The thermal diffusivity and conductivity of several ceramic composites were determined experimentally to observe the effect of temperature, heat treatment and orientation on these properties. The thermal conductivity and diffusivity of SiC whisker reinforced Ba-osumilite glass-ceramic exceeded that of SiC fiber reinforced osumilite due to higher thermal conductivity and diffusivity of the whiskers. An anisotropy was observed in thermal conductivity of the whisker composite due to whisker orientation normal to hot-pressing direction. Thermal conductivity of carbon fiber reinforced borosilicate glass parallel to the fiber plane was about twice that of the normal orientation and of the matrix. Heating the composite to above 600°C resulted in permanent decrease in thermal conductivity due to void formation by relaxation of the elastically bent fibers by viscous flow of the matrix. Thermal conductivity of iniaxial carbon fiber reinforced lithia-aluminosilicate glass-ceramic was over ten times higher parallel to the fibers than perpendicular. Permanent decrease of thermal conductivity normal to the fibers was due to matrix cracking caused by relief of internal stresses due to matrix crystallization and thermal gradients during fabrication. Modification of the original theories of Maxwell and Rayleigh permitted derivation of expressions for thermal conductivity of composites of a continuous matrix with dilute concentrations of spherical and cylindrical geometries and of parallel flat plates with thermal resistance at the interfaces. / M.S.

Volatile fatty acids (VFA) are important products of ruminal fermentation. The VFA are not only the major source of energy to the ruminant animals but also influence methane production in the rumen. Therefore it is important to understand mechanism controlling VFA production and to depict VFA production in a model. This will allow us to devise strategies to enhance energy utilization and reduce methane production in ruminant livestock. An evaluation of a mechanistic model in predicting VFA production was conducted and equations were introduced into the model to improve the predictions. Later a continuous culture experiment was conducted to test the hypothesis on which those equations were based on. A mechanistic model -" Molly, was evaluated using a dataset with reported VFA production rates. The results of residual error analysis indicated that the root mean square prediction errors (RMSPE) were 63, 63, and 49% for acetate, propionate and butyrate, respectively. An assessment from two studies reporting VFA production revealed a potential of reducing errors of prediction by representing interconversion among VFA. In the second study, equations based on thermodynamics influence of pH and VFA concentration were introduced in the model to represent interconversion among VFA. The parameters for de novo VFA production and VFA absorption were re derived with (VFAInt) and without (BASE) the new interconversion equations. There were some improvements in the VFA concentration predictions but the improvements were both in VFAInt and BASE models. The RMSPE of VFA production were still above 50% for acetate, propionate and butyrate. The larger errors of predictions were attributed to measurement variation in VFA production literature, or possible incorrect rate constants for interconversion equations. Finally, a third study was conducted to assess the effect of pH, and VFA concentration on VFA and methane production in continuous culture. The treatments consisted of control, 20 mmol/d acetate infusion (INFAC), 7 mmol/d propionate infusion (INFPR), and low pH (LOWPH). Individual isotopes of acetate, propionate and butyrate were infused in the fermenters to estimate interconversions among VFA. With LOWPH treatment methane emission was reduced whereas production of propionate was increased. Hydrogen production was higher in INFAC indicating that some of the acetate could have been degraded to CO2 and H2. It was estimated that around 3 % of de novo acetate was converted to propionate and 9 % to butyrate. Exchange between propionate and butyrate was insignificant and below 1% of de novo production of either VFA. However, treatments did not affect interconversion rates among VFA. These results indicated that pH and VFA concentration do not have thermodynamic influence on VFA interconversion as hypothesized. / Ph. D.

