Thesis (M.S.)--Mississippi State University. Department of Mechanical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1971. / Includes bibliographical references (p. 111-114).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1969. / Bibliography: leaves 89-91.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1964. / Bibliography: leaves 191-192.

Photocatalysis is a promising technique for the remediation of indoor air pollution. Photocatalysis utilizes semiconductor photocatalysts (such as TiO2 or ZnO) and appropriate light to produce strong oxidizing agents (OH*) that are able to break down organic compounds and inactivate bacteria and viruses. The overall goal of the research is to develop an efficient photocatalytic reactor based on mass transfer for indoor air purification. This study has focused on the enhancement of the effectiveness of the photocatalytic process by the introduction of artificial roughness on the reactor catalyst surface. The major effect of artificial roughness elements on the catalytic surface is to create local wall turbulence and enhance the convective mass transfer of the contaminants to the catalyst surface and thus lead to an increase in the effectiveness of photocatalysis. Air flow properties in a model photoreactor channel with various roughness patterns on the interior wall surface were theoretically investigated. The optimum shapes, sizes, and arrangements of roughness were determined for the maximum enhancement of turbulence intensity in the channel. The possible order of photocatalytic reactor performance for various roughness patterns was also determined. In order to verify the theoretical analysis results, experimental studies were carried out. A plate type photocatalytic reactor was designed and fabricated on the basis of the theoretical results. It was determined that the photocatalytic reactor performance is greatly improved with various rough catalyst surfaces. The experimental results verified the theoretical results. The relationship between the overall reaction rate constant (k) of the reactor and the magnitude of the turbulence intensity was found out. An empirical correlation expression was also proposed. This is the first study of the effect mass transfer in a rough catalytic surface for photocatalytic reactor. Photocatalyst development has also been studied. Zinc oxide (ZnO) and iron doped zinc oxide (ZnO/Fe) nanowires were synthesized on glass substrates through a conventional hydrothermal method. The photocatalytic activities under ultraviolet (UV) light and white light irradiation were separately investigated. The ZnO/Fe nanowires exhibited an enhanced photocatalytic activity as compared to ZnO nanowires regardless of the type of contaminants and light sources.

To screen amine solvents for application in CO2 capture from coal-fired power plants, the equilibrium CO2 partial pressure and liquid film mass transfer coefficient were characterized for CO2-loaded and highly concentrated aqueous amines at 40 – 100 °C over a range of CO2 loading with a Wetted Wall Column (WWC). The acyclic amines tested were ethylenediamine, 1,2-diaminopropane, diglycolamine®, methyldiethanolamine (MDEA)/Piperazine (PZ), 3-(methylamino)propylamine, 2-amino-2-methyl-1-propanol and 2-amino-2-methyl-1-propanol/PZ. The cyclic amines tested were piperazine derivatives including proline, 2-piperidineethanol, N-(2-hydroxyethyl)piperazine, 1-(2-aminoethyl)piperazine, N-methylpiperazine (NMPZ), 2-methylpiperazine (2MPZ), 2,5-trans-dimethylpiperazine, 2MPZ/PZ, and PZ/NMPZ/1,4-dimethylpiperazine (1,4-DMPZ). The cyclic CO2 capacity and heat of CO2 absorption were estimated with a semi-empirical vapor-liquid-equilibrium model. 5 m MDEA/5 m PZ, 8 m 2MPZ, 4 m 2MPZ/4 m PZ and 3.75 m PZ/3.75 m NMPZ/0.5 m 1,4-DMPZ were identified as promising solvent candidates for their large CO2 capacity, fast mass transfer rate and moderately high heat of absorption. The speciation in 8 m 2MPZ and 4 m 2MPZ / 4 m PZ at 40 °C at varied CO2 loading was investigated using quantitative 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. In 8 m 2MPZ at 40 °C over the CO2 loading range of 0 – 0.37 mol CO2/mol alkalinity, more than 75% of the dissolved CO2 exists in the form of unhindered 2MPZ monocarbamate, and the rest is in the form of bicarbonate and dicarbamate; 19% - 56% of 2MPZ is converted to 2MPZ carbamate at 0.1 - 0.37 mol CO2/mol alkalinity. A rigorous thermodynamic model was developed for 8 m 2MPZ in the framework of the Electrolyte Nonrandom Two-Liquid (ENRTL) model. At 40 °C, the reaction stoichiometry for 2MPZ and CO2 is around 2 at lean loading but diminishes to 0 at rich loading. Bicarbonate becomes the major product at CO2 loading greater than 0.35 mol/mol alkalinity. The predicted heat of CO2 absorption is 75 kJ/mol at 140 °C and decreases with temperature when CO2 loading is above 0.25. The mass transfer rate data for 8 m 2MPZ was represented with a rate-based WWC model created in Aspen Plus®. The reaction rate was described with termolecular mechanism on an activity basis. With minor CO2 loading adjustment and regression of pre-exponential kinetic constants and diffusion activation energy, a majority of the measured CO2 fluxes in the WWC experiments were fitted by the model within ±20% over 40 – 100 °C and 0.1 – 0.37 mol CO2/mol alkalinity. The diffusion activation energy for 8 m 2MPZ at the rich loading is about 28 kJ/mol. The activity-based reaction rate constant at 40 °C for 2MPZ carbamate formation catalyzed by 2MPZ is 1.94×1010 kmol/m3•s. The calculated liquid film mass transfer coefficients are in close agreement with the experimental values. The liquid film mass transfer rate is dependent on the diffusion coefficients of amine and CO2 to the same extent at lean loading and 40 °C. The sum of the powers for the two diffusivities is approximately equal to 0.5 over the loading range of 0 – 0.4 mol CO2/mol alkalinity. The sum of the powers for the dependence of the liquid film mass transfer coefficient on the carbamate formation rate constants (k2MPZ-2MPZ and k2MPZCOO--2MPZ) approaches 0.5 at very lean loading at low temperature, but it decreases as CO2 loading and temperature is increased. At 100 °C, the physical liquid film mass transfer coefficient is the most important factor that determines the liquid mass transfer rate. The pseudo-first order region shifts to higher range of physical liquid film transfer coefficient as temperature increases. / text

