THE ORIGIN OF THE FISH-HOOK EFFECT IN HYDROCYCLONE SEPARATORS

Experimental evidence suggests that under certain circumstances the se lectivity (or classification) function for hydrocyclones does not alwa ys conform the expected 'S' shape but exhibits a dip in regions of the finer particle sizes (typically less than 20 mu m). This dip is known as the 'fish-hook effect' and is of considerable industrial significa nce because it mediates the classification efficiency of ultra-fine ma terials. Only two previous attempts have been carried out to model the effect and, moreover, the existence of the phenomenon itself has been disputed. This paper presents a critical assessment of previous work and new evidence for its existence based on in situ particle size meas urements on the process streams coupled with robust data reconciliatio n procedures. A theory to account for the phenomenon and a new empiric al model are proposed and tested.