Small cyclones with conical contraction bodies

Abstract

The performance (i.e., cyclone pressure drop and particle penetration curve) of small cyclones with conical contraction bodies was investigated, with the cyclone used either as the size-selective inlet of a miniature/compact particle sensor/monitor or as a personal particle sampler. Prototype cyclones having inner bodies with conical contraction angles of 0°, 15° and 30° were constructed, and their performance was evaluated at various operational flow rates (viz., 1.0–7.0 L min–1); the results indicate that a cyclone with a high body contraction angle is capable of collecting smaller particles than one with a low contraction angle at the same cyclone pressure drop. The effect of the vortex finder insertion length on the cyclone’s performance was also studied and was found to be negligible. A linear relationship between the dimensionless particle cut-off size and the annular flow Reynolds number, Reann (in the log-log plot), could be found for the studied cyclones with characteristic cyclone velocity, calculated with the assumption of conservation of angular momentum for the swirling flow in a cyclone. Compared with previous studies, cyclones with conical contraction bodies have an advantage during lower pressure drops (up to 50%) for the same dimensionless particle cut-off size.