A Numerical Model for Brownian Motions of Nano-Particles in Supersonic and Hypersonic Impactors

In this paper, transport and deposition processes of nano-particles in supersonic and hypersonic impactors were investigated using a computational modeling approach. Axisymmetric forms of the compressible Navier-Stokes and energy equations were solved and the airflow and thermal condition in the impactor including the upstream nozzle were evaluated. A computer simulation model for solving the Lagrangian particle equation of motion including all the relevant forces was developed. The importance of the accurate modeling of the Brownian motion of nano-particles was further emphasized. The motion of nano- and micro-particles in the supersonic and hypersonic impactors were then simulated and the impactor capture efficiencies under various operating conditions were studied. For dilute particle concentrations, the assumption of one-way interaction was used. Particular attention was given to proper evaluation of the Brownian motion of the nano-particles in the upstream nozzle and in the body of impactor. The simulation results for collection efficiency were found to be in good agreement with experimental data. In particular, the model accurately predicted the loss of the nano-particles in the upstream nozzle due to their Brownian motion.