Thesis (Ph. D.)--Lehigh University, 2004. / Includes vita. Includes bibliographical references (leaves 142-160).

This dissertation entails the calculation of the release of gaseous fission products and iodine from the Pebble Bed modular reactor (PBMR) 400MW core under a Depressurised Loss of Forced Coolant (DLOFC), where the temperature history of fuel sphere is taken into account. The release is calculated by developing a computer code (REALESE) based on a simple coated particle failure and a gas diffusion model. The computer code calculates failure fraction, kernel release fraction, layer release, Iodine decay correction, core release fraction and other parameters pertaining to a PBMR. This source code is developed in the FORTRAN 77 programming language on a Compaq Virtual FORTRAN Development Platform. Verification of the results is done in Mathcad and the Getter code. RELEASE calculations compare very well with the MathCAD calculations with deviation from 0-5%. The effects of a number of parameters on fission product release are investigated by means of sensitivity analysis involving parameters like temperature, failure fraction and diffusion coefficient. Sensitivity analysis showed that the variation of failure fraction has the greatest effect on release fission products in a PMBR. The RELEASE results are compared with GETTER calculations in addition to the MathCAD verification. RELEASE calculations showed an expected value of 2.00x10 12 Bq whereas GETTER calculations produced an expected value of 2.13x10 12 Bq, representing a percentage deviation of 6%. / Thesis (MSc. ARST) North-West University, Mafikeng campus, 2003

The Comparison of Climate Change Rates in Rural versus Urban Areas in Tennessee An analysis of climate data was performed in three counties in Tennessee. The goal of this study is to identify the different rates of climate change in counties of varying urbanization levels. Davidson County, which contains the city of Nashville, is used as the most urban county. Two counties outside Nashville, Sumner and Dickson Counties, are used as a moderately urban county and a rural county, respectively. The level of urbanization was adopted from Tennessee Advisory Commission on Intergovernmental Relations' Index of Relative Rurality. Yearly average temperature and daily mean temperature for the warm season (May through October) were collected on each county from the years of 1960-2020 via the PRISM Climate Group at Oregon State University. A Mann-Kendall (MK) trend test was used for each individual county’s data to determine if the series had a monotonic upward trend, meaning overall temperature increase. The hypothesis of this analysis is that the most urban county will have the highest rate of warming due to the urban heat island (UHI) effect. The analysis of the yearly average temperature data for the three counties showed that Davidson and Sumner had higher Sen’s slopes and Kendall’s Taus, which were the prominent factors examined to determine the extent of climate change. Comparatively, Dickson County was found to have a lower Sen’s slope and Kendall’s Tau, which implies a lower overall rate of warming. Significance was found within all the results, since P-values were α Laina Caywood: Environmental Health, East Tennessee State University. Ying Li: Environmental Health, East Tennessee State University. Andrew Joyner: Department of Geosciences, East Tennessee State University.

South Africa is a land blessed with an abundance of mineral deposits. Yet, despite this, very little value adding of minerals exists. Most of the mined minerals are exported, where it is reworked into valued items. The country subsequently imports the valuable items at a much higher cost. In the 2006/7 financial year, the government made the decision to support several projects aimed at adding value to the mined minerals and by so doing, creating job opportunities. One such project was identified for the mineral Fluorite (CaF2). Fluorite is exposed to a controlled burn in a plasma reactor, producing an array of different fluorocarbon gases used in the electronics industry and for commercial polymers like Teflon®. Currently, fluorocarbon gases are separated using a series of cryogenic distillation columns. Although this technique has proven to be successful, it has several negative aspects such as the high cost involved when operating at cryogenic conditions as well as difficulty handling the gases at these sub–zero temperatures. It was proposed to study the possibility of using membranes to separate fluorocarbon gases at ambient conditions. Several membranes were screened to determine which one is best suited for this application. Two Teflon® based membranes were selected from this data. One of the membranes had a PAN support, while the other had a PEI support. Pure gas data for both membranes showed promising results. It yielded the highest flux for C3F6, followed by N2 and CF4. c–C4F8 was not used because it was demonstrated that the gas tends to condensate at low pressures. It is recommended to rather use pressure swing condensation to remove this gas from the mixture before the remainder is purified using membranes. Both membranes behaved similarly, with selectivity between C3F6 and CF4, and N2 and CF4; all above 10. By including the permeate pressure in the Solution–diffusion model, it was possible to model the pure gas data Binary feed gas mixture experiments showed a large amount of coupling existing between the feed gas mixtures. The result is a decrease in the selectivity as well as the total flux of the gas mixture. Partial fluxes were modelled by introducing a thermodynamic factor that was shown to follow a power law equation. The PAN–supported membrane outperformed the PEI–supported one; it was decided to use this membrane from this point onwards. Analysis of the ternary feed mixtures showed a strong selectivity towards the gas abundant in the feed blend. The existence of convective diffusion was proven, and included in the modelling, as well as a breakthrough pressure constant. This is indicative of strong interaction between the different gases and the membrane. Throughout the study it became clear that the difference in surface charge between the gases and the membrane were decisive. Opposite charges between a gas (C3F6) and the membrane aided in gas permeation. Membrane separation of fluorocarbon gases at ambient conditions is possible. Teflon® based membranes are recommended. It will be advantageous to study the effect of elevated temperatures on the separation efficiency of such a system. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

