A model for the absorption rate in electrically charged droplets

Charged droplets are produced by electrosprays or sometimes generated by natural phenomena, and nowadays their application is also investigated as a tool for process intensification in heat and mass transfer processes typical of chemical engineering. This paper analyses the absorption of slightly soluble trace gases into electrically charged droplets: it reports a new mass transfer model taking into account the electrophoretic motion of gas molecules and the possible alteration of the interfacial properties induced by the imposed electric charges. The model is successfully validated against existing experiments on the absorption of SO2 into electrified water droplets. These experiments are useful both for the robustness of data available for the SO2-air-water system and for its significance in atmospheric chemistry and physics, and chemical engineering applications. Considering the same SO2-air-water system as a case study, the model predicts that the absorption rate for a droplet produced with a conventional electrospray is up to 42% faster than that of an uncharged droplet with the same size and morphology, while the electrophoretic drift provides an improvement of the gas-side mass transfer coefficient mainly for droplets finer than 500 & mu;m.