A Brownian dynamics simulation of aerosol deposition onto spherical collectors

The inclusion of Brownian motion in aerosol deposition studies has often been treated separately from deposition due to other causes (e.g., inertial and electrical forces). A unified approach based on the full solution to the so-called ordinary Langevin equation of motion is presented to study particle deposition on a single spherical collector. The “Brownian dynamics” method given here is useful when the inertial, external, and particle-particle interaction forces are comparable to the diffusive, or Brownian, force. Several example calculations are considered for both the clean, or steady-state, deposition efficiencies, as well as for the unsteady-state efficiencies (particle-particle deposition problem). In particular, for the steady-state behavior, the classic Levich-Lighthill solution to the problem of convective-diffusion to a freely falling sphere has been reproduced. Additionally, an approximate analytical solution for the combined case of inertial and diffusional deposition, recently given by J. Fernandez de la Mora and D. E. Rosner [J. Fluid Mech. 125, 379 (1982)], has been verified and the so-called principle of superposition for the combined case of inertial and electrostatic deposition has been criticized. For the unsteady-state problem, the charge neutralization of an initially uniform charged collecting sphere by the deposition of oppositely charged Brownian particles has been examined. This latter study represents a generalization of the previously proposed “aerosol dynamics” method (M. H. Peters, R. K. Jalan, and D. Gupta, Chem. Eng. Sci., in press) which now includes the Brownian motion of the aerosol particles.

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