South Africa is a land blessed with an abundance of mineral deposits. Yet, despite this, very little value adding of minerals exists. Most of the mined minerals are exported, where it is reworked into valued items. The country subsequently imports the valuable items at a much higher cost. In the 2006/7 financial year, the government made the decision to support several projects aimed at adding value to the mined minerals and by so doing, creating job opportunities. One such project was identified for the mineral Fluorite (CaF2). Fluorite is exposed to a controlled burn in a plasma reactor, producing an array of different fluorocarbon gases used in the electronics industry and for commercial polymers like Teflon®. Currently, fluorocarbon gases are separated using a series of cryogenic distillation columns. Although this technique has proven to be successful, it has several negative aspects such as the high cost involved when operating at cryogenic conditions as well as difficulty handling the gases at these sub–zero temperatures. It was proposed to study the possibility of using membranes to separate fluorocarbon gases at ambient conditions. Several membranes were screened to determine which one is best suited for this application. Two Teflon® based membranes were selected from this data. One of the membranes had a PAN support, while the other had a PEI support. Pure gas data for both membranes showed promising results. It yielded the highest flux for C3F6, followed by N2 and CF4. c–C4F8 was not used because it was demonstrated that the gas tends to condensate at low pressures. It is recommended to rather use pressure swing condensation to remove this gas from the mixture before the remainder is purified using membranes. Both membranes behaved similarly, with selectivity between C3F6 and CF4, and N2 and CF4; all above 10. By including the permeate pressure in the Solution–diffusion model, it was possible to model the pure gas data Binary feed gas mixture experiments showed a large amount of coupling existing between the feed gas mixtures. The result is a decrease in the selectivity as well as the total flux of the gas mixture. Partial fluxes were modelled by introducing a thermodynamic factor that was shown to follow a power law equation. The PAN–supported membrane outperformed the PEI–supported one; it was decided to use this membrane from this point onwards. Analysis of the ternary feed mixtures showed a strong selectivity towards the gas abundant in the feed blend. The existence of convective diffusion was proven, and included in the modelling, as well as a breakthrough pressure constant. This is indicative of strong interaction between the different gases and the membrane. Throughout the study it became clear that the difference in surface charge between the gases and the membrane were decisive. Opposite charges between a gas (C3F6) and the membrane aided in gas permeation. Membrane separation of fluorocarbon gases at ambient conditions is possible. Teflon® based membranes are recommended. It will be advantageous to study the effect of elevated temperatures on the separation efficiency of such a system. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

No description available.

