křemenný prach

A quartz test powder aerosol was dispersed in a cylindrical resuspension chamber (V=0.437 m3, S=0.35 m2, S/V=8.38) and the temporal variation of size distribution was viewed on-line by an APS (Aerodynamic Particle Sizer) analyzer under the conditions of a controlled temperature of 20°C and a relative humidity (RH) of 50 %. The optimal mass load of the powder (with the highest mass concentrations after suspension) was 10 mg. The total number of 300 size distributions was used to calculate the average number and mass size distribution. The number or mass median particle diameter was 1.07 μm or 2.42 μm respectively. the median particle diameters were later used as input parameters into the mathematical models of project SPREAD. Deposition velocities of the particles suspended in the chamber were studied under the conditions of ventilators on and ventilators off. The calculated deposition velocity obtained with switched off ventilators was compared to the model of terminal settling velocity. The results were within 10 % agreement. The particle median diameters were inputted together with the surface parameters used in project SPREAD in the Raupach model and the change of deposition velocity with increasing wind speed was evaluated. It was found that increasing wind velocity and obstacles have the highest influence on the deposition velocity of particles of this size.