Experiments and CFD Modelling of Fast Chemical Reaction in Turbulent Liquid Flows

Abstract

Fast chemical reactions in turbulent liquid flows are studied experimentally and computationally. Experiments are carried out for reactive mixing in order to obtain local mean and fluctuating concentrations. The experimental findings are used to test the performance of numerical models for turbulence, mixing and chemical reactions.The experiments are carried out in a mixing channel with two inlets separated by a block. A reactive Planar Laser Induced Fluorescence (PLIF) technique is used to obtain instantaneous concentration fields of product from an acid-base reaction. Two different flow cases are studied. For the first flow case, there are equal flow rates of acid and base, whereas the flow rate of acid is reduced to half the flow rate of base in the second flow case. The amount of product formed is found to be strongly dependent on how well the two inlet streams are mixed.The turbulent flow is modelled in two-dimensions by solving the Reynolds Averaged Navier-Stokes equations in combination with a standard k-? turbulence model. Two different micro-mixing models are adopted, namely the multiple-time-scale turbulent mixer model (MTS) and the multi-peak presumed PDF-model.The simple reaction model, the eddy dissipation concept (EDC), developed for combustion reactions is found to be inadequate for liquid phase reactions. Modifying the model with a multiple-timescale turbulent mixer model (EDC-MTS) gives a substantial improvement.The multi-peak presumed PDF model and the two EDC-models are tested against reactive mixing experiments. The multi-peak presumed PDF model is found to give the best agreement between measured and predicted product concentration. The modified version of the EDC model, the EDC-MTS model, gives results which are close to the multi-peak presumed PDF model.