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Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Amy R. Betz / Boiling is a very effective way of heat transfer due to the latent heat of vaporization. Large amount of heat can be removed as bubbles form and leave the heated surface. Boiling heat transfer has lots of applications both in our daily lives and in the industry. The performance of boiling can be described with two important parameters, i.e. the heat transfer coefficient (HTC) and the critical heat flux (CHF). Enhancing the performance of boiling will greatly increase the efficiency of thermal systems, decrease the size of heat exchangers, and improve the safety of thermal facilities. Boiling heat transfer is an extremely complex process. After over a century of research, the mechanism for the HTC and CHF enhancement is still elusive. Previous research has demonstrated that fluid properties, system pressures, surface properties, and heater properties etc. have huge impact on the performance of boiling. Numerous methods, both active and passive, have been developed to enhance boiling heat transfer. In this work, the effect of pressure was investigated on a plain copper substrate from atmospheric pressure to 45 psig. Boiling heat transfer performance enhancement was then investigated on Teflon© coated copper surfaces, and graphene oxide coated copper surfaces under various system pressures. It was found that both HTC and CHF increases with the system pressure on all three types of surfaces. Enhancement of HTC on the Teflon© coated copper surface is contributed by the decrease in wettability. It is also hypothesized that the enhancement in both HTC and CHF on the graphene oxide coated surface is due to pinning from micro and nanostructures in the graphene oxide coating or non-homogeneous wettability. Condensation and freezing experiments were conducted on engineered surfaces in order to further characterize the pinning effect of non-homogeneous wettability and micro/nano structure of the surface.

Radar backscatter intensity data from the ERS-1 and ERS-2 scatterometers are compared with daily rainfall data in two areas in the Free State province of South Africa. Knowledge of the relation between daily rainfall data and ERS C-band scatterometer data for a specific area can be useful to make reliable soil moisture measurements. The assumption is made that an increase in rainfall will lead to higher radar backscatter data values. This is based on the fact that moisture increases the dielectric properties of surfaces. This leads to higher backscatter intensities when incident radar energy is reflected back to the sensor. Various techniques are used to study the relationship between daily rainfall data and ERS scattrerometer data. It includes correlations, interpolations, visual interpretations, statistical analysis, and a simple model. Weak positive correlations were found between radar and rainfall data in arid areas. This is supported by literature regarding the Sahel. No correlation was found in agricultural areas receiving more rainfall. Vegetation also increases radar backscatter intensities, even in the absence of rain. There is thus a relationship between rainfall and radar data but it is more visible in arid areas and over longer periods of time. / Dissertation (MA)--University of Pretoria, 2008. / Geography, Geoinformatics and Meteorology / MA / Unrestricted

A study of laminar free convection about horizontal plates of finite width with one side heated isothermally and the other insulated is presented in this thesis. This investigation forms part of a continuing program, and its technological origin and significance are discussed in the introduction. The governing partial differential equations comprising the continuity, momentum and energy equations are solved numerically through a finite difference method using a successive-over relaxation technique for a Rayleigh number range from 0.22 to 500, at three values of Prandtl number (0.72, 5.0 and 10.0). The variation of the flow, vorticity and temperature fields with the change of both Grashof and Prandtl numbers is discussed on the basis of the streamline, iso-vorticity and isothermal plots obtained . The effect of Prandtl number alone on the momentum field, energy distribution and heat transfer rate is discussed, by a comparison of the isotherms, streamlines and correlation curves obtained for the three different Prandtl numbers. The theoretical analysis places emphasis on the singular nature of the boundary conditions specified and on the influence of the finite size of the domain of the finite difference scheme. Some results for an upward facing horizontal isothermally heated plate of finite width were also obtained, and were compared to data for the downward facing case. A semi-focussing Schlieren colour system was used order to investigate experimentally the flow behaviour on a horizontal plate with the heated surface facing-downward The experimental results sought were evidence of the non-boundary layer nature of the flow. The evidence of non-boundary layer flow was obtained conclusively. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A one dimensional analysis of the boundary conditions of the electron energy eigenfunc-tion at a sharp interface between two crystals was made. An attempt to evaluate these conditions in terms of known band structure was made. It was concluded that this cannot be done in general. It was shown, however, that if the interface has the proper symmetry properties, the boundary conditions can be expressed in terms of only one unknown, energy-dependent parameter. It was concluded that setting this parameter equal to one gives boundary conditions which, though more general, are equivalent to the commonly used effective mass boundary conditions when they are applicable. It was concluded from numerical results for the transmission coefficient of the symmetric interface, that in general, these boundary conditions, which depend only on known band structure, do not give a good approximation to the exact answer. Since the energy dependence of the parameter mentioned above is described quite well qualitatively using the nearly free electron approximation or the tight-binding approximation, the applicability of any boundary conditions depending only on band structure can be predicted using these simple theories. The exact numerical results were calculated using the transfer matrix method. It was also concluded that the presence of symmetry in the interface either maximizes or minimizes the transmission coefficient. A tight-binding calculation showed that the transmission coefficient depends on an interface parameter which is independent of band structure. The transmission coefficient is maximized when this parameter is ignored. It was concluded that the effective mass equation is of little use when applied to this problem. Some transfer matrix results pertaining to the barrier and the superlattice were obtained. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Matrix assisted laser desorption/ionisation mass spectrometry (MALDI-MS) for small molecule analysis has been plagued with inherent problems associated with matrix interference. The matrix plays an important role in MALDI-MS where it has the ability to absorb UV energy from the laser employed and transfer it to the analyte, acts as a proton donor and protecting the analytes from being obliterated. For decades, research has been performed to eradicate matrix interference by matrix avoidance, finding alternative matrices, suppression through sample preparation methods and via chemical modification.In this investigation a number of the above mentioned approaches have been undertaken. First, a mesoporous silica powder, SBA-16, functionalised with a phenyl group to absorb UV from the MALDI-MS laser gave unfruitful results due to inhomogeneous dispersion of the SBA-16 powder. Therefore the same material was prepared but as a thin film and a homogeneously coated surface was generated with the phenyl group incorporated into the silica and this was compared with a conventional matrix, 2,5-dihydroxybenzoic acid (DHB). This was by far the most sensitive method which was accurate, with little background noise and importantly for small molecule analysis clear of matrix interference. Other surface systems were also tested such as graphene on copper and silver on copper, but the functionalised SBA-16 thin film remained the best. Graphite and 2B pencil were also investigated for MALDI-MS but were compared with conventional matrices (DHB and α-cyano-4-hydroxycinnamic acid (CHCA)) in a functional genomics study. The ability of all methods to find subtle phenotypic differences in various yeast strains was assessed with the help of multivariate data analysis (MVDA). Although DHB came out best, 2B pencil produce notably good separations that correlated nicely with the different genotypes. Therefore in addition to conventional matrices, 2B pencil should be considered for functional genomic studies when MALDI-MS is used as it is such a rapid and inexpensive method. Finally, chemical modifications were performed on amino acids where picolinic acid was used to attach a chromophore to the compounds, therefore, allowing UV absorption from the laser. Upon attaching the picolinate UV absorbing group, the amino acid compounds were detected LC-MS at an increased intensity of 10 to 100-fold. Moreover, enhanced separation in LC-MS was also observed.This project has successfully investigated alternative approaches to matrix-free MALDI-MS analysis. Functionalised SBA-16 thin films were by far the best method and this novel surface for MALDI-MS has the potential to transform small molecule analysis.

