Effect of vessel size scale on the aerosol spray scavenging efficiency with water mist

Abstract

Research interest in eliminating airborne aerosol particles has been growing for decades. Aerosol particles with aerodynamic diameters between 0.2 and 1 μm are difficult to remove by traditional spray systems. To improve the aerosol scavenging efficiency, a new method is proposed that employs the addition of water mist. Water mist is supposed to aggregate with aerosol particles to form large-sized coagulated aerosol-mist particle clusters, which can subsequently be removed by spray droplets with a higher efficiency. To investigate the effect of the vessel's size scale on the aerosol collection efficiency, aerosol spray scavenging experiments without and with water mist were conducted in both the UTARTS facility and TOSQAN facility. The cylindrical vessels of the two facilities have the same internal diameter, but the vessel of the TOSQAN facility has a larger height. Experimental results show that water mist has the potential to improve aerosol scavenging efficiency in both facilities but to a higher degree inside the TOSQAN facility. Numerical simulations of aerosol removal by spray droplets without mist were conducted, and different scaling criteria for the geometry of the vessel and gaseous entrainment rate were discussed to explain the experimental results. With water mist, the coagulated aerosol-mist particles have a stronger inertia and a larger Stokes number; these particles are easier to capture by using spray droplets and a water film. The contribution of the spray injection height, spray spread volume, and water film to aerosol removal in cases with mist increased to a larger degree than that of the gaseous entrainment rate, finally resulting in a higher improvement ratio of aerosol removal efficiency in the TOSQAN facility.