• Energy Research

The Monte Carlo method was used to simulate particle segregation in gravitational fields. Systems containing one or two types of spherical particles were simulated, assuming that the particles interact according to a quasi-hard core potential. Systems with 1000 particles were simulated, replicated by periodical boundary conditions in the directions perpendicular to the gravitational field; at the top and bottom of the simulation box, the existence of rigid walls was assumed. Results for local composition and local voidage as a function of the height of the solid sediment are presented. The results for binary systems show that when very light particles are present in the mixture, it is possible, under certain conditions, to obtain configurations in which the particles with the smallest diameter concentrate at the top of the solid sediment. In order to observe the three-dimensional system configurations that result from the simulations, computational programs were developed in the virtual reality modeling language (VRML).

Knowledge of the properties of granular materials is important for efficient and safe design of industrial equipment. In this work, the Monte Carlo method is used for simulating granular systems of spherocylindrical particles. After presenting an overview of such method and of overlap detection in systems of hard spherocylinders, the application of the method for granular systems is discussed. Then, porosities, calculated for simulated monodispersed beds, are presented as functions of the particle elongation. Next, results for vibration-induced segregation of binary mixtures of spherocylinders with identical volume and density, but with different elongations, are evaluated, showing the influence of the particle shape on this phenomenon. Finally, effects of size and shape on such segregation are contrasted using results with simultaneous variation of particle volume and elongation.

In this work, the Monte Carlo method (MC) was extended to simulate the packing and segregation of particles subjected to a gravitational field and confined inside rigid walls. The method was used in systems containing spheres inside cylinders. The calculation of void fraction profiles in both the axial and radial directions was formulated, and some results are presented. In agreement with experimental data, the simulations show that the packed beds present structural ordering near the cylindrical walls up to a distance of about 4 particle diameters. The simulations also indicate that the presence of the cylindrical wall does not seem to have a strong effect on the gravitational segregation phenomenon.

Mean-field theories that include nonelectrostatic interactions acting on ions near interfaces have been found to accommodate many experimentally observed ion specific effects. However, it is clear that this approach does not fully account for the liquid molecular structure and hydration effects. This is now improved by using parametrized ionic potentials deduced from recent nonprimitive model molecular dynamics (MD) simulations in a generalized Poisson-Boltzmann equation. We investigate how ion distributions and double layer forces depend on the choice of background salt. There is a strong ion specific double layer force set up due to unequal ion specific short-range potentials acting between ions and surfaces.