Abstract :
Gas absorption by a liquid aerosol in the absence of flow is analyzed, in which three different methods, including the perfect absorption model (PAM), rapid diffusion model (RDM), and fully numerical method (FNM), are carried out. By introducing a mass diffusion number, which represents the driving-force ratio between the external and the internal mass transfers, solute uptake characteristics of a variety of gaseous species (CO2, SO2, HCl, and NH3) of interest are elucidated. The analyzed results indicate that, over the investigated range of the mass diffusion number (Dm 10−4–0.12), the gas phase and the interfacial concentrations are highly relevant to the number. Specifically, when the mass diffusion number is small, such as CO2 and SO2, the mass transfer processes in the gas phase and at the interface can be approximated well by the RDM all the time. In contrast, when the number is large to a certain extent, say, NH3, the PAM is capable of providing a fundamental insight into the gas-phase mass transport phenomenon in the initial absorption period. With regard to the aerosol interior, because the liquid phase controls the two-phase mass transfer, the internal transport and absorption processes are merely affected by the mass diffusion number slightly. As a result, for the investigated gas the RDM is also applicable in predicting the solute uptake process in the liquid phase, no matter what the gas.
