Abstract--
Published data for four cyclone designs were analysed with multi-linear regression, in
order to determine which parameters influenced the cyclone collection efficiency. The dependence of
the cyclone cut-off size on fluid flow was expressed by two parameters (the ratio of the cut-off size to
the cyclone body diameter, and a Reynolds number based on the inlet velocity and the annular
distance between the vortex tube and the cyclone wall) originally proposed by Moore and McFarland.
The steepness of the collection efficiency curve was found to be mainly influenced by the ratio
of the cyclone body diameter to the vortex tube inner diameter, and independent of the Reynolds
number. A literature review provided an explanation of the different behaviour between long- and
short-coned cyclones, which stems from differences in the vortex flow: At low Reynolds numbers
there is practically no turbulence, at intermediate Reynolds numbers the vortex is distorted by
periodic waves and is attached to the cyclone wall, and at high Reynolds numbers the turbulent
mixing is considerable and the vortex is attached to the cyclone bottom. The transition between the
intermediate and the high Reynolds number vortex flow regimes is determined by the Reynolds
number based on the cyclone inlet.