Quantifying Mixing using Magnetic Resonance Imaging

Abstract

Mixing is a unit operation that combines two or more components into a homogeneous mixture. This work involves mixing two viscous liquid streams using an in-line static mixer. The mixer is a split-and-recombine design that employs shear and extensional flow to increase the interfacial contact between the components. A prototype split-and-recombine (SAR) mixer was constructed by aligning a series of thin laser-cut Poly (methyl methacrylate) (PMMA) plates held in place in a PVC pipe. Red dye was added to a portion of the test fluid and used as the minor component being mixed into the major (undyed) component. At the inlet of the mixer, the injected layer of tracer fluid is split into two layers as it flows through the mixing section. On each subsequent mixing section, the number of horizontal layers is duplicated. Ultimately, the single stream of dye is uniformly dispersed throughout the cross section of the device. Using a non-Newtonian test fluid of 0.2% Carbopol and a doped tracer fluid of similar composition, mixing in the unit is visualized using magnetic resonance imaging (MRI) (FlowScanreal-time rheology system, Aspect Imaging). MRI is a very powerful experimental probe of molecular chemical and physical environment as well as sample structure on the length scales from microns to centimeters. This sensitivity has resulted in broad application of these techniques to characterize physical, chemical and/or biological properties of materials ranging from humans to foods to porous media 1, 2. The equipment and conditions used here are suitable for imaging liquids containing substantial amounts of NMR mobile 1H such as ordinary water and organic liquids including oils. Traditionally MRI has utilized super conducting magnets which are not suitable for industrial environments and not portable within a laboratory. Recent advances in magnet technology have permitted the construction of large volume industrially compatible magnets suitable for imaging process flows. Here, MRI provides spatially resolved component concentrations at different axial locations during the mixing process. This work documents real-time mixing of highly viscous fluids via distributive mixing with an application to personal care products. This JOVE case is presented by Michael J. McCarthy, PhD, Professor and Chair, Department of Food Science and Technology at UC Davis and by William Hartt, Corporate Engineering and Technology Laboratory, Procter & Gamble Company.

Keywords

Rheology, real-time mixing, in-line static mixing, non-Newtonian measurement, imaging process flows, real-time mixing of highly viscous fluids

Applications

Real-time rheology, real-time mixing and composition analysis

Relevant Product(s)

FlowScan™ real-time rheology system

Michael J. McCarthy, PhD

Michael J. McCarthy, PhD

Professor and Chair, Department of Food Science and Technology Professor, Department of Biological and Agricultural Engineering University of California, Davis

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