Browsing by Author "Nielsen, T. K."

Now showing 1 - 7 of 7
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    Consolidation of Empirical Methods for Performance Prediction of Pump Used as Turbine
    (Department of Mechanical and Industrial Engineering, University of Dar es Salaam, 2016-09-01) Mdee, O. J.; Kihedu, J.; Kimambo, C. Z.; Nielsen, T. K.
    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.
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    Experimental Study on a Simplified Crossflow Turbine
    (www.IJEE.IEEFoundation.org, 2014) Kaunda, C. S.; Kimambo, C. Z. M.; Nielsen, T. K.
    The main aim of the study is to enhance the design of a Crossflow turbine, as an appropriate technology for small-scale power generation. This study evaluates the performance of a simplified Crossflow turbine at conditions other than the ‘best efficiency point’. It also explores the ‘reaction’ behavior of the Crossflow turbine as well as characterizes the torque transfer in the two stages of the turbine. The experiments were conducted on a physical simplified Crossflow turbine model using the test facilities in the Waterpower Laboratory at the Norwegian University of Science and Technology. The results show that the maximum turbine efficiency is 79%, achieved at a head of 5m and reduced speed of 13.4; making it a low speed turbine. This turbine efficiency compares well with some reported efficiency values. The result also show that the turbine is efficient when it operates with a degree of reaction and this is achieved at large valve openings; validating observations that the Crossflow turbine is not a pure impulse turbine. Performance evaluation outside the best efficiency point shows that the efficiency decreases with increase in head above the best efficiency head. The turbine efficiency is not sensitive to flow variations: except at a head of 3m, at all tested heads, 25% of the flow at best efficiency point still generates efficiency of above 50%. Torque characterization shows that the second stage plays a significant role in torque transfer, especially when at large valve openings. Therefore, design efforts must also look at how the flow inside the runner interior space can be controlled so that the jet enters the second stage with optimum flow angles. The use of strain gauge to characterize the torque produced using momentum principle as employed in this study presents an additional opportunity to analyze the trends in the torque transfer.
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    Microhydropower: A Comprehensive Technological Review
    (2013) Kaunda, C. S.; Kimambo, C. Z. M.; Nielsen, T. K.
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    A Numerical Investigation of Flow Profile and Performance of a Low Cost Crossflow Turbine
    (www.IJEE.IEEFoundation.org, 2014) Kaunda, C. S.; Kimambo, C. Z. M.; Nielsen, T. K.
    Low efficiency is the main drawback of a Crossflow turbine, despite the turbine being an important low cost technology for micro hydropower generation. Poor flow profile has been mentioned by other Crossflow turbine performance investigators as one of the reasons for the underperformance. This paper has investigated, using numerical method, the flow profile in the turbine at best efficiency point and at operating conditions that are away from best efficiency point. Numerical method has also been used to calculate and predict the efficiency of the turbine. The flow physics in a Crossflow turbine runner is a two-phase with a movable free surface. Such flow physics is difficult to analyse even numerically. A procedure for numerical analysis was followed and ANSYS CFX® was used to solve the governing equations and to process the simulation results. Actual pictures of the flow were taken so as to compare the actual flow with the numerically determined flow profile. Turbine efficiency results from the previous performance evaluation experiment conducted on the model Crossflow turbine were compared with the numerically obtained efficiency results. It has been observed that the numerically obtained flow profile compare favorably with the actual flow pictures. The numerical analysis over-predicts the efficiency, especially for runner speeds that were more than the best efficiency point speed. Pockets of negative pressures and flow circulation have been observed in the flow profile. At constant head and valve opening, the velocity profile was found to vary more with runner speed than the pressure profile. The numerically obtained flow pattern showed positions where the flow gives maximum efficiency. Therefore, the study has shown that numerical method is a superior design tool for Crossflow turbines.
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    Potential of Small-Scale Hydropower for Electricity Generation in Sub-Saharan Africa
    (Hindawi Publishing Corporation, http://www.hindawi.com/journals/isrn, 2012) Kaunda, C. S.; Kimambo, C. Z. M.; Nielsen, T. K.
