Numerical simulations of reacting nano-scale flows

Rapport, 2013

The outcome of the CheSC pilot project "Numerical simulations of reacting nano-scale flows" is reported. A Direct Simulation Monte Carlo (DSMC) code has been developed that is able to treat molecular motion in wall-bounded systems with a prescribed pressure difference between an inlet and an outlet. Both homogeneous and heterogeneous chemical reactions can be handled by the code. A number of validation cases are presented to support these claims. An algorithm has been devised and implemented that allows optimization of the distribution of a catalytically active material within a 3D pore where the flow field is described by the present code. The objective function is the outlet concentration of computational molecules that have interacted with the catalytically active surface, and the optimization method used is simulated annealing. The application of a stochastic optimization heuristic is shown to be more efficient within the present DSMC framework than using a macroscopic overlay method. Furthermore, it is shown that the performance of the developed method is superior to that of a gradient search method for the current class of problems. The code produced in the current project represents a suitable starting-point for addressing a number of related research questions, such as reacting multiphase flows on the nano-scale and reacting heterogeneous flows with surface diffusion. The report also contains a discussion on how the present code can be extended to allow for a detailed investigation of these issues.