Modeling of coagulation-sedimentation effects on transmission of visible/IR laser beams in aerosol media

It has been shown that the size distribution of dense polydisperse aerosol particles settling in a quiet chamber can be retrieved from the time dependence of optical extinction of a laser beam traversing the aerosol. However, in this method, the effect of coagulation on the size distribution was completely ignored. In order to understand the effects of coagulation, a parametric study of the separate and combined effects of sedimentation and (thermal) coagulation on the time dependence of extinction of four visible and IR laser beams traversing such an aerosol medium has been carried out, and the results are presented in this paper. The method of numerically modeling the change of aerosol size distribution with time due to thermal coagulation and the cutoff of larger aerosols due to gravitational sedimentation is described in detail. Results of the study show that, whereas the coagulation effects are predominant for smaller size particles (diameter <1.4 ,microm in the particular experimental setup under stud , the sedimentation effects are predominant for particles larger than 2.0 microm in diameter.