Study On Internal Flow Field And Collection Efficiency Of Dust Deposition Sampler

Aeolian dust deposition is one of the main process for the exchange between atmosphere and earth-surface.The intensity,particle size distribution,physical and chemical properties and settlement rate of dust can be known through monitoring Aeolian dust,which is used for deducing source of aeolian dust,migration pathway,depositional environment and the effect of dustfall on environment.In summary,the study of dustfall has important significance for the research of long distance transmission of air pollutant,quaternary terrigenous sediment and biogeochemical cycles of elements.Dust collector as a collection device to observe directly Aeolian dust deposition has great significance on accurate collection of dust.But the problem of accurate observation of dust has not been resolved because the problem of dust floating in the dust collector cannot be solved of most collection devices and different collection methods are not applicable to all the regions.In order to select several efficient dust deposition gauge and accomplish accurate observation,the improving design methods(add funnel,mesh and opening holes)were implemented and analyzed.The main results were as follows:(1)The results of PIV internal flow field tests showed that in the status of empty deposition sampler,it has complex vortex and high wind zone occurred in upper part of the deposition sampler with the phenomenon of dust re-entrainment;in the status of empty deposition sampler with a funnel,only in the funnel mouth can air flow runout which prevent external air flow entry the sampler;in the status of empty deposition sampler with holes,a funnel and mesh,dust is easier to fall and hold which because high wind zone is not occurred in funnel.(2)The results of wind tunnel test showed that:(1)dust deposition gauge with mesh can significantly increase collection efficiency that can be increased by 18% and 19.7% compared with empty dust deposition gauge;(2)collection efficiency of dust deposition gauge when the distance between funnel and top of dust sampler is 5 cm or 10 cm are higher than that is 0cm.It can be increased by 18.7% and 18.8% compared with empty dust deposition gauge when thewind speed is 2 m/s,it can be increased by 16.1% and 21.6% compared with empty dust deposition gauge when the wind speed is 3 m/s,it can be increased by 12.9% and 11%compared with empty dust deposition gauge when the wind speed is 4m/s;(3)collection efficiency of dust sampler with 30°and 45°between funnel and barrel are higher than that with 60°;(4)collection efficiency of dust deposition gauge with upper middle opening ways is significantly higher than other opening ways,it can be increased by 24.6%,26.4% and14.3% compared with empty dust deposition gauge when the wind speed is 2 m/s,3 m/s and 4m/s;(5)collection efficiency shows a sharp drop with increasing wind speeds when the wind speed is less than 4 m/s.The dust deposition gauge has the highest collection efficiency that is about 80%.(3)The results of field observation test showed that:(1)dust sampler with funnel,mesh and opening holes can significantly increase collection efficiency;(2)collection efficiency of dust sampler is stable when the distance between funnel and top of dust sampler is 5 cm or 10cm;(3)collection efficiency of dust sampler with 30°and 45°between funnel and barrel are better than that with 60°,and the former is 20% higher than the latter;(4)collection efficiency of dust sampler with upper opening way and upper middle opening ways are 65%-89% and16%-40% higher than other opening ways.(4)Four types of dust deposition gauge were selected through PIV test,wind tunnel test and field observation that are as follows: dust deposition gauge with the distance between funnel and top of dust sampler is 5 cm,30° between funnel and barrel and upper middle opening ways;dust deposition gauge with the distance between funnel and top of dust sampler is 5 cm,45° between funnel and barrel and upper middle opening ways;dust deposition gauge with the distance between funnel and top of dust sampler is 10 cm,30° between funnel and barrel and upper middle opening ways;dust deposition gauge with the distance between funnel and top of dust sampler is 5 cm,45° between funnel and barrel and upper middle opening ways.