Dana Grecov

Associate Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Mar 2019)
Numerical simulation of flow and microstructure in nematic liquid crystalline materials (2013)

No abstract available.

Mathematical modeling of interaction of wet particles and application to fluidized beds (2011)

In many industrial operations, such as fluidized bed granulators, coaters, and fluid cokers, a binding or reacting liquid is introduced into the system. Due to the effects of liquid, the multi-phase transport phenomena of these systems are more complicated compared to conventional gas-solid fluidization systems. In this thesis, mathematical modeling is used to study the interaction of wet particles. First, a coalescence model is developed to describe the binary collision of wet particles. The model is in the form of a wet coefficient of restitution and is used to determine the critical velocity—the boundary between coalescence or rebound outcomes—for a range of capillary numbers. Model predictions are compared with the available experimental data and good agreement is found. The model accounts for both liquid viscosity and surface tension effects and is used to investigate the boundary between collisions with dominant capillary and respective viscous effects. Then, by incorporating time- and temperature-dependant variations of the viscosity and thickness of the liquid coating, the model is used to determine the agglomeration tendency of bitumen-coated coke particles in fluid cokers. A simplified mathematical model and numerical solution of the Navier-Stokes equations are used to study the rupture of stretching liquid bridges between two solid spherical particles. The simplified model considers the geometry of the problem in which the gas-liquid interface is represented with a parabola. The numerical simulations of the Navier Stokes equations are performed with FLUENT and are used to investigate the viscous, surface tension, inertial, gravitational, and contact angle effects on the rupture distance and liquid distribution. Finally, the interaction of multiple wet particles is addressed by implementing the wet coefficient of restitution proposed in this thesis, using MFIX, an open-source Discrete Element Method (DEM) tool. DEM simulations of a fluidized bed consisting of mono-sized solid spherical particles pre-coated with identical liquid coatings are performed, and the effect of coating viscosity and thickness on the fluidization behaviour is investigated. Snapshots of the instantaneous particle positions are presented, and time-averaged values of the bed centroid in the y-direction, wet coefficient of restitution, and relative normal collision velocity are analyzed.

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Master's Student Supervision (2010-2017)
Industrial bio-lubricants performance and characterization (2013)

The general trend towards the use of high performance lubricants and environmentally friendly products supports the design of new industrial lubricants. Therefore, there are good practical reasons to extend the research related to lubrication. Bio-oils, as promising growing substitutes for mineral oils, need more research to deal with new and inherited problems. Meanwhile, there is no complete understanding of the lubrication phenomenon, nor a complete rheological characterization of oil lubricants. This research is an effort to study industrial bio-lubricants and to develop a more comprehensive approach, at the same time correlating their rheological and tribological behavior. Different commercial canola oil based lubricants were studied using different techniques. For validation and comparison, engine oil, silicone oil and mineral hydraulic oil were tested. Bio-lubricants exhibited constant viscosity at both moderate and high shear rates and shear thinning at low shear rates and temperatures below 30 degrees Celsius. Frequency sweep tests revealed a significant viscoelasticity of bio-lubricant which developed over time.Time dependence, structure recovery, gap size effect, surfactant behavior, and geometry’s material influence were all investigated. A high pressure cell and a polarized light microscope coupled with the rheometer were used to investigate the bio-lubricants. Thermal analysis was conducted using a differential scanning calorimeter. Several transition points were identified in the range of temperatures from -30 to 100 degrees Celsius, and the results have been connected to the viscoelastic behavior. Different tribological tests were used to investigate the lubricity of lubricants and bio-lubricants added by liquid crystals. The coefficient of friction, at tested temperatures, and the wear rate were observed over time. Adding two percent of ionic liquid crystals improved the wear resistance of the oil, but the bio-lubricant had the lowest coefficient of friction. This research could be considered as pioneer work. An attempt was made to achieve profound perspective matching between rheometry, tribology and thermal analysis. Some assumptions explaining the rheological and tribological behavior were hypothesized and associated with arguments and discussions. Based on, Imaginary scenario of bio-hydraulic oil behavior within a small gap was visualized.

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Osteoarthritic synovial fluid rheology and correlation with protein concentration (2013)

Synovial fluid (SF) is a lubricant for articulating joints. The study of SF rheological properties has gained significance due to SF viscoelastic properties, and SF’s ability to sustain a considerable load. The rheological performance of SF is linked to the joint’s condition. A joint disease such as osteoarthritis (OA) reduces SF rheological properties. This study is aimed at investigating the shear and extensional rheological properties of osteoarthritic synovial fluid (OA SF). Additionally, this study is aimed at correlating SF rheological properties with its protein concentration.Shear rheological properties of 35 OA SF samples were investigated at a physiological temperature (37 °C) using cone-and-plate shear rheometer. Furthermore, the effects of the temperature, the centrifugation, and the storage at -20 °C for two weeks were also studied on some samples. Additionally, the time-dependent rheological properties were investigated by rotation and oscillation tests. Extensional rheological properties were studied using a capillary breakup extensional rheometer (CaBER). First, the effects of different CaBER configurations on the extensional rheological measurements were investigated in order to determine the optimal configuration. Then, the extensional rheological properties of 21 OA SF samples were studied. The protein concentrations of SF were determined using a bicinchoninic acid (BCA) protein assay kit. I also investigate the correlations between rheological properties and protein concentration.The understanding of SF rheological properties will lead to a better understanding of its lubrication properties, and to the development of a rheological analogue to SF or to a periprosthetic fluid.

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