(526a) The Mixing Mechanism Change and Age Distribution in a Kenics Static Mixer

Scalar mixing and Age distribution in a Kenics static mixer will be studied by species concentration and mean age solutions. In order to resolve diffusion effect, a microscaled mixer is used by CFD method. The spatial distribution of mean age reveals locations of older material that could potentially cause process fouling and product defects. At the micro scales of the mixer, both convection and diffusion strongly affect concentration and age distributions. A method is developed to compute an average effective diffusivity to measure false diffusion due to numerical errors. The range of Peclet number is found that the scalar solution is not affected by false diffusion. The effect of convection and diffusion is studied for Re numbers that cover the full range of laminar flows in the mixer. It is found that a mixing mechanism change results a transition of mixing efficiency. Diffusion broadening is also found to have strong effect on the striation structures in the mixer. Mixing and age distribution in the mixer is quantitatively measured with frequency distribution function and two different variances, the variance of residence time and the variance of mean age. It is found that concentration variance reaches a peak while mean age variance decay rate increases almost monotonically as Re increases.