Sampling Cyclones for Respirable Dust

Abstract: The performance of cyclones used in occupational hygiene for sampling respirable dust was studied. Test methods for experimental determination of cyclone penetration have been designed and validated. The penetration curve for a sampling cyclone presently used in Europe was measured. The sampler's performance relative to three sampling conventions for respirable dust was determined. The cyclone was optimised to the 1993 international sampling convention for respirable dust, by varying the cyclone flow rate and the dimensions of the vortex tube. Published investigations on the collection characteristics for four cyclone designs were analysed with regression analysis, in order to derive a semi-empirical relationship between the cut-off size and the steepness of a cyclone's collection efficiency, and operating conditions and cyclone design. This work has shown that performance requirements based on acceptance band along the sampling convention are inferior to those based on estimated errors in sampled mass concentrations, and by modifying a cyclone's internal dimensions, it is possible to achieve a good emulation of a sampling convention over the whole particle size range. The estimated resulting bias in sampled mass concentrations for the optimised cyclone was generally within ±4% relative to the 1993 international sampling convention for respirable dust. It has been shown for a wide range of cyclones and operating conditions that the cyclone's cut-off size is mainly determined by the annular vortex, whereas the steepness of the collection efficiency seems to primarily depend on the ratio of the cyclone body diameter to the vortex tube inner diameter.