Mixing performance of viscoelastic fluids in a Kenics KM in-line static mixer

•Kenics KM static mixer shows poor mixing performance with viscoelastic fluids.•Viscoelastic fluids show greater pressure drop across mixer than predicted.•Significant time variation in mixing quality at mixer outlet.•Mixing quality correlates to generalised Reynolds number Reg = Re/(1 + 2Wi).

The mixing of ideal viscoelastic (Boger) fluids within a Kenics KM static mixer has been assessed by the analysis of images obtained by Planar Laser Induced Fluorescence (PLIF). The effect of fluid elasticity and fluid superficial velocity has been investigated, with mixing performance quantified using the traditional measure of coefficient of variance CoV alongside the areal method developed by Alberini et al. (2013). As previously reported for non-Newtonian shear thinning fluids, trends in the coefficient of variance follow no set pattern, whilst areal analysis has shown that the >90% mixed fraction (i.e. portion of the flow that is within ±10% of the perfectly mixed concentration) decreases as fluid elasticity increases. Further, the >90% mixed fraction does not collapse onto a single curve with traditional dimensionless parameters such as Reynolds number Re and Weissenberg number Wi, and thus a generalised Reynolds number Reg = Re/(1 + 2Wi) has been implemented with data showing a good correlation to this parameter.