Investigation of mixing in jet reactors using fast, competitive—consecutive reactions

Abstract

Although several aspects of turbulent free jets have already been studied, multi-step mixing-controlled reactions in liquid jets were not widely investigated. A network of five well-characterized chemical reactions having a mixing-sensitive product distribution was considered here. A model of turbulent mixing and reaction was first built up. It considers the near-field as well as the fully developed flow regions and includes radial and axial variations in the jet velocity and time-averaged concentrations, axial variation and intermittency in the turbulent energy dissipation rate, expansion of the jet with entrainment and intermittency of its boundary, micromixing controlled by engulfment and inertial-convective decay of segregation (mesomixing). The radical distribution of the energy dissipation rate as well as its axial variation in the near-field region could not be adequately specified from the literature. Two parameters, determined from experiments, were employed to describe this axial profile. The resulting model then predicted well the influences of jet velocity, reagent volume and stoichiometric ratios, reagent concentrations and feed rate on the product distribution. A viscous silicone oil was dispersed in the jet and the measured maximum stable drop size was compared with predictions based on the maximum energy dissipation rates. Measured drops were somewhat smaller and indicated local maxima in the dissipation rate up to 40,000 W/kg. The simple and robust jet reactor is suitable for competitive reactions needing dissipation rates of order 10 2−10 4 W/kg to attain high selectivities.