Expansion of Granular Filters During Backwashing

Abstract

In practice, the analysis of fluidization problems, particularly in the backwashing of water filters, is generally carried out on the basis of empirical and semiempirical criteria. In this paper, Bond's hindered settling velocity is adapted since it is based on the continuity equation and applied to any hydraulic flow regime. The modification is based on simple physical conditions and accounts for the initial fixed bed, as well as the instantaneous backwashing conditions, e.g., porosity, physical conditions of backwashing fluid and grains, and the depth of bed. The present study describes the development of a new backwashing model applied to unisize granular media, particularly sand, and anthracite, and directly or indirectly incorporates variables such as flow conditions and physical properties (length, porosity, etc.) of the bed, which affect the backwashing process. In addition, the model predicts the value of the expanded length at any predetermined conditions.