The objective of this research was to apply the TK!Solver program for thermodynamic calculations. The TK!Solver program is equation-solving software that can solve both linear and non-linear sets of equations. To achieve the above objective, six programs have been developed. Program ESTATE.TK calculates volumetric properties of compounds using the ideal gas law, Pitzer correlation, van der Waals, Redlich-Kwong, Dieterici, or Berthelot equation of state. The volumetric properties include temperature, pressure, volume, and compressibility factor. Program RESIDUAL.TK calculates residual and total properties of compounds as a function of temperature and pressure using the Pitzer correlation, van der Waals, or Redlich-Kwong equation of state. The residual and total properties include residual volume, residual internal energy, residual enthalpy, and residual entropy. Program FRENERGY.TK calculates standard free energy of formation, standard enthalpy of formation, and standard entropy of formation for a compound or a reaction as a function of temperature. This program also calculates the equilibrium constant for a reaction as a function of temperature. Program CHON.TK calculates the equilibrium composition for an adiabatic or non-adiabatic reactor as a function of the temperature and pressure of the reactor, hydrogen-to-oxygen ratio, and nitrogen-to-oxygen ratio in the feed. The feed to the reactor consists of the elements carbon, hydrogen, oxygen, and nitrogen. The products of the reactor are methane, water, carbon monoxide, carbon dioxide, hydrogen, and nitrogen. Program CRITICAL.TK furnishes critical data for more than fifty compounds. The critical data includes critical temperature, critical pressure, critical volume, critical compressibility factor, and the acentric factor. Programs ESTATE.TR and RESIDUAL.TK have access to data file CRITICAL.TK for state property calculations. Program DATBANK1.TK supplies heat capacity data, heat of formation, and entropy of formation data for more than one hundred compounds. Programs RESIDUAL.TK and FRENERGY.TK have access to data file DATBANK1.TK for enthalpy and entropy calculations. These six programs may be considered as a basis for an "expert" system for thermodynamic calculations. Data can be easily added to extend the calculations to include additional compounds. / M.S.

The purpose of this work was to determine the enthalpies and specific heats of polymethyl methacrylate, polydimethylaminoethyl methacrylate, polycyclohexyl methacrylate, polyallyl methacrylate, and polyethyl acrylate from 120 to 300°C, and to determine a method for estimating their specific heats. Enthalpies of the selected polymers were determined by using a drop calorimeter constructed by the Chemical Engineering Department of Virginia Polytechnic Institute. Specific heats were obtained by measuring the slopes of the enthalpy-temperature curves. Good agreement with existing data for polymethyl methacrylate was obtained. An existing semi-theoretical quantum mechanical method was modified to provide specific heat estimations for linear methacrylic polymers accurate within six percent. An empirical correlation yielding estimations within twenty percent was proposed. / Master of Science

The thermodynamic properties of aqueous sulfur species were estimated using a structure-based, group contribution additivity method that is based upon first-order approximations. Structural groups were chosen so as to minimize subjectivity and maximize the ease of recognition and include: (1) Sn^*, polymeric sulfur (as 1/n, where n is the length of the longest continuous sulfur chain in the species), (2) O₃S^IV; (3) O₃S^VI; (4) O₂S^III and (5) bridging oxygen. In addition, a modified "charge-to-size" ratio (C) is used to model the coulombic interaction between ions and the solvent. Multiple linear regressions of these thermodynamic data were performed in terms of structural groups to yield fundamental equations for the model. Regression coefficients were used to estimate thermodynamic properties of a number of aqueous species for which no experimental data currently exist. Model-derived thermodynamic data were used to find the thermodynamic stability of intermediate sulfur species that occur during the aqueous oxidation of sulfide minerals, which identified at least one thermodynamically feasible pathway for the overall reaction. The data were also used to construct an EhpH diagram for aqueous sulfur species with average sulfur oxidation states less than sulfate (VI). The structure-thermodynamic correlation was used to determine the likely structure of the aqueous S₂O₅²⁻ ion, which has been debated over the past 50 years. The rate of decomposition of the ferric thiosulfate complex was observed to vary as the square of the concentration of the complex. The decomposition of this complex in acid solutions is strongly dependent on temperature, E_a = 120(±15) kJ mol⁻¹. The rate of reaction increases was observed to increase with increasing ionic strength, consistent with the interaction of two positively charged ions to form the activated complex. This study resolves many of the inconsistencies found in earlier studies and shows that reaction with H⁺ is a more important sink for S₂O₃²⁻ than reaction with Fe³⁺ when pH > -1.7. Comprehensive rate laws for aqueous pyrite oxidation were produced using experimentally determined data and data reported in the literature. Rate data available in the literature for the reaction of pyrite with dissolved oxygen (DO) to were compiled to produce a rate law that is applicable over three and one half orders of magnitude in DO concentration over the pH range 2-10. A series of batch, and mixed flow reactor experiments were performed to determine the effect of SO₄²⁻, Cl⁻, ionic strength and dissolved oxygen on the rate of reaction of pyrite with ferric tron. Only dissolved oxygen was found to have any appreciable effect. The results of this study were combined with kinetic data reported in the literature to formulate rate laws that are applicable over a six order of magnitude range in Fe³⁺ and Fe²⁺ concentration for the pH range ~0.5-3.0. Fundamental rates laws were formulated for each system and showed that the reaction order for ferric iron changed, thus suggesting a change in reaction mechanism. An observed rate correlation with the Fe³⁺/Fe²⁺ ratio indicates that the rate is proportional to Eh, and is best modelled by a non-ideal, non-site specific Freundlich multilayer isotherm. Because rate is observed to be positively correlated with the concentration of the aqueous oxidant only, the rate determining step for the aqueous oxidation of pyrite can be identified as the electron transfer from the mineral to the oxidant. / Ph. D.

