Investigating the Fluid Dynamics of Aerosolisation and the Effects on Biological Organisms

Sarah Windiate, R. Thomas, M. Walker

The effect of spray devices on microbial organisms during their dissemination is poorly understood. Mathematical methods have been applied to better understand the conditions experienced by organisms, so that they can be related to the experimentally observed level of damage. The overall aim is to better understand the hazard posed by such spray devices in order to assess the potential risk from their misuse.
Two spray devices are of interest for this numerical study; the Collison nebuliser and a generic paint sprayer based on twin-fluid atomisation. The Collison nebuliser is used in laboratories for spray applications. It uses a compressed air driven Venturi effect to draw fluid up from a reservoir which is then dispersed into droplets by the air jet. A paint sprayer was chosen as an example twin-fluid atomiser and works in a similar way, by drawing fluid through either a gravity fed or siphon reservoir using compressed air. The resultant fluid is then shaped by air jets at the exit.
Three different approaches have been used to model the Collison nebuliser and a generic paint sprayer. A compartmental model of the Collison nebuliser has been developed to relate experimental observations to levels of damage caused by the fluid recirculating through the system. Computational fluid dynamics (CFD) models have been developed of the internal liquid flow within a paint spraying device. In addition, analytical expressions have been developed to better understand the general behaviour of fluid within an atomisation device.

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