Model of aerosol evolution in high supersaturated glycerol-air vapor mixtures.

Introduction:
This article presents a mathematical model for the formation of condensation aerosols from highly supersaturated vapor-air mixtures. The model is suitable for systems with very high nucleation rates that result in aerosol mass densities >1 g/m3. It accounts for nucleation, non-isothermal condensation, coagulation and indirectly for coalescence of the newly formed particles. It applies kinetic theory to determine the nucleation rate and treats nucleation and coagulation in separate stages, but both are coupled with non-isothermal condensation. a statistical approach based on the Weibull function is used to estimate the size distribution of the droplets (particles). The model has been applied to study the formation of glycerol aerosols in Electronic Nicotine Delivery Systems.

Key Points:

* The model describes several processes that can be reasonably separated in time dealing with nucleation, growth by condensation, coagulation, and indirectly coalescence.
* Nucleation is modeled using collision theory, which assumes that a stable particle is formed when three molecules collide resulting in the formation of a dimer with the third molecule carrying away the energy of the collision.
* The Weibull distribution function is used to predict the final aerosol distribution resulting from the initial monodisperse model due to Brownian collisions of the aerosols.
* The model has been applied to study the formation of glycerol aerosols in Electronic Nicotine Delivery Systems.
* The model qualitatively reproduces the observed trend that the aerosol particle size decreases as the puff flow rate increases.
* The model suggests that at lower puff flow rates higher particle concentrations occur leading to higher rates of coagulation which result in larger particlesize aerosol.
* The model does not take into account any particular ENDS design and provides an independent general approach that can be incorporated with any mixing model for a specific devices configuration.

Main Message:
The model presented in this article provides a framework for understanding the formation and evolution of high concentration aerosols formed by condensation after the mixing of a stream of a hot vapor mixture with a separate stream of cold gas. The model is generally applicable to many aerosol production systems and has been applied to study the formation of glycerol aerosols in Electronic Nicotine Delivery Systems. The model suggests that the aerosol particle size decreases as the puff flow rate increases, this is due to lower initial particle formation at the higher air flow rates resulting in a lower particle number density, and therefore, allowing for more coagulation cycles within the one second period the aerosol evolved, leading to larger particles. The model can be a useful tool for optimizing product performance and in regulatory filings related to these products.

Fisenko SP, Rostami aa, Kane DB, et al. Model of aerosol evolution in high supersaturated glycerol-air vapor mixtures. aerosol Sci Technol. 2021;55:871-885. doi:10.1080/02786826.2021.1904130