The large scale and smaller production scale motions contain over the half of turbulent kinetic energy in the flow. These motions are responsible for sediment transport and deposition processes, contaminant mixing and stream bio-diversity. These motions are corresponded to the left and right bounds of -1 power region of the spectral energy. The most well recognized and highly studied power law has been upon Kolmogorov’s -5/3 power law region of the streamwise spectral energy density and this research focused on investigating the -1 power region bounds and energy. Energy budget and time-average turbulence calculations along with spectral analysis are performed to investigate the characteristics of large scale and smaller production scale motions in the flow. Spectral analyses of turbulent flows offers the utility of investigating the distribution of turbulent energy across wavenumber scales as well as identifying prominent wavenumbers at which the periodicity of coherent processes are centered. In turn, the results of spectral analyses can be coupled with visualization of coherent vortices and time-average turbulence results to advance our understanding of turbulent energy distribution and dominant processes that drive environmental phenomena such as sediment transport and solute transfer. A new method for identifying the wavenumbers associated to the macroturbulence and bursting is introduced. Also this study offers a new scaling method of energy spectral that derived from the turbulence energy model for an equilibrium boundary layer. Results of this study show an equilibrium boundary layer for the outer region of the flow in which the flow is uniform and fully-developed. Also for a given roughness, the results of this study provide an approach to calculate the streamwise turbulence kinetic energy of bursting and macroturbulence which show a linkage of this work to applications such as bedload and suspended load sediment transport.

Part I: A remarkable feature of life on Earth is that despite the apparent observed diversity, the underlying chemistry that powers it is highly conserved. From the level of the nucleobases, through the amino acids and proteins they encode, to the metabolic pathways of chemical reactions catalyzed by these proteins, biology often utilizes identical solutions in vastly disparate organisms. This universality is intriguing as it raises the question of whether these recurring features exist because they represent some truly optimal solution to a given problem in biology, or whether they simply exist by chance, having arisen very early in life's history. In this project we consider the universality of metabolism { the set of chemical reactions providing the energy and building blocks for cells to grow and divide. We develop an algorithm to construct the complete network of all possible biochemically feasible compounds and reactions, including many that could have been utilized by life but never were. Using this network we investigate the most highly conserved piece of metabolism in all of biology, the trunk pathway of glycolysis. We design a method which allows a comparison between the large number of alternatives to this pathway and which takes into account both thermodynamic and biophysical constraints, finding evidence that the existing version of this pathway produces optimal metabolic fluxes under physiologically relevant intracellular conditions. We then extend our method to include an evolutionary simulation so as to more fully explore the biochemical space. Part II: Studies of population dynamics have a long history and have been used to understand the properties of complex networks of ecological interactions, extinction events, biological diversity and the transmission of infectious disease. One aspect of these models that is known to be of great importance, but one which nonetheless is often neglected, is spatial structure. Various classes of models have been proposed with each allowing different insights into the role space plays. Here we use a lattice-based approach. Motivated by gene transfer and parasite dynamics, we extend the well-studied contact process of statistical physics to include multiple levels. Doing so generates a simple model which captures in a general way the most important features of such biological systems: spatial structure and the inclusion of both vertical as well as horizontal transmission. We show that spatial structure can produce a qualitatively new effect: a coupling between the dynamics of the infection and of the underlying host population, even when the infection does not affect the fitness of the host. Extending the model to an arbitrary number of levels, we find a transition between regimes where both a finite and infinite number of parasite levels are sustainable, and conjecture that this transition is related to the roughening transition of related surface growth models.

The fascinating field of molecular capsules has recently begun to see the creation of structures that, medicated by the encapsulation of guest molecules within their central cavity, are able to change the properties or reactivity of the substrate. The current capsule designs are however, prone to exchange of either part or whole ligands. This exchange or the capsule's subsequent disassembly can lead to loss of the cavity or modification of their external properties, and is a barrier to their more widespread application, a problem this work seeks to address by creating more a robust capsule structure. This thesis presents the design, synthesis and properties displayed by three novel capsules. All the species presented share a similar supramolecular tetrahedral structure, but their properties deviate significantly, showing either switchable behaviour, spin-crossover or a novel synthetic route to a kinetically inert structure. Improvements in the design have led to a final capsule that is water-soluble, robust, non-toxic and has been shown to encapsulate a range of guests. Chapter 1 includes an overview of the types of capsule constructed in literature and their possible application. The fundamental properties of these capsules are identified, with emphasis given to a discussion of mechanisms underlying their encapsulation phenomena. Chapter 2 describes efforts to construct a tetrahedral capsule based on iron(II) and an oxime ligand. While the use of an oxime motif achieved the aim of preventing exchange of the external groups, the capsule also displayed the surprising property of possessing a solvent responsive assembly-disassembly process. This potentially provides a basis for 'on-demand' encapsulation by being able to choose when to have hydrophobic cavity available for guests. Chapter 3 details the synthesis of a tetrahedral capsule containing iron (II) coordinated by a pyridyl-triazole bonding motif. the spin-crossover properties of the complex were initially demonstrated in the solid state, however, when in solution the capsule displayed the unusual ability of spin-crossover mediated structural rearrangement. Chapter 4 demonstrates the synthesis of a robust capsule. The synthetic route shown alleviates the problems surrounding the construction of inert species in a self-assembly process. Based around a cobalt (III) cation, the stability of the capsule to carious conditions is examined and its host-guest chemistry is explored, revealing some insights into the encapsulation behaviour of this structure.

