July 1-6, 2007
Wood pulp fibre suspensions and model synthetic fibre suspensions have been shown previously to mitigate effectively calcium sulphate fouling in heat exchangers. Fibre flexibility was found to be a decisive fibre property in fouling mitigation. Adding fibres to a fouling fluid is environmentally benign and can be applied during operation without shutting down the heat exchanger. Because polymer fibres are more robust in a hostile environment, further work was initiated with two types of rayon fibre and one acrylic fibre of the same fibre length. Experiments were performed at both constant and varying fibre volume concentrations. The more flexible rayon fibres in suspension produced lower ultimate-fouling resistance values than the stiffer acrylic fibres. Fibres were embedded in the fouling layer and it is believed that this mechanism contributed to the overall fouling resistance and was a counterpart to the positive effects of fibres mitigating fouling. The more flexible fibres momentarily form viscoelastic bundles that can ‘absorb’ hydrodynamic shear forces, modify the turbulent stresses, and lower the fouling matter removal rate. Stiff fibres embedded in the deposit protrude into the bulk flow and entrap more fibres as they are less likely to deflect, bend, and be flattened by the shear stresses near the wall.
M. Rost and G. G. Duffy, "FOULING MITIGATION WITH SYNTHETIC FIBRES IN A CASO4 SUPERSATURATED SOLUTION" in "Heat Exchanger Fouling and Cleaning VII", Hans Müller-Steinhagen, Institute of Technical Thermodynamics, German Aerospace Centre (DLR) and Institute for Thermodynamics and Thermal Engineering, University of Stuttgart, Germany; M. Reza Malayeri, University of Stuttgart, Germany; A. Paul Watkinson, The University of British Columbia, Canada Eds, ECI Symposium Series, (2007). http://dc.engconfintl.org/heatexchanger2007/26