Moving granular filter bed of quartz sand with louvered-walls and flow-corrective inserts

Abstract

This study investigated the effect of a simple flow-corrective element, a vertical plate, on the flow patterns and wall stresses in a two-dimensional louvered-wall moving granular filter bed of quartz sand. The static wall stress distributions produced by the granular solids were measured, and compared with the theoretical prediction, using the differential slice and Runge–Kutta (order four) methods. The variations in the dynamic wall stresses over time were obtained using a two-directional pressure gauge. The results show that a vertical plate placed in each stage of the granular filter bed effectively diminished the quasi-stagnant zone adjacent to the louvered-wall, and reduced the wall pressure pulsation. For example, the ratio of the stagnant zone area in the second stage to the area of quartz sand in the second stage decreased from 50.66% (without an insert) to 27.86% (with a vertical plate). The maximum dynamic normal wall stress on the convergent section of third-stage louvered-wall (louver angle: 40°) declined remarkably from 9.95 kPa (without an insert) to 5.9 kPa (with a vertical plate), and then the reduction of the maximum dynamic normal wall stress was up to 40.7%. Furthermore, a vertical plate installed at an appropriate location satisfies the following requirements: (1) it shrinks the stagnant zone and reduces the wall stresses on the louvered wall of a moving granular filter bed; and (2) it solves the potential problem of a roof-type insert, on which the stagnant zone may sit.