Development of a dichotomous slit nozzle virtual impactor

A high-volume slit nozzle virtual impactor has been developed to collect fine and coarse particles. The size cut-off and particle loss characteristics of the developed slit virtual impactor agree well with those of the 16.7 l min(-1) commercially available dichotomous sampler. The effects of various how and physical design parameters on the collection of both fine and coarse particles have been investigated. The results of these tests indicated that many of the theoretical principles established for round nozzle virtual impactors can be successfully applied to slit nozzle virtual impactors. However, the effects of the flow volume and Reynolds number (Re) on the cut-off behavior and particle losses are more pronounced for slit virtual impactors. The impactor's particle size cutpoint decreased as the total inlet flow and Re increased. For Re < 7000, particle losses increased with particle size. For Re of about 7000, particle losses exhibited a maximum near the 50% cutpoint, which is typical in round nozzle virtual impactors. For Re < 7000, losses of fine particles were significant, while coarse particle losses were low. Changes in the minor-to-total flow ratio and collection slit width also affected particle losses. (C) 2000 Elsevier Science Ltd. All rights reserved.