UNSTEADY STATE DIFFUSION WITHIN POROUS SOLID PARTICLES

Effect of unsteady-state condition on oxygen diffusion through biological floc particles.

Solid-State Diffusion and NMR

Diffusion in solids, which requires the presence of crystal defects or disorder, has both microscopic and macroscopic aspects. Nuclear magnetic resonance techniques provide access to microscopic diffusion parameters like atomic jump rates and activation energies as well as to the tracer diffusion coefficient for macroscopic transport. Microscopic NMR methods include spin-lattice relaxation spec...

Diffusion of finite-sized Brownian particles in porous media

The effective diffusion coefficient D, for porous media composed of identical obstacles of radius A in which the diffusing particles have finite radius PR (fl>O) is determined by an efficient Brownian motion simulation technique. This is accomplished by first computing D, for diffusion of “point” Brownian particles in a certain system of interpenetrable spherical obstacles and then employing an...

Diffusion-limited retention of porous particles at density interfaces.

Downward carbon flux in the ocean is largely governed by particle settling. Most marine particles settle at low Reynolds numbers and are highly porous, yet the fluid dynamics of this regime have remained unexplored. We present results of an experimental investigation of porous particles settling through a density interface at Reynolds numbers between 0.1 and 1. We tracked 100 to 500 μm hydrogel...

Discretization of an unsteady flow through a porous solid modeled by Darcy’s equations

The system of unsteady Darcy’s equations considered here models the time-dependent flow of an incompressible fluid such as water in a rigid porous medium. We propose a discretization of this problem that relies on a backward Euler’s scheme for the time variable and finite elements for the space variables. We prove a priori error estimates that justify the optimal convergence properties of the d...