http://ir.bdu.edu.et/handle/123456789/10408 2001-01-13T06:39:03Z http://ir.bdu.edu.et/handle/123456789/16591 DESIGN AND PERFORMANCE INVESTIGATION ON ROUGHENED SOLAR-ABSORBER DRYER Urmale, Wegaso Kambo Solar air heaters have been used for many purposes requiring low to medium grade thermal energy, mainly due to their low manufacturing cost, simple design and operation, and maintenance. Their usefulness and the quantitative energy collection has been limited because of low thermal efficiency primarily as a result of low convective heat transfer coefficient, between the absorber plate and air leading to higher plate temperature, and thus resulting in greater thermal losses. One of several methods that have been proposed and investigated for the enhancement of heat transfer coefficient is the use of artificial roughness. Since the use of inclined and transverse wire rib roughness has shown to enhance the heat transfer rate considerably, it is worth exploring. Experimental investigation has been carried out to study heat transfer enhancement by using small diameter wire ribs on absorber plate of solar air heater duct, with the roughened wall exposed to the glazing side while the remaining three walls insulated. The roughened wall has relative roughness height (e/Dh) 0.023, relative roughness pitch (p/e) 11.1, rib height 0.9 mm, angle of attack of 90° for transverse and 45° for inclined configuration, and duct aspect ratio of 12. The air flow rate corresponds to Reynolds number between 2500 – 18,000. Results of the experimental investigation revealed that provision of artificial wire rib roughness resulted in a considerable enhancement in heat transfer and friction factor. It has been found that the heat transfer coefficient could be improved by a factor up to 2.2 and the friction factor had been found to increase by a factor of 1.2 times that of the smooth duct. The investigation emphasized that the secondary flow rolling along the inclined ribs is responsible for higher heat transfer rates. Based on minimum unit energy cost criteria a set of roughness parameters can be selected by the designer for a given operating condition. Key Words: Solar air heater, wire rib roughness, air duct, inclined ribs, unit energy cost. 2024-08-01T00:00:00Z http://ir.bdu.edu.et/handle/123456789/16590 Optimization of Modified Bach-Type Savonius Wind Turbine With Obstacle Shielding and Deflector Plate Using Gentic Algorithm and NLopt Biniam, Tewbo The Savonius wind turbine is a drag-based vertical axis wind turbine and is used as an alternative source in small-scale energy generation. Design simplicity, low cost, easy installation, good starting ability, relatively low operating speed, and independent wind directions are the main advantages of this rotor. However, because of its low efficiency and high negative torque produced by the returning blade, this rotor concept rarely gained popularity. Over the last few decades, although some investigations around the world have reported performance gains of the Savonius rotor, the available technical design is still not able to fulfill the demand for efficient small-scale wind energy converter at low wind speeds. This study presents a comprehensive computational investigation into the performance enhancement of Savonius vertical axis wind turbines (VAWTs) through optimization in augmentation technique. The research focuses on optimizing the turbine's efficiency and power output by integrating three novel features: obstacle shielding returning blades and deflector plate with a modified Bach blade shape. The obstacle shielding returning blades aim to mitigate the adverse effects of wind obstacles commonly encountered in urban and turbulent environments, while the modified Bach blade shape seeks to improve aerodynamic performance and torque generation. Computational fluid dynamics (CFD) simulations are employed to analyze the flow behavior, pressure distribution, and performance characteristics of the enhanced Savonius turbine design. The study evaluates various design parameters, including blade geometry, obstacle placement, and airflow patterns, to determine their impact on turbine performance metrics such as power coefficient, torque, and rotational speed. This automatic optimization is carried out by coupling an in-house optimization library (OPAL) in Visual Studio compiled with NLopt and SFML with an industrial flow simulation code (ANSYS Fluent). Inlet velocity 9m/s, turbulence intensity 4% and no slip condition consider. K-ω turbulence model used for simulation. A considerable improvement in the performance of Savonius turbines can be obtained in this manner, in particular a relative increase of the power output coefficient by more than 46.5%. It is furthermore demonstrated that the optimized configuration involving A modified Bach-type turbine is good for improvement. KEYWORD: Savonius, modified Bach