Experimental study on airborne contaminant release from the impact of a liquid on a horizontal solid surface.*

 

The airborne release of dry contamination residues resulting from a liquid jet impinging a surface is an important mechanism by which Codiv-19 virus or radioactive contamination can reach human respiratory airways. The very fine evaporable droplets responsible for this threat are hard to quantify due both to their small size and short lifespan. We developed an experimental bench, which is able of quantifying in very accurate way, the evaporated dry contamination using a tracer. We evaluate the aerosol release fraction (ARF), corresponding to the ratio between the mass of airborne particles and the mass of dispersible tracer dissolved in the impinging liquid jet, in relation with the jet dynamic. The purpose of this present work is to present our measurements of aerosols release when a broken circular liquid jet, due the capillary instability, impacts a solid surface.

It was found that, when the liquid jet is in the Rayleigh regime, the Airborne Release Fraction increase with the jet velocity for the same jet diameter. In this regime, the ARF is around 10^-5. The airborne aerosol size distribution reveals particles of aerodynamic diameter within the respirable range (below 10 µm). The distribution exhibits features, which characteristics seem to indicate competing aerosol generation mechanisms in relation with the jet diameter and velocity. The particle size distribution of the 2 mm diameter liquid jet looks like unimodal whereas the 1 mm seems trimodal. The Rayleigh Plateau instabilities seem to be the origin of this difference.  Indeed, high speed camera visualization pointed out the fact that there are several mechanisms at the origin of the airborne release aerosols and we are trying to determine which one lead the ARF.