21 research outputs found
Dynamic Characterization of Permeabilities and Flows in Microchannels
We make an analytical study of the nonsteady flow of Newtonian fluids in microchannels. We consider the slip boundary condition at the solid walls with Navier hypothesis and calculate the dynamic permeability, which gives the system's response to dynamic pressure gradients. We find a scaling relation in the absence of slip that is broken in its presence. We discuss how this might be useful to experimentally determine by means of microparticle image velocimetry technology whether slip exists or not in a system, the value of the slip length, and the validity of Navier hypothesis in dynamic situations
Mode-coupling approach to non-Newtonian Hele-Shaw flow
The Saffman-Taylor viscous fingering problem is investigated for the
displacement of a non-Newtonian fluid by a Newtonian one in a radial Hele-Shaw
cell. We execute a mode-coupling approach to the problem and examine the
morphology of the fluid-fluid interface in the weak shear limit. A differential
equation describing the early nonlinear evolution of the interface modes is
derived in detail. Owing to vorticity arising from our modified Darcy's law, we
introduce a vector potential for the velocity in contrast to the conventional
scalar potential. Our analytical results address how mode-coupling dynamics
relates to tip-splitting and side branching in both shear thinning and shear
thickening cases. The development of non-Newtonian interfacial patterns in
rectangular Hele-Shaw cells is also analyzed.Comment: 14 pages, 5 ps figures, Revtex4, accepted for publication in Phys.
Rev.
A phase-field model of Hele-Shaw flows in the high viscosity contrast regime
A one-sided phase-field model is proposed to study the dynamics of unstable
interfaces of Hele-Shaw flows in the high viscosity contrast regime. The
corresponding macroscopic equations are obtained by means of an asymptotic
expansion from the phase-field model. Numerical integrations of the phase-field
model in a rectangular Hele-Shaw cell reproduce finger competition with the
final evolution to a steady state finger the width of which goes to one half of
the channel width as the velocity increases
Historiografia econômica do dízimo agrário na Ibero-América: os casos do Brasil e Nova Espanha, século XVIII
Maximizing the dynamic permeability during occlusions
We study the dynamic permeability of a viscoelastic fluid flowing in
an occluded tube due to either central or peripheral obstructions.
We find that for occluded systems, the dynamic permeability
decreases. We also find that the value of the dynamic permeability
for the occluded systems, can be made as large as the dynamic
permeability for the non-occluded system when the proper frequency
is imposed to the flow
Fluctuations in Saffman-Taylor fingers with quenched disorder
We make an experimental characterization of the effect that static disorder has on the shape of a normal Saffman-Taylor finger. We find that static noise induces a small amplitude and long wavelength instability on the sides of the finger. Fluctuations on the finger sides have a dominant wavelength, indicating that the system acts as a selective amplifier of static noise. The dominant wavelength does not seem to be very sensitive to the intensity of static noise present in the system. On the other hand, at a given flow rate, rms fluctuations of the finger width, decrease with decreasing intensity of static noise. This might explain why the sides of the fingers are flat for typical Saffman-Taylor experiments. Comparison with previous numerical studies of the effect that temporal noise has on the Saffman-Taylor finger, leads to conclude that the effect of temporal noise and static noise are similar. The behavior of fluctuations of the finger width found in our experiments, is qualitatively similar to one recently reported, in the sense that, the magnitude of the width fluctuations decays as a power law of the capillary number, at low flow rates, and increases with capillary number for larger flow rates
Fluctuations in Saffman-Taylor fingers with quenched disorder
We make an experimental characterization of the effect that static disorder has on the shape of a normal Saffman-Taylor finger. We find that static noise induces a small amplitude and long wavelength instability on the sides of the finger. Fluctuations on the finger sides have a dominant wavelength, indicating that the system acts as a selective amplifier of static noise. The dominant wavelength does not seem to be very sensitive to the intensity of static noise present in the system. On the other hand, at a given flow rate, rms fluctuations of the finger width, decrease with decreasing intensity of static noise. This might explain why the sides of the fingers are flat for typical Saffman-Taylor experiments. Comparison with previous numerical studies of the effect that temporal noise has on the Saffman-Taylor finger, leads to conclude that the effect of temporal noise and static noise are similar. The behavior of fluctuations of the finger width found in our experiments, is qualitatively similar to one recently reported, in the sense that, the magnitude of the width fluctuations decays as a power law of the capillary number, at low flow rates, and increases with capillary number for larger flow rates
Growth and morphology in Langmuir monolayers
We show that domain growth of condensed phases from a metastable phase in
Langmuir monolayers presents several stages. At the very beginning,
depending on the supersaturation level, structures evolve through a
tip-splitting dynamics. If supersaturation levels are high, there is a
morphological transition, domains grow with needle tips that show as growth
proceeds, side branching. The way in which the instability starts at round
domains when a small lateral pressure jump is applied to the monolayer is
also shown. A model for a monolayer interacting with the subphase is
presented. This model can be related to the theory of dynamic phase
transitions, where morphological structures and morphological transitions
are predicted