Dr Ombeni J Mdee | The University of Dodoma, Tanzania (original) (raw)

Uploads

Papers by Dr Ombeni J Mdee

Water practice and technology, Jul 8, 2024

Tanzania Journal of Engineering and Technology

In many parts of the world, artisanal and small-scale gold mines (ASGM) employed numbers of peopl... more In many parts of the world, artisanal and small-scale gold mines (ASGM) employed numbers of people compared to large-scale mines. The ASGM has been played a crucial role in poverty alleviation and rural development, particularly in developing countries. The mined ore is crushed and ground for beneficiation of gold. The grinding process involved the size reduction of blasted materials to acquire minerals of interest. This paper presents the size distribution of hand-crushed for blasted materials using sieve analysis and digital image processing. The sieve test results for hand-crushed blasted material of three muck-piles were ranged between 17 mm and 36 mm that is equivalent to 20% and 80% passings respectively, with an average of 26 mm. The digital image processing results were about 19.8 mm for 20% passing and 58 mm for 80% passing, with an average of 36.06 mm. The hand-crushed provided a wide range of material distribution than the required size in the grinding unit and increased ...

Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020

The Weibull distribution function with shape (k) and scale (c) parameters predicts wind speed dis... more The Weibull distribution function with shape (k) and scale (c) parameters predicts wind speed distribution for different locations. The k and c parameters have been estimated by using several analytical methods, but it provides different results in the same wind speed distribution data. In this work, the correlation technique was applied to evaluate the performance of analytical methods using several empirical methods. The analytical methods presented including Method of Moments (MoM), Energy Pattern Density (EPD), Graphic Method (GM), and Maximum Likelihood Estimator (MLE). Five empirical methods were evaluated graphically by using the GM method to estimate the Weibull two-parameter. The Weibull two-parameter of correlation coefficient (r) of greater than 0.9503 indicated from four empirical methods. Again, five empirical methods for k parameter and four empirical methods for c parameter were used in the special case of MoM and EPD methods. The results indicated four empirical methods for estimating k parameter and two empirical methods for estimating c parameter having the r of greater than 0.7. When empirical methods of k and c parameter correlated, six matching patterns were identified from 20 possible pairs. Comparison of GM, MLE, and selected pairs of k and c values predicted from empirical methods resulted from MoM and EPD indicated the average coefficient of best-fit of 0.8851 and root-mean-square-error of 0.2083. Therefore, the use of more than one empirical method in one analytical method of MoM, EPD, and GM would improve the prediction of Weibull distribution.

Journal of Fluids Engineering, 2018

Head and flow rate are the important parameters for proper selection of centrifugal pump. However... more 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 consi...

Tanzania Journal of Engineering and Technology

This study uses a mass balance model and economic analysis technique to present an estimation of ... more This study uses a mass balance model and economic analysis technique to present an estimation of roofing areas and storage tank capacity for Rainwater Harvesting (RWH) system. The water-saved benefits were estimated using the monthly rainfall of over 39 years from 1981 to 2020 and five roofing areas. The proposed roof-storage-ratio method presents the minimum requirement of roof area and storage tank size when the ratio value is closer to 1. The benefit-cost ratio and percentage of reliability indicated the optimal roofing areas ranging between 200 and 300 m2 for storage tank capacity between 20 and 25 m3, with a minimum discount rate of 5%. The increased capacity of storage tank and roofing area would also be a potential factor to increase the investment cost for installing the RWH system.

Different performance characteristics have been indicated when running centrifugal pumps in the r... more 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) values were of 0.890 and 0.708, respectively. Also, the graph of head versus flow rate coefficients, which is a secondorder polynomial function, has shown the value of R of 0.954 for pump-specific speed rangi...

This work part of a PhD Study Programme at the University of Dar es Salaam, Tanzania and Norwegia... more 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.

Arabian Journal of Geosciences

The rapid growth of socioeconomic activities brings the overpressure to the water sources in the ... more The rapid growth of socioeconomic activities brings the overpressure to the water sources in the semi-arid areas. This paper identifies potential sites for surface runoff harvesting from seasonal rainfall. The potential sites were determined using the analytic hierarchy process (AHP) and weighted linear combination (WLC) techniques with four parameters including runoff depth, drainage density, slope, and lineament density under the GIS environment. The runoff depth was estimated using the Soil Conservation Service method with the three factors such as land use, rainfall, and soil parameters. The normalized weights obtained from the AHP technique were multiplied with the individual weights for each parameter using the WLC technique to acquire the weighted classes (WCs) for defining suitable for surface runoff harvesting. The covered area of about 5.5% for a very high suitable site was obtained followed by 76.4% of the highly suitable site with the WC ranged from 433 to 500% and 372 to 433%, respectively. The covered area of about 18.1% for the medium to a very low suitable site for harvesting surface runoff with the WC between 271 and 372%. The developed potential site map would provide access for harvesting the surface runoff to improve the water shortage during long dry periods, minimize flooding, or reduce the land use across the drainage network in the semi-arid areas.

Renewable Energy and Sustainable Buildings

Environment and Water Resource Management / 837: Health Informatics / 838: Modelling and Simulation / 839: Power and Energy Systems, 2016

This paper presents the operation of centrifugal pumps as turbines for micro hydropower applicati... more This 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.

