A quantitative analysis of turbulent drag reduction in a hydrocyclone

Abstract

Turbulent drag reduction has been observed to occur over a wide range of additive systems, such as solution of synthetic or natural polymers, and fibre suspensions. In this study, the influence of softwood kraft pulp fibres and synthetic polymer additives on turbulent drag reduction (DR) in a hydrocyclone is investigated. It was demonstrated that cellulose fibre suspensions and aqueous polymeric solutions reduce the fluid energy losses in comparison to water during hydrocyclone operation within the range of reject ratios studied. A maximum drag reduction of 58 % and 55 % was found to occur at a volume split fraction of 50 % for a 0.9 % fibre suspension and a 300 ppm anionic polyacrylamide solution, respectively. Polymer degradation or polymer chain decay displayed adverse effects for 100 ppm and 150 ppm solutions after 22 min of run time at 11.2 kW pumping power and a reject ratio of 25 %. Synergistic effects were observed with pulp suspensions containing both cationic and anionic polyacrylamide (CPAM and APAM, respectively); a maximum DR of 41 % was observed for a 0.7 % fibre suspension containing 100–300 ppm of polymer at a reject ratio of 50 %. Similarly to aqueous polymer solutions, the degradation of 300 ppm APAM or CPAM in a 0.7 % fibre suspension decreased the observed DR up to 38 % after 30 min of run time at 11.2 kW pumping power and a reject ratio of 25 %. The near 43 % reduction in CPAM concentration, due to surface adsorption, when present in a 0.7 % fibre suspension assisted in quantifying the DR variations observed between suspensions containing APAM or CPAM.