Evaporation of an aerosol plume from an inkjet printhead

Abstract

The size of aerosol droplets is a critical factor in evaluating the risks associated with airborne pathogen transmission, yet it is highly variable due to evaporation. Additionally, the close proximity of water droplets within an aerosol plume can slow their evaporation, thereby further complicating risk assessments. To investigate these complexities, a versatile experimental setup was developed using the XAAR XJ128 inkjet printhead to generate droplets of 50 μm in diameter for detailed evaporation characterization within a plume. The droplet evaporation process was monitored via Phase Doppler Anemometry (PDA), which provided size distribution and velocity measurements at various positions along the vertical axis of the falling droplets. These experimental results were compared to a theoretical model for isolated droplet evaporation in quiescent air. Droplet number density significantly influenced evaporation, with measured evaporation rates in the plume, originally at a relative humidity of 30%, comparable to the theoretical model under 60-80% relative humidity when nearly all printhead nozzles were active. The effect of number density on evaporation was also analytically evaluated. Notably, the complete evaporation of droplets in this configuration could theoretically increase relative humidity up to 89% locally when all nozzles were used, while using about one-third of the nozzles resulted in a local relative humidity up to 33%. These insights underscore the importance of further investigating the evaporation dynamics of airborne aerosol droplets in the context of pathogen transmission. The use of an inkjet printhead demonstrates its significant potential for generating a controlled aerosol plume, offering a promising avenue for future research in this critical area.