Search results for "Péclet number"
showing 8 items of 8 documents
Stratification Dynamics in Drying Colloidal Mixtures
2017
Stratification in binary colloidal mixtures was investigated using implicit-solvent molecular dynamics simulations. For large particle size ratios and film Péclet numbers greater than unity, smaller colloids migrated to the top of the film, while big colloids were pushed to the bottom, creating an "inverted" stratification. This peculiar behavior was observed in recent simulations and experiments conducted by Fortini et al. [ Phys. Rev. Lett. 2016 , 116 , 118301 ]. To rationalize this behavior, particle size ratios and drying rates spanning qualitatively different Péclet number regimes were systematically studied, and the dynamics of the inverted stratification were quantified in detail. Th…
Conformational Changes and Charge Transfer in Biomolecules Resolved Using Dynamic Enhanced Raman Correlation Spectroscopy
2019
International audience; In this contribution, we report that conforma-tional changes of molecules that are often buried in a wide-distributed Gaussian distribution can be discerned by analyzing the dynamics of specific Raman lines. We investigate the pertinence of the auto-and cross-correlation functions applied to the dynamics of three Raman lines of an amino acid, the tryptophan. The cross-correlation between intensity and the Raman band is an indicator of the charge transfer during the diffusion limited reaction of tryptophan and the gold surface. The Pećlet number Pe can provide a valuable indicator of the convective and/or diffusive features of each Raman band. Adsorption induced confo…
Active nonlinear microrheology in a glass-forming Yukawa fluid.
2012
A molecular dynamics computer simulation of a glass-forming Yukawa mixture is used to study the anisotropic dynamics of a single particle pulled by a constant force. Beyond linear response, a scaling regime is found where a force-temperature superposition principle of a Peclet number holds. In the latter regime, the diffusion dynamics perpendicular to the force can be mapped on the equilibrium dynamics in terms of an effective temperature, whereas parallel to the force a superdiffusive behavior is seen in the long-time limit. This behavior is associated with a hopping motion from cage to cage and can be qualitatively understood by a simple trap model.
Nonlinear active micro-rheology in a glass-forming soft-sphere mixture.
2013
We present extensive molecular dynamics computer simulations of a glass-forming Yukawa mixture, investigating the nonlinear response of a single particle that is pulled through the system by a constant force. Structural changes around the pulled particle are analyzed by pair correlation functions, measured in the deeply supercooled state of the system. A regime of intermediate force strengths is found where the structural changes around the pulled particle are small, although its steady-state velocity shows a strong nonlinear response. This nonlinear response regime is characterized by a force-temperature superposition principle of a Peclet number and anisotropic diffusive behavior. In the …
Thermally unstable throughflow of a power–law fluid in a vertical porous cylinder with arbitrary cross–section
2021
Abstract The present paper investigates how the cross–sectional shape of a vertical porous cylinder affects the onset of thermoconvective instability of the Rayleigh–Benard type. The fluid saturating the porous medium is assumed to be a non–Newtonian power–law fluid. A linear stability analysis of the vertical thorughflow is carried out. Three special shapes of the cylinder cross–section are analysed: square, circular and elliptical. The effect of changing the power–law index is investigated. The stability of a steady base state with vertical throughflow is analysed. The resulting stability problem is a differential eigenvalue problem that is solved numerically through the shooting method. …
Linear instability of the vertical throughflow in a horizontal porous layer saturated by a power-law fluid
2016
Abstract The effects of the vertical throughflow of a non-Newtonian power-law fluid on the onset of convective instability in a horizontal porous layer are investigated. The extended Darcy’s model of momentum diffusion is employed together with the Oberbeck–Boussinesq approximation. A stationary basic solution for the vertical throughflow is determined analytically. The basic velocity and temperature fields turn out to be independent of the non-Newtonian rheology. A linear stability analysis is carried out, leading to a fourth-order eigenvalue problem. A numerical solution of the eigenvalue problem is employed to obtain the neutral stability curves and the critical Rayleigh number for the o…
An analytical model of heat transfer and fluid dynamic performances of an unconventional NTR engine for manned interplanetary missions
2009
Abstract An analytical model of fluid flow and heat transfer of a Nuclear Thermal Rocket (NTR) engine concept is presented. The engine is based on the direct conversion of the kinetic energy of the fission fragments (FFs) into the propellant enthalpy. The FFs can escape from an extremely thin layer of fissionable material: a sufficiently large surface coated with few micrometers of Americium 242m, confined by a neutron moderator–reflector, may become a critical reactor. Three dimensional coupled CFD-Monte Carlo simulations have already been presented in Di Piazza and Mulas (2006) . In this paper, an analytical integral 1-D model of fluid dynamics and heat transfer is built in order to fores…
Process intensification in a photocatalytic membrane reactor: Analysis of the techniques to integrate reaction and separation
2017
Abstract Different methods to integrate reaction and separation in a membrane reactor are studied in the present work, with the aim being to highlight the pros and cons of the different alternatives and the effects of the intervening parameters. The coupling of the two processes can take place inside a single apparatus or using separate units. If a single apparatus is utilized, the coupling is more direct, but separate units offer higher degrees of freedom for the design with more opportunities to optimize the system without constraints. However, when using separate units, the integration of the two unit operations depends largely on the parameters intervening in the coupling procedure. The…