Mjv Goldschmidt

Hydrodynamic modelling of dense gas-fluidised beds using the kinetic theory of granular flow: effect of coefficient of restitution on bed dynamics

A radio frequency (RF) glow discharge plasma etch electrode design is disclosed which is capable of creating high power density plasma with uniform etch rates, while providing access for automatic loading semiconductor wafers from outside of the plasma region. The electrode assembly comprises of an electrode to which RF energy is applied surrounded by an insulator, which in turn surrounded a grounded surface all of which have cylindrical symmetry. When placed a small distance from a flat, grounded substrate, the electrode assembly creates a volume which can effectively combine a high power density plasma, while maintaining a sufficient channel for pumping a gas flow and for observing the plasma optically. The same channel is widened for automatic transport of semiconductor wafers from outside of the plasma reactor chamber. Such confined high power density plasma are important for high rate, uniform, anisotropic etching, especially for silicon dioxide.

Hydrodynamic modelling of dense gas-fluidised beds: Comparison of the kinetic theory of granular flow with 3D hard-sphere discrete particle simulations

A novel technique to sample particle velocity distributions and collision characteristics from dynamic discrete particle simulations of intrinsically unsteady, non-homogeneous systems, such as those encountered in dense gas-fluidised beds, is presented. The results are compared to the isotropic Maxwellian particle velocity distribution and the impact velocity distribution that constitute the zeroth-order Enskog approximation for the kinetic theory of granular flow. Excellent agreement with the kinetic theory is obtained for elastic particles. The individual particle velocity distribution function is isotropic and Maxwellian. A good fit of the collision velocity distribution and frequency is obtained, using the radial distribution function proposed by Carnahan and Starling (J. Chem. Phys. 51 (1969) 635). However, for inelastic and rough particles an anisotropic Maxwellian velocity distribution is obtained. It is concluded that the formation of dense particle clusters disturbs spatial homogeneity and results in collisional anisotropy. Analysis of the impact velocity shows that, in dense gas-fluidised beds, not all impact angles are of equal likelihood. The observed anisotropy becomes more pronounced with increasing degree of inelasticity of the particles.

Heterogeneous mass transfer models for gas absorption in multiphase systems

Heterogeneous, instationary 2-D and 3-D mass transfer models were developed to study the effect of dispersed liquid-phase droplets near the gas–liquid interface on the local gas absorption rate. It was found among other things that droplets (or particles) influence local mass transfer rates over an area exceeding largely the projection of the droplets on the gas–liquid interface. For a specific application particle–particle interaction was studied and could be described by a single parameter, depending only on the minimum interparticle distance. For gas absorption flux prediction an unit cell must be defined. The sensitivity of the absorption flux to the definition of the unit cell was investigated. Finally, a complete strategy to arrive at gas absorption flux prediction from single particle simulations has been proposed.