Browsing by Subject "Numerical model"
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Item Analysis of a novel thermoelectric generator in the built environment(2011-08) Lozano, Adolfo; Webber, Michael E., 1971-; Schmidt, Philip S.This study centered on a novel thermoelectric generator (TEG) integrated into the built environment. Designed by Watts Thermoelectric LLC, the TEG is essentially a novel assembly of thermoelectric modules whose required temperature differential is supplied by hot and cold streams of water flowing through the TEG. Per its recommended operating conditions, the TEG nominally generates 83 Watts of electrical power. In its default configuration in the built environment, solar-thermal energy serves as the TEG’s hot stream source and geothermal energy serves as its cold stream source. Two systems-level, thermodynamic analyses were performed, which were based on the TEG’s upcoming characterization testing, scheduled to occur later in 2011 in Detroit, Michigan. The first analysis considered the TEG coupled with a solar collector system. A numerical model of the coupled system was constructed in order to estimate the system’s annual energetic performance. It was determined numerically that over the course of a sample year, the solar collector system could deliver 39.73 megawatt-hours (MWh) of thermal energy to the TEG. The TEG converted that thermal energy into a net of 266.5 kilowatt-hours of electricity in that year. The second analysis focused on the TEG itself during operation with the purpose of providing a preliminary thermodynamic characterization of the TEG. Using experimental data, this analysis found the TEG’s operating efficiency to be 1.72%. Next, the annual emissions that would be avoided by implementing the zero-emission TEG were considered. The emission factor of Michigan’s electric grid, RFCM, was calculated to be 0.830 tons of carbon dioxide-equivalent (CO2e) per MWh, and with the TEG’s annual energy output, it was concluded that 0.221 tons CO2e would be avoided each year with the TEG. It is important to note that the TEG can be linearly scaled up by including additional modules. Thus, these benefits can be multiplied through the incorporation of more TEG units. Finally, the levelized cost of electricity (LCOE) of the TEG integrated into the built environment with the solar-thermal hot source and passive ground-based cold source was considered. The LCOE of the system was estimated to be approximately $8,404/MWh, which is substantially greater than current generation technologies. Note that this calculation was based on one particular configuration with a particular and narrow set of assumptions, and is not intended to be a general conclusion about TEG systems overall. It was concluded that while solar-thermal energy systems can sustain the TEG, they are capital-intensive and therefore not economically suitable for the TEG given the assumptions of this analysis. In the end, because of the large costs associated with the solar-thermal system, waste heat recovery is proposed as a potentially more cost-effective provider of the TEG’s hot stream source.Item Effect of Atlantic Meridional Overturning Circulation Changes on Tropical Coupled Ocean-Atmosphere System(2010-01-14) Wan, XiuquanThe objective of this study is to investigate the effect of Atlantic meridional overturning circulation (AMOC) changes on tropical coupled ocean-atmosphere system via oceanic and atmospheric processes. A suite of numerical simulations have been conducted and the results show that both oceanic and atmospheric circulation changes induced by AMOC changes can have a profound impact on tropical sea surface temperature (SST) and sea surface salinity (SSS) conditions, but their dominance varies in different parts of the tropical oceans. The oceanic process has a dominant control on SST and SSS response to AMOC changes in the South Tropical Atlantic, while the atmospheric teleconnection is mainly responsible for SST and SSS changes over the North Tropical Atlantic and Pacific Oceans during the period of reduced AMOC. The finding has significant implication for the interpretation of the paleotemperature reconstructions over the southern Caribbean and the western Tropical Atlantic regions during the Younger Dryas. It suggests that the strong spatial inhomogeneity of the SST change revealed by the proxy records in these regions may be attributed to the competing oceanic and atmospheric processes that dominate the SST response. Similar mechanisms may also explain the reconstructed paleo-salinity change in the tropical Atlantic, which shows a basin-wide increase in SSS during the Younger Dryas, according to recent paleo climate studies. Finally, we show that atmospheric teleconnection induced by the surface cooling of the North Atlantic and the North Pacific in response to a weakened AMOC, is a leading physical mechanism that dictates the behavior of El Nino/Southern Oscillation (ENSO) response to AMOC changes. However, depending on its origin, the atmospheric teleconnection can affect ENSO variability in different ways. The atmospheric process associated with the North Atlantic cooling tends to enhance El Nino occurrence with a deepened mean thermocline depth in the eastern Pacific, whereas the atmospheric process associated with the North Pacific cooling tends to produce more La Nina events with a reduced mean thermocline depth in the eastern Pacific. Preliminary analysis suggests that the change in ENSO characteristics is associated with the change in internal atmospheric variability caused by the surface cooling in the North Atlantic and North Pacific. Complex nature of the underlying dynamics concerning the effect of the AMOC on ENSO calls for further investigation into this problem.Item Mechanistic - based models for slug flow in vertical pipes(Texas Tech University, 2005-05) Zhao, Xiaodong; Lawal, Akanni S. L.; Heinze, Lloyd R.Slug flow is one of the most common flow regimes encountered in petroleum, chemical and nuclear industries. This flow regime is characterized by pseudo-periodic occurrence of Taylor bubbles and liquid slugs. The approaches for slug flow modeling include empirical methods, mechanistic