The size and optical properties of soot particles

Abstract

The emissivity of soot particles makes an important contribution to heat transfer by radiation from industrial flames. This investigation has involved the measurement of the size distribution of aggregates of soot particles from both a soot generator and a flame. The techniques involved sampling by electrostatic precipitation, filtration and impingement. Subsequent measurements of particle size were carried out with the aid of an electron microscope and an image analysing microscope (Quantimet). Spectral transmission measurements in the visible range were also made on both the flame and the generator. Calculations, based on the Mie theory, were made for the measured volume-equivalent particle size distributions to predict the variation of the spectral transmission with wavelength and the ratio of polarised components of scattered light with angle. It was concluded that spectral transmission measurements are more sensitive to particle size distribution than measurements of angular scattering. The measured particle sizes were found to follow a log-normal distribution and a complex refractive index for soot of 1.9-0.35 i gave the closest agreement between experimental and calculated results.