Nitrogen (N) fertilizer is a required mineral nutrient in containerized crop production that is necessary for crop growth and development. Due to production aspects, the N added to crops far exceeds the amount that the plant uses and such inefficiency results in adverse environmental impacts related to N gaseous and aqueous emissions from containers on the production site. Growers are responsible for optimizing nutrient usage in crop production. Three studies were conducted to investigate and better understand the fate of applied N fertilizers, the transformations associated with individual N sources, and the influence of substrate texture on losses of aqueous and gaseous N species. The first study conducted a mass balance looking at the four major avenues of N fate in an open-air container production setting (plant uptake, immobilized or bound N in a pine bark substrate, leached aqueous N, and gaseous emissions of N), the mass balance was speciated to measure applied and intermediary forms of N fertilizer species to provide insight into the overall fate of applied N. Show Off® Forsythia ×intermedia' Mindor' were grown using two control-release fertilizer (CRF) treatments [AN (ammonium-nitrate based) or UAN (urea ammonium-nitrate)] products. This study determined that 97% of the released N from the CRF treatments was lost via aqueous or gaseous pathways. The aqueous losses were inferred to be predominately composed of NO3-N, while the gaseous emissions were inferred to be predominately lost as inert nitrogen gas (N2). During a second experiment, individual N sources treatments [urea (CH4N2O), ammonium (NH4+), and nitrate (NO3-)] were applied to established containers of At LastⓇ Rosa x 'HORCOGJIL' grown in a pine bark substrate in either open wall high tunnel or a glass greenhouse to determine subsequent reaction sequence and fate based on applied N source. By applying an individual form of N it was determined that based on the N source applied, a sequential set of reactions occurs based on the N source. This study determined that the reactive N gaseous species occurred from the hydrolysis of CH4N2O-N to NH4+ and the nitrification of NH4+ to NO3- and then the denitrification of NO3- to N2. Hibiscus moscheutos' Vintage wine' was grown in either a coarse or fine texture substrate utilizing either a water-soluble fertilizer or a CRF to compare the influence of pine bark texture on N leachate losses and RN gaseous emissions. There were few differences between the two substrate texture treatments related to aqueous or gaseous N losses. In both experiments, the Hibiscus grown in the fine texture substrate resulted in higher above and below-ground biomass at experimental termination. Working with growers to develop best management practices will help to improve the use of N fertilizers and impact growers economically, while simultaneously reducing losses leading to less environmental impact on the areas surrounding production sites. / Doctor of Philosophy / Nitrogen (N) fertilizer is a crucial mineral nutrient input to produce container crops, however excessive application can have detrimental effects on the environment including gaseous N emissions and N leaching leading to water pollution. Therefore, three studies were conducted to investigate N losses during production and potential mitigation strategies using common management practices in the production of container crops. During the first study investigating how N fertilizer is lost from production, results showed that a significant portion of the N added to the containers is either emitted from the containers into the atmosphere or leached from the container. Only a small fraction of the applied N was utilized by the plants for growth and development. The second study investigated the reactions and transformations of different N fertilizers sources. When applying single N sources urea (CH4N2O), ammonium (NH4+), or nitrate (NO3-) result in a set of sequential reactions that occur based on the applied N source. Urea is hydrolyzed via CH4N2O hydrolysis leading to the formation of NH4+ which is nitrified via nitrification to NO3- which is denitrified via denitrification leading to the production of N2 gas. In the final study two pine bark substrate classes were compared when using either a water-soluble fertilizer (WSF) or a controlled-release fertilizer (CRF). Surprisingly there were only a few differences between the two substrate treatments in either the WSF or CRF studies. This body of work show the importance of investigating N fertilizer usage in container crop production. Collaboration between researchers and growers is crucial to develop management practices that maximize the associated economic input of N fertilizers and minimize losses of N that are detrimental to the environment.

In the kingdom of Saudi Arabia (KSA), the current seawater desalination technologies are completely relying on burning unsustainable crude oil as their main energy driver. Saudi authorities have realized that the KSA is not going to be protected from the future global energy crisis and have started to set up a plan to diversify its energy resources. Membrane Distillation (MD) has emerged as an attractive alternative desalination process. It combines advantages from both thermal and membrane-based technologies and holds the potential of being a cost-effective separation process that can utilize low-grade waste heat or renewable energy. MD has four different configurations; among them is Air Gap Membrane Distillation (AGMD) which is the second most commonly tested and the most commercially available pilot-plant design. AGMD has a stagnant thin layer of air between the membrane and the condensation surface. This layer introduces a mass transfer resistance that makes the process require a large membrane surface area if a large quantity of fresh water is desired. This dissertation reports on experimental and theoretical work conducted to enhance the AGMD flux by removing non-condensable gases from the module and replacing it with either vacuum, liquid water or porous materials. At first, a mathematical model for AGMD was developed and validated experimentally to create a baseline for improvements that could be achieved after the removal of non-condensable gases. The mathematical model was then modified to simulate the process under vacuum where it showed a flux enhancement that reached 286%. The Water Gap Membrane Distillation (WGMD) configuration improved the flux by almost the same percentage. Since enhancing the flux is expected to increase temperature polarization effects, a theoretical study was conducted on the effect of temperature polarization in a Vacuum Membrane Distillation (VMD) configuration. The study showed that the effect of temperature polarization at small temperature difference (3-7) degree Celsius between the bulk feed and coolant temperatures is significantly high. This may indicate the importance of mitigating the effect of temperature polarization in large scale modules operating at small temperature difference across the membrane. The dissertation concluded with some recommendations for future work.