methods and numerical methods. Numerical methods involve large amount of computation and therefore not suitable for the application in petroleum industry. In contrast to empirical methods that are limited in the range of application, mechanistic models are more applicable because they capture the essential mechanism of the slug flow regime. However, the mechanistic models require some correlations to obtain closure, which bring unexpected error and need to be improved before getting results matching with experimental data. This project established a computational model to simulate the flowing field around Taylor bubble. Boundary fitted structured grid system is built for the simulation model and the turbulence is accounted for by the low Reynolds-number k- model. The previous turbulence model is modified to predict smooth transition from laminar to turbulent flow. To obtain the configuration of the Taylor bubble, circular geometry is assumed at the top of the bubble and Bernoulli equation is applied to estimate the shape of the tail part. The fifth order of polynomial function is used to ensure the convergence of the bubble configuration which has uniform pressure along the interface. Based on the results from the numerical model and previous experimental studies, the currently used mechanistic model is improved to get more accurate prediction for the slug flow in vertical pipes. The improved model is validated by previously reported experimental data. The geometric parameters of slug flow analyzed in this project can provide a basis for studying flow regime transition from slug flow to other flow regimes. The significance of this work is to help us understand more details about slug flow in vertical pipes. The knowledge gained from this work can be used to reestablish existing empirical correlations that are limited to particular conditions but necessary to the mechanistic models. The improvement of mechanistic models can benefit the design of tubing and surface facilities and the determination of artificial-lift methods.Item Mechanistic - based models for slug flow in vertical pipes(2005-05) Zhao, Xiaodong; Lawal, Akanni S. L.; Heinze, Lloyd R.; Mann, Uzi; Parameswaran, SivaSlug flow is one of the most common flow regimes encountered in petroleum, chemical and nuclear industries. This flow regime is characterized by pseudo-periodic occurrence of Taylor bubbles and liquid slugs. The approaches for slug flow modeling include empirical methods, mechanistic methods and numerical methods. Numerical methods involve large amount of computation and therefore not suitable for the application in petroleum industry. In contrast to empirical methods that are limited in the range of application, mechanistic models are more applicable because they capture the essential mechanism of the slug flow regime. However, the mechanistic models require some correlations to obtain closure, which bring unexpected error and need to be improved before getting results matching with experimental data. This project established a computational model to simulate the flowing field around Taylor bubble. Boundary fitted structured grid system is built for the simulation model and the turbulence is accounted for by the low Reynolds-number k- model. The previous turbulence model is modified to predict smooth transition from laminar to turbulent flow. To obtain the configuration of the Taylor bubble, circular geometry is assumed at the top of the bubble and Bernoulli equation is applied to estimate the shape of the tail part. The fifth order of polynomial function is used to ensure the convergence of the bubble configuration which has uniform pressure along the interface. Based on the results from the numerical model and previous experimental studies, the currently used mechanistic model is improved to get more accurate prediction for the slug flow in vertical pipes. The improved model is validated by previously reported experimental data. The geometric parameters of slug flow analyzed in this project can provide a basis for studying flow regime transition from slug flow to other flow regimes. The significance of this work is to help us understand more details about slug flow in vertical pipes. The knowledge gained from this work can be used to reestablish existing empirical correlations that are limited to particular conditions but necessary to the mechanistic models. The improvement of mechanistic models can benefit the design of tubing and surface facilities and the determination of artificial-lift methods.Item Validation of a reduced-complexity numerical model for resolving deltaic dynamics : internal consistency and morphodynamics(2015-05) Van Dyk, Corey John; Passalacqua, Paola; Mohrig, DavidRiver deltas are fragile ecosystems that have immense ecological, economic, and social importance. The ability to understand them is facilitated by numerical models that can resolve the complex hydrodynamics and morphodynamics of deltas. DeltaRCM is one such model, and to validate its behavior, internal consistency is tested with variable input parameters; results indicate realistic growth with predictable patterns. The morphodynamics are tested against experimental and real deltas with the use of metrics: specifically, delta growth metrics like shoreline-to-area ratio and relative shoreline roughness, channel overlap, and avulsion behavior. DeltaRCM performs very well when compared to real systems with growth rate and relative shoreline roughness, and fairly well for shoreline-to-area ratio. The channel overlap metric suggests DeltaRCM displays a slightly higher degree of channel stability than an experimental delta, though the general trend of memory decay remains the same. A similar link exists between DeltaRCM and reality for the wetted fraction, in that general trends are similar but comparison breaks down at finer scales. Furthermore, based on DeltaRCM results, wetted fraction is an imperfect tool for determining avulsion timescale. A new metric, the sedimentograph, is introduced as a way of describing delta growth at the subsurface level; DeltaRCM gives reasonable results for this metric, though comparison to real systems is difficult.