UBC Theses and Dissertations

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UBC Theses and Dissertations

Numerical study of a transient bifurcating-flow near slotted apertures Li, Weiyin


This thesis numerically studied the transient flow near slotted apertures inside a pulp screen. The capacity of pressure screen is generally defined as the maximum mass throughput before the apertures plug with pulp. Increased capacity follows from factors that either reduce fiber deposition at the aperture or increase the effectiveness with which fibers are removed. This thesis considers this latter effect and in particular the factors that increase the backflush pulse that clears any deposited fibers from the aperture. Three major factors are discussed in this thesis: (1) higher rotor tip speeds and lower slot velocities support longer and higher reversal flows to backflush and clear the apertures, (2) a foil angle-of-attack of 5-degree generated the longest reversal flow duration and maximum negative pressure pulse, and (3) the maximum reversal velocity was found for an intermediate contour height of 0.9 mm. The reversal flow time increases with the increasing contour height when the slot velocity is reduced. The study also showed a backflush “flow tunnel” between the vortex and the backside of the wire. When the reversal flow happens, the vortex center would move away from the aperture and the backflush flow tunnel could be found.

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