Hydrodynamics and mixing performance of Hartridge Roughton mixers: Influence of the mixing chamber design

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 283; pp. 375 - 387
• Main Authors: Di Patrizio, Nicolas, Bagnaro, Marc, Gaunand, Alain, Hochepied, Jean-François, Horbez, Dominique, Pitiot, Pascal
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2016
• Subjects: Hartridge–Roughton mixers; Segregation index; Turbulent Mixer Model; Villermaux Dushman reaction; Segregation index; Villermaux Dushman reaction; Hartridge–Roughton mixers; Turbulent Mixer Model
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2015.06.116

•Three vortex mixers are compared with the Villermaux Dushman reaction and CFD.•Vortex mixers with a separate mixing chamber have better mixing performances.•Without a mixing chamber, a spiral structure slows the mixing. Mixing efficiency of three Hartridge–Roughton mixers with different geometries is characterized by a segregation index measured via the Villermaux/Dushman test reaction and by Computational Fluid Dynamics. The small values of the segregation index (always lower than 0.025 for the concentrations and the flow rate studied) confirm these vortex mixers achieve very good mixing performance. The use of the Turbulent Mixing Model indicates that mixing times are less than 5ms for inlet flowrates faster than 5L/h. Mixing performance is even better when these devices have a separate mixing chamber upstream of a narrower outlet pipe, whose diameter is half that of the chamber. Computational Fluid Dynamics shows the internal flow depends on the geometry of the mixer and has a direct influence on its efficiency. When no separate chamber is present, the flow has a double spiral structure. The two inlet fluids roll up together as they pass through the mixer, which slows down the mixing process. For precipitation reactions, we recommend the use of a mixer with conical narrowing which has a high mixing efficiency and a lower risk to be obstructed by the particle agglomeration.