Initial size distribution of cough particles for CFD simulations based on particle sizer measurements and evaporation model

Expiratory particles are known to be capable of carrying viruses that cause respiratory diseases. To predict exposure to these particles, computational fluid dynamics (CFD) simulations can be used, with the initial size distribution of particles as an important input parameter. This study aims to explore the appropriate initial size distribution of cough particles to enhance the prediction accuracy. A novel inference method is proposed, based on experimental measurements with an optical particle sizer and a CFD simulation. The CFD simulation employs the Lagrangian method to track the dispersion of cough particles, incorporating an evaporation model; thus, the response relationship between the initial size distribution and measurements can be established. In the previous experiment by the authors, the number concentration of cough particles (0.3–10 μm) was measured at distances ranging from 1 to 60 cm from the mouth. The CFD results provided the response relationship for particle size (shrinkage factor) and particle number (relative number) at different distances. Under the current model, particles with initial diameters less than 32 μm reached a quasi-equilibrium size at all distances, and the shrinkage factors were 0.26–0.27 under a relative humidity of 34 %. Consequently, the initial size distribution for cough particles can be determined using measurements at 30–60 cm from the mouth, along with CFD derived response relationships. This distribution has been verified for reliability and can be used to predict particle size distributions at interpersonal conversation distances. In addition, this study further investigates the necessity of integrating the evaporation model into predictions of particle exposure. The results show that adding the evaporation model in CFD simulations has little impact on the predicted exposed particle number concentration. However, it significantly affects the predicted exposed particle size, which in turn influences the exposure to cough particles.