Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 112-116).

Th. doct.-ing--Grenoble 1, 1983. N°: 36.

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The need of the experimental support for validation of the computational tools to be applied to analyze the mixing of diluted slugs has been recognized in various countries. The test series for the International Standard Problem ISP-43 provides a platform for experiences to be applied to the simulation of a well-defined test series. Test A and B of the UM2x4 loop test facility were calculated with the CFD Code CFX-4.3. Sensitivity studies were made to analyze the used turbulence model and numerical errors. The results show good agreement with the experimental data for both tests.

The relative abundances of the stable and long-lived Isotopes of rubidium, cesium, strontium, cerium, neodymium, and samarium resulting from the ther­mal neutron fission of U^235 and Pu^239 were determined mass spectrometrically. Special precautions were taken to eliminate or at least minimize contamination of the sub-microgram quantities of fission products with the naturally occurring elements. By using isotope dilution the yields of isotopes of different elements were related with very good precision. Sufficient information was available to evaluate from such results the absolute cumulative yields of twenty-seven mass chains for U^235 fission. It was possible from the results of the present study of make a quantitative comparison between the yields of the heavy fragments for U^235 and Pu^239 fission, with special attention being given to the fine structure supposedly resulting from the influence of nuclear shells involving 50 and 82 neutrons. / Thesis / Master of Science (MS)

No description available.

The determination of limiting activity coefficients in liquid mixtures has become an important tool in chemical engineering. It has been investigated intensively during the past in order to find new alternatives and improved methods for its accurate detennination. The limiting activity coefficient is a fundamental thermodynamic quantity which measures the solution non-ideality and acts as a correction factor to deviations from Raoult's Law. This dissertation involves the determination of limiting activity coefficients using the inert gas stripping (IGS) technique only. It is considered to be the best method as it is a direct method involving exact concentrations of components in the mixtures encountered in industry. A comprehensive study of activity coefficients at infinite dilution for various systems, using the inert gas stripping (IGS) method has been undertaken. Various other methods and their suitability have also been discussed but preference is given to the superior quality of measurements obtained using the inert gas stripping technique. Extensive research has been conducted into the background and origination of the technique. Various improvements of the equilibrium cell designed by various authors for different types of systems have been outlined along with the various equations derived by the authors. The equipment was designed for use with the double-cell technique as well as the single-cell technique and in some cases both techniques were used. The techniques involve the use of a dilutor cell in which the highly diluted, volatile solute is stripped from a liquid solution using the inert gas nitrogen, introduced into the cell through capillaries and dispersed through the solution as small bubbles, at a constant flow rate. Analysis of the stripped solution is accomplished through the use of a gas chromatograph; the peak areas obtained from these analyses as well as the residence times and other system data such as temperature, pressure, mass and flow rate were used to compute the infinite dilution activity coefficient through the use of the various equations available in literature. The original equipment was designed for the use of the single cell technique by Soni (2004). Various modifications have been made to the equipment in order to measure limiting activity coefficients of more diverse systems with high accuracy. A major change to the equipment was the introduction of a second saturation cell of similar design to the dilutor cell. This enabled the determination of activity coefficients at infinite dilution of difficult systems i.e. systems where the solvent volatility is high and for higher order systems. The equipment was redesigned and built using ideas and improvements by previous researchers in the field and commissioned using test systems that have been classed as easy systems for this technique. The new equipment is now applicable to almost all systems, however good separation in the GC column could be a problem for complex systems. The determination of infinite dilution activity coefficients for one-component solute + onecomponent solvent systems and multi-component solvent systems were accomplished. The systems that were investigated consisted of a mixture of components of alkanes, alkenes, phenols and ketones, mostly in binary mixtures. Multi-component mixtures have also been investigated in the form of ternary systems involving a binary solvent mixture at varying concentrations, and a solute in order to show the diversity, uniqueness and efficiency of the IGS technique. Major variables affecting the system (the dilutor cell), namely the stripping gas flow rate and the dilutor cell temperature, were also investigated for all systems. Two test systems, cyclohexane in 1-methyl-2-pyrrolidone (NMP) and n-heptane in NMP were used to determine if the equipment is operating properly by comparing values obtained, to literature values where the inert gas stripping technique was used to determine the activity coefficients at infinite dilution. Another test system n-hexane in NMP was used to compare the two techniques, Le. the results of the single cell technique with the results of the double cell technique. The experimental results were thereafter compared to published literature values. Systems where the inert gas stripping technique has not been used to determine activity coefficients at infinite dilution were also investigated. These systems include 1-hexene in 0- cresol as well as the ternary systems '-hexene in various concentrations of NMP + o-cresol. A thorough literature survey has been completed and the relevant theory has been summarized. The validity of the equations proposed by Bao and Han (1995), Duhem and Vidal (1978), Leroi et a!. (1977), Hovorka and Dohnal (1997) and Krummen et al. (2000) for the determination of activity coefficients at infinite dilution were investigated. The experimental values obtained were consistent with literature values, with percentage errors of less than 1 % where the same equation was used to determine the limiting activity coefficient. Comparing limiting activity coefficients with the values obtained from other equations proposed by other authors mentioned above resulted in deviations no greater than 2.5 %, and where possible limiting activity coefficients were compared to values obtained from the single-cell technique. The theory section of this thesis covers all the various formulae (and where possible a summary of their derivation) used in the analysis of results. Some limiting activity coefficients for the systems involving n-heptane, n-hexane, n-hexene, cyclohexane, o-cresol and n-methyl-2-pyrrolidone under various experimental conditions have been reported making it readily available for use in other works. The effect of two major variables temperature and inert gas flow rate on the limiting activity coefficients with regard to all the systems studied have also been investigated and reported. This was also done in order to check that the data was reproducible. A sensitivity analysis was also performed in order to check the effect that certain measured variables would have on the limiting activity coefficient. These errors are estimated possible errors and may not exist at all, so not much consideration was given to this when reporting limiting activity coefficients for the various systems. The maximum error range for any given limiting activity coefficient as determined by the sensitivity analysis is ±11 %. The inert gas stripping technique is also extended to the determination of Hendry's constants. The actual values for the Hendry's constants were not determined but a comprehensive study of its determination was undertaken by Miyano et al. (2003) and summarized here. In addition the suitability and diversity of the inert gas stripping technique has been outlined, along with the advantages and disadvantages of the technique. The various designs of equilibrium cells have been outlined taking into account mass transfer considerations as proposed by Richon et al. (1980). The assumptions and limits of the method have also been outlined and must be taken into consideration when using the technique. A detailed description of the equipment setup and experimental procedure has been provided. The purpose, suitability, operation and applicability, of the various pieces of equipment used to make up the final equipment have been discussed in detail. Details for consideration when designing the equilibrium cells have also been provided. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

