Redhouane Henda

Numerical analysis of a reaction-diffusion-convection system

Abstract This paper is concerned with the numerical analysis of the behavior of a homogeneous tubular reactor in which a cubic autocatalytic reaction is coupled to diffusion and convection transport. The set of one-dimensional partial differential equations describing the reaction–diffusion–convection system is analyzed using different standard reduction techniques (finite difference, orthogonal collocation, and finite element methods) within the framework of the method of lines. Both steady state and dynamic behaviors of the system are considered. Special high-resolution finite difference methods such as essentially non oscillatory (ENO) and total variation diminishing (TVD) are applied to the convectively dominant case. The calculation results that special high-resolution schemes such as ENO are essential to track efficiently steep moving fronts exhibited by the strongly convective problems. The strengths and limitations of the different numerical schemes considered are examined and discussed.

Accelerating voltage effect on the ablation process during pulsed electron deposition

In this study, we have analyzed the effect of electron beam accelerating voltage on the maximum temperature of a graphite target during pulsed electron beam ablation (PEBA). To this end, a two stage, one dimensional thermal model is used. The target is subjected to an electron pulse with accelerating voltages of 10, 13, 15, 17 and 18 kV. The surface temperature, vaporization front velocity, ablated depth, and ablation rate are estimated from the solution of the model. Simulation results have shown that target surface temperature is not proportional to the accelerating voltage. It has been found that the surface temperature increases with the accelerating voltage from 10 kV to 15 kV, and reaches a maximum value (7500 K) at 15 kV. After 15 kV, the temperature decreases with increasing accelerating voltage. Similar trends have been observed in the vaporization front velocity, ablated depth and ablation rate, with maximum values (75 m/s, 2.1 μm, and 4 μg/mm2) at 15 kV. The calculation results are in good agreement with relevant experimental data from the literature.

Estimation of Requirements for the Formation of Nanocrystalline Diamond Driven by Electron Beam Ablation

Conditions for the formation of thin films of nanocrystalline diamond by electron-beam ablation of a graphite target are studied. The analysis is based on the predictions of the analytical solutions of two models describing the expansion of the plasma plume into a background gas and toward a substrate. The models allow the calculation of the pressure and temperature of ablated nanoparticles upon impact with the substrate where the film is deposited. The calculation data are reported on the phase diagram of carbon and are used to assess conditions under which the diamond phase is likely to form on the substrate. The results show that decreasing gas pressure and target to substrate distance, over the practical range of accelerating voltage, is conducive to diamond formation.