No description available.

published_or_final_version / Economics and Finance / Master / Master of Economics

The South African based petrochemical company, SASOL, operates three large plants for the recovery and purification of the chemical 1-hexene. The thermodynamic models available in commercial simulation packages fail to predict or correlate the plant data presently observed by SASOL. The focus of this project is the accruement of comprehensive and accurate modelling parameters that would assist SASOL in optimizing the operation of the three plants and meet their purity specifications. The experimental requirements of the project are the measurement of isothermal vapour-liquid equilibrium (VLE) data for selected binary systems, using a dynamic still. The binary systems investigated were 1-hexene + n-methylpyrrolidone (NMP) at 40, 62 and 90 °C, water + NMP at 70, 90 and 107 °C and 1-hexene + 3methylcyclopentene (3MCP) at 40, 50 and 60 °C. With respect to the modelling of the VLE data, the combined (gamma-phi) and direct (phi-phi) regression procedures were utilized. The results of the analysis show the combined method as the more flexible of the two, when used for low pressure systems. The excess Gibbs energy correlations investigated were the Margules, Van Laar, Wilson, NRTL and UNIQUAC. The NRTL and Van Laar models dominated the modelling results across the range of temperatures for each binary system and for both the direct and combined methods of data regression. The experimental data for the systems of water (1) + NMP (2) at 107 °C and at 70 °C were compared to literature data. The first system showed excellent correlation with the literature results while the second plot at 70 °C showed a positive bias of the experimental data between xj of 0.3 and 0.8. Thermodynamic consistency tests for the VLE data are also required to verify the accuracy of the data. For this project, the point and direct (Van Ness) consistency tests were used as the area test was considered as too mild. All systems passed the point and direct tests for the combined method and therefore verify the thermodynamic consistency of the experimental data. The systems failed in most cases for the direct method as the combined method is the more flexible of the two modelling methods. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

VLE data is essential for the design and optimisation of industrial separation processes. Carboxylic acids are of significant interest because of their importance in both industrial and biological processes. Carboxylic acids are used as raw materials for a wide range of products, which include soaps , detergents, nylon , biodegradable plastics, medical drugs and food additives, They are also used both as solvents and as additives and co solvents under a wide range of conditions. Carboxylic acids exhibit strong self and cross -association through hydrogen bonds in both liquid and vapour phases. A thorough understanding of how these molecules interact both with themselves and with other solvents becomes necessary if existing processes may be optimised and new processes developed. Vapour-liquid equilibrium (VLE) data were measured for carboxylic acid systems ranging from C3 to C6• New vapour-liquid equilibrium data were measured for the following binary carboxylic acid systems: • Propionic acid + Hexanoic acid at 20 kPa, 403.15 K, 408.15 K and 413.15 K. • Isobutyric acid + Hexanoic acids at 20 kPa, 413.15 K and 423.15 K. • Valerie acid + Hexanoic acid at 15 kPa, 423 .15 K and 433.15 K. • Hexanoic acid + Heptanoic acid at 10 kPa and 443.15 K. A highly refined dynamic VLE Still by Raal (Raal and Muhlbauer [1998]) was used to undertake the VLE measurements. The still was operated either isothermally or isobarically using a computer control scheme. The isobaric and isothermal control was measured to be ±0.03 kPa and ±0.02 K respectively. The experimental procedure was verified with the highly volatile cyclohexane (l) + ethanol (2) system. The cyclohexane (l) + ethanol (2) measured VLE data was found to be in good agreement with that of Joseph (2001) and passed both the direct test and point test for thermodynamic consistency. A high degree of confidence was then placed on the equipment set-up and experimental procedure, as well as the new carboxylic acids VLE data . The VLE data for all the systems measured were modelled. Two data reduction methods were used: I. The combined ( r- ¢ ) method u. The direct method (¢ - ¢ ) method. In the combined method, the vapour phase non-idea lity was corrected using the Pitzer-Curl (1957) correlation and the Hayden and O' Connell (1975) chemical theory approach. Three liquid phase activity coefficient models were used namely the Wilson, NRTL, and UNIQUAC equations. The Peng-Robinson equation of state (Peng and Robinson [1976]) in combination with the Twu and Coon mixin g rule was used in the direct method. Thermodynamic consistency tests were done on all the systems measured. The point test (Van Ness et a!. [1973]) and the direct test Van Ness ([ 1995]) were used for consistency tests . The direct test could not be carried out on the carboxylic acids data because of the model's inability to adequately characterise the experimental activity coefficients. Generally the models fitted the data well but failed to accurately predict the "S" shape of the carboxylic acids phase diagrams. Considerable work still exists for further investigation into carboxylic acids. Currently, many experimentalists are working in this area . Penget a!. (2004) present ed their progress on developing an equation of state incorporating chemical theory to specifically handle carboxylic acids at the ICCT conference in Beijing, 2004. Raal and Clifford (University of Kwa-Zulu Natal, Thermodynamics Research Unit) are currently developing activity coefficient models incorporating chemical theory for a binary mixture of carboxylic acids. This work is part of the continuing research to under stand the phase behaviour of carboxylic acids. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.

