Collection efficiency of round-nozzle impactors with horizontal annular inlet

•Horizontal annular inlet was applied to round nozzle inertial impactors.•Horizontal annular inlet impactors were compared with vertical inlet impactors.•Impactor collection efficiency was numerically and experimentally investigated.•Cut-off size was reduced by about 30% with the use of the horizontal annular inlet.

In this study, a horizontal annular inlet was applied to a round-nozzle impactor in an effort to reduce the cut-off diameter. The collection efficiencies of round-nozzle impactors with either a vertical inlet, which has conventionally been used, or a horizontal annular inlet were investigated both numerically and experimentally. For the comparison, the nozzle width, nozzle-to-plate distance, impaction plate diameter, and flow rate of the aerosol drawn into the impactor were set the same for both the vertical inlet impactor and horizontal annular inlet impactor. A parametric study was performed to analyze the effects of the width of the horizontal annular inlet and nozzle throat length on the collection efficiency of round-nozzle impactors with nozzle Reynolds numbers ranging from 500 to 2600. By replacing the vertical inlet with the horizontal annular inlet, the square root of the Stokes number corresponding to the cut-off diameter could be reduced by approximately 30%. In other words, the value of (Stk50)1/2 was decreased from 0.49 to 0.32 or 0.33 when considering the effect of gravity.