Modification and evaluation of the WINS Impactor. Final Report
The EPA well-type impactor ninety-six (WNS) impactor was modified and evaluated to serve as a separation device for a proposed federal reference method for particulate matter under 2.5 µm. Design modification to the WINS focused on the requirement of sharpening the penetration versus particle aerodynamic diameter curve. The ratio of the throat length over the jet width, the T/W ratio, was reduced from 5.5 to 1.6 to sharpen the shape of the penetration versus particle aerodynamic diameter curve. The diameter of the well was increased from 30 mm to 37 mm to accommodate the larger nozzle necessary for the T/W alteration. The jet-to-plate distance over the jet width (S/W) was increased from 2 to 3 with the intention that higher loadings would affect the shape and position of the penetration curve to a lesser degree. Additionally, the screw threads of the anti-spill ring on the well were changed to an o-ring for simplicity, ease of use, and to prevent oil leakage. The performance curve of the redesigned WINS has a geometric standard deviation of 1.18 as compared to 1.24 of the original design.