The particle collection efficiencies of axial flow cyclones with eight different geometric configurations, operated at 50 lpm aerosol flowrate, have been evaluated in this study. The geometric variation of test cyclones includes the optional addition of an upside-down cup, two vortex finder lengths, and two cyclone base shapes. Under various configurations, the cutoff aerodynamic particle size of axial flow cyclones changed from 272 to 448 nm. Our study shows that configuration effects on the collection efficiency of axial flow cyclones are different from those of tangential flow cyclones. The observation of different geometric effects on particle collection by axial and tangential flow cyclones is attributed to the flow pattern difference between cyclones of two types. It is further concluded that the optimal configuration for axial flow cyclones is with an abrupt contraction base, without an upside-down cup and with an increased vortex finder length. A simple model combining the model of Leith and Licht (1972) and the tubing loss in 90 degrees bends at high Reynolds numbers has also been proposed to predict the particle collection efficiency curve of the optimal axial flow cyclone among those tested. (C) 2010 Elsevier Ltd. All rights reserved.