Browsing by Author "Kachira, John Peter"

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    Assessment of the Influence of Tip Speed Ratio, Solidity and Reynolds Number on the Aerodynamic Performance of Selected Locally Fabricated Wind Turbines in Tanzania
    (The University Of Dar Es Salaam, 2019) Kachira, John Peter
    The sites with good wind energy conditions in Tanzania have motivated some local craftsmen to manufacture wind turbines using local and imported materials. However, some studies have shown that these turbines have low performance. In this study, theoretical approach has been carried out to assess the influence of TSR, solidity and Re on the aerodynamic performance of nine selected locally fabricated wind turbines in Tanzania. Three manufacturing centers namely, Dar es Salaam, Singida and Makambako were selected and three different HAWT rotor blades from each center were put under testing. Their respective rotor radii and chord widths were measured and used to determine their TSR, solidity and Re. The measured TSRs were 0.63, 0.70, 0.79, 0.90, 1.57, 2.09, 2.51, 3.14, and 4.19. Unlike 4.19, the rest values were below the recommended range between 4 and 10 for which WECS are recommended to generate large scale electricity. The respective measured solidities were, 0.90, 0.10, 0.13, 0.17, 0.18, 0.28, 0.88, 1.07 and 1.22. These solidities were found to be above the proposed range between 0.01 and 0.05 for which WECS are designed to generate large scale electricity. These high solidities lead into high torques reducing rotational speed of the WECS. The measured Res were 86,030, 99,265, 100,589, 102,574, 125,736, 138,972, 145,589, 145,589 and 152,207. These Re values are below the standard Re which is at least 6 110 implying that they exhibit turbulent flow with high level of drag coefficient that influences low performance of the WECS. The 3 - bladed wind turbine from Matiya in Singida was found to have good TSR of 4.19 though its solidity was found to be above the recommended standard values range. It needs an optimization of its chord and radius to improve its efficiency. Therefore, these wind turbines can only generate small scale electricity due to their poor aerodynamic performances
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    First-Principles Study of the Structural, Electronic, Mechanical, and Optical Properties of Zintl-Phase K2AgBi Ternary Compound for Optoelectronic Applications.
    (2025-04-23) Kachira, John Peter; Musembi, Robinson; Nyongesa, Francis; Mbilo, Mwende; Nyamuga, Martin; Musanyi, Ibrahim
    A comprehensive first-principles study was conducted to explore the structural, electronic, mechanical, thermophysical, and optical proper ties of a Zintl-phase K2AgBi ternary semiconductor compound using density functional theory. The calculations employed the local density approximation (LDA), generalized gradient approximation (GGA), and meta-GGA methods. The computed negative formation energies proved the thermodynamic stability of the K2AgBi ternary compound. The computed bandgap values were 0.6732 and 0.7848 eV for the LDA and GGA, respectively. More refined bandgap estimates were obtained using meta-GGA methods, with the Tran–Blaha modified Becke–Johnson potential yielding 0.9346 eV and the revised strongly constrained and appropriately normed functional yielding 0.9778 eV. The projected density of states study revealed that the Ag3d, Bi2p, and K1s orbitals dominate the formation of the valence band, whereas the K4p, Ag2p, and K2s orbitals contribute significantly to the formation of the conduction band. Analysis of the mechanical properties confirmed that K2AgBi is mechanically stable and ductile. Optical analysis revealed strong absorption in the 1.0–15 eV energy range, high refractive index in the low-energy region, and distinct plasmonic response, suggesting potential applications in photovoltaics, optoelectronics, and plasmonic-based technologies.