Investigation of residence time distribution and local mean age of fluid to determine dead-zones in flow field

Abstract

Residence time and local mean age of fluid are important parameters of the fluid flow, with which we are able to detect the functioning and non-functioning zones. It is a novel approach to estimate the effect of dead-zones on chemical and biological processes. In this paper, we introduce a numerical tracer study, which is calibrated by field measurements and which is applied in different cases such as settling tank and aeration tank of wastewater treatment. Using an advective-diffusive passive scalar transport equation, the age of the fluid can be calculated. It also shows the short-circuits and dead-zones of the fluid and this corresponds with our observations. This method helps eliminate potential hydraulic problems at the early stage of design.