Measurement of Continuum Breakdown Using a Disc Spin-Down Experiment in Low Pressure Air

As flow becomes rarefied, a quantity called as the tangential momentum accommodation coefficient (TMAC) becomes important because it is a measure of the momentum transport from a gas molecule to a surface. Very few experimental measurements of continuum breakdown in boundary layer flows exist. All experimental measurements of the TMAC in macro-scale boundary layer flows have been done in the continuum slip and the transition flow regimes. Moreover the experimental apparatus used by previous researchers cannot accommodate for materials that are planar by nature such as those used in the field of aerospace and microfabrication. The objectives of this research include the experimental measurement of continuum breakdown in a macro-scale boundary layer flow, development of a test facility such that TMAC may be measured in the free molecular flow regime, and the measurement of TMAC for various gases versus material interactions. An experimental facility is built which consists of a disc spin down experiment in various gas pressures from atmospheric pressure through the free molecular flow regime. The real time deceleration torque is measured during the disc spin-down in each ambient pressure. The deceleration torque is non-dimensionalized suitably and is plotted against Reynolds number. The non-dimensional curves show self-similarity and therefore continuity in the viscous flow regime. Self-similarity breaks down when the viscous forces are no longer dominant and therefore it is a measure of continuum breakdown. This is also confirmed through the departure of the CFD and the semi-analytic von Karman curves from the experimental curves. A differential scavenging system is designed and incorporated into the apparatus and it facilitates measurements in the free molecular flow regime. TMAC for interactions between several gases and certain aerospace materials are measured in the free molecular flow regime. While most measurements show TMAC values of 0.7 or above in the different gases, the values are consistently low in carbon dioxide. The results are of significant impact for future space missions to Mars because the Martian atmosphere contains carbon dioxide predominantly and a lower TMAC suggests lower atmospheric drag on space vehicles

Freezing processes in cell suspensions evaluated using cryomicroscopy

This thesis aims at evaluating the freezing response of three different cell types, Pacific Oyster embryos, Jurkats and Helas, using the technique of cryomicroscopy. The choice of cells was primarily based on supporting ongoing research work at the Bioengineering Laboratory, Department of Mechanical Engineering at Louisiana State University in Baton Rouge. On a secondary basis, the cells were chosen based on their contrasting nature. While Pacific Oyster being a favorite food in USA calls for successful techniques of cryopreservation of their embryos in order to keep up with the growing demand, Jurkat and HeLa are undesired malignant human cells that require successful cryosurgical techniques for their destruction. The fourth chapter of the thesis addresses the freezing experiments performed on Oyster embryos at freezing rates of 5 deg C/min and 10 deg C/min. During these experiments, embryos were investigated for either dehydration (water transport) or intracellular ice formation (IIF). The next two chapters address the freezing experiments performed on Jurkat cells and HeLa cells respectively. Freezing rates ranging from 1 deg C/min to 50 deg C/min were used for these cells. Once dehydration was observed, the cells were examined for their volume shrinkage. A graph of temperature against normalized volume was plotted using the experimental results. The key cell level parameters were: Reference permeability of cell membrane to water (Lpg), apparent activation energy (ELp), inactive cell volume (Vb), and the ratio of surface area for water transport to the volume of intracellular water (SA/WV). The values of ‘Vb’ for the chosen cells were known from earlier literature. The experimental data was fit into the water transport equation, using a numerical model, in order to obtain the values of the unknown cell level parameters i.e. Lpg and ELp. Finally, Generic Optimal Cooling Rate Equation (GOCRE) was used to determine the optimal cooling rate for the chosen variety of cells. Hence, higher freezing rates were used on the cells, which were investigated for IIF. IIF observed using cryomicroscopy, through darkening probably supported the results for optimal freezing rates, obtained using the water transport experiments and subsequent numerical simulations

A New Materials and Design Approach for Roads, Bridges, Pavement, and Concrete

Increased understanding of demand for transport energy and how to improve road pavement materials would enable decision makers to make environmental, financial, and other positive changes in future planning and design of roads, bridges, and other important transportation structures. This research comprises three studies focused on pavement materials and a fourth study that examines energy demand within the road transportation sector. These studies are as follows: 1. A techno-economic study of ground tire rubber as an asphalt modifier; 2. A computational fluid dynamics analysis comparing the urban heat island effect of two different pavement materials – asphalt and Portland Cement Concrete; 3. A new approach that modifies the surface of ground tire rubber using low-cost chemicals and treatment methods to be used in asphalt applications; and 4. Analysis of road transport energy demand in California and the United States. The findings of these studies include that 1. GTR is an effective and economically suitable additive for modified asphalt, 2. the suitability of PCC pavements in urban settings should be reexamined, 3. Surface modification of GTR materials can improve compatibilization of particles for the manufacture of asphalt materials, and 4. gasoline sales are generally price inelastic in both the U.S. and California. Ultimately, these four studies improve understanding of road pavement materials and transport energy demand. They lay out important information about the future of the relationship between materials and design in the transportation industry. These findings may be used by engineers, policymakers, and others in the industry to better consider implications of decisions involved in design, creation, and modification of structures using pavement and concrete, including roads, bridges, etc