Browsing by Author "Nielsen, Torbjorn K."

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    Analysis of performance characteristics predicted from several experimental data and conversion methods for pumps as turbine application using statistical techniques
    (University of Dar es Salaam, 2020) Mdee, Ombeni J.; Kimambo, Cuthbert Z. M.; Nielsen, Torbjorn K.; Kihedu, Joseph
    Different performance characteristics have been indicated when running centrifugal pumps in the reverse direction. The water flows from the discharge side of the pump to the suction side to run in the reverse direction and generate the mechanical rotational energy for the micro-hydropower plant. The current study evaluates the extent of variation of performance characteristics predicted by several experimental data from different pump-specific speeds and conversion methods. The performance characteristics discussed include the head, flow rate, efficiency and specific speed. The flow rate and head of a pump operating in pump mode divided with the characteristic of the pump operating in the reverse mode, at the best efficiency point, the resulting coefficient of determination (R 2 ) values were of 0.890 and 0.708, respectively. Also, the graph of head versus flow rate coefficients, which is a second- order polynomial function, has shown the value of R 2 of 0.954 for pump-specific speed ranging between 9 and 94 rpm. However, the pump in the reverse mode has smaller performance characteristics for efficiency and specific speed compared to the pump mode operation with R 2 of 0.966 and 0.999, respectively. Furthermore, schematic empirical statistical models were developed to predict the performance characteristics of several conversion methods using pump data obtained from the manufacturers.
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    Analytical Evaluation of Head and Flow Rate Off-Design Characteristics for Pump as Turbine Application
    (The American Society of Mechanical Engineers, 2019) Mdee, Ombeni J.; Kimambo, Cuthbert Z.; Nielsen, Torbjorn K.; Kihedu, Joseph
    Head and flow rate are the important parameters for proper selection of centrifugal pump. However, the reversed operation of centrifugal pump leads to the off-design characteristic of head and flow rate. This paper presents an analytical model developed by using the system curves and velocity relations derived from pump application. Also, the differential technique is applied to the analytical model to develop the off-design characteristics of head ratio and flow rate ratio relations. The off-design characteristic relations were compared with literature and available conversion methods. Then, the analytical model coefficient (AMC) with the range between −4 and +4 was developed from the off-design characteristics of head ratio and flow rate ratio relations. The AMC value was equal to 1 when the pump operates in turbine mode and pump mode at the pump best efficiency point (BEP) and extended to either side up to ±4 when tested with literature data. Therefore, the analytical model consists of the off-design head and flow rate characteristics, when simplified leading to the AMC that could be applied to select the possible boundary limits of head and flow rate for different pumps.
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    Assessment of hydropower resources in Tanzania. A review article
    (EDP Sciences, 2018) Mdee, Ombeni J.; Nielsen, Torbjorn K.; Kimambo, Cuthbert Z.; Kihedu, Joseph
    The hydropower resources have become an attractive means of generating electricity to the off-grid network, especially in rural areas. This article assesses the small, mini and large hydropower resources and identified to reach 5.3GW for electricity generation in Tanzania. The technology development discussed comprises of hydro turbine manufacturers, classification and turbine selection. The barriers presented include the presence of sediment in the hydropower reservoirs, financial viability, policy and regulatory issues related to hydropower development. This reviewed article serves the investors and policymakers to understand the status of hydropower resources in Tanzania.
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    Measurement methods for hydropower resources: a review
    (E.W. Publications, 2018) Mdee, Ombeni J.; Kimambo, Cuthbert Z.; Nielsen, Torbjorn K.; Kihedu, Joseph
    Each hydropower plant is usually designed for specific amount of discharge and gross head. This paper presents the methods used to measure the discharge and gross head variables with additional of assessment tools. Discharge measurement methods covered include bucket, float, velocity-area, dilution, hydraulic structure and advanced discharge measurement while gross head measurement methods covered include topographic and DEM maps, hose level with pressure gauge, sight level, spirit level and advanced survey instruments. The assessment tools presented include SMART MINI-IDRO, Integrated Method for Power Analysis, VIPIDRO ASTE 4.0, Hydromatch, Hydrohelp and Renewable Energy Technology Screen tool. The assessment tools used to estimate the potential of hydropower resources in terms of energy, hydropower plant components and financial analysis. Therefore, this review paper indicated the possibility of conducting a pre-feasibility study of hydropower estimation by using the open access tools and accessible equipment in the carpentry and mason works, especially in the developing countries.
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    A technical evaluation of performance characteristics for pump as turbine application
    (Springer, 2019) Mdee, Ombeni J.; Kimambo, Cuthbert Z. M.; Nielsen, Torbjorn K.; Kihedu, Joseph
    It is very important to gain a better understanding of pump series of different specific speeds when running in reverse mode. The pump is running in reverse mode to serve as turbine for mechanical rotational energy generation in the hydropower and processing plants. This review chapter employs a technical analysis as a tool to evaluate pump when running in reverse mode by assessing the technological development gathered from the literature. The operational parameters discussed include head, flow rate, power, efficiency, and specific speed. The number of modified pump components includes the blade angle, impeller size and tips, edges of shroud and hub plates, volute casing attached with guide vanes, and modified inlet casing rings and eye enlargement. The internal characteristics also occurred in the form of swirl flow between blades and discharge part, time dependent on flow circulation, radial and axial thrust, blade angle variation, pressure pulsation, cavitation effects, and energy losses between blades, volute casing, and discharge part. Furthermore, the conversion methods discussed were related to pump efficiency, specific speed and constant values to predict the head and flow rate. The conversion methods are mostly used to select the off-the-shelf pumps to run as turbine. Therefore, this paper provides the technological development of running the pump in reverse mode that would give insights for further studies in the four knowledge areas that include operational parameter characteristic, pump component modification, internal flow characteristics at the full- and part-load conditions, and also the development of conversion methods related to pump geometry, fluid properties, performance and system curves to improve the off-the-shelf pump selection.