    The importance of renewable energy such as small hydropower for sustainable power generation in relation to its capacity to contribute towards alleviating acute shortage of rural electricity supply in the sub-Saharan African region has been discussed. A relatively comprehensive small hydropower technology review has been presented. Rural electricity supply scenario in the region has been presented and, in general, the region has very low electricity access levels coupled with various challenges. Small hydropower technology has been discussed as one of the promising decentralised power generation system for rural electricity supply in the region. Despite challenges in data acquisition, this paper has shown that the SSA has significant hydropower resources, but the level of installation is very low. Challenges hampering SHP technology development in the region have been identified and discussed, such as those concerning technology, climate change, finance, and policy. This is basically a paper where the authors consulted a wide range of literature including journals, conference proceedings, and reports as well as expert knowledge in the area. It is hoped that this paper contributes to the information base on SHP technology which is quite lacking in the region.
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    A Technical Discussion on Microhydropower Technology and its Turbines
    (Elsevier, 2014-07) Kaunda, C. S.; Kimambo, C. Z. M.; Nielsen, T. K.
    Shortage of electricity supply and other forms of modern energy is serious in most of the developing countries, contributing to low economic and social development. The situation is worse in rural communities, which are often marginalised from grid-based electricity supply because of economic and technical reasons. Currently, development agencies involved in rural power supply in developing countries recommend microhydropower (MHP) as the most robust and reliable source of off-grid power generation. However, in scholarly articles, MHP technology is not popular compared to other renewable energy technologies. This may have contributed to its limited application in off-grid power supply in some countries. Availability of scholarly literature on MHP as the case with wind and solar energies can therefore help to scale-up the level of discourse on the technology among both technical and non-technical stakeholders. In this paper, the MHP technology has been reviewed in general and the turbines in particular. General description of the technology including challenges and factors for successful implementation of the technology has been given. It has been found that technological issues are among the major challenges and that the turbine is one of the critical technological components of the MHP project. The paper has reviewed common MHP turbines, focusing on their operating principles, merits and demerits with respect to MHP and suitable operating conditions. Factors to consider when selecting suitable turbine for the site and procedure for selecting the turbine have also been outlined in the paper. The paper has been written in a tutorial manner so that the discussions therein, though technical, are shared with stakeholders of different professional backgrounds. It is hoped that the paper provides additional knowledge on MHP technology and in particular on turbines that are used in MHP supply. This can lead to better practical implementation of the technology.
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    A Technical Discussion on Microhydropower Technology and its Turbines
    (Elsevier, 2014-07) Kaunda, C. S.; Kimambo, C. Z. M.; Nielsen, T. K.
    Shortage of electricity supply and other forms of modern energy is serious in most of the developing countries, contributing to low economic and social development. The situation is worse in rural communities, which are often marginalised from grid-based electricity supply because of economic and technical reasons. Currently, development agencies involved in rural power supply in developing countries recommend microhydropower (MHP) as the most robust and reliable source of off-grid power generation. However, in scholarly articles, MHP technology is not popular compared to other renewable energy technologies. This may have contributed to its limited application in off-grid power supply in some countries. Availability of scholarly literature on MHP as the case with wind and solar energies can therefore help to scale-up the level of discourse on the technology among both technical and non-technical stakeholders. In this paper, the MHP technology has been reviewed in general and the turbines in particular. General description of the technology including challenges and factors for successful implementation of the technology has been given. It has been found that technological issues are among the major challenges and that the turbine is one of the critical technological components of the MHP project. The paper has reviewed common MHP turbines, focusing on their operating principles, merits and demerits with respect to MHP and suitable operating conditions. Factors to consider when selecting suitable turbine for the site and procedure for selecting the turbine have also been outlined in the paper. The paper has been written in a tutorial manner so that the discussions therein, though technical, are shared with stakeholders of different professional backgrounds. It is hoped that the paper provides additional knowledge on MHP technology and in particular on turbines that are used in MHP supply. This can lead to better practical implementation of the technology.