EFFECTS OF INJECTION LOCATION, FLOW RATIO AND GEOMETRY ON KENICS MIXER PERFORMANCE

The performance of the Kenics static mixer for mixing small streams of passive tracer into the bulk flow is investigated as a function of in jection location and flow ratio. Flow ratios of 1/99 and 10/90 are sim ulated at nine different injection locations, and two alternative geom etries are considered in addition to the standard Kenics mixer. Mixing is evaluated qualitatively by examining the spread of the tracer on c ross-sectional slices from the mixer and quantitatively by computing t he variation coefficient as a function of axial position. For the stan dard Kenics geometry, injection location strongly affects the extent o f mixing only for the first few elements, after which the mixing rate is independent of injection location. rn a sufficiently long mixer mat erial injected at arty location spreads to the entire flow but the lea st effective injection locations require up to four elements more than the most effective locations to achieve the same variation coefficien t. A faster rate of decrease in variation coefficient is observed for a flow ratio of 1/99 us. 10/90. An alternative geometry in which the e lements have 120 degrees of twist instead of the standard 180 degrees of twist shows a similar dependence an injection location and flow rat io but is more energy-efficient than the standard Kenics geometry. In another alternative geometry in which all elements have the same direc tion of twist, segregated islands exist in the flow. For injection loc ations inside the segregated islands, virtually no mixing takes place; for injection locations outside of the segregated islands, the tracer spreads to the remaining flow but does not penetrate the islands.