The flow patterns and stresses on the wall in a symmetric louvered-wall moving granular filter bed

The flow patterns and stresses on the wall in a symmetric two-dimensional louvered-wall moving granular filter bed were investigated. 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 with time in a moving granular filter bed were obtained. In addition, the effect of the louver angle upon the flow patterns and wall stresses was investigated. Four different flow regions were observed in a moving granular filter bed. As the angle of the louver decreases, the quasi-stagnant zone area adjacent to the side wall becomes smaller and the static normal stress acting on the convergent section of the side wall becomes larger. The magnitude of the static normal stress acting on the convergent section is approximately 10 times as large as that acting on the vertical section. When the normal stress measured by pressure gauge installed on the upper stage decreases to zero, the normal wall stress measured by pressure gauge installed on the adjacent lower stage then begins to descend and fluctuate under the static normal wall stress during granular material withdrawal. Employing the results obtained using stress measurements and image processing, the pressure pulsation phenomenon in a symmetric two-dimensional louvered-wall moving granular filter bed may be further understood. (C) 2002 Elsevier Science B.V. All rights reserved.