Effects of Aggregation on Gravity Settlement of Submicron Aerosols Under High Temperature and High Humidity Conditions

Coupling aerosol gravity sedimentation mechanism and aggregation effect, considering the correction of submicron particle free path and gas dynamic viscosity in thermal environment, a gravitational sedimentation model suitable for submicron aerosol accompanied by coalescence effect under high temperature and high humidity conditions is established, and the established model is verified by the results of thermal experiments. The aerosol aggregation model is established using the discretization method. By controlling whether the aggregation mechanism occurs in the established model, the influence of aggregation on gravitational settling when steam fraction and ambient pressure are changed is studied. In the study, it was found that the aggregation effect has a nearly 1-fold acceleration effect on the decay constant of the number concentration of submicron aerosols during gravitational sedimentation, and the acceleration effect on the decay constant of the mass concentration can be ignored, but there is an acceleration trend. When submicron aerosols settle under high temperature and high humidity conditions, the number median particle size tends to increase, that is, the increase of the number median particle size by the aggregation effect is greater than the decrease of the number median particle size by gravity sedimentation. After considering the aggregation effect, the number concentration decay constant and the mass concentration decay constant when the submicron aerosol undergoes gravitational sedimentation will decrease with the increase of the ambient pressure, and increase with the increase of the steam fraction. However, the number concentration decay constant changes larger, the mass concentration decay constant has a trend of change, and the change range is relatively weak. In addition, in the sensitivity analysis of the aerosol coalescence and gravitational sedimentation models, it is found that the molecular free path has a greater impact on the calculation results of aerosol coalescence and deposition in a thermal environment than the dynamic viscosity. Moreover, the influence of Brownian coalescence on the aerosol particle size spectrum is much greater than that caused by gravitational coalescence.