| A disk separation apparatus was previously designed to remove adhesive particles and other contaminants from recycled pulp fiber slurry, increasing the resultant recovered fiber product's value. The mechanism of this apparatus is not well understood. The equipment apparently separates by particle length and density, as do current industrial cleaners, but also by particle wettability. This feature is attractive when contaminant particles and pulp fibers are so similar in size and density that traditional cleaners are not effective.; The disk separator is a small spinning disk with an outer beveled edge. A slurry is fed to the disk center, the fluid moves over the disk surface in a thin film until it reaches the disk "shoulder," and then either follows the beveled lip or ejects radially. The two resultant streams produce an upper "rejects" fraction and a lower "accepts" fraction. In previous studies the majority of fluid and pulp fibers were in the accepts fraction, while a high percentage of contaminants deposited in the rejects fraction.; In the current study, a factorial design incorporated many variables in an economy of runs. The variables included solid length, diameter, density and wettability characteristics, fluid surface tension, feed stock concentration, disk speed, and flow rate. Four textile fibers (rayon, nylon, polyester and polypropylene) of various lengths and diameters gave a wide range of solids characteristics. Two nonionic polyoxyethylene alcohol surfactants and two cationic dimethyl alkyl benzyl ammonium chloride quaternary surfactants were used to alter fiber wettability and fluid surface tension characteristics.; Statistical regression analysis evaluated the results and dimensional analysis further characterized the fluid flow model and generated a predictive equation for solids fractionation yield.; Fluid fractionation was found to be a function of a Weber number; that is, a dimensionless relation between inertial and surface tension forces. The solids yield was found to be a function of four dimensionless parameters: the fluid yield; the length to diameter aspect ratio; the density ratio of solid to fluid; and the solid wettability, expressed as a modified Weber number with work of adhesion as the interfacial tension force. |