blade, negative torque, obstacle shielding, deflector plate, CFD simulations 2024-06-01T00:00:00Z http://ir.bdu.edu.et/handle/123456789/15867 DEVELOPMENT AND EXPERIMENTAL TESTING OF THE PERFORMANCE OF SOLAR DRYER EQUIPPED TO EVACUATED TUBE COLLECTOR WITH INTEGRATION OF ROCK BED AND REFLECTORS: (CASE OF POTATO SLICE DRYING) Semahagn, Yematawu Desta Several researchers have attempted to enhance the performance of solar dryers by adding different features to the air heating system. Besides, developing a solar dryer supposed to sustain the drying operation even in non-shining times is necessarily important. This research is aimed to develop a reliable solar dryer system to vegetables and fruits. Thus, this work is going to develop a solar dryer system that employs an evacuated tube collector (ETC) for shining hours by integrating an independent rock bed as thermal storage in a way as able to discharge heat during the non-shining time. Here, the rock bed has to be built from a thermally insulated tank with transparent double glassed top coverage to absorb and store the solar flux during sunny hours. This system had been designed to dry potato slice weighting 7.5kg sample from its wet base initial moisture content of 80.1% to the optimum (7-13%) within eight hours at an average temperature of 65℃. Then, the drying chamber having size of 85cm x 61cm x 62cm, 1.3m 2 area of evacuated tube collector, 0.137m 3 volume of rock bed (with a solar absorbing area of 0.52m 2 and depth of 0.26m) have been designed with the blower requiring 330W electrical power. Finally, the solar dryer system prototype developed from locally available materials, and tested with loading slices at different air flow rates (i.e., at 0.016 m 3 /s, 0.008 m 3 /s and 0.024 m 3 /s) and open sun. Here, the more moisture reduction (9.3% within eight hours), higher efficiency of the collector (62.02%), more drying temperature (60℃), as well as higher efficiency of the dryer (23.87%) was occurred at 0.016m 3 /s compared to lower and higher airflow rates. Finally, 20% of drying time was saved compared to open sun drying (takes ten hours). Besides that, the significance of the rock bed as well as the reflectors was also studied by conducting tests using ETC having extended reflectors and using ETC only at the best air flow rate of the first test (0.016m 3 /s). Finally, integration of the rock bed is significant for reliable heat supply (due to it increased by 9.56%), more moisture reduction (due drying rate increased by 3.6% compared to the case of using ETC only); and the presence of reflectors also results for increment of heat production from the collector (increased by 5.1% -16.9%) and from the total thermal system (8.6% average increment), which results for higher drying rate (increased by 15.5%) and saved 12.5% of drying time relative to using ETC only and with the assistance of rock bed, and 30 % relative to open sun. Keywords: Solar collector, Evacuated tube, Thermal Storage, Rock bed, Reflector & performance. 2023-03-07T00:00:00Z http://ir.bdu.edu.et/handle/123456789/15866 Experimental and numerical performance analysis of a spiral pipe flat plate solar collector using nanofluids. Hailegiworges, Nigatu Existing Flat plate solar thermal collectors suffers from comparatively low efficiency. This clearly indicates that further research is still needed in the area to improve efficiency of those types of collectors by employing different techniques. Therefore this study aims to evaluate how different parameters like spiral tube arrangement, working fluid flow rate and thermal characteristics affect the thermal efficiency of a flat plate solar collector. An experimental test is conducted for five different fluid flow rates. In order to investigate the effect of the fluid thermal characteristics on the efficiency of the collector water, Cuo and nanofluids with two different nanoparticle volume concentrations are used. The numerical simulation of the collector has been performed by means of the Finite Volume Method (FVM) using commercial ANSYS Fluent 19.2 software. Both the numerical and experimental results showed that the spiral type flat plate collector shows a greater efficiency than the conventional type of collector. The collector efficiency was maximum for all the fluid types when the fluid flow rate is fixed at 2L/m. and generally the efficiency obtained for all the working fluids during the experimental test at the optimum 2L/m fluid flow rate was 60.3 for water, 66.5 for Cuo nanofluids and the maximum efficiency belongs for Nano fluid which is 68% at 0.4% nanoparticle volume concentration. The results obtained from the experimental test as well as the numerical results are fairly in good agreement with only a maximum of 2.85% deviation that shows the simulations were quite satisfactory. Key words: flat plate collector, collector efficiency: spiral tube: nanofluids: finite volