(36e) Measurement of Mixing Quality In Multiphase Systems

Commonly used methods to assess the state of a mixture are based on sampling and the measurement over time of the concentration of a key component at various locations, in order to determine how fast the variance of the sample concentration values (COV in fluid mixing and RSD in solids mixing) decreases to some asymptotic value. However, these tools are known to have intrinsic limitations due to their lack in capturing important spatial information. Moreover, their reliability is based on the number of samples considered, which can be cumbersome to obtain, be it experimentally or even numerically by post-processing simulation results.

The purpose of this talk is to show the potential of two mixing indices that were developed recently by our group to assess the mixing efficiency of fluid, granular and multiphase systems. Based on the concept of mixing in the weak and strong sense, they can be calculated from tracer trajectories either numerically through computer simulation or experimentally by means of non intrusive methods. We will recall how these two indices can provide the main mixing directions in a flow system as well as upper bounds for the mixing times. Three different cases will be discussed to illustrate the limitations of conventional mixing measures in properly characterizing mixing, and the wealth of detail provided by the two new indices.