Design and characterization of a high-performance curved-blade static mixer for use in wastewater treatment

Static mixers are mixing devices that contain no moving part and are mainly used for continuous mixing of fluids. They usually redistribute the fluid in a direction normal to the direction of flow and provide favorable mixing efficiency at lower shear rates. They are very promising for a wide range of applications, such as chemical reactions, food processing, pharmaceuticals, and wastewater treatment processes including carbon mixing, aeration and sludge digestion. A curved-blade static mixer was designed for inline mixing of fluids at Reynolds numbers from 700 to 6000. The mixer consists of four equally spaced curved blades mounted on cylindrical housing with 45° rotation relative to the circumference. It was tested in three different compartments of 6, 8 and 10 mixing elements. A seven-point sampling probe was used to measure concentration downstream the mixer. The mixing quality was measured by the coefficient of variance (CoV). For the case of 10 mixing elements, a good mixing performance (typically more than 95% mixedness or CoV 0.05) achieved, although a marginally good mixing performance could also be achieved by 8 mixing elements. The friction factors were correlated as f = C1/Re + C2/Ren with an average deviation of ±10% from experimental data. Both in laminar and turbulent flow regimes, the friction factors are apparently smaller than those from SMV, Kenics and baffle-type static mixers.