The dynamic still originally designed by Raal (Raal and Muhlbauer [1998]) has been transformed into a valuable still that can now be used for measuring both low pressure vapour-liquid equilibria (VLE) for systems that are completely miscible and vapour-liquid-liquid equilibria (VLLE) for systems that are partially miscible. The resultant equilibrium data are important in the design and analysis of distillation and allied separation process equipment, with VLLE data, in particular, being useful in the design of heterogeneous azeotropic distillation columns. The original Raal still was based on the designs of Heertjies [1960] and Yerazunis [1964], who successfully used a packed equilibrium chamber where the liquid and vapour phases are forced downward co-currently to achieve rapid and dynamic equilibrium (Joseph et al [2001]). Direct analysis of the vapour composition prior to condensation through a new heated valving system with superheated sample conveyance to a gas chromatograph, a modification incorporated into the Raal still, ensured that accurate and reproducible equilibrium data were obtained. This new arrangement dispenses with the impossible task of getting the actual vapour composition that would result were the vapours allowed to condense and form two liquid phases. The initial testing of the still which established the operating procedures was conducted on two previously measured systems - the first which was homogeneous and the second heterogeneous. For the homogeneous system the new vapour sampling system was tested by comparing the measured composition to that of a condensed sample sent manually to the GC using a gas-tight syringe. In order to completely describe the VLLE for the systems studied, the liquid-liquid equilibrium (LLE) data for these systems were also measured. The LLE measurements were conducted in a newly-developed small jacketed glass cell with temperatures maintained constant by circulating water from a bath maintained at the desired temperatures. The main focus of this project was thus the development of an apparatus and procedures for measuring low pressure vapour-liquid-liquid equilibria. The project also went on to measuring and modeling VLE, VLLE and LLE data for selected binary and ternary systems. Both the Gamma-Phi and the Phi-Phi methods of VLE analysis were carried out on the measured data. The NRTL, Wilson, TK-Wi1son and UNIQUAC activity coefficient models were used in the Gamma- Phi method together with the Virial equation of state for vapour phase non-idealities. In the Phi-Phi method, The Peng and Robinson Equation of State (EOS), the Soave Redlich-Kwong EOS and the Stryjek and Vera modified Peng and Robinson EOS were all used, first with the classical mixing rules and then with the theoretically correct Wong and Sandler [1992] mixing rules. Ternary LLE binodal curves were correlated to the Hlavaty correlation, the beta function and the log gamma function while the corresponding tie-lines were fitted to the NRTL model. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

