Numerical analysis on temporal size change of expiratory droplets by considering component variation

¹ Graduate School of Engineering, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
² Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan

^* Corresponding author: bychen@iis.u-tokyo.ac.jp

Abstract

When conducting computational fluid dynamics (CFD) simulations to investigate the evaporation characteristics of respiratory particles, the over-simplification of droplet compositions may cause inaccuracies in the results. Although some researchers have conducted parametric studies on droplet components, an investigation using CFD simulation is still lacking. Therefore, this study aimed to determine the effect of different components on the temporal size change of expiratory droplets using CFD simulation. Two droplet sizes (10 μm and 100 μm) were selected, and two types of component combinations were considered, both with a volume fraction of 98.2% for water and 1.8% for non-volatile parts. In Scenario 1, the non-volatile part is composed of NaCl (density: 2200 kg/m³, molecular weight: 58.5 kg/kmol), whereas in Scenario 2, the non-volatile part is composed of NaCl, KCl, lactate, and protein (density: 1000 kg/m³, average molecular weight: 293 kg/kmol). Computations were conducted under constant temperature (25 °C) and different relative humidity (0 and 90%). The results showed that the equilibrium size and equilibrium time were strongly dependent on the droplet components. In subsequent investigations, the effects of different droplet components should be considered in the CFD simulations to obtain more accurate results.