Subduction zones are an important recycling center at which material from the exterior of the Earth is transported to Earth's interior. The processes that occur along subduction zones have important implications for elemental cycles, geodynamics, and material mass transport. The cold, dense subducting lithosphere experiences prograde metamorphism as it transitions from blueschist to eclogite facies resulting in the breakdown of volatile-bearing minerals and producing anhydrous minerals and a free fluid phase. Previous works attempting to understand the evolution of subducted lithologies have provided a firm foundation in which to apply field work, computational thermodynamic modeling, and geochronological techniques in order to better constraint the Pressure-Temperature-time (P-T-t) paths and dehydration of subducted lithologies. This dissertation; 1.) Explores novel approaches to modeling and predicting fluid/rock interactions during deep (>60km) subduction, and 2.) Questions what the calculated P-T-t path from eclogite lithologies reveals about early exhumation of subducted terrains. The second chapter focuses on how externally-derived hydrous fluids can decarbonate subducted basalt, liberate carbon and transfer it to the overlying mantle wedge, where it can be incorporated into melt that forms volcanic arcs. Here, the thermodynamic response to the infiltration of external fluids assuming open system, pervasive fluid flow, is quantified. It was determined that while hotter subduction zones have more favorable P-T conditions in which to facilitate decarbonation than colder subduction, the extent of decarbonation is largely dependent on the availability of fluid from the dehydration of underlying serpentine. The third chapter constrains the P-T-t paths of subducted lithologies from Syros, Greece using a combination of thermodynamic modeling, 147Sm/144Nd garnet geochronology, and quartz-in-garnet geobarometry. This provides insight into early exhumation of subducted lithologies, and allows for the exploration of assumptions made in thermodynamic modeling and in quartz-in-garnet geobarometry. Results suggest that garnet grew over a 4.31my period from 45.71±0.98Ma to 41.4±1.7Ma, during initial exhumation from maximum subducted depths. Calculated exhumation rates are a relatively rapid, 0.4-1.7 cm/yr. Because field relationships on Syros suggest the width of the subduction channel along the slab/mantle interface is not adequate to facilitate buoyancy-driven ascension of metabasic blocks, initiation of southward retreat of the Hellenic Subduction Zone and subsequent slab rollback is proposed to have played an important role in the exhumation of subducted lithologies. The final chapter investigates the compositional controls on the P-T conditions at which dehydration due to the breakdown of hydrous minerals occur during subduction (blueschist/eclogite boundary), and the implications they have on the rheology, seismicity, and densification of the down going slab. Total Alkali Silica (TAS) diagrams reveal that eclogites are more alkali rich, implying that initial alteration of the seafloor controls the mineral evolution of subducted basalt in many cases. / Ph. D. / Subduction zones are an important ‘recycling center’ at which material from the exterior of the Earth is transported to Earth’s interior. The processes that occur along subduction zones have important implications for elemental cycles, geodynamics, and material mass transport. The cold, dense rock that gets heated and deeply buried (high pressure metamorphism) releases fluid as water-bearing minerals breakdown. Previous works attempting to understand the history of subducted rocks have provided a firm foundation in which to apply field work, modeling, and dating techniques in order to better constraint the depths and temperatures a rock experienced, and over what time interval metamorphism and subsequent fluid loss occurred. This dissertation; 1.) Explores novel approaches in modeling and predicting fluid/rock interactions during deep (>60km) subduction, and 2.) Asks what does the calculated Pressure-Temperature-time (P-T-t) path from eclogite lithologies reveal about early exhumation of subducted terrains. The second chapter focuses how water-rich fluids can infiltrate a subducted rock and liberate carbon, which migrates upwards and can be incorporated into melt that forms volcanic arcs. It was determined that while the potential to release more carbon is higher in hotter subduction zones, the extent of decarbonation is largely dependent on the availability of fluid from the dehydration of the water bearing mineral., serpentine. The third chapter constrains the P-T-t paths of subducted lithologies from Syros, Greece using a combination of techniques, which not only provides insight into the return of subducted rocks back to the surface, but allows for the exploration of assumptions made in various analytical methodologies. Results suggest that garnet grew over a span from 45.71±0.98Ma to 41.4±1.7Ma, as the rock moved at a rate of 0.4–1.7 cm/yr to travel approximately 18km back to the surface, which suggests that a large-scale tectonic mechanism is needed to facilitate the rock’s return journey. The final chapter investigates the compositional controls on the P-T conditions in which the breakdown of hydrous minerals, and subsequent fluid loss, occur during subduction (blueschist/eclogite boundary), and the implication they have on the physical properties and behavior of the subducting rock. Chemical data reveal that subducted rocks that dehydrate earlier are more enrich in K and Na, implying that initial alteration of the seafloor controls the mineral evolution of subducted basalt.

