To characterize a cloud of particles physically and chemically, we need to know two important parameters: the size distribution and the complex refractive index of the particles. We have developed an experimental device to carry out the two operations simultaneously, without any physical contact, in media such as flames, particle spray and aerosol clouds in process.

The particle size distribution is determined by the analysis of a diffraction pattern produced by a coherent beam falling on a particle cloud.

To determine the complex refractive index for polydispersed spherical particles, two parameters are needed: the particle size distribution and the optical transmission. The transmission is related to the extinction coefficient by Beer’s law. The determination of n* then becomes possible using the Mie’s theory and the Kramers-kronig relations. An optimization algorithm (Metropolis) minimizes the standard deviation between experimental and calculated data.

Some results are presented on Titanium Tetrachloride and Graphite in powder as well as in a pulverized coal burner flame.

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