Characterization of mixing in T-jets mixers Kateryna Krupa a , M.Ashar Sultan a , Cláudio P. Fonte a , Maria I. Nunes b , Madalena M. Dias a , José Carlos B. Lopes a , Ricardo J. Santos a,⇑ a Laboratory of Separation and Reaction Engineering, Universidade do Porto, Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal b Centre for Environmental and Marine Studies (CESAM), Departamento de Ambiente e Ordenamento, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal highlights " This paper concerns the study of micromixing in T-jets mixers. " The effect of geometry, Reynolds number and flow rate ratio is assessed. " A consecutive–competitive chemical test reaction (Bourne’s reaction) is used. " The study covers four flow regimes in T-jets mixers. article info Article history: Available online 24 July 2012 Keywords: T-jets Micromixing Reynolds number Test reaction abstract The product distribution of a fast chemical reaction system was used for the characterization of micromixing in T-jets mixers; several geometries were assessed under different operational conditions (Reynolds number and jets flow rate ratio). The micromixing test system was the reaction between 1- naphthol and diazotized sulfanilic acid in an aqueous medium. The results obtained show that for all geometries mixing is enhanced with Reynolds number and with the operation at flow rate ratios close to unity. The geometrical parameters of T-jets mixers have a critical influence on the product distribution of the test reaction; particularly the ratio between the mixing chamber width and the inlet jet width, and also the mixing chamber depth. Micromixing is shown to be mainly related to the flow field regime observed at each geometry and operational conditions, which were previously set using Planar Laser Induced Fluorescence. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Confined impinging-jet mixers (CIJ) [1–5] and T-jets mixers [6–12] are the two most common types of opposed jets mixers and are well suited for many important chemical processes which require rapid mixing. These mixers have a wide range of applica- tions in different industrial processes such as nanoparticle precip- itation and reactive polymerization. The main concept underlying these mixers is the impingement of two reactant streams in a con- fined space where mixing proceeds without stirring devices, i.e. static mixing. Recently, mixing in T-jets reactors has been studied focusing on factors such as the influence of the aspect ratio of the mixer and fluid speed and flow regimes. Three flow regimes have been previ- ously reported [10,13,14]:  Segregated flow regime – a steady flow regime where two par- allel streams of fluid are formed, each stream fed from one of the jets. The two fluid streams flow from injectors to the outlet without mixing; the segregation plane between the streams coincides with the mixing chamber axis. Fig. 1a shows an image of mixing in this flow regime obtained with Planar Laser Induced Fluorescence (PLIF).  Vortex flow regime – a steady flow regime, which is character- ized by two streams of fluid that have helicoidal vortices with a rotation axis aligned with the mixing chamber axis. The division between the two streams is still marked by the mixing chamber axis, although the vortices promote some dragging of fluid from the opposite stream.  Engulfment flow regime – a flow regime where the fluid streams issuing from each jet rotate over the chamber axis and promote transport of fluid from one half of the chamber to the other half. A fourth flow regime, a self-sustainable chaotic flow regime, was recently reported by Sultan et al. [15], characterized by the 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.07.062 ⇑ Corresponding author. Tel.: +351 225081669. E-mail address: rsantos@fe.up.pt (R.J. Santos). Chemical Engineering Journal 207–208 (2012) 931–937 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej