College of Engineering and Technology

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    Ethanol - Activated Carbon Solar Refrigeration
    (University of Reading, 1986-08) Kimambo, C. Z. M.
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    Development of Insulators in Tanzania
    (ANSTI EE, 1987) Mwinyiwiwa, Bakari M. M.; Kadete, H.
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    Bubble Size and Gas-Liquid Interfacial Area Measurements Using Molten Paraffin Waxes in Bubble Columns
    (American Institute of Chemical Engineers, 1987) Bukur, Dragomir B.; Patel, Snehal A.; Daly, James G.; Raphael, Matheo L.
    Experiments were conducted in 0.05 m ID and 0.23 m ID by 3 m tall bubble columns with different types of molten waxes as the liquid medium and nitrogen as the gas, under processing conditions typical or Fischer-Tropsch synthesis over iron catalysts (i.e. gas velocities up to 0.15 m s, and temperatures between 200 and 270/sup 0/C) to estimate gas liquid interfacial area from measured values of average gas hold-up and Sauter mean bubble diameter. The gas hold-up was estimated from visual observations of the expanded and static liquid heights, and the Sauter was estimated from bubble size measurements obtained by photography and dynamic gas disengagement. The paraffin wax (FT-300) used in the authors' studies is non-coalescing and has a tendency to foam. The amount of foam is greater for runs conducted in the order of increasing gas velocities, than in runs with decreasing velocities. Thus, two values of hold-up are possible and the start-up procedure determines which one will be attained. At higher gas velocities (> 0.05 m/s) the foam disappears and a transition to the slug flow, churn-turbulent regime takes place. Reactor waxes are coalescing in nature and do not produce foam. Despite similar hold-ups for the different waxes at higher gas velocities, the Sauters are significantly different and this is reflected in the specific gas-liquid interfacial areas, with larger values obtained with the paraffin wax compared to values with reactor waxes.
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    Hydrodynamics of Fischer-Tropsch Synthesis in Slurry Bubble Column Reactors
    (1987) Bukur, Dragomir B.; Daly, James G.; Patel, Snehal A.; Raphael, Matheo L.; Tatterson, Garry B.
    An improved photographic technique was employed to obtain pictures, for bubble size analysis, in experiments conducted in the Unit AMk2G (511 cm ID, 305 cm tall glass column)] During these experiments measurements of the average gas hold-up were made at 200 and 265oc using FTk300 paraffin wax as the liquid medium and nitrogen as the gas. Additional experiments were performed adding oxygenates, stearyl alcohol and stearic acid, (5 - 10 % by weight) to the wax at a temperature of 265°C. The addition of oxygenates did not have a significant effect on the average gas hold'up.
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    Construction and Test of a Delta Modulated Buck Type 3 Phase Converter
    (McGill University, 1989) Mwinyiwiwa, Bakari M. M.
    A Delta Modulated, Buck Type, Three Phase PWM Converter was constructed and tested. The converter is of the current source type and can be used in conjunction with current source inverters. The d.c. current is regulated by proportional feedback control loop. By delta modulation of the voltages across the a.c. terminaIs of the converter, the a.c. source currents are "indirectly" controlled so that the fundamental components remain in a predefined phase with respect to the source voltages. Test results have shown that the converter draws near sinusoidal a.c. currents at unit y power factor, with leading power factor a possibility.
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    Effect of Pond Depth on Bacterial Mortality Rate
    (American Society of Civil Engineers, 1989) Mayo, Aloyce W.
    The bactericidal action of solar radiation was investigated in pilot scale waste stabilization ponds under the tropical climate of Dar es Salaam, Tanzania. Bacterial reduction was observed to proceed with increasing direct solar intensity and hydraulic detention time. The mortality rate of faecal coliforms used as test micro-organisms was higher in samples incubated near the surface and decreased rapidly when the samples were incubated at greater depths in the pond. The disappearance rate of faecal coliforms for samples incubated at the pond surface and at a depth of 1.0 m was 1.66 d-1 and 0.37 d-1 respectively. Faecal coliforms were also found to be reduced rapidly in shallow ponds. The mortality rate in 1.0 m and 1.5 m deep ponds was respectively 0.43 and 0.32 d-1. The dieoff rate constant was observed to vary significantly with pond depth but was independent of hydraulic detention time.
