Fouling mitigation of heat exchangers with natural fibres

Fouling mitigation research has been extended to investigate the effects of fibre concentration, fibre length, and fibre flexibility, on heat transfer fouling with supersaturated calcium sulphate solutions. Two long-fibre softwood pulp fibres (pine and spruce) of similar mean length but different fibre flexibility were used as well as a short-fibre, hardwood eucalypt pulp. Fouling was prevented altogether with a 0.25% suspension concentration of long-fibre pine fibres for more than 46 days, and for 38 days with a 0.1% suspension of short-fibre. At 0.05%, concentration, the onset of fouling was delayed for 14.5 days with the short-fibre hardwood pulp. The final asymptotic level of fouling was about 30% of the fibre-free fouling solution. The shorter-fibre hardwood pulp fibres are more effective than either of the long-fibre softwood pulps at the same concentration of 0.05% (higher population). Fouling started at about 1.8 days for both long fibre pulps at 0.05% concentration, and heat transfer augmentation was still achieved in the induction period. Stiffer pine fibres were more effective at fouling mitigation than the more flexible spruce fibres. An equal percentage mixture of hardwood and pine pulp at 0.05% concentration also showed that the shorter hardwood fibres are more effective in mitigating fouling.