Multiple Phase Systems

Multi-phase systems are commonly encountered in chemical and biological systems. While the analytical framework (e.g. the equations describing the transport of mass, momentum, or energy) is relatively well established for the single-phase systems, much needs to be done for multi-phase systems. Our approach is to build a tool box consisting of experimental (including flow visualization), theoretical, and numerical simulation techniques that may be used to understand variety of multiphase systems. Given below is a brief description of some of the multi-phase systems examined by the researchers in the department. (See also Complex fluids for additional examples.)

Acoustic Probe for Characterizing Suspensions

Monitoring the amount of solids in slurries flowing through a pipe is important to quality control in process industry. The figure on the left shows a device that uses attenuation of ultrasonic sound waves through slurry to determine the solid content. Small amounts of bubbles that are often present in slurries normally pose serious challenge in the use of ultrasound technology but we have been able to develop software that uses theoretical understanding of acoustics of three-phase systems to filter out the noise introduced by the bubbles if present, and yield the estimates of solids on a continuous basis. This is illustrated by the figure on the right in which bubbles are introduced in a flowing slurry so that overall attenuation of sound increases as indicated by the upper curve. A theory for removing the noise by bubbles allows us to obtain the concentration of particles as indicated by the lower curve. This method forms the basis for a pending patent application (U. S. Patent 0245137 by Tavlarides, Norato, Shcherbakov, and Sangani ).

Bone Cements

Nanosphere containing two-solution bone cement after polymerization and fracture. Note the highly packed and uniform nanospheres of cross-linked PMMA (Taken from Rodrigues et al., JBMR-B, 2010)

Two solution bone cement is an innovation in the formulation and properties of orthopedic bone cement used to fix total joint replacements in bone or to perform vertebroplasty or kyphoplasty (i.e., repair of osteoporotic spine). These cements are acrylic based and consist of high-viscosity mixtures of monomer, linear polymer, surface modified cross-linked polymer beads (including nanobeads of approximately 300 nm) which have brush polymer and/or reactive moieties. One aspect of this multiphase material is its non-linear rheometric behavior. This behavior, which is thixotropic and pseudoplastic, has important consequences for the delivery and positioning of the cement in bone. The surgeon wants a cement that is doughy, yet can pass through a small gage needle with low force and then can set up quickly as a stiff material once it reaches its site in the body. In one version of this cement, uniform nanospheres are added to reduce the overall monomer level while maintaining the appropriate viscosity.

Recent Publications

Rodrigues, DC, Gilbert, JL, Hasenwinkel, JM, “Two-solution Bone Cements with Cross-linked Micro- and Nano-particles for Vertebral Fracture Applications: Effects of Zircomium Dioxide Content on the Material and Setting Properties”, JBMR-B, Vol. 92, No 1, Jan. 2010, p 12-23.

Rodrigues, DC, Gilbert, JL, Hasenwinkel, JM, “Pseudoplasticity and Setting Properties of Two-Solution Bone Cement Containing Poly(Methyl Methacrylate) Microspheres and Nanospheres for Kyphoplasty and Vertebroplasty”, J. Biomed. Mat Res Part-B, Vol. 91 No(1), Oct. 2009, p 248-256.

Supercritical fuel sprays

Clockwise: hexane at 24 oC; hexane-CO2 at 24 oC, hexane-CO2 at 90 oC; hexane-CO2 at 120 oC; hexane-CO2 at 135 oC; hexane-CO2 at 155 oC.

Shown in these figures are the effects of temperature at constant pressure of 413 bar on the sprays of hexane–carbon dioxide solutions injected in ambient air. At higher temperatures, close to the supercritical conditions for the mixture of hexane and carbon dioxide, the spray fuel–CO2–air becomes mostly homogeneous. Such homogeneity is highly desirable to improve the efficiency of the fuel combustion and decrease the concentrations of NOx, particulate matter, and other undesirable pollutants.