Under steady state conditions where the rate of biological oxygen production is balanced by oxygen evasion to the atmosphere, net community production (NCP) can be estimated from mixed layer oxygen/argon measurements. This method is effective in the open ocean but not in coastal zones where upwelling of low oxygen water violates the simple steady state assumption. Since these upwelling regions are highly productive, excluding them can lead to significant underestimations of global productivity. Here, I use a quasi-2D version of the Regional Ocean Modelling System (ROMS), including oxygen and argon as prognostic variables, to model the relationship between NCP and the sea-to-air flux of biological oxygen in a coastal upwelling system. The relationship between the sea-to-air flux of biological oxygen and NCP is poorest near the shore during upwelling favourable winds when waters that are undersaturated in oxygen reach the surface and depress the oxygen/argon ratio. I averaged NCP temporally and spatially over the residence time with respect to gas exchange and the Lagrangian motion of a water parcel. I found that the maximum distance travelled (∼25 km) over this time period indicated a distance from the upwelling plume at which much of the the low oxygen signal is erased. When the sea-to-air flux of biological oxygen was below 20 mmol m−2 day−1, NCP was usually also found in that range. Above that range the sea-to-air flux of biological oxygen is a lower bound for NCP. NCP occurring below the mixed layer can affect the sea-to-air flux of biological oxygen either by entrainment or diffusion into the mixed layer causing an overestimation of NCP, but this process had a minimal effect on most of my model data. Removing values with mixed layers deeper than 25 m improves the estimation, although further studies may reveal that this depth should be adjusted based on mean wind forcing. / Graduate / 0415

Traditional agricultural practices often result in gaseous losses of nitrous oxide (N2O), ammonia (NH3), and carbon dioxide (CO2), representing a net loss of nutrients from agricultural soils, which negatively impacts crop yield and requires farmers to increase nutrient inputs. By adopting best management practices (BMPs; i.e., no-tillage, cover crops, sub-surface manure application, and proper manure application timing), there is great potential to reduce these losses. Because N2O and CO2 are also greenhouse gases (GHGs), climate change mitigation via BMP adoption and emissions reductions would be an important co-benefit. However, adopting a no-tillage and cover cropping system has had setbacks within the Northeast, primarily due to concerns regarding manure nitrogen (N) losses in no-tillage systems as well as uncertainty surrounding the benefits of cover crops. This thesis used two field-trials located in Alburgh, Vermont to assess differences in (i) GHG emissions from agricultural soils, (ii) nitrate and ammonium retention, (iii) corn yield and protein content, and (iv) N uptake and retention via cover crop scavenging under a combination of different BMPs. Chapter 1 evaluates the effects of different reduced-tillage practices and manure application methods (i.e., vertical-tillage, no-tillage, manure injection, and broadcast manure application) on reducing N2O and CO2 emissions, retaining inorganic N, and improving crop yields. Greenhouse gas measurements were collected every other week for the growing season of 2015-2017 via static chamber method using a photoacoustic gas analyzer. Results from this study showed that tillage regimes and manure application method did not interact to affect any of the three research objectives, although differences between individual BMPs were observed. Notably, vertical tillage enhanced CO2 emissions relative to no-tillage, demonstrating the role of soil disturbance and aeration on aerobic microbial C transformations. Manure injection was found to significantly enhance both N2O and CO2 emission relative to broadcast application, likely due to the formation of anerobic micro-zones created from liquid manure injection. However, plots that received manure injection retained greater concentrations of soil nitrate, a vital nutrient for quality crop production, thereby highlighting a major tradeoff between gaseous N losses and N retention with manure injection. Chapter 2 evaluates the effects of tillage practices and timing of manure application to increase N retention with the use of cover crops in order to mitigate GHG emissions, enhance soil nitrate and ammonium retention, and improve cropping system N uptake. Treatments at this field trial consisted of a combination of the presence or absence of cover crops, no-tillage or conventional-tillage, and spring or fall manure application. Greenhouse gas emissions were measured every other week via static chamber method using a gas chromatograph for the growing season of 2018. Results from this study showed that the presence of cover crops enhanced both N2O and CO2 emissions relative to fallow land, irrespective of tillage regime and manure application season, likely as a result of greater N and carbon substrates entering the soil upon cover crop decomposition. Due to enhanced N2O emissions with cover crops, cover crops did not retain significantly greater inorganic N in the system upon termination.