As the world faces global conflict and energy crises, major efforts are underway to find sustainable engineering solutions to reduce industrial dependence on fossil fuels and minimize climate impacts from carbon emissions. Research in the combustible fuel sector is crucial to address economic reliance on cheap carbon-based fuels for increased energy capacity and reduced greenhouse gas emissions. Ammonia (NH₃) offers high energy potential and zero carbon emissions (CO and CO₂) while serving as an effective hydrogen (H₂) carrier in power and transportation applications. Turbine-combustion research on NH₃ and H₂ fuels has been conducted to identify combustion performance parameters for high-pressure, sustainable turbomachinery. Studies on NH₃ and H₂ performance capabilities have revealed sources of thermodynamic instabilities, such as uncontrolled flames or flashback, by assessing fuel laminar burning speed (LBS) with optical data. LBS is a key combustion parameter that informs turbine design engineers about combustion physiochemistry, flashback, and efficiency. State of the art literature shows that H₂ enhances the LBS of NH₃ (φ = 1.0, SL = 5.0 – 21 cm/s) for all equivalence ratios at 1 atm and 298 K. However, H₂ dilution to NH₃ results in excess N₂O and NOx emissions, which are toxic to biological systems. Thus, further efforts are needed to reduce toxic gas emissions and identify thermodynamic engineering controls to maintain stable NH₃-H₂ flames. In this work, NH₃ and H₂ mixtures were ignited at an initial temperature and pressure of 293 – 323 K and 5 – 10 atm to understand their performance properties. The LBS was calculated using a multizone, constant volume combustion model. Experimental results showed that H₂ dilution enhances the LBS of NH₃, and chemical-kinetic sensitivity analyses identified reactions facilitating this effect. Additional flame stabilization studies investigating the Lewis number of experimental mixtures revealed that helium (He) effectively mitigates thermal-diffusion, as shown by Schlieren optical measurements.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: See PDF for abstract. / AFRIKKANSE OPSOMMING: Sien PDF vir die opsomming.

Knowledge of thermodynamic fluid properties, such as density and phase behavior, is important for the design, operation, and safety of several processes including drilling, extraction, transportation, and separation that are required in the petroleum. The knowledge is even more critical at extreme temperature and pressure conditions as the search for more crude oil reserves lead to harsher conditions. Currently, there is dearth of experimental data at these conditions and as such, the predictive capability of the existing modeling tools are unproven. The objective of this research is to develop a fundamental understanding of the impact of molecular architecture on fluid phase behavior at temperatures to 523 K (250 °C) and pressures to 275 MPa (40,000 psi). These high-temperature and high-pressure (HTHP) conditions are typical of operating conditions often encountered in petroleum exploration and recovery from ultra-deep wells that are encountered in the Gulf of Mexico. This PhD study focuses on the fluid phase behavior of a low molecular weight compound, two moderately high molecular weight compounds, three asymmetric binary mixtures of a light gas and a heavy hydrocarbon compound with varying molecular size. The compounds are selected to represent the family of saturated compounds found in typical crude oils. Furthermore, this study reports experimental data for two "dead" crude oil samples obtained from the Gulf of Mexico and their mixtures with methane from ambient to HTHP conditions. A variable-volume view cell coupled with a linear variable differential transformer is used to experimentally measure the high-pressure properties of these compounds and mixtures. The reported density data compare well to the limited available data in the literature with deviations that are less than 0.9%, which is the experimental uncertainty of the density data reported in this study. The phase behavior and density data obtained in this study are modeled using the Peng-Robinson (PR), the volume-translated (VT) PR, and the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equations of state (EoS). The EoS pure component parameters, typically obtained from the open literature, are derived