Browsing by Subject "Mechanical Engineering"
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Item A preliminary investigation of the effects of environmentally assisted cracking on natural gas transmission pipelines(Texas A&M University, 2005-08-29) Curbo, Jason WayneConcepts for the development of a model to predict natural gas transmission pipeline lifetime in a corrosive environment are constructed. Primarily, the effects of environmentally assisted cracking (EAC) are explored. Tensile test specimens from a sample of API 5L X-52 pipeline were tested in a simulated groundwater solution and subsequently analyzed. The results suggested that the simulated environment ultimately reduced the ductility of the test specimens; however, no evidence of ??classical?? stress corrosion crack morphology was discovered. However, corrosion pits up to 0.75 mm (0.03 in) were revealed during metallographic analysis. A Marin factor analogy and an energy method concept are suggested and explored. Ultimately, the test data set was too small for the results to be of any directly applicable significance.Item Design with Uncertain Technology Evolution(2012-10-19) Arendt, Jonathan LeeDesign is an uncertain human activity involving decisions with uncertain outcomes. Sources of uncertainty in product design include uncertainty in modeling methods, market preferences, and performance levels of subsystem technologies, among many others. The performance of a technology evolves over time exhibiting improving performance as research and development efforts continue. As the performance of a technology in the future is uncertain, quantifying the evolution of these technologies poses a challenge in making design decisions. Designing systems involving evolving technologies is a poorly understood problem. The objective of this research is to create a computational method allowing designers to make decisions encompassing the evolution of technology. Techniques for modeling evolution of a technology that has multiple performance attributes are developed. An S-curve technology evolution model is used. The performance of a technology develops slowly at first, quickly during heavy R&D effort, and slowly again as the performance approaches its limits. Pareto frontiers represent the set of optimal solutions that the decision maker can select from. As the performance of a technology develops, the Pareto frontier shifts to a new location. The assumed S-curve form of technology development allows the designer to apply the uncertainty of technology development directly to the S-curve evolution model rather than applying the uncertainty to the performance, giving a more focused application of uncertainty in the problem. Monte Carlo simulations are used to the propagate uncertainty through the decision. The decision-making methods give designers greater insight when making long-term decisions regarding evolving technologies. The scenario of an automotive manufacturing firm entering the electric vehicle market deciding which battery technology to include in their new line of electric cars is used to demonstrate the decision-making method. Another scenario of a wind turbine energy company deciding which technology to invest in demonstrates a more sophisticated technology evolution modeling technique and the decision making under uncertainty method.Item Fluctuations in ASHRAE Refrigerant Physical Properties and the Effect on Single and Two Phase Flow(2014-11-17) Nagy, PaulThroughout the course of the American Society of Heating Refrigeration and Air Conditioning, data of refrigerant physical properties have been published in their Handbooks. However, this information is not constant, rather varying as each subsequent handbook edition is released. Thirteen properties (liquid and vapor viscosity, thermal conductivity, specific heat, enthalpy, surface tension, density and specific volume) from five widely used refrigerants (R-22, R-134a, R-410a, R-152a, R-600a) are examined at temperatures of 100 and 40 degrees Fahrenheit. Also, standard correlations to design variables such as effect on Reynolds number are obtained using these properties. Mass flux rates of 100 and 300 lbm/ft^2-s are considered with pipe diameter of 8.52mm. The resultant values are compared to 2013, the most recent ASHRAE Handbook edition, as well as between editions beginning in 1981 in a standard percent change format. It is seen that physical properties can vary by nearly 30% with respect to edition 2013 and up to 25% between editions with a stabilizing effect appearing near more current editions. Additionally, design variables showed a similar trend however, as equations became a function of more physical properties, percent change became more erratic. With regards to mass flux rate, percent change was not affected for the selected single phase design variables as mass flux increased due to a scaling factor response, yet at lower mass flux pipe friction factor could be affected. Two phase flow calculations resulted in R-600a showing discrepancies of nearly plus and minus 50 percent through the quality range of 0.2 to 0.8 for condensation and plus 15 percent to negative 20 percent for qualities of 0.2 and 0.8, respectively. R-22 showed the lowest error with R-152a revealing at times negative 40 percent error for condensation and plus 7 percent error for evaporation.