Industrial & Engineering Chemistry Research, Vol.50, No.15, 8932-8940, 2011
Novel Features of Aerosol Coagulation in Nonisothermal Environments
Local supersaturations and the rapid homogeneous nucleation of often subcooled nanometric particles occur when vapors from a high-temperature source diffuse into adjacent regions of much lower temperature. While earlier experimental and theoretical studies were focused on the macroscopic mass transfer rate consequences of such localized condensation (Turkdogan and Mills (1964), Epstein and Rosner (1970)), we identify and describe here, from a broader perspective, several expected novel features of aerosol coagulation dynamics in nonisothermal environments, including the expected particle size "spectra". In the simplest (limiting) case, differential thermal particle drift down the local temperature gradient dominates the Brownian diffusion-controlled collision rate, and, for a population of thermally conductive mist droplets coagulating by this mechanism, we have calculated and displayed (e.g., Rosner, D. E.; Arias-Zugasti, M. Thermophoretically-dominated aerosol coagulation. Phys. Rev. Lett. 2011, 106, 015502.) the expected coagulation-aged "self-preserving" droplet size distribution. However, in most applications the more familiar Brownian diffusion contribution to the coagulation rate must also be included, and we summarize here our recent analysis of this combined case, which enables another test of the frequently made assumption of "additive rate constants" and leads to quasi-self-preserving droplet size distributions. Because fully miscible mist droplets may also be distributed with respect to composition (and, hence, thermal conductivity) we take this opportunity to outline how these, and more general phoretic mechanisms (including thermocapillary flow), can be incorporated into the present formulation.