Numerical simulation of particles distribution of environmental tobacco smoke (ETS) and its concentration in a closed environment

Humans are frequently exposed to various chemical hazards, with smoking being a significant source of indoor air pollution. This pollution is particularly pronounced in environments such as smoking rooms, conference halls, cafes, and coffee houses. This study focuses on analyzing the concentration, distribution, and behavior of emitted particles from both mainstream and sidestream smoke in a controlled smoking room environment. A critical aspect of the research is the consideration of the thermal plume generated by the smoker's body, particularly around the breathing zone, which plays a crucial role in the dispersion and inhalation of pollutants. To conduct this analysis, a computational fluid dynamics approach was employed, incorporating a displacement ventilation (DV) system integrated with a detailed surface mesh model of a standing manikin. A Lagrangian approach was utilized to track the particle paths, considering factors such as particle size, density, and initial velocity. This approach was complemented by an Eulerian method to simulate the complex airflow patterns within the smoking room, accounting for turbulent flow and temperature variations. The integration of these methods provides a comprehensive understanding of both the macroscopic and microscopic behaviors of smoke particles. The motion equations governing the particles incorporated several forces, including inertial drag force, viscous drag force, buoyancy force, and gravitational force. Additionally, the study examined the interaction between thermal plumes and smoke particles, particularly how temperature gradients around the body affect particle dispersion and concentration. The study meticulously evaluated the distribution and volume average of respirable suspended particles (RSPs) and nicotine by analyzing a plane opposite to the breathing zone of both heated and unheated manikins. It was observed that the thermal plume generated by the temperature gradient around the body could significantly alter the flow field of both sidestream and mainstream smoke between puff periods. The simulation results demonstrated that the thermal plume increased the concentration of RSPs in the breathing zone, highlighting a critical exposure pathway for smokers and nonsmokers alike. A significant increase of approximately 70% in the nicotine concentration is due to the thermal plume. The concentration of nicotine peaks at approximately 0.003 mg/m3 by the third second in smoker#1's (6 smokers' position) breathing zone. Specific configurations of the DV system showed varying efficiencies in reducing pollutant concentrations, emphasizing the need for targeted ventilation strategies. In a chamber with six smokers, researchers found that the time required for suspended particles to reach a cleaning ratio, considering the dynamics of particle movement due to smoking activity, was approximately 184 s per puff.