Abstract
The performance of Kenics KM static mixers has been determined for the blending of two shear-thinning fluid streams with identical or different rheology. Planar Laser Induced Fluorescence (PLIF) has been used to obtain the concentration distribution at the mixer outlet by doping one fluid stream with fluorescent dye upstream of the mixer inlet. The effect of scale of the static mixer, total flow rate, flow ratio between the fluid streams and inlet configuration have been investigated. The applicability of different methods to characterise mixing performance is examined by comparing conventional mixing measures such as coefficient of variation and maximum striation area against recent alternative methods presented in the literature, such as the areal distribution method developed by Alberini et al. (2014). A method of characterising individual striations by determining their distribution as a function of size and concentration is also presented. These findings illustrate the complexity of information-rich PLIF images, and highlight how different methods of analysis may be appropriate given the dependencies of the downstream process.
Highlights
Whilst there is a reasonable amount of data and design information available for the blending of Newtonian materials using static mixers (e.g. Shah and Kale, 1991), and analysis of mixing performance characterising the influence of viscosity (Ventresca et al, 2002), there is a comparative dearth of published material on non-Newtonian mixing
Whilst these fundamental data are valuable for the verification of Computational Fluid Dynamics (CFD) simulations (e.g. Peryt-Stawiarska and Jaworski, 2008; Rahmani and Keith, 2006), they do not allow the mixing performance to be determined ab initio and there is an absence of experimental work where an analysis based upon the concentration distribution in the pipe cross-section at the mixer outlet is performed
This paper examines the effect of changing system and fluid parameters upon the mixing performance of a Kenics KM static mixer equipped with six elements for the blending of two shear thinning fluids, where a minor secondary flow is blended into a major primary flow
Summary
Whilst there is a reasonable amount of data and design information available for the blending of Newtonian materials using static mixers (e.g. Shah and Kale, 1991), and analysis of mixing performance characterising the influence of viscosity (Ventresca et al, 2002), there is a comparative dearth of published material on non-Newtonian mixing. The traditional approach for the calculation of mixing quality in low Reynolds number (laminar) flows is to assess the distribution of the concentration of a passive scalar, Ci, via statistical methods This leads to the calculation of parameters such as the coefficient of variation (CoV) as described in Etchells and Meyer (2004) or striation thickness (Kukukova et al., 2011). Different approaches to obtain the scale of segregation have been compared by Kukukova et al (2011); they found that determination of the area of the largest striation, termed the maximum striation area, was the fastest method in terms of processing time, but that this analysis was limited in its description of the whole mixing field. They illustrated other approaches to characterise mixing which provided more information but led to higher processing times; a common factor is the assumption of improved mixing with a decrease in maximum striation area (Spencer and Wiley, 1951), but this does not consider the concentration, or degree of mixing within the striation
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