Filtration with Multiple Species of Particles

Transport in Porous Media - Membrane filtration of feed containing multiple species of particles is a common process in the industrial setting. In this work, we propose a model for filtration of a...     

Velocity profiles in repulsive athermal systems under shear

We conduct molecular dynamics simulations of athermal systems undergoing boundary-driven planar shear flow in two and three spatial dimensions. We find that these systems possess nonlinear mean velocity profiles when the velocity u of the shearing wall exceeds a critical value u(c). Above u(c), we also show that the packing fraction and mean-square velocity profiles become spatially dependent with dilation and enhanced velocity fluctuations near the moving boundary. In systems with overdamped dynamics, u(c) is only weakly dependent on packing fraction phi. However, in systems with underdamped dynamics, u(c) is set by the speed of shear waves in the material and tends to zero as phi approaches phi(c), which is near random close packing at small damping. For underdamped systems with phi相似文献   

Contact line instabilities of thin liquid films

We present results of fully nonlinear time-dependent simulations of a thin liquid film flowing down an inclined plane. Within the lubrication approximation, and assuming complete wetting, we find that varying the inclination angle considerably modifies the shape of the emerging patterns (fingers versus sawtooth). Our results strongly suggest that the shape of the patterns is not necessarily related to either partial or complete coverage of the substrate, a technologically important feature of the flow. We find quantitative agreement with reported experiments and suggest new ones.     

Dynamics of spherical particles on a surface: collision-induced sliding and other effects

We present a model for the motion of hard spherical particles on a two-dimensional surface. The model includes both the interaction between the particles via collisions and the interaction of the particles with the substrate. We analyze in detail the effects of sliding and rolling friction, which are usually overlooked. It is found that the properties of this particulate system are influenced significantly by the substrate-particle interactions. In particular, sliding of the particles relative to the substrate after a collision leads to considerable energy loss for common experimental conditions. The presented results provide a basis that can be used to realistically model the dynamical properties of the system, and provide further insight into density fluctuations and related phenomena of clustering and structure formation.     

Dynamic structure formation at the fronts of volatile liquid drops

We report on instabilities during the spreading of volatile liquids, with emphasis on the novel instability observed when isopropyl alcohol is deposited on a monocrystalline Si wafer. This instability is characterized by emission of drops ahead of the expanding front, with each drop followed by smaller, satellite droplets, forming the structures which we nickname "octopi" due to their appearance. A less volatile liquid, or a substrate of larger heat conductivity, suppresses this instability. We formulate a theoretical model that reproduces the main features of the experiment.     

Breakup of finite fluid films

We study the dewetting process of thin fluid films that partially wet a solid surface. Using long wave (lubrication) approximation, we formulate a nonlinear partial differential equation governing the evolution of the film thickness, h. This equation includes the effects of capillarity, gravity, and additional conjoining/disjoining pressure term to account for intermolecular forces. We perform standard linear stability analysis of an infinite flat film, and identify the corresponding stable, unstable and metastable regions. Within this framework, we analyze the evolution of a semi-infinite film of length L in one direction. The numerical simulations show that for long and thin films, the dewetting fronts of the film generate a pearling process involving successive formation of ridges at the film ends and consecutive pinch-off behind these ridges. On the other hand, for shorter and thicker films, the evolution ends up by forming a single drop. The time evolution as well as the final drops pattern shows a competition between the dewetting mechanisms caused by nucleation and by free surface instability. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Competing liquid phase instabilities during pulsed laser induced self-assembly of copper rings into ordered nanoparticle arrays on SiO2

Nanoscale copper rings of different radii, thicknesses, and widths were synthesized on silicon dioxide thin films and were subsequently liquefied via a nanosecond pulse laser treatment. During the nanoscale liquid lifetimes, the rings experience competing retraction dynamics and thin film and/or Rayleigh-Plateau types of instabilities, which lead to arrays of ordered nanodroplets. Surprisingly, the results are significantly different from those of similar experiments carried out on a Si surface. We use hydrodynamic simulations to elucidate how the different liquid/solid interactions control the different instability mechanisms in the present problem.     

Instabilities of nanoscale patterned metal films

The European Physical Journal Special Topics - We consider the evolution and related instabilities of thin metal films liquefied by laser pulses. The films are patterned by large-scale...     

Dependence of single-bubble sonoluminescence on ambient pressure

Kondic et al.'s theory makes several specific predictions on the dependence of single-bubble sonoluminescence (SBSL) on ambient pressure. We have carried out experiments to verify these predictions for air bubbles in a water-glycerine mixture at about 17.5 kHz. The results show an increase in SBSL with reduced ambient pressure down to a critical value below which SBSL is extinguished. The results are all in good agreement with Kondic et al.'s theory and are also compatible with the dissociation hypothesis of Lohse et al.     

Octopus-shaped instabilities of evaporating drops

We report on instabilities during spreading of volatile liquids, with emphasis on the novel instability observed when isopropyl alcohol (IPA) is deposited on a monocrystaline Si wafer. This instability is characterized by emission of drops ahead of the expanding front, with each drop followed by smaller, satellite droplets, forming the structures which we nickname ‘octopi’ due to their appearance. A less volatile liquid, or a substrate of larger heat conductivity, suppress this instability. We have formulated a theoretical model that reproduces the main features of the experiment. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)