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    Evaluation of Recycled Asphalt Pavements in Cold Climates
    (Civil Engineering, University of Calgary, 1990) Mushule, Nurdin K.
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    Modelling of a Three Phase BUPC for Stability Analysis
    (Uhandisi Journal, 1990-12) Mwinyiwiwa, Bakari M. M.; Kadete, H.
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    Effect of H-Mordenite Zeolite as a Component in Co-Mo-Al2O3 Hydroprocessing Catalysts Used for the Conversion of Boscan Heavy Oil
    (Elsevier, 1991) Minja, Rwaichi J. A.; Ternan, Marten
    The effect of H-mordenite zeolite as a component in Co-Mo-Al2O3 hydroprocessing catalysts has been studied. Catalysts containing up to 20% H-mordenite were used for hydrocracking Boscan heavy oil at 13.9 MPa. Although the acidic sites on the external surface of the zeolite crystals were expected to increase cracking reactions, little effect on conversion was observed. As the H-mordenite content of the catalyst increased, the bulk density and the specific surface area of the catalysts decreased substantially. When the reaction results were expressed on the basis of constant residence time and constant catalyst surface area there was an increase in the reaction parameter with increasing H-mordenite content of the catalyst. It was also found that coke deposition increased with the increasing H-mordenite content of the catalyst. These two observations suggest that H-mordenite caused an increase in the number of acidic sites in the catalyst. The results indicate that catalysts with H-mordenite would produce greater conversions than catalysts without H-mordenite, if the extrudates could be prepared in such a way that the catalyst bulk density does not change when the H-mordenite is added.
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    Operating Limits of the Current Regulated Delta Modulated Current Source PWM Rectifier
    (IEEE Transactions on Industrial Electronics, 1991) Ooi, B. T.; Mwinyiwiwa, Bakari M. M.; Wang, X.; Joos, G.
    A stand alone, three-phase, delta-modulated, current-source PWM rectifier has been built and has been shown to be capable of operating with near sinusoidal current waveforms, unity power factor. and good DC current regulation. A mathematical model that has been justified against experimental measurements and results from digital simulations is presented. The current waveform distortion limit and the asymptotic stability limit are established. It is shown that the rectifier can operate safely within these limits in the entire range of its power ratings
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    Rainwater Harvesting For Domestic Use in Tanzania a Case Study: University of Dar Es Salaam Staff Houses
    (Taylor and Francis, 1991) Mayo, Aloyce W.; Mashauri, Damas A.
    The bacteriological, chemical and physical analyses of water samples from rainwater cistern system at the University of Dar es Salaam in Tanzania were carried out between October 1988 and December 1989. Faecal coliforms, total coliforms and faecal streptococci were enumerated. The results shows that 86% of the samples were free from faecal coliforms. However, faecal streptococci were obtained in 53% of the samples and 45% of the samples tested for total coliforms were positive. The physical quality of water was found to be appealing during the whole study period with turbidity less than 5 NTU and colour less than 5 mg Pt/l. However, about 54% of the consumers raised objections over the taste of water.
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    Hydrocracking Boscan Heavy Oil with a Cobalt-Molybdenum/Alumina Catalyst Containing an H-Mordenite Zeolite Component
    (1991) Minja, Rwaichi J. A.; Ternan, Marten
    Co-Mo/Al2O3 catalysts for hydrocracking heavy oil and residue were modified by adding up to 20 wt % hydrogen-mordenite zeolite. The acidic sites on the external surface of the mordenite crystals were expected to increase cracking reactions. In fact, there was a slight decrease in the +525-degrees-C resid conversion, although vanadium and nickel hydrodemetallization increased as the mordenite content of the catalyst increased. On the other hand, the pseudo turnover frequency for metals removal, i.e, the number of reactions per second per reaction site (or in this case per (nm)2), was greater for catalysts containing greater amounts of mordenite. The catalyst performance was attributed to a combination of two factors. First, both the catalyst bulk density (grams of catalyst per milliliter of reactor volume) and the catalyst specific surface area (m2/g) in pores larger than 3 nm decreased as the mordenite content increased. Hence, a smaller quantity of catalyst could be placed into the reactor and the catalyst that was in the reactor had less surface area per unit mass. Clearly the mordenite changed the structure of the alumina support, which resulted in a net decrease in the effective catalyst surface area. Second, the catalyst acidity, as measured by temperature-programmed desorption of benzofuran, increased as the mordenite component of the catalyst increased. It was concluded that the improved overall hydrodemetallization was caused by both the increased number of acidic sites of the exterior surfaces of the mordenite and the changes in catalyst pore geometry, which improved the rate of diffusion to the catalyst surface.