from fitting the particular EoS to, critical point, or to vapor pressure and saturated liquid density data, or to HTHP density data. For the density data reported here, the PREoS provided the worst predictions, while the VT-PREoS gives an improved performance as compared to the PREoS. However, the PC-SAFT EoS provided the best HTHP density predictions especially when using HTHP pure component parameters. The situation is however reversed in the modeling performance for the phase behavior data whereby the PC-SAFT EoS with HTHP parameters provided the worst vapor-liquid equilibria predictions. Better predictions are obtained with the PC-SAFT EoS when using parameters obtained from fit of the vapor pressure data and is comparable to the PREoS predictions. This reversal in performance is not surprising since the phase behavior data occur at moderately low pressures. The performance of the PC-SAFT EoS is extended to the experimental density data reported for the dead crude oil samples and their mixtures with methane. The PC-SAFT EoS with either set of pure component parameters yield similar predictions that are within 3% of the reported crude oil density data. However, when using the HTHP parameters, the PC-SAFT gives a good representation of the slope of experimental data, which is crucial in the calculation of second-derivative properties such has isothermal compressibility. The PC-SAFT EoS is also employed to model the crude oil HTHP density data for both the dead crude oils and their mixtures with methane using correlations for both the Low-P parameters and the HTHP parameters. The Low-P parameters are derived from fitting the PC-SAFT EoS to pure compound vapor pressure and saturated liquid density data, while the HTHP parameters are obtained from fitting the PC-SAFT EoS to pure compound HTHP liquid density data. Interestingly, the PC-SAFT EoS with the Low-P parameters provided better HTHP density predictions that are within 1.5% of the experimental data for the dead oils than the HTHP parameters that are within 2 to 4% of the data. Density predictions for the dead oil mixtures with methane are however comparable for both sets of parameters and are within 1% on average. However, the PC-SAFT EoS with HTHP parameters clearly provided better representation of the isothermal property, a derivative property obtained from density data, within 10% while predictions with the Low-P parameters can be as high as 37%. The successful completion of the thesis work expands the current knowledge base of fluid phase behavior at the extreme operating conditions encountered by engineers in the petroleum industries. Furthermore, the reported HTHP experimental data also provide a means to scientists and researchers for the development, improvement, and validation of equations with improved modeling performance.

Ip Lai Nang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 67-71). / Abstracts in English and Chinese. / ABSTRACT (ENGLISH) --- p.iii / ABSTRACT (CHINESE) --- p.iv / ACKNOWLEDGEMENTS --- p.v / TABLE OF CONTENTS --- p.vi / LIST OF TABLES --- p.viii / LIST OF FIGURES --- p.ix / LIST OF APPENDIX --- p.x / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter CHAPTER 2 --- BACKGROUND --- p.3 / Chapter 2.1 --- Structure of DNA --- p.3 / Chapter 2.2 --- Sequence dependent stability --- p.8 / Chapter 2.3 --- Thermodynamics of DNA --- p.9 / Chapter 2.4 --- Model for predicting thermodynamic parameters of DNA sequence --- p.15 / Chapter 2.4.1 --- The nearest-neighbor (NN) model / Chapter 2.4.1.1 --- Background --- p.15 / Chapter 2.4.1.2 --- Method for predicting thermodynamic parameters --- p.16 / Chapter 2.4.1.3 --- Limitation of the NN model --- p.19 / Chapter CHAPTER 3 --- EXPERIMENTAL METHOD --- p.20 / Chapter 3.1 --- Design of DNA sequences PAGE --- p.20 / Chapter 3.2 --- DNA synthesis and purification --- p.22 / Chapter 3.3 --- UV measurement --- p.23 / Chapter CHAPTER 4 --- THE NEXT NEAREST-NEIGHBOR (NNN) MODEL --- p.27 / Chapter 4.1 --- Method for extracting the NNN thermodynamic parameters --- p.30 / Chapter 4.2 --- Discussions --- p.34 / Chapter 4.2.1 --- Comparison of the NN model and the NNN model --- p.34 / Chapter 4.2.2 --- The NNN effect --- p.38 / Chapter 4.2.3 --- Sequence-specific local structure of DNA and the NNN effect / Chapter CHAPTER 5 --- SUMMARY AND FUTURE WORK --- p.49 / APPENDIX I´ؤ XVI --- p.51 / REFERENCE --- p.67