Experimental Study of the Effective Vortex Length in Small-Diameter Cyclones

Abstract This study experimentally investigated the effective vortex length (L ev ) in cyclone separators to resolve discrepancies between theoretical predictions and actual performance. Unlike previous studies that focused on the natural vortex length (L n ) derived from flow visualization or theoretical models, L ev was defined based on particle collection and pressure-drop behavior. It represents the portion of the cyclone body that effectively contributes to particle separation, beyond which further increases in body length do not produce measurable changes in performance. Using the very sharp cut cyclone as the baseline, systematic variations of geometric parameters were tested, including body height (H/D = 0.77–11.92), inlet diameter (R/D = 0.22–0.33), vortex finder diameter (D e /D = 0.20–0.40), and flow rate (Q = 3.8–25.0 L min −1 ). The effective vortex length was determined from both particle penetration and pressure-drop measurements, yielding consistent results. Experiments demonstrated that L ev consistently ranged between 4 and 6D, a narrower and more realistic range than the 2D–13D values typically predicted for L n . Normalization analysis identified cyclone body diameter and flow rate as the dominant parameters controlling L ev , with normalized sensitivities of 0.615 and 0.458, respectively. Other geometric factors showed minimal influence. The results suggest that the effective vortex length provides a more functional representation of cyclone separation performance than the traditionally defined natural vortex length. Whereas L n describes the full extent of the swirling airflow, L ev reflects the region that actively contributes to particle separation and pressure development. This experimentally based definition bridges the gap between fluid-dynamic characterization and actual particle collection behavior, offering a practical foundation for optimizing cyclone design and operation. Graphical abstract