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Item Multiscale characterization of oilwell cement cured under HPHT conditions(OnePetro, 2021) Qin, Jiankun; Pang, Xueyu; Zhang, Zhen; Fikeni, Kenedy GeofreyAs a complex composite material, the macroscopic mechanical property of oilwell cement is determined by its microscopic mechanical properties. During this study, the properties of oilwell cement specimens cured under high pressure and high temperature (HPHT) conditions were evaluated at both macro- and microscales. Short-term sonic strength analysis suggested that the HPHT strength retrogression occurred in the early stage. Specimens were cured at 200°C and 150MPa for different time periods of 14d, 30d, and 69d, to study the long-term mechanical property stability of silica-enriched oil well cement systems. Uniaxial compression tests were conducted on 25mm × 50 mm cylindrical specimens for macroscopic characterization of strength, modulus, and Poisson's ratio. Furthermore, microscopic testing was conducted using X-ray diffraction, mercury intrusion, and nano-indenter. Test results revealed that the damage during experiment may significantly influence the macroscopic properties of oilwell cement, but it had little effect on the microscopic level. On the micro-scale, the deterioration is characterized by increases in the proportion of a low-modulus and low-hardness phase. Additionally, the dependences of nanoindentation test results on testing parameters such as maximum load and appropriate grid size were also evaluated.Item Hydrogeochemical characteristics of shallow groundwater in volcanic rock aquifer systems in the western and northern flanks of Mount Meru, Tanzania(Ghent University, 2018) Bennett, George; Walraevens, Kristine; Van Reybrouck, Jill; Segers, Laura; Shemsanga, Ceven; Kisaka, Mary; Kervyn, Matthieu; Fontijn, Karen.No abstractItem Geogenic groundwater pollution in volcanic rock aquifer systems on the eastern, western and northern flanks of Mount Meru, Tanzania–special reference to fluoride(Vrije Universiteit Brussel, 2019) Bennett, George; Rombaut, Stefanie; Van Reybrouck, Jill; Shemsanga, Ceven; Kisaka, Mary; Tomašek, Ines; Fontijn, Karen; Kervyn, Matthieu; Walraevens, KristineNo abstractItem Consolidation of empirical methods for performance prediction of pump used as turbine. 4th international conference on mechanical and industrial engineering (MIE) conference, 1 - 2, 56-62. Arusha, Tanzania(The University of Dar es Salaam, 2016) Mdee, Ombeni, J.; Kihedu, Joseph, H.; Kimambo, Cuthbert, Z.; Nielsen, Tobjorn, K.This work part of a PhD Study Programme at the University of Dar es Salaam, Tanzania and Norwegian University of Science and Technology, Trondheim, Norway. This paper presents the consolidated of existing empirical methods used to predict the increased factor of head and flow rate when centrifugal pumps operated as water turbines. Performance characteristics of the thirty four (34) centrifugal pumps are collected from the existing in the local market of Tanzania with specific speed ranged from 13 to 71 (m, m3/s). Pump performance characteristics are converted to turbine characteristics based on the five head ratio and flow rate ratio empirical methods. Also, the study collects the empirical methods to estimate PAT efficiency. The Pump as Turbine (PAT) power varies significantly with pump horsepower. The study also validates the power estimated by using the head ratio, flow rate ratio and efficiency empirical methods with power prediction method. Furthermore, the study presents the comparison of the specific speed, power and efficiency in pump and turbine modes. The proposed methods of using empirical methods can be applied as the alternative solution and emphasizing to conduct experimental investigation of PAT for the specific hydropower site.Item Reversing centrifugal pumps as alternative to conventional turbines for micro hydropower: A review.(Power and Energy Systems (AfricaPES), 2018) Mdee, O. J.; Kihedu, J.; Kimambo, C. Z.; Nielsen, T. KThis paper presents the operation of centrifugal pumps as turbines for micro hydropower application. Block diagrams are used to present components required from intake chamber to hydropower plant and their electrical energy mechanism for micro hydropower system. A comparison of operational parameters of pump as turbine and conventional turbines is discussed. Also, the paper discusses three types of methods for selecting the centrifugal pump as turbine based on the head, flow rate, rotational speed and specific speed. Furthermore, the technique used to determine the flow rate characteristics are discussed as well as the technical guideline is tabulated to assist the application of centrifugal pump as turbine for micro hydropower scheme development.Item Transesterification reaction kinetics of jatropha oil for biodiesel production(2011) Okullo, A.; Temu, A. K.; Ntalikwa, J. W.Biodiesel, defined as the monoalkyl esters of vegetable oils and animal fats, is becoming prominent among alternatives to conventional petro-diesel due to economic, environmental and social factors. Transesterification is the most preferred method of biodiesel production. Knowledge of transesterification reaction kinetic enables prediction of the extent of the chemical reaction (or the conversion) at any time under particular conditions. It is also essential in the optimization of operating conditions in industrial applications and in the design of reactors for biodiesel production. In this study, transesterification of jatropha oil with methanol was carried out in a well mixed reactor at different agitation speeds (600-900 rpm) and temperatures (35-65 oC) using sodium hydroxide as a catalyst. The methanol to oil molar ratio of 6:1 was used and catalyst loading was 0.5% weight of oil. Mass transfer controlled state was assumed to be minimal using the above agitation speeds. A second order kinetic model was used to determine the reaction rate constants. The goodness of fit predicting the moles of methyl ester in the reaction products was determined by correlation coefficient (R2) and least square curve fit. The forward reactions were the most important as revealed by the rate constants.Item Methodological approach of performance evaluation for using pump as Micro Hydro-turbine(International Solar Energy Society, 2017) Mdee, O. J.; Kimambo, C. Z.; Nielsen, T. K.; Kihedu, J.The pumps work differently in terms of performance characteristics when operated in reverse mode to generate mechanical rotational energy driven by the water energy. The performance characteristics related to head, flow rate, specific speed and efficiency have been predicted differently from available conversion methods. Also, the procedure of selecting pump as hydro-turbine varies from different conversion methods. This article presents the methodological approach of evaluating the pump as hydro-turbine related to selection procedures, performance characteristics and challenges.