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Abstract:
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Ultrafiltration (UF) is one of the many technologies used in the treatment of process and wastewaters. Tubular UF membrane modules are used to treat fiber suspensions for effluent control and chemical recovery in the pulp and paper industry. However, the treatment of pulp suspensions with modules containing tubes having an inside diameter of less than 2.54 cm is typically problematic. Severe blockage occurs at the inlet of the tubes due to the accumulation of pulp fibers within the header. In the present study, the commercial computational fluid dynamics package, CFD-ACE+ was used to simulate the hydrodynamics within the header of a simplified system. The hydrodynamics were simplified by approximating the two-phase pulp suspension with a single-phase Newtonian fluid. The main flow structures within various header geometries were analyzed. Header geometry was varied by chamfering the inlet of a tube at four specific angles. These four angles, referred to as inlet angles, were 0$\sp\circ,$ 30$\sp\circ,$ 45$\sp\circ,$ and 55$\sp\circ.$ The hydrodynamic features within the different header configurations were compared. A central eddy in the shape of a torus of varying cross section was observed at lower inlet angles. The eddy was less discernable at larger inlet angles. The eddy intensity within the header was identified as the key hydrodynamic structure affecting fiber accumulation. Changes in the average velocity of recirculation of the eddy were found to be closely correlated (r$\sp2$ = 0.9986) to previously reported fiber accumulation results. |
