A Numerical Approach for Simulation of Turbulent Mixing and Chemical Reaction at High Schmidt Numbers

Many chemical engineering processes take place in aqueous solutions at high Reynolds numbers. An accurate numerical prediction of such processes is very challenging as the reaction rate depends on large scale features, such as stirring motions, geometry of the mixing device, etc., and on the distribution of the mixture fraction on the smallest scales. The spacing between the largest and the smallest scales can become enormous with increasing Reynolds and Schmidt number so one is not able to compute all scales directly with todays computer power. In this contribution we present a complete numerical approach for the description of a precipitation process in an aqueous solution in a confined impinging jet reactor, also called T-mixer. We first present a detailed analysis of the flow and passive scalar mixing in such a device at

Sc

= 1 by direct numerical simulation. The large scale mixing at high Sc is analysed for the same flow with the SEMI DNS method and the results are validated with LIF measurements.With both results, a description of the precipitation is possible along Lagrangian particle paths, resulting in two consecutive simulations for describing the precipitation process. For an integrate approach we combine a DNS of the flow field with a filtered density function simulation of the scalar field where the chemical source term is closed. We develop a model for the micro-mixing term in the FDF transport equation and show first results of the micro-mixing and precipitation process in a T-mixer at

Sc

= 1000.