The aim of this work was to extend the theory of Everett and Cruickshank, for the determination of activity coefficients at infinite dilution, Y 13 (where 1 refers to the solute and 3 to the solvent), to accommodate solvents of moderate volatility, using the gas liquid chromatography (GLC) method. A novel data treatment procedure is introduced to account for the loss of solvent off the column, during the experiment. The method also allows us to determine the vapour pressure of the solvent. No auxiliary equipment is required, and the method does not employ the use of a presaturator. Further, the effect of a polar involatile solute is examined using various types of solutes. The activity coefficient was found to be independent of column packing and flowrate. Considering the volatile solvent, the systems investigated by the GLC method were straight chain hydrocarbons, (n-pentane, n-hexane and n-heptane), cyclic hydrocarbons (cyclopentane, and cyclohexane) and an aromatic compound, benzene. The systems were investigated at 2 temperatures, 280.15 K and 298.15 K. The results indicate a clear dependence of the activity coefficient on temperature. For the polar nonvolatile solvent, sulfolane (tetrahydrothiophene, 1,1 dioxane) was used. The systems studied were sulfolane + n-pentane, n-hexane, n-heptane, cyclopentane, cyclohexane, benzene, tetrahydrofuran, and tetrahydropyran. The systems were studied at one temperature, 303.15 K, due to the low melting point of sulfolane i.e. 301.60 K. Part of this study into the thermodynamics of solutions'\vas conducted at the Technical University of Warsaw, where the equilibria of sulfolane was studied using· two techniques, a dynamic solid-liquid equilibrium method (SLE), and an ebulliometriGI vapor-liquid method (VLE) . The main purpose of this was to apply solution theories to this data in order to predict the.activity coefficient at infinite dilution for the sulfolane mixtures. The systems measured using solid liquid equilibrium are sulfolane + tetrahydrofuran, or, 1,4-dioxane, or, I-heptyne, or, 1, 1, l,-trichloroethane, or, benzene, and cyclohexane. The results of these measurements were then described using various solution theories, and· new interaction parameters obtained. The vapour liquid equilibrium systems measured were sulfolane + I-heptyne, or, tetrahyrdofuran, or, 1,1, I-trichloroethane, and tetrachloromethane. Here as in SLE the results were described using solution theories. The results of both the VLE and SLE measurements were used in a multiple optimization procedure to produce new parameters for the interaction of sulfolane with various groups, using two group contribution method, DISQUAC and modified UNIFAC. The predicted activity coefficients compare well with the measured values using GLC. / Thesis (Ph.D.)-University of Natal, 1995.

