Numerical simulations of thermal confinement of particles in rarefied gases with molecular dynamics

The European Space Agency (ESA) in an “Invitation to Tender”, dated August 15, 2006, illustrated a feasibility study of the Interaction in Cosmic and Atmospheric Particle System (ICAPS) experiment. The experiment consists essentially of thermal elements, contained in a cylindrical box, the center of which is a trapping area for thermally confined particles floating in a rarefied gas within the chamber. Thermophoretic forces induced by thermal gradients concentrate particles carried from the gas into the trapping area. Particles are eventually collected from this area. The physical dimensions of the experiment and of its components, temperature gradients and locations the thermal elements within the chamber are free parameters that should be experimentally and numerically investigated to enhance the efficiency of the experiment in collecting particles in the trapping area. To enable numerical investigations of the proposed device a two-dimensional computer program called THERCONF-2D (THERmal CONFinement in 2D) has been build up as a first step towards a full three-dimensional representation of the experiment. This code version describes the displacement due to thermophoresis of tiny particles in a gas-filled domain subjected to a temperature gradient. The behavior of the gas molecules and their interaction with material surfaces and with the particles floating in the gas are modeled with the statistical methods of molecular dynamics, based on the “Direct Simulation Monte Carlo” (DSMC). In case of polyatomic molecules sharing of the energy between translational and rotational modes is simulated with the Larsen-Borgnakke model. Interaction of polyatomic molecules with material surfaces is computed on the basis of the Cercignani-Lampis-Lord model. The computational code has extensive post-processing capabilities for visualization of computational results. After verification of the code, current work is aiming at identifying the optimum combination of physical parameters allowing for the best efficiency of the thermal confinement, minimizing the loss of particles escaping from the collecting area. A variant of the code is being installed on parallel processors. The article presents the state-of-the-art of this computational endeavor.