Sharp inlets, although prevalent, tend to reduce mixing efficiency in hydraulic contact tanks by affecting fluid and scalar transport throughout the entire system. Superior inlets are often not an option because of the prohibitive cost of upgrading preexisting tanks. To remedy this, seven inexpensive yet easily implemented attachments to a sharp inlet were tested on a full‐scale, baffled, prototypical contact tank. Cumulative residence time distributions of a conservative, passive scalar were obtained for each attachment to assess their performance. A study using computational fluid dynamics of the same tank with the various attachments was then performed to strengthen the empirical results by explaining them from a hydrodynamic perspective. Six modifications improved mixing efficiency as estimated by the baffling factor parameter. Five of these modifications produced gains of roughly 30% over the unmodified scenario, whereas the horizontal tee attachment resulted in an increase of over 70%.

This study focuses on understanding the hydraulic design of baffled contact tanks using computational fluid dynamics simulations. In particular, we address the key question: for a given footprint of a rectangular tank with a specified inlet width (W inlet ), how does the hydraulic efficiency of a baffled tank depend on the configuration of internal baffles? In an effort to address this question, a carefully conceived parametric study consisting of 30 high-resolution two-dimensional (planar) simulations was conducted to quantify the hydraulic efficiency of a laboratory scale tank as a function of dimensional relationships between key baffle design dimensions (baffle opening length L bo , baffle channel width W ch , and baffle channel length L T ). Simulated longitudinal velocity profiles and flow through curves show good agreement with previous experimental results. The results indicate that the hydraulic efficiency can be optimized by ensuring that L bo /W ch ≈ 1 and orienting baffles along the longer direction of the rectangular footprint.