Aerosol discharge velocity and particle size characteristics of a low powered e-cigarette by phase Doppler anemometer

Electronic cigarettes, also known as e-cigarettes, may have become a tool to improve smoking cessation due to their ability to provide nicotine at a selected rate. However, caution still needs to be taken when using e-cigarettes due to the presence of addictive nicotine and harmful substances, produced from the heating process of aerosolization. The aerosol particle size distribution (PSD) and associated velocities generated by e-cigarettes have significant influence on aerosol deposition in different regions of human respiratory tracts. Due to the importance regarding inhalation risk reduction, deeper understanding of particle velocity and size characteristics of e-cigarettes demands thorough investigation. However, comprehensive study on PSD and velocity of e-cigarettes with a standard testing condition at relatively low heating powers (e.g., power <10 W), which are beneficial considering a reduced emission of toxic chemicals, is still lacking. On another note, while different dilution methods can mislead the comparison and assessment of device performances, data about particle size and velocity of undiluted e-cigarette aerosols are scarce. The present study aims to measure particle number count and size distribution of undiluted aerosols of a latest fourth-generation e-cigarette at a low power of 2.5 W. Temporal and spatial growth of particle velocity and size distribution of an aerosol flow are examined using a phase Doppler anemometry (PDA) technique. To the authors’ best knowledge, application of PDA in e-cigarette aerosol measurement is rarely reported. Velocity measurement revealed a time duration of optimum heating operation for the atomizer. The centerline mean velocity decay of the aerosol discharge suggested a limited mixing and entrainment characteristic compared to a typical air/water jet due to the presence of aerosol particles in the flow region. The particle interactions and collisions in the aerosol flow field possibly increased the centerline turbulence intensity level compared to a canonical free laminar jet. The particle size measurement depicted a continuous increase in particle diameters during a puff period due to potential volatility of e-liquid, and vigorous aerosolization and particle coagulation processes. Spatial evolution of arithmetic mean diameter, count median diameter, and geometric standard deviation of aerosol discharge along the flow centerline and transverse direction are reported. Based on these results, moisture absorption of hygroscopic aerosols, particle evaporation, and particle size re-distribution phenomena are explained as the flow propagated downstream. This present study makes an important contribution to the advancement and optimization of aerosol-generating devices. Also, this study has potential implications in PSD simulation and validation of aerosol dosimetry models.