Millisecond mixing of two liquid streams in a mixer model

Abstract

Fast liquid mixing in the flow channels at millimeter size was studied by planar laser induced fluorescence (PLIF) technique in experiments and the large eddy simulation (LES) as well. A simplified mixer model was applied, where two liquid streams impinge into each other in the confined channels. A dynamic kinetic energy sub-grid scale (SGS) model of LES was employed to simulate the fast liquid mixing. The results show that LES predictions with high-density meshes have good agreement with the experimental data in terms of the instantaneous and time-averaged concentration fields, and the probability density function (PDF) of concentration fluctuations. Hence, the mixing quality characterized by the intensity of segregation (IOS) and 95% mixing time can be also predicted reasonably. The LES simulations further predict the significant effect of cross-flow angle on the mixing process. The cross-flow angle of 90 ∘ gives the fastest mixing of two liquids in the millimeter channels at 1–2 ms. The mixing layer between the two liquid streams cannot be observed under the geometry with larger cross-flow angles. This indicates different mixing mechanisms compared with the mixing of two liquids flowing in parallel. Vorticity in the turbulent mixing process is discussed for a better understanding on the physical factors controlling the mixing process.