MEASUREMENT OF MASS-TRANSFER TO AGGLOMERATE AEROSOLS

The mass transfer to agglomerate titanium dioxide aerosols produced in a thermal reactor was measured and compared to the mass transfer for spheres of the same mobility. The material transferred to the particles was ultrafine radioactive lead clusters produced via the decay chain of Ac-227. The lead attachment rate was measured with an epiphaniometer, a device that mixes a fixed concentration of radioactive lead atoms with the sample for a period of several minutes and then measures the quantity of lead attached to the particles. In the free-molecular regime, where the particle diameter is small compared with the mean free path of the gas and the diffusing species, previous studies have shown by theory and experiment that the mass transfer to an aerosol is inversely proportional to the particle mobility. This study showed that this is also true for particles in the transition regime, where the particle diameter is comparable to the mean free path. Further, the mass transfer rate is shown to be independent of particle shape for particles of the same mobility, at least when the mean free paths of the gas and the diffusing species are comparable.