Furnace geometry effects on plume dynamics in laser ablation for nanotube synthesis

Laser ablation (LA) has become a popular method for production of carbon nanotubes where formation of gaseous carbon plume and liberation of catalyst particles are caused by the laser pulse. The plume dynamics in laser ablation is somewhat similar to point explosion where a large amount of energy is liberated in a small volume. The aim of this study is to explore thermal dynamics of catalyst particles that is crucial for the formation of carbon nanotubes. The challenge of this case is to describe numerically the strong shock wave propagation and reflections in the working space of laser furnace and its effect on plume dynamics and temperature regime of catalyst particles. The proposed model includes a multi-species formulation for concentration of chemical components combined with the compressible Euler equations. An axisymmetric unsteady computational gas dynamic model of plume expansion into ambient gas has been developed. In the present work, the system of governing PDEs is solved numerically using the relaxing TVD scheme in generalized curvilinear coordinates. To obtain the thermal behavior of catalyst particles the Eulerian solver has been combined with Lagrangian tracking of catalyst particles. The developed software has been implemented and tested using the set of test cases described in the paper. Reflected shock waves interact with the plume and catalyst particles, heat them, and cause temperature oscillations. The contradictory requirements of sustained high temperature of catalyst particles and minimum of temperature oscillations are discussed using the series of representative working space shapes.