Quantifying mixing using magnetic resonance imaging.

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. Mixing in this device is illustrated in the photograph in Fig. 1. 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). 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 (1)H 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 (Fig. 2). 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

Long-Term Effects of Cathodic Protection on Prestressed Concrete Bridge Components

DTFH61-92-C-00058While cathodic protection effectively reduces or stops ongoing corrosion of reinforcing steel in concrete, applicability of this technology to prestressing steel has been limited because of concerns of possible bond loss and hydrogen embrittlement. Within this context the present research was intended as a comprehensive, multifaceted undertaking to elevate the understanding of prestressed concrete cathodic protection to the same level as for reinforced concrete. The experimental part of the program involved three approaches: 1) constant extension rate tests (CERT) upon straight tendon wire, 2) monitoring of cathodically polarized prestressed beams for both bond loss and hydrogen embrittlement, and 3) concrete block pullout tests involving both tendon and wire. Findings to date include the following: 1) High chromium bearing microalloyed prestressing steel is more susceptible to embrittlement than ordinary steel, and the previously proposed -0.90 v (SCE) lower potential limit is not conservative in this case; 2) Prestressed concrete structures can be qualified for cathodic protection based upon the amount of uniform and localized corrosion wire cross section loss; 3) Loss of bond within the anticipated remaining service life of most prestressed concrete structures should not be a concern provided current density is within the normal range and is not locally concentrated. These and related findings are evaluated within the context of standards for prestressing steel and criteria for cathodic protection