Cloud chamber investigation into the mechanisms of artificial warm fog dissipation using hygroscopic materials
Heavy fog significantly impacts modern transportation and public health.Thus,artificial fog dispersal crucial for disaster prevention and mitigation.Despite its importance,the mechanism underlying fog dispersal and the optimal particle size of dispersal catalyst remains uncertain.This study,conducted in a 15 000 cubic meter cloud chamber,explores the influence of different catalyst particle sizes on warm fog clearance.We found that cat-alyst A,with a particle size of 75 pm,effectively reduced the number concentration of fog droplets from 5 800 g/cm3 to 2 000 g/cm3 within 8 minutes and further to 1 000 g/cm3 within 10 minutes,while decreasing the liquid water content from 2.45 g/m3 to 0.2 g/m3.The mean volume diameter of the fog droplets increased from 6-8μm to 10-20 μm,accelerating the fog clearance to 20％of the time required for natural sedimentation.In con-trast,Catalyst B(with a particle size of 100 µm)induced raindrop formation under heavy fog conditions,clearing the fog in 40％of the time taken by natural sedimentation,albeit with slightly less effectiveness than cata-lyst A.To determine the optimal catalyst particle size,we employed a gravitational continuous collision and growth model to evaluate the fog dispersal efficacy of different particle sizes,providing a theoretical basis for selecting the most effective size.Theoretical calculations suggest that for a droplet radius of 6 μm in a 25 m high cloud chamber,the collision efficiencies catalyst particles sized 50 µm and 100 μm are comparable(approximately 80％),requiring a catalyst mass of 3.52 kg.Ho we ver,the dispersal for 50 µm radius particles is twice as long as for 100 µm particles.The study indicates that for droplets radii of 6-15 µm,catalyst particles in the 60-100 μm range are most effective.Further analysis revealed that excessively small catalyst particles capture fewer fog droplets,require more time for fog dispersal,and consume less water during collisions.Conversely,overly large catalyst particles clear fog faster and have higher descent speed but are less effective in water consumption and droplet capture.There-fore,an optimal catalyst particle diameter of 40-80 µm is suggested.The findings presented here are based on a simplified gravitational continuous collision and growth model and do not consider factors such as vertical velocity and variations in liquid water content with height.Future studies should address these to refine the theoret-ical mechanisms of fog clearance and improve catalyst dosage calculations.
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