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    On the Switching Behaviour of a Single Phase CS PWM Converter
    (Uhandisi Journal, 1991) Mwinyiwiwa, Bakari M. M.
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    Behaviour of Recycled Asphalt Pavements at Low Temperatures
    (NRC Research Press, 1991) Sargious, M.; Mushule, Nurdin K.
    This paper summarizes the results of a study conducted to evaluate the behaviour of recycled asphalt pavements with respect to low-temperature cracking. For this purpose, a recycled mix consisting of 45.2% reclaimed materials and 54.8% virgin materials as well as a virgin control mix were used in the research program. In the design of both mixes, their initial properties were kept as close as possible to each other to allow for a proper comparison between recycled and virgin asphalt pavements. Using mix properties that were determined experimentally in the laboratory, thermal stresses resulted from drop in temperature and the expected cracking temperatures were determined for both mixes. An experimental analysis based on laboratory tests that consider the pavement properties only as well as a more complete theoretical analysis based on a finite element computer program known as FETAB were included in this study. The program incorporates subgrade parameters, as well as pavement properties and thickness. Using these variables as inputs to the program, the expected performance of recycled and virgin asphalt pavements of various thicknesses and resting on different types of subgrade, with respect to low-temperature cracking, was studied. The results of the study indicated that recycled asphalt pavements would perform better than virgin asphalt pavements of similar initial properties. Key words: asphalt, finite element, low-temperature cracking, reclaimed, recycled, thermal stresses.
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    System Identification of Linear Vibrating Structures
    (1991) Nalitolela, Noel Gerald
    Methods of dynamic modelling and analysis of structures, for example the finite element method, are well developed. However, it is generally agreed that accurate modelling of complex structures is difficult and for critical applications it is necessary to validate or update the theoretical models using data measured from actual structures. The techniques of identifying the parameters of linear dynamic models using Vibration test data have attracted considerable interest recently. However, no method has received a general acceptance due to a number of difficulties. These difficulties are mainly due to (i) Incomplete number of Vibration modes that can be excited and measured, (ii) Incomplete number of coordinates that can be measured, (iii) Inaccuracy in the experimental data (iv) Inaccuracy in the model structure. This thesis reports on a new approach to update the parameters of a finite element model as well as a lumped parameter model with a diagonal mass matrix. The structure and its theoretical model are equally perturbed by adding mass or stiffness and the incomplete number of eigen-data is measured. The parameters are then identified by an iterative updating of the initial estimates, by sensitivity analysis, using eigenvalues or both eigenvalues and eigenvectors of the structure before and after perturbation. It is shown that with a suitable choice of the perturbing coordinates exact parameters can be identified if the data and the model structure are exact. The theoretical basis of the technique is presented. To cope with measurement errors and possible inaccuracies in the model structure, a well known Bayesian approach is used to minimize the least squares difference between the updated and the initial parameters. The eigen-data of the structure with added mass or stiffness is also determined using the frequency response data of the unmodified structure by a structural modification technique. Thus, mass or stiffness do not have to be added physically. The mass-stiffness addition technique is demonstrated by simulation examples and Laboratory experiments on beams and an H-frame.
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    DC Drive System Using Delta Modulated CS Delta Modulated PWM Converter
    (ANSTI EE, 1991-11) Mwinyiwiwa, Bakari M. M.
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    The Running and Gating of Light Alloys
    (1992) Runyoro, Joseph J.; Campbell, J.