Experimental Investigation of Fiber-concentration Distributions of Pulp Liquid Flow through a Divergent Tube

Abstract

An experimental study was performed on the fiber-concentration distributions of wood pulp liquid flowing through a divergent tube at a divergence angle of θ = 12°.The study was conducted to verify the tube’s effectiveness for application to the tube banks of papermaking machines. Experiments were conducted at bulk pulp-fiber concentrations of C<SUB>s</SUB> = 0.2-0.6 wt% and inflow velocities of U<SUB>a</SUB> = 0.1-2 m/s. The flow in the horizontal plane that contained the tube axis was visualized using the light-section method. In addition, the distributions of the time-averaged and fluctuating fiber concentrations (C<SUB>a</SUB> and C’, respectively) were measured. We then investigated the effect of the average flow rate on the variations in the directions of flow of the concentration distributions. Ata low flow rate (U<SUB>a</SUB><0.3m/s), the fluid of the annular water layer formed in the upstream tube divided the flow into two in the divergent tube, and the C<SUB>a</SUB> and C’ distributions exhibited shapes that had considerable differences in the cross-section. When the flow velocity was increased to U<SUB>a</SUB> ≥ 0.5 m/s, the shape of the C<SUB>a</SUB> distribution flattened, and C’ reduced gradually in the flow direction. The results related to the non-uniformity of fiber concentration demonstrated that the divergent tube is suitable for use in a tube-bank channel of the headbox of a papermaking machine.