The Critical Zone (CZ) is the surficial layer of the planet that sustains life on Earth and extends from the base of the weathered bedrock to the top of the vegetation canopy. Its structure influences water fluxes, biogeochemistry and vegetation. In this dissertation, I explore the relationships between climate, water fluxes, vegetation dynamics, biogeochemistry, and effective energy and mass transfer fluxes (EEMT) in a semi-arid critical zone. This research was carried out in the upper Jemez River Basin in northern New Mexico across gradients of climate and elevation. The main research objectives were to (i) quantify relations among inputs of mass and energy (EEMT), hydrological and biogeochemical processes within the CZ, (ii) determine water fluxes and vegetation dynamics in high elevation mountain catchments with different terrain aspect and solar radiation, and (iii) study temporal variability of climate and its influence on the CZ water availability, forest productivity and energy and mass fluxes. The key findings of this study include (i) significant correlations between EEMT, water transit times (WTT) and mineral weathering products around Redondo Peak. Significant correlations were observed between dissolved weathering products (Na⁺ and DIC) and maximum EEMT. Similarly, ³H concentrations measured at the springs were significantly correlated with maximum EEMT; (ii) terrain aspect strongly controls energy, water distribution, and vegetation productivity in high elevation ecosystems in catchments draining different aspects of Redondo Peak. The predominantly north facing catchment, when compared to the other two eastern catchments, receives less solar radiation, exhibits less forest cover and smaller biomass, has more surface runoff and smaller vegetation water consumption. Furthermore, the north facing catchment showed smaller NDVI values and shorter growing season length as a consequence of energy limitation, and (iii) from 1984 to 2012 a decreasing trend in water availability, increased vegetation water use, a reduction in both forest productivity and EEMT was observed at the upper Jemez River Basin. These changes point towards a hotter, drier and less productive ecosystem which may alter critical zone processes in high elevation semi-arid systems.

No description available.

Spacer-filled channels are employed in membrane modules in many industrial applications where feed-flow spacers (employed to separate membrane sheets and create flow channels) tend to enhance mass transport characteristics, possibly mitigating fouling and concentration polarization phenomena. In this work direct numerical simulation was performed for the flow in the spacer-filled channels to obtain a better understanding of fluid flow and mass transfer phenomena in these channels. A solute with a Schmidt number of 1 at Reynolds numbers of 300, 500 and 800 (based on the bulk velocity and spacer diameter) was considered. The effect of spacer location was also studied for three different configurations, spacer at the centre of the channel, at off-centre location, and attached to the wall. Instantaneous velocity fields and flow structures such as separation of boundary layer on the walls and on the cylinder, eddies on the walls, recirculation regions and vortex shedding were investigated. A Fourier analysis was carried out on the time series velocity data. Using this analysis the Strouhal number was calculated and the development of the flow towards a broader turbulent state at higher Reynolds number was captured. Other statistical characteristics such as time-averaged velocities and wall shear rates are obtained and discussed. The average pressure loss which represents the operation cost of membrane modules was calculated for the channels and found to be highest for spacer at the centre of the channel and lowest for spacer attached to the wall. Scalar transport equation is directly solved along with Navier-Stokes equation to get the concentration field. Local Sherwood number is obtained on the walls and the relationship between shear stress, vortex shedding, and mass transfer enhancement was explored. The overall Sherwood number and Stanton number of the channels, which indicate the mass transfer performance of the channels, are obtained. It was observed that as spacer approaches the wall mass transfer rate is decreasing. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2010-11-30 11:44:07.479

No description available.