EFFECT OF CLEAN-AIR CORE GEOMETRY ON FINE-PARTICLE CONTAMINATION AND CALIBRATION OF A VIRTUAL IMPACTOR

The optimum diameter and position of the clean air core in a clean air core virtual impactor were experimentally determined. It was found th at the clean air core diameter should be at least twice as large as th e converging nozzle diameter and that the clean air core should be pos itioned so that the ratio of the clean air flow velocity to the aeroso l flow velocity ranges from 1.5 to 5.0 at the outlet of the clean air tube. Use of a laminator in a virtual impactor was found to increase t he particle loss while maintaining almost the same collection efficien cy curve. (C) 1997 American Association for Aerosol Research.