Use of Polyurethane Foam as the Impaction Substrate/Collection Medium in Conventional Inertial Impactors

摘要

Open pore polyurethane foam (PUF) can be used effectively a substrate for conventional inertial impactors with both high p~ ticle collection efficiency and minimal vaporization of semi-volat particle components. The collection characteristics of PUF as : impaction substrate were studied as a function of PUF densil Reynolds number. impaction substrate diameter. and nozzle-j plate distance. The conventional impaction substrate of the PM Harvard Impactor sampler was replaced with the PUF substral The use of PUF resulted in significant changes in the collection 4 ficiency curve. with the 50% cut-off size (dso) decreasing from 2., to 1.12 JLm. corresponding to VStk = 0.24. While the theory f conventional Rat impaction substrates accurately predicts dso v: ues (at VStk = 0.49). for PUF substrates this same theory predil dso values much larger than the experimentally determined valw After the collision of the particles with the PUF. a greater fractil of their excess kinetic energy may be absorbed by the substr~ than is absorbed by conventional substrates. reducing the amou of particles that would otherwise bounce off or be reentrain~ Furthermore. qualitatively similar results were obtained for PI densities between 1.9 X 104 and 5.0 X 104 g/m3. Results obtainl for varying Reynolds numbers also suggest that the difference collection efficiency curves between PUF and oil-coated substraj is due to different Row patterns. In addition. tests showed that ti overall impactor performance was better for larger impaction pl~ diameters for both PUF and conventional substrates. Finally. si nificant distortion of the collection efficiency curve was observl for larger nozzle-to-plate distance.