Combustion dynamics of a carbon particle in a CO2 laser beam

Abstract

It is usually assumed in research on the combustion of solid particles that the burning particles are in a heated medium. The heat balance for a particle is determined by the combustion rate, the heat of reaction, and the heat transfer to the medium. When a high-power light beam acts on a particle, there is an additional source of heat due to the absorption. In this paper are presented theoretical and experimental studies of the combustion of a single particle in a high-power laser beam. The theory is based on the actual temperature dependence of the transport coefficients. The burning rate is determined by the temperature and the particle radius. However, the particle temperature is dependent on the energy flux density in the optical field, so ultimately the burning rate is dependent on both radius and flux density. Equations are derived incorporating the burning rate, flux density, particle radius, temperature and the physico-chemical properties of the particle. Experiments performed with a continuous-wave CO/sub 2/ laser acting on carbon particles of diameter 90-210 ..mu.. m shows good agreement with theoretical estimates. Experimental data shows that the combustion of a particle of this size occurs in the diffusion mode. For particles ofmore » carbon burning on an Al substrate, it was found that the particles did not become uniformly heated over the volume, and the burning front followed directly behind the heating front.« less