Flammability limit is a most significant property of substances to ensure safety of chemical processes and fuel application. Although there are numerous flammability literature data available for pure substances, for fuel mixtures these are not always available. Especially, for fuel mixture storage, operation, and transportation, inert gas inerting and blanketing have been widely applied in chemical process industries while the related date are even more scarce. Lower and upper flammability limits of hydrocarbon mixtures in air with and without additional nitrogen were measured in this research. Typically, the fuel mixture lower flammability limit almost keeps constant at different contents of added nitrogen. The fuel mixture upper flammability limit approximately linearly varies with the added nitrogen except mixtures containing ethylene. The minimum added nitrogen concentration at which lower flammability limit and upper flammability limit merge together is the minimum inerting concentration for nitrogen, roughly falling into the range of 45 plus/minus 10 vol % for all the tested hydrocarbon mixtures. Numerical analysis of inert gas dilution effect on lower flammability limit and upper flammability limit was conducted by introducing the parameter of inert gas dilution coefficient. Fuel mixture flammability limit can be quantitatively characterized using inert gas dilution coefficient plus the original Le Chatelier's law or modified Le Chatelier's law. An extended application of calculated adiabatic flame temperature modeling was proposed to predict fuel mixture flammability limits at different inert gas loading. The modeling lower flammability limit results can represent experimental data well except the flammability nose zone close to minimum inerting concentration. Le Chatelier's law is a well-recognized mixing rule for fuel mixture flammability limit estimation. Its application, unfortunately, is limited to lower flammability limit for accurate purpose. Here, firstly a detailed derivation was conducted on lower flammability limit to shed a light on the inherent principle residing in this rule, and then its application was evaluated at non-ambient conditions, as well as fuel mixture diluted with inert gases and varied oxygen concentrations. Results showed that this law can be extended to all these conditions.

This thesis investigates the laminar flame speed of C₁-C₃ alkanes and their binary mixtures at conditions of interest in natural gas based gas turbines viz. high temperature, pressure and dilution. Laminar flame speed has been found useful not only for validating chemical kinetics mechanisms but also for developing empirical scaling laws for practical combustion systems. The thesis addresses the lack of laminar flame speed data of C₁-C₃ alkanes at preheat (300-650 K), pressure (1-10 atm) and significant oxidizer dilution (15-21 vol% O₂). Over 400 measurements are reported over a wide range of conditions along with comparison to predictions from leading chemical mechanisms. Unstretched flame speed measurements were performed using a modified Bunsen flame technique based on reaction zone area from chemiluminescence imaging, whereas the strain sensitivity measurements were performed using a bluff-body stabilized stagnation flame with high resolution PIV. These measurements are used to: (i) discern the uncertainties associated with the measurements, (ii) understand the effect of fuel mixture and vitiation on flame speed, and (iii) validate the performance of the leading chemical kinetics mechanisms. Extensive testing shows the unstretched flame speed measurements from the modified Bunsen technique are reasonably accurate. Vitiation studies for methane and propane flames at high preheat show the reduction in flame speed results primarily from the thermal effect of the diluent and that the relative change in flame speed from the undiluted mixture is well correlated to the fractional change in the adiabatic flame temperature over a range of conditions. Significant difference in the measured and predicted flame speeds were observed for rich, atmospheric pressure, propane and lean, high pressure, methane/ethane mixtures with dilution. This highlights possible avenues for improvements in the chemical kinetics mechanisms. Systematic errors were also identified in the Bunsen flame measurements at certain conditions, such as for rich flames with dilution, indicating a need for better understanding of the Bunsen flame technique at these conditions. The difference in the measured and predicted flame speed does not show any clear correlation with the flame height or the strain sensitivity of the mixture. Finally previously proposed mixing rules for estimating flame speed of fuel mixtures from pure fuel components are shown to be reasonably accurate over a range of pressure, reactant temperature and dilution conditions.