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Many aerosols present in nature (e.g., atmosphere) or artificially generated for various purposes (e.g., inhalation) are composed of liquids that are prone to continuous evolution due to thermodynamical changes of surrounding conditions as for example temperature and humidity. Thermodynamical changes influence the aerosol dynamics causing condensation or evaporation and subsequent aerosol size growth or shrinkage. These evolution mechanisms simultaneously influence the aerosol deposition due to particle size dependent nature of the aerosol deposition mechanisms (i.e., inertial and diffusional deposition). As the experimental measurements of evolving liquid aerosol deposition are challenging, development and validation of computational models allowing aerosol simulations are important to explore and understand the underlying physics. In this manuscript, we present our multispecies evaporation/condensation model implemented in an Eulerian aerosol framework. The model is validated by comparing with the available literature data for droplet evaporation/condensation under controlled conditions. We applied the model to explore the effect of the temperature and humidity variations on the aerosol size change and its consequent influence on the aerosol deposition in a bent pipe for single- and multispecies mixtures. We show influence of condensation on the aerosol deposition efficiency for various particle sizes. Our results demonstrate that particle size growth favoring inertial deposition and inhibiting diffusional deposition can significantly influence the number of depositing particles and result in an increase of the deposited liquid mass on the walls. These effects are caused by subtle interaction of flowing aerosols in the laminar boundary layer with surrounding vapors available for condensation and they are dependent on the gradient of temperature between flowing mixture and walls.

Accurate predictions of aerosol transport, evolution, and deposition in the human airways are crucial for inhalation dosimetry investigations. Inhaled aerosol transported through the airways undergoes thermodynamic changes due to changes in temperature and humidity. Aerosol evolution processes are particularly important for liquid multispecies aerosols. These aerosols are sensitive to condensation and/or evaporation dynamics, which can modify gas/liquid partitioning of each species and particle size distribution. In this manuscript, we present computational fluid dynamics simulations of complex aerosol mixtures in a realistic geometry of the human respiratory tract cast model. We used a publicly available computational framework, AeroSolved, developed for simulation of evolving multispecies aerosol mixtures. We evaluated the dynamics of liquid particles in physiologically relevant conditions of 100 % relative humidity at the temperature of 37 ° C . We studied two separate inhalation flow scenarios: in the first case, a warm aerosol at 50 ° C was inhaled and subsequently cooled down while flowing in the airways. In the second case, an aerosol at room temperature was inhaled and heated up to the temperature of 37 ° C . Our results demonstrated that aerosol evolution mainly occurs in the upper segments of the airways (throat and trachea) at the very short timescales. Apart from showing the significant influence of temperature and humidity conditions on aerosol dynamics and evolution, we also measured aerosol deposition fluxes investigating the dependence of the delivered aerosol mass on evolution mechanisms. We showed that the delivered regional mass of each species depends on the physico-chemical properties of the mixture, and it is also significantly influenced by the airways’ humidity and thermal conditions. It was also shown that the species-specific properties of the liquid mixture (e.g., activity coefficient) play an important role in gas/liquid partitioning of the species. With AeroSolved such dependencies can be further investigated with greater attention towards specific needs and physiologically important conditions (e.g., transient flow inhalation patterns, aerosol mixture composition and its properties).