Recent Publications

Anitescu, G., Lin, R-H., Tavlarides, L. L. Preparation, Injection and Combustion of Supercritical Fuels; Poster P-2 presented at Directions in Engine-Efficiency and Emissions Research (DEER) Conference, Dearborn, MI, August 3–6, 2009.

Anitescu, G.; Tavlarides, L. L.; Geana, D. Phase Transitions and Thermal Behavior of Fuel-Diluent Mixtures. Energy & Fuels 2009, 23, 3068–3077.

Numerical simulations and theory

Numerical simulation techniques that account for detailed particle-particle and particle-fluid interactions for variety of particle-scale physics phenomena are developed by Sangani and co-workers. As a result of the efficient algorithms that are developed over last two decades it is possible to carry out large scale simulations of tens of thousands of particles. The results of simulations have enabled us to develop theories

Supercritical fuel sprays

Clockwise: hexane at 24 oC; hexane-CO2 at 24 oC, hexane-CO2 at 90 oC; hexane-CO2 at 120 oC; hexane-CO2 at 135 oC; hexane-CO2 at 155 oC.

Shown in these figures are the effects of temperature at constant pressure of 413 bar on the sprays of hexane–carbon dioxide solutions injected in ambient air. At higher temperatures, close to the supercritical conditions for the mixture of hexane and carbon dioxide, the spray fuel–CO2–air becomes mostly homogeneous. Such homogeneity is highly desirable to improve the efficiency of the fuel combustion and decrease the concentrations of NOx, particulate matter, and other undesirable pollutants.

Recent Publications

Anitescu, G., Lin, R-H., Tavlarides, L. L. Preparation, Injection and Combustion of Supercritical Fuels; Poster P-2 presented at Directions in Engine-Efficiency and Emissions Research (DEER) Conference, Dearborn, MI, August 3–6, 2009.

Anitescu, G.; Tavlarides, L. L.; Geana, D. Phase Transitions and Thermal Behavior of Fuel-Diluent Mixtures. Energy & Fuels 2009, 23, 3068–3077.

Numerical simulations and theory

Numerical simulation techniques that account for detailed particle-particle and particle-fluid interactions for variety of particle-scale physics phenomena are developed by Sangani and co-workers. As a result of the efficient algorithms that are developed over last two decades it is possible to carry out large scale simulations of tens of thousands of particles. The results of simulations have enabled us to develop theories for multi-phase systems.

Carbon Fiber Reinforced Polymeric Composites

Figure: SEM micrographs of uncoated carbon fiber (a, x 2000) and polypyrrole-coated carbon fibers: (b) after 10 minutes of coating (b, x 2000), after 60 minutes of coating (c, x 2000; d, x 10000). Reaction conditions: [Pyrrole] = 0.2 M; [H2SO4] = 0.1 M; Current Density10 mA/cm2). From Bin, Sureshkumar and Kardos, Chemical Engineering Science, 56, 6563-75 (2001)

Carbon fibers are used as reinforcements in advanced composites because of their excellent specific mechanical properties. However, adhesion between the carbon fibers and the polymeric matrix is usually weak. Hence, surface treatment methods are required to improve fiber–matrix bonding and to efficiently transmit the applied load through the matrix to the fibers. Typical industrial treatments include gas phase oxidation, ozone or plasma etching, electrochemical oxidation, whiskerization, and polymer coating. Modification of carbon fibers by applying electropolymerized coatings has attracted considerable attention. In order to improve the adhesion between the carbon fibers and the matrix, polymer coatings are applied directly onto the fiber surface by electropolymerization. Advantages of this technique over other traditional surface treatment methods include superior wetability of the individual fiber filaments in a bundle, control of the structures and properties of the coatings through control of monomer functionality and electropolymerization parameters, accessibility of the state-of-the-art electroanalytical techniques to study reactions, and relatively low processing cost. Moreover, electropolymerization appears to be a suitable process to maximize the impact strength and fracture toughness, while retaining the required optimum levels of other mechanical properties. Our work has focused on identifying process-morphology relationships in electropolymerization of C fibers with polypyrrole.

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