TECHNIQUE FOR AEROSOL FLOW CHECK IN DIFFERENTIAL MOBILITY ANALYZER AND ITS INFLUENCE ON CLASSIFICATION PERFORMANCE

The flow pattern of aerosol and sheath air in a cylindrical annulus of a Differential Mobility Analyzer (DMA) is critical to determine the c lassification performance of the DMA. In the present work, a new techn ique to check aerosol flow inside the DMA is proposed and the influenc es of aerosol flow distortion and broadening on the classification per formance are investigated by means of the Tandem DMA method. As a resu lt, it is found that (1) the annular flow inside the studied DMA is a fully developed laminar flow with a negligible mixing between aerosol and sheath air when the aerosol flow rate is less than 3 l/min and the sheath air flow rate is 17.5 l/min, (2) a larger width of aerosol ent rance slit causes uneven distribution of aerosol flow in the circumfer ential direction, and (3) both the uneven distribution and broadening of the aerosol flow lead to a broader band of classified particle elec trical mobility, as well as a shift of peak electrical mobility to a s maller range. These results suggest that aerosol flow inside a short-t ype DMA is more sensitive to the flow rates and its structure compared to the conventional TSI type DMA.