Abstract
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.
Highlights
The formulation of complex fluid products in industrial processes offers many challenges
I.D. unplasticised poly(vinyl chloride) pipe encased in a transparent poly(methyl methacrylate) square-section box filled with water
Upon investigation of the mixing performance of Newtonian and viscoelastic fluids in a Kenics KM static mixer, it has been found that viscoelasticity significantly affects the mixing performance of fluids at the outlet of a 6-element Kenics KM static mixer
Summary
The formulation of complex fluid products in industrial processes offers many challenges. Some studies have implemented a combined approach, using dimensionless groups such as the Elasticity number El (Stokes, 1998; Ozcan-Taskin and Nienow, 1995), or more recently the generalised Reynolds number Reg, which seeks to correct the viscous stress term present within the Reynolds number for elastic effects (Bertrand et al, 2002) All of these recent studies applied optical flow measurement techniques such as Particle Image Velocimetry (PIV) (Faes and Glasmacher, 2008; Hall et al, 2005; Szalai et al, 2004; Zalc et al, 2001; Pianko-Oprych et al, 2009; Gabriele et al, 2009; Stobiac et al, 2014), Planar Laser-Induced Fluorescence (PLIF) (Kling and Mewes, 2004; Arratia and Muzzio, 2004; Alvarez et al, 2002; Chung et al, 2009; Guillard et al, 2000) or dye decolourisation techniques (Shervin et al, 1991; Fradette et al, 2007) and were focussed on viscoelastic mixing behaviour in stirred tanks; to date there have been very few publications investigating viscoelastic fluids within static mixers (Chandra and Kale, 1992; Li et al, 1997). Key performance parameters such final mixing quality assessed through areal analysis and coefficients of variance (CoV) have been calculated over a range of industrially relevant process conditions and compared to a range of dimensionless hydrodynamic parameters and process energy inputs in order to determine the underlying controlling mechanisms for mixing performance
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