compared to Newtonian droplets. Matrix viscoelasticity, on the other hand, induced a destabilization with a minimum in critical capillary number as a function of confinement ratio, resulting from a complex interplay of viscoelastic stresses. magnified image

Section: Comparison Of the Effects Of Component And Interfacial Rheologysupporting

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Breakup Criteria for Confined Droplets: Effects of Compatibilization and Component Viscoelasticity

Vananroye

Puyvelde

et al. 2011

Macro Materials & Eng

“…Finally, it can be noted that no vorticity elongation, which was often encountered in systems with viscoelastic components (Levitt et al 1996;Migler 2000;Mighri et al 2001;Cherdhirankorn et al 2004;Mighri and Huneault 2006;Tanpaiboonkul et al 2007;Li and Sundararaj 2008), has been observed in the present work, neither in bulk, nor in confined conditions. Vorticity elongation has been attributed to normal stresses, either in the droplet or in the matrix fluid (Levitt et al 1996;Migler 2000).…”

Section: Binary Versus Multiple Droplet Breakupcontrasting

confidence: 54%

Critical conditions and breakup of non-squashed microconfined droplets: effects of fluid viscoelasticity

Moldenaers

2010

Microfluid Nanofluid

Droplet breakup in systems with either a viscoelastic matrix or a viscoelastic droplet is studied microscopically in bulk and confined shear flow, using a parallel plate counter rotating shear flow cell. The ratio of droplet diameter to gap spacing is systematically varied between 0.1 and 0.85. In bulk shear flow, the effects of matrix and droplet viscoelasticity on the critical capillary number for breakup are very moderate under the studied conditions. However, in confined conditions a profoundly different behaviour is observed: the critical capillary numbers of a viscoelastic droplet are simi- E-mail: paula.moldenaers@cit.kuleuven.be 2 critical dimensionless droplet length, the critical capillary number and the dimensionless droplet length at breakup show a similar dependency on confinement ratio. As a result, confined droplets in a viscoelastic matrix have a smaller dimensionless length at breakup than droplets in a Newtonian matrix, which affects the breakup mode.Whereas confined droplets in a Newtonian matrix can break up into multiple parts, only two daughter droplets are obtained after breakup in a viscoelastic matrix, up to very large confinement ratios.

“…For instance, Migler [28] reports the alignment and breakup in the vorticity direction for highly elastic droplets under strong shear. A variety of systems, flow types, and experimental conditions give rise to this phenomenon [27,29,30,31,32,33]. It is generally accepted that alignment and breakup along the vorticity direction involve a complicated interplay between the first and second normal stress differences of both phases, the viscosity ratio, shearthinning behavior, and the applied capillary number.…”

Section: Introductionmentioning

confidence: 99%

Influence of viscoelasticity on drop deformation and orientation in shear flow. Part 2: Dynamics

Verhulst

Journal of Non-Newtonian Fluid Mechanics

Moldenaers

et al. 2009

An experimental study of drop dynamics under shear is conducted for five fluid pairs: a reference Newtonian system, two systems with a viscoelastic drop in a Newtonian matrix, one with a Newtonian drop in a viscoelastic matrix, all at drop to matrix viscosity ratio λ = 1.5, and a separate case at λ = 0.75. The viscoelastic liquids are either a Boger fluid or a shear-thinning viscoelastic fluid satisfying an Ellis model. Deborah numbers in the range 1 to 2 and a range of capillary numbers from low to above breakup conditions are addressed. The results focus on three aspects: relaxation after cessation of shear, a new viscoelastic drop breakup scenario, and the effect of shear flow history on drop breakup. Numerical simulations with the 3D volume-of-fluid PROST method complement the experimental results.