Visual Investigation of Pulp Floc Dispersion Mechanism in Axisymmetric Step Expansion Tube, 2001 Engineering / Finishing & Converting Conference Proceedings

C. Park, C. Aidun--The presence of pulp fiber agglomerates referred to as flocs in pulp suspension causes the quality defect of paper products and process failures. Formation and dispersion of pulp flocs depend on flow conditions at the various stages of the papermaking process. In this study, the dispersion mechanism of the model pulp floc passing through an axisymmetric expansion tube was visually investigated using the high-speed imaging technique. The model floc is prepared by the rolling drum technique (Jacqueline’s method) and characterized by the mass fraction measurement and scanning electron microscopy (SEM). The mass fraction, the degree of entanglement, and the homogeneity of the network structure increase with the rolling time while the surface roughness decreases. The model floc of 24-hour rolling time that is used in this study appears to have nearly homogeneous and uniform fiber network properties, and to be reproducible. The dispersion process in an axisymmetric expansion tube is not a random process but a sequentially proceeds with following stages: deformation, rupture, fragmentation and fiber scale dispersion (DRFD mechanism). The dispersion rate is proportional to the step Reynolds number, and normalizing with convective time scale, the universal dispersion rate curve is found, which represents floc dispersion mechanism in axisymmetric expansion tube. An empirical model is developed to express the floc dispersion rate in an axisymmetric expansion, predicting pulp floc dispersion rate in an axisymmetric expansion.