The focus of this study was to determine the coexistence phase equilibria for three groups of long-chain linear hydrocarbons (n-alkanes, 1-alkenes and 1-alcohols) using Monte Carlo simulation. Three common transferable united-atom force fields were used in the simulations: OPLS-UA (Jorgensen et al., 1984), TraPPE-UA (Martin and Siepmann, 1998) and NERD (Nath, Escobedo, de Pablo and Patramai, 1998). Isothermal phase equilibria was calculated over a temperature range from approximately the normal boiling point up to just below the critical temperature. The liquid and vapour densities and vapour pressures were determined from the simulations. The density results were then fitted using least-squares regression to the scaling law and the law of rectilinear diameters in order to estimate the critical properties. The vapour pressure data were fitted using least-squares to the Clausius-Clapeyron equation to estimate the normal boiling points. The NVT-Gibbs ensemble method was used to simulate the pure-component coexistence of the vapour and liquid phases. The NPT-Gibbs ensemble was used to simulate the n-alkane binary mixtures. Two forms of configurational-bias Monte Carlo (standard CBMC and coupled-decoupled CBMC) were used to increase the number of swap moves accepted during the simulations. Dual-cutoff CBMC was implemented with a second cut-off of sA in order to speed up the CBMC calculations. Minimum image and a spherical potential truncation after 14A were implemented with standard tail corrections. BICMAC and TOWHEE were the two Fortran-77 codes used to simulate the hydrocarbon compounds. BICMAC was used in the simulations of non-polar molecules and TOWHEE was used in the simulations of polar molecules. System sizes ranged from 300 (for the CB'S) down to 100 molecules (for the Czo's). The simulations were typically equilibrated for at least 30000 cycles and production runs ranged from 50000 to 120000 cycles for the different hydrocarbon groups. Standard deviations of the calculated thermophysical properties were between 1-3% for the liquid densities and 10-20% for the vapour densities and vapour pressures. It was found that the coexistence density curves were generally in good agreement with experiment for all the hydrocarbon groups investigated (the OPL5-UA force field being the exception). The chain-length appeared to have littl e effect on the quality of the calculated thermophysical properties. The chain-length did however increase the time required to perform the simulations substantially. The va pour pressures were consistently over-predicted by NERD and TraPPE-UA. The normal boiling pOints were typically under-predicted by 2-5%. The critical tempe ratures and densities were predicted to within 1-5% of experimental values. The n-alkane mixtures were satisfactorily predicted using the NPT-Gibbs ensemble. While both the NERD and TraPPE-UA force fields were shown to be substantially more accurate compared to the OPLS-UA force field, there was little difference between their predictions. Thus, it is likely that the added complexity of using the bond-stretching potential (used by NERD) is unnecessary. The results of this study show that Monte Carlo simulation may be used to predict vapour-liquid coexistence properties of long-chain hydrocarbons and to approximate critical properties. However, current force fields require more refinement in ord er to accurately predict the hydrocarbon thermophysical properties. Plus, faster computing speeds are required before Monte Carlo simulation becomes an industrially viable method. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

The thermodynamic knowledge of accurate phase equilibrium data plays an important role in the design and optimization of separation processes in chemical and engineering industries. Vapour-liquid equilibrium data are essential for the design of efficient separation processes such as distillation. The presented research study is mainly focused on the vapour-liquid equilibrium data measurement of fluorochemical and hydrocarbon binary systems at various temperatures and at high pressures. A new static analytical apparatus was constructed and commissioned for the measurement of accurate and precise vapour-liquid equilibrium data at temperatures and absolute pressures ranging from low temperatures to 323.15 K and 0 to 10 MPa respectively. The new apparatus incorporates the ROLSI TM sampler, a sampling technique developed by the CEP/TEP laboratory in Fontainebleau, France. Isothermal high pressure VLE data were measured for three binary systems comprising of hexafluoroethane (R116) + propane, HFPO + propane and ethane + octafluoropropane (R218). The R116 + propane system at 263.15 K was measured as a test system using the new static apparatus. These measurements helped to confirm the functioning of the experimental apparatus. The reliability and the reproducibility of the experimental procedure were also checked. The data obtained were in excellent agreement with data in the literature. Thereafter, measurements of previously unmeasured systems were undertaken. Isothermal vapour-liquid equilibrium data measurements for the ethane + octafluoropropane system were performed at five isotherms with temperatures and pressures ranging from 264.05 to 308.04 K and 0.298 to 4.600 MPa respectively. The five isotherms constitute new experimental data. The HFPO + propane system was also investigated and vapour-liquid equilibrium data were measured at three isotherms (283.05, 303.05 and 323.05 K) with pressures ranging from 0.437 to 2.000 MPa. The data measured also constitute a set of a new HPVLE data. The uncertainties in the measurement for both systems were within ± 0.09 K, ± 0.0016 MPa and less than 2% for temperatures, pressures and mole fractions, respectively. All experimental data were correlated via the direct method using the Peng-Robinson equation of state with the Mathias-Copeman alpha function and the Wong-Sandler mixing rules incorporating the NRTL activity coefficient model. The consistency of the measured VLE data was tested using the Van Ness point test which yielded few points of difference between the measured and calculated data, suggesting a low error rate. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.