Effect of gas temperature on the capture of charged particles by oppositely charged water droplets

This work reports experimental results on the effects of temperature (25, 45, and 65 degrees C at different relative humidity) on the scrubbing of charged submicron particles by means of cold (25 degrees C) droplets charged with opposite polarity. The aim of the study is to experiment how the capture of particles is influenced by the simultaneous presence of electrostatic and phoretic forces related to the occurrence of thermal and water vapor gradients close to the droplet surface. This information plays an important role in the development of wet electrostatic scrubbing (WES), an emerging technology for submicron and ultrafine particle capture. Tests were performed in a lab-scale system in which the particle laden-gas was scrubbed by a train of identic droplets. Particles were charged by a corona source while droplets are generated by electrospraying. Experiments revealed that for particles larger than about 250-300nm, there were higher removal efficiencies in nonisothermal conditions, with limited differences between 45 and 65 degrees C tests. For particles finer than about 150nm, we sometimes observed lower removal efficiencies for higher gas temperatures, probably due to the difficulties in controlling particle charging for these particles. The experiments were interpreted with a consolidated stochastic model that predicted successfully the data at isothermal conditions, but was less effective for tests at higher gas temperatures. In our opinion, this discrepancy relies on synergies among the fluid dynamic field induced by droplet evaporation/condensation, the phoretic and the electrostatic forces, which are not considered in the model.(c) 2016 American Association for Aerosol Research