Deposition and coagulation of polydisperse nanoparticles by Brownian motion and turbulence

Turbulent and Brownian coagulation rates as well as deposition coefficients of polydisperse nanoparticles were measured experimentally. The coagulation rates were obtained from the change in the total number concentration of polydisperse sodium chloride aerosols, with geometric mean diameters ranging from 30 to 120 nm, in a closed chamber at atmospheric pressure. The geometric standard deviations of the experiments were in the range of 1.55–1.65. The experimental coagulation rates took deposition rates into account, because coagulation and deposition occur simultaneously in a closed chamber. As a result of deposition, it was shown that the experimental deposition coefficients of polydisperse aerosols were agreed well with the theoretical data of Park et al. [(2001). Wall loss rate of polydispersed aerosols. Aerosol Science and Technology, 35, 710–717]. It was shown that the effect of the coagulation was much greater than that of the deposition in the high particle number concentration. In addition, the results represented that bigger turbulent coefficients, caused by higher fan rotation speeds, make the turbulent coagulation process become stronger. In the small particle size range, however, the coagulation rates tend to converge though turbulent coefficients are different. In conclusion, it was shown that experimental coagulation rates followed the values of Lee and Chen [(1984). Coagulation rate of polydisperse particles. Aerosol Science and Technology, 3, 327–334], which were calculated for polydispere aerosols in the gas-slip regime and free-molecule regime.