Renewable Energy and Environmental Sustainability

The hydropower resources have become an attractive means of generating electricity to the off-gri... more 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 5.3 GW 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.

Water practice and technology, Jul 8, 2024

Tanzania Journal of Engineering and Technology

In many parts of the world, artisanal and small-scale gold mines (ASGM) employed numbers of peopl... more In many parts of the world, artisanal and small-scale gold mines (ASGM) employed numbers of people compared to large-scale mines. The ASGM has been played a crucial role in poverty alleviation and rural development, particularly in developing countries. The mined ore is crushed and ground for beneficiation of gold. The grinding process involved the size reduction of blasted materials to acquire minerals of interest. This paper presents the size distribution of hand-crushed for blasted materials using sieve analysis and digital image processing. The sieve test results for hand-crushed blasted material of three muck-piles were ranged between 17 mm and 36 mm that is equivalent to 20% and 80% passings respectively, with an average of 26 mm. The digital image processing results were about 19.8 mm for 20% passing and 58 mm for 80% passing, with an average of 36.06 mm. The hand-crushed provided a wide range of material distribution than the required size in the grinding unit and increased ...

Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020

The Weibull distribution function with shape (k) and scale (c) parameters predicts wind speed dis... more The Weibull distribution function with shape (k) and scale (c) parameters predicts wind speed distribution for different locations. The k and c parameters have been estimated by using several analytical methods, but it provides different results in the same wind speed distribution data. In this work, the correlation technique was applied to evaluate the performance of analytical methods using several empirical methods. The analytical methods presented including Method of Moments (MoM), Energy Pattern Density (EPD), Graphic Method (GM), and Maximum Likelihood Estimator (MLE). Five empirical methods were evaluated graphically by using the GM method to estimate the Weibull two-parameter. The Weibull two-parameter of correlation coefficient (r) of greater than 0.9503 indicated from four empirical methods. Again, five empirical methods for k parameter and four empirical methods for c parameter were used in the special case of MoM and EPD methods. The results indicated four empirical methods for estimating k parameter and two empirical methods for estimating c parameter having the r of greater than 0.7. When empirical methods of k and c parameter correlated, six matching patterns were identified from 20 possible pairs. Comparison of GM, MLE, and selected pairs of k and c values predicted from empirical methods resulted from MoM and EPD indicated the average coefficient of best-fit of 0.8851 and root-mean-square-error of 0.2083. Therefore, the use of more than one empirical method in one analytical method of MoM, EPD, and GM would improve the prediction of Weibull distribution.

Journal of Fluids Engineering, 2018

Head and flow rate are the important parameters for proper selection of centrifugal pump. However... more 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 consi...

Tanzania Journal of Engineering and Technology

This study uses a mass balance model and economic analysis technique to present an estimation of ... more This study uses a mass balance model and economic analysis technique to present an estimation of roofing areas and storage tank capacity for Rainwater Harvesting (RWH) system. The water-saved benefits were estimated using the monthly rainfall of over 39 years from 1981 to 2020 and five roofing areas. The proposed roof-storage-ratio method presents the minimum requirement of roof area and storage tank size when the ratio value is closer to 1. The benefit-cost ratio and percentage of reliability indicated the optimal roofing areas ranging between 200 and 300 m2 for storage tank capacity between 20 and 25 m3, with a minimum discount rate of 5%. The increased capacity of storage tank and roofing area would also be a potential factor to increase the investment cost for installing the RWH system.

Different performance characteristics have been indicated when running centrifugal pumps in the r... more 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) values were of 0.890 and 0.708, respectively. Also, the graph of head versus flow rate coefficients, which is a secondorder polynomial function, has shown the value of R of 0.954 for pump-specific speed rangi...

This work part of a PhD Study Programme at the University of Dar es Salaam, Tanzania and Norwegia... more 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.

Arabian Journal of Geosciences

The rapid growth of socioeconomic activities brings the overpressure to the water sources in the ... more The rapid growth of socioeconomic activities brings the overpressure to the water sources in the semi-arid areas. This paper identifies potential sites for surface runoff harvesting from seasonal rainfall. The potential sites were determined using the analytic hierarchy process (AHP) and weighted linear combination (WLC) techniques with four parameters including runoff depth, drainage density, slope, and lineament density under the GIS environment. The runoff depth was estimated using the Soil Conservation Service method with the three factors such as land use, rainfall, and soil parameters. The normalized weights obtained from the AHP technique were multiplied with the individual weights for each parameter using the WLC technique to acquire the weighted classes (WCs) for defining suitable for surface runoff harvesting. The covered area of about 5.5% for a very high suitable site was obtained followed by 76.4% of the highly suitable site with the WC ranged from 433 to 500% and 372 to 433%, respectively. The covered area of about 18.1% for the medium to a very low suitable site for harvesting surface runoff with the WC between 271 and 372%. The developed potential site map would provide access for harvesting the surface runoff to improve the water shortage during long dry periods, minimize flooding, or reduce the land use across the drainage network in the semi-arid areas.

Renewable Energy and Sustainable Buildings

Environment and Water Resource Management / 837: Health Informatics / 838: Modelling and Simulation / 839: Power and Energy Systems, 2016

This paper presents the operation of centrifugal pumps as turbines for micro hydropower applicati... more This 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.

Renewable Energy and Environmental Sustainability

The hydropower resources have become an attractive means of generating electricity to the off-gri... more 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 5.3 GW 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.