MICROMIXING IN STATIC MIXERS - AN EXPERIMENTAL-STUDY

Static mixers develop high rates of energy dissipation relative to an empty pipe and have short residence times, which are useful characteristics for those rapid reactions needing fast mixing to obtain high yield. Hardly any information on this application however exists. The competitive coupling of 1- and 2-naphthols with diazotized sulfanilic acid was applied in aqueous solution to two commercially available designs of static mixer. The rate of turbulent energy dissipation was deduced from the measured product distribution over a range of flow rates. Chemical reaction did not take place throughout a whole element, but was localized over a distance of around 0.01 m. The reaction zone shifted somewhat depending on the operating conditions, e.g., concentrations, which introduced some inaccuracy into the determination of energy dissipation due to its inhomogeneity. Product distributions could nevertheless be adequately predicted using the engulfment model of micromixing as some operating conditions were changed. The mixer element having an open structure without excessive constriction of the flow gave faster micromixing and better energy utilization. This could be a clue to further improvements in design.