Air Dynamics Through Filter Media During Air Scour

Abstract

The dynamics of air motion through filter media under conditions of air scour alone, simultaneous air and subfluidization water flow and simultaneous air and fluidization water flow were studied. Particular combinations of simultaneous air and subfluidization water flows cause the formation and collapse of air pockets within the bed: termed Collapse‐Pulsing. This condition probably created significant abrasion between the filter media grains because the intensity of abrasion is related to the effective stresses between the grains and the magnitude of their relative movement. It is rationalized that collapsepulsing is the probable optimum condition for air scour. Three sands of effective sizes, 0.46 mm, 0.64 mm, and 0.88 mm, were experimentally studied and a simple empirical predictive equation for collapse‐pulsing was established. The equation is also shown to be valid for predicting the condition for a minimum loss of media during backwash. The equation could be used for the design of air scour systems t...