Design and Test of 2.5 μ m Cutoff Size Inlet Based on a Particle Cup Impactor Configuration

Based on the particle cup impactor configuration, an inlet for sampling fine particles smaller than 2.5 w m in diameter was designed for operation at a flow rate of 25 l/min. To determine the optimal dimensions of the particle cup impactor applicable to the PM 2.5 inlet, calibration experiments were carried out at wind velocities of 2 and 24 km/h in a wind tunnel. It was noted that the particle cup impactor having an impaction nozzle diameter of 3.2 mm and the nozzle-to-cup spacing of 3.6 mm yielded a sharp size cutoff. Supplementary experiments were conducted on sampling performance with the inlet having the optimally selected configuration at a near-zero wind speed in the test chamber. Results of the tests showed the inlet had a cutoff size of 2.43 w m in aerodynamic diameter, at 25 l/min, and that particles larger than 2.5 w m were trapped in the cup. Additional experiments covering a flow rate between 10 and 40 l/min with particle sizes between 0.8 and 4.3 w m were conducted in the test chamber. A field test was performed to examine the PM 2.5 inlet in real situations. The performance indicated that the inlet design met the basic requirements of fine-particle sampling.