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Io, the most volcanically active body in the solar system, also has some of the tallest and steepest mountains. The mountains seem to be tectonic in origin, yet the methods of their formation have not been decisively constrained and their associations with volcanic paterae are yet unclear. We have compiled global spatial statistics on mountain dimensions and orientations, lineations attributed to structures, straight patera margins, and patera dimensions in order to better define their genetic relationships and the mechanisms forming each type of feature. Additionally, we have produced 4 regional structural maps of mountain complexes and have proposed tectonic histories. Global statistics show that paterae and mountains and their associated lineations are more common at low latitudes and that lineations attributed to tectonics have preferred azimuths of 45° and 135°, whereas straight patera margins and azimuths appear more random. Additionally, tectonic lineations tend to cluster to those of similar types and are smaller when closer together. Mountains in general on Io are isolated, varied in size and shape, and have no significant geographic patterns in those variations. These results may indicate that global-scale processes are involved in forming Io's tectonic structures, but that the diversity of mountain characteristics and the collapse of paterae adjacent to mountain complexes may be more regionally controlled. Mapping of the Hi'iaka, Shamshu, Tohil, and Zal regions has shown that Io's mountains reside in large, faulted-bounded crustal blocks, which have undergone modification through local responses of subsurface structures. Strike-slip motion along reactivated faults has led to the formation of both transpressional and transtensional features, creating tall peaks and low basins, some of which are now occupied by paterae. Subsurface structures play a large role in Io's mountain diversity. Based on interpretation of statistical results and on our localized mapping, we propose that Io's mountains result from a combination of crustal stresses involving both global and local-scale processes. Multiple faults and fractures in a variety of orientations formed in Io's lithosphere, created over billions of years by stresses imposed by volcanic loading and tidal flexing. These faults have been progressively buried over time under multiple layers of volcanic material. Stresses continuing from loading and tidal massaging sometimes occur at oblique angles to pre-existing faults, reactivating them as reverse, normal, or strike-slip faults. Because of this, large, cohesive fault-bounded blocks have undergone both transpressional and transtensional modification. Further degradation of mountains has also occurred from extensive mass wasting, gravitational collapse, and erosion by sublimation and sapping of sulfur-rich layers within the crust. This model of fault-bounded blocks being modified by continual stresses and local structural response accounts for the variation and patterns of mountain sizes, shapes, and orientations, along with their isolation and interactions with other features. It presents an explanation for the influence of global and regional tectonics and a more detailed account of the formation of some of Io's remarkable mountains.

In the past, tool life tests have been performed using a conventional Taylor testing technique. This methodology is expensive and time-consuming. It requires wearing a number of tools until the tool failure criterion has been reached. A number of short-term tests designed to replace the Taylor test have been proposed but they suffer from a number of drawbacks. Many of these tests are performed under non- standard cutting conditions or require special workpiece preparation or equipment. As a result, tool life models developed from these tests are of limited usefulness in predicting tool failure times for conventional machining operations. A methodology is required which combines the time and cost advantages of non-conventional tests with statistical validity and robustness. In this research, two short-term tests are presented which are based on the Taylor test. Response surface models are used to develop the parameters of Taylor's tool life equation. The tests are shortened by using regression equations of flank wear data to predict the tool failure time without wearing the tool to failure. The two methods, abbreviated conventional testing and sequential composite testing, are statistically validated and compared with the Hill Taylor test. The results show that these tests can accurately predict tool life and the resulting Taylor models are not significantly different from those estimated by conventional means. / Master of Engineering