Abstract Number: 259 Working Group: Aerosol Modeling
Abstract Using an idealized mouth-throat (MT) airway as a test bed, simulations were carried out to investigate the impact of flow rate on hygroscopic aerosol transport and deposition (Longest et al., 2010). Specifically, a multi-layer structure, including the airway tissue and mucus layer, was constructed to simulate heat transfer across the MT boundary layer, i.e., conduction in the mucus layer and tissue, latent heat loss due to mucus evaporation, and convection over the mucus layer. The transport and deposition of the hygroscopic aerosols was simulated with a validated numerical program at three flow rates, i.e., 15 L/min, 30 L/min, and 60 L/min. The aerosols contained four components: water, ethanol, sodium chloride (NaCl), and fluorescein. The transition shear stress transport (SST) model and discrete phase model (DPM) were employed for the prediction of the air flow and aerosol transport, respectively. Modeling and validation of the aerosol deposition efficiency and aerosol-vapor interaction are discussed in our previous study (Chen et al., 2017).
The temperature of the tissue boundary toward the body surface side was set at 37 ˚C. The temperature of the mucus layer, which decides the saturation pressure of the water vapor, was determined by the heat transfer conditions, i.e., mucus evaporation, convection of the air and the conduction between the mucus layer and airway tissue. The air inhaled was assumed to be at room conditions, i.e., 26.7 ˚C and RH = 34%. For each flow rate, simulations with various initial aerosol diameters ranging from 2μm to 20μm were conducted to obtain the functional dependence between the aerosol deposition efficiency and the Stokes number.
The results are as follows:
1) Significant temperature gradients can be observed in the mucus-tissue region due to the latent heat loss of the mucus layer and convection along the air-mucus interface; especially under elevated flow rates.
2) The multi-component aerosols quickly evaporate in the relatively low humidity air, resulting in solid particles containing two components, i.e., NaCl and fluorescein.
3) Local regions of high RH (> 80%) almost disappear near the boundary at large inhalation flow rates, e.g., 60 L/min; hence, hygroscopic growth of NaCl and fluorescein particles is suppressed.
4) The growth ratios of the deposited and escaped aerosols both decrease with increasing flow rates.
References
Longest, P.W., McLeskey Jr, J.T., & Hindle, M. (2010). Characterization of nano aerosol size change during enhanced condensational growth. Aerosol Science and Technology, 44, 473-483.
Chen, X., Feng, Y., Zhong, W., & Kleinstreuer, C. (2017). Numerical investigation of the interaction, transport and deposition of multicomponent droplets in a simple mouth-throat model. Journal of Aerosol Science, 105, 108-127.