Use of polyurethane foam as the impaction substrate/collection medium in conventional inertial impactors

Open pore polyurethane foam (PUF) ran be used effectively as a substrate fo r conventional inertial impactors with both high particle collection effici ency and minimal vaporization of semi-volatile particle components. The col lection characteristics of PUF as an impaction substrate were studied as a function of PUF density, Reynolds number, impaction substrate diameter, and nozzle-to-plate distance. The conventional impaction substrate of the PM2. 5 Harvard Impactor sampler was replaced with the PUF substrate, The use of PUF resulted in significant changes in the collection efficiency curve, wit h the 50% cut-off size (d(50)) decreasing from 2.48 to 1.12 mum, correspond ing to root Stk = 0.24, While the theory for conventional hat impaction sub strates accurately predicts d(50) values (at root Stk = 0.49), for PUF subs trates this same theory predicts d(50) values much larger than the experime ntally determined values. After the collision of the particles with the PUF , a greater fraction of their excess kinetic energy may be absorbed by the substrate than is absorbed by conventional substrates, reducing the amount of particles that would otherwise bounce off or be reentrained, Furthermore , qualitatively similar results were obtained for PUF densities between 1.9 x 10(4) and 5.0 x 10(4) g/m(3), Results obtained for varying Reynolds numb ers also suggest that the difference in collection efficiency curves betwee n PUF and oil-coated substrates is due to different flow patterns, In addit ion, tests shelved that the overall impactor performance was better for lar ger impaction plate diameters for both PUF and conventional substrates. Fin ally, significant distortion of the collection efficiency curve was observe d for larger nozzle-to-plate distance.