Browsing by Author "Mdee, Ombeni John"

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    Improvement of performance prediction methods for selecting pump as turbine in micro hydropower systems
    (University of Dar es Salaam, 2019) Mdee, Ombeni John
    Even though pumprunning in a reverse direction as a turbine to generate mechanical rotational energy is a more than 50-year-old concept, the technology development is still growing and more pumps are being installed on the micro hydropower scales. This study assessed four technological developments, which included pump component modification, internal flow characteristics, control mechanism, and conversion methods. The constructed open-circuit test rig indicated the first pump of specific 57.7 rpmhas a head of 5.9 m and flow rate of 34.14 l/s with the maximum efficiency of 60%. The second pump of specific speed of 27.6 rpm indicated the performance characteristic ratios in turbine mode over pump mode in terms of head, flow rate and efficiency are 2.106, 1.448 and 0.941; respectively. Both the experimental result and literature data indicated the pump designed point is easier to change when running in turbine mode that makes the difficulties during off-the-shelf pump selection. However, the use of conversion methods to select the off-the-shelf pumps contains numerous inaccuracies and do not provide an acceptable prediction coefficient of head and flow rate. This study used the velocity relations of pump geometrical shape and site conditions related to head and flow rate to develop the Analytical Model Equation (AME). The improvement of performance prediction method was obtained by applying differential calculus technique to AME and it resulted inanalytical head ratio and flow rate ratio equations. The derivative results of AME indicated the coefficient of determination (R2) of greater than 0.9 when compared together conversion method sat the 95% confidence level. Also, the prediction coefficient equation was developed when combined with the derivative results of AME and tested with pumps of specific speed ranging from 9.08 to 94.4 rpm. The AME coefficient is equal to 1 when deduced from the minimum head ratio and flow rate ratio of one and extended between -4 and +4 as varying the head ratio and flow rate ratio. Therefore, the prediction coefficient equation would be used to define the acceptable prediction range of head and flow rate that has been predicted by conversion methods.
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    Regional mapping of non-prolific sediment source catchments for small hydropower development in Tanzania
    (University of Dar es Salaam, 2014) Mdee, Ombeni John
    Run-of-River schemes are the main Small Hydropower (SHP) developments in sediment-laden rivers in Tanzania. Investments in this sector are not guided by non-prolific sediment source catchment map. Development of such maps requires extensive sediment load measurements on a frequent time basis, hence costly and logistically demanding. The Pacific Southwest Inter-Agency Committee (PSIAC) approach is the main framework but considered inexpensive method, after being evaluated and validated is applied in this study under ArcGIS 9.3 software environment to map suitable zones in Tanzania for SHP development. The zones of non-prolific and prolific sediment source catchments were based on Suspended Sediment Concentration (SSC) data with a recommended threshold of 3 g/l for hydropower turbine sustainability. The SSC was spatially derived as the ratio of Specific Sediment Yield (SSY) to mean annual runoff data using a computational grid of 0.02 degree. Area for non-prolific sediment source catchments zone in Tanzania covered 58.6 % with the SSC of 0 g/l to 3 g/l and the coverage area of the prolific sediment source catchments zone was 41.4 % with SSC of 3 g/l to 24.7 g/l. It should be noted that the SSC data can be used to guide the selection of the SHP development. However, the author acknowledges that more data on dam sedimentation and sediment mineralogy would improve PSIAC model prediction performance and influence the choice of SSC threshold, respectively, hence better results.