Determining jet mixing characteristics using electrical resistance tomography

Abstract

Coaxial jet and side entry mixers are used in a wide range of industries for a variety of processes including precipitation, polymerization and neutralization duties [Wei H, Garside J. Application of CFD modelling to precipitation systems. Chem Eng Res Des 1995; 75 (2): 219–27; Kolhapure NH, Tilton JN, Pereira CJ. Integration of CFD and condensation polymerization chemistry for a commercial multijet tubular reactor. Chem Eng Sci 2004; 59: 5177–84; Pipino M, Fox RO. Reactive mixing in a tubular jet reactor: A comparison of PDF simulations with experimental data. Chem Eng Sci 1994; 49 (24B): 5229–41]. Jet mixers are characterized by short contact times between the fluids and can be operated in continuous or semi-batch modes. Coaxial and side entry jets can be designed in order to deliver rapid turbulent mixing using short sections of pipeline. As the energy required for mixing is provided by the addition stream, the process-side pressure drop required for homogeneity is very low. A key design parameter for jet mixers is the mixing length, i.e. the length of pipe downstream of the injection point required to achieve a given degree of homogeneity. The mixing length can be affected by the addition geometry (for example, coaxial or side entry), orifice size and shape, operating conditions and material properties. This paper presents the use of electrical resistance tomography (ERT) to monitor jet mixing via the addition of a conductivity tracer through coaxial and side entry jets. Multiple ERT sensors are fitted along the pipe downstream of the jet addition point. The ERT sensors enable real time, noninvasive measurement of conductivity within the pipe, utilizing a 3D finite element mesh consisting of ∼2500 tetrahedral elements. The effect of secondary (main pipe) flow rate and jet configuration on the nature of the tracer plume evolution and axial mixing is determined using this technique.