Laminar and turbulent regime changes in drinking water contact tanks

Abstract

Transitions in flow regimes that can occur in drinking water contact tanks may significantly affect the disinfection efficiency of the system. To demonstrate these effects, the authors investigated the internal velocity fields and flow regime of a drinking water contact tank located in Jamestown, Colo. The baffling factor (BF) of the system fluctuated annually between 0.5 and 0.6 because of a shift in flow regime caused by changes in the flow rate of the system. The authors studied the effects of the regime change from laminar to turbulent flow (or vice versa) using computational fluid dynamics (CFD) models and physical tracer studies. Several inlet modifications were then investigated using CFD to determine which alteration would be most beneficial. Key findings showed that with proper inlet modification, the BF of the system could be stabilized at 0.6 during periods of high or low flow.

Baffling efficiency insights gained from tracer studies at 32 Washington treatment plants

“…For laminar flow, it is possible that the cross‐sectional flow is not uniform, and more short‐circuiting within a channel is possible. Barnett and Venayagamoorthy () noted a similar increase in baffling factor efficiency between turbulent and laminar flows in a study of a contact tank in Colorado.…”

Rapid Analysis of Disinfection Efficiency Through Computational Fluid Dynamics

“…However, dependence on the RTD curve is a limitation of the SFM because the curve is usually obtained from experiments that cost time and money. Alternatively, the RTD can be obtained from CFD (Angeloudis et al 2015, Barnett & Venayagamoorthy 2014, Kim et al 2013, Rauen et al 2012, Khan et al 2006, Greene 2002, Stamou 2002). The latter approach was investigated in this research and for the first time evaluated in detail in what is referred to as hybrid CFD/SFM or CFD–SFM model.…”

Contact Tank Design Impact on Process Performance

“…This can be attributed to the design of the inlet of CTs, which is typically a pipe or channel [26,32] and which promotes flow three-dimensionality and mixing early in the tank as shown by Angeloudis et al [4], Barnett and Venayagamoorthy [8]) and Greene et al [14]. In the case of CT-1, the very shallow inlet channel created an inflow jet, which led to a large vertical recirculation zone that occupied the entire first compartment of the tank and caused further complex hydrodynamic structures downstream [4].…”