EFFECT OF RADIATIVE HEAT-TRANSFER ON THE COAGULATION DYNAMICS OF COMBUSTION-GENERATED PARTICLES

We examine the influences of radiation heat transfer on the size and n umber density evolution of small coagulating particles. On a microscop ic level, radiative emission and/or absorption by the particle will pe rturb the ps temperature field adjacent to each particle. As a result of thermophoretic particle transport, the nonequilibrium condition can alter the collision rates with neighboring particles. A simplified an alysis of the thermophoretic coagulation mechanism suggests that net r adiative cooling of the particles can lead to an accelerated growth of mum-sized particles, whereas net radiative heating can act to essenti ally freeze coagulation rates. On the macroscopic level, the addition or removal of heat in the ps through radiative absorption/emission by the particle cloud can also significantly alter, through thermophoreti c transport, the local particle number density. Under certain cases th ese effects can augment the accelerated coagulation rates that occur u nder radiative cooling conditions. We also examine the particular situ ation of equilibrium between particle cloud radiative absorption and e mission-which results in no net macroscopic effect on the gas. Under c onditions where the spectral distribution of the incident radiation di ffers from that of the emitted radiation, radiative equilibrium can le ad to accelerated growth of certain particle sizes and retarded growth of others. Using numerical solutions to the general dynamic equation for particle growth, we demonstrate the possibility of using incident radiation of controlled intensity and spectral distribution to narrow the particle size distribution function of coagulating aerosols.