Modelling of direct ultraviolet photoionization and charge recombination of aerosol nanoparticles in continuous flow

Ultrafine aerosol particles are electrically charged in a range of devices to enable their detection, capture, and control. Direct ultraviolet (UV) photoionization enables increased charging of some nanoparticle materials over alternative charging mechanisms such as diffusion charging, particularly in size ranges below 50 nm diameter. The aim of this work is to provide modelling and simulation of ion and particle charge and discharge processes and transport and collection in a continuous flow. A non-dimensional analysis indicates regimes under which the photocharging process is dominated by diffusion, electric field transport, convection, photoionization, or recombination. The computational fluid dynamics (CFD) model developed in this work is the first to include UV photoionization and detailed ion and particle recombination theory. The validity of assumptions made for diffusional wall losses and external electric field action is evaluated by comparison with 0D Numerical and 3D CFD models. Regimes are identified to distinguish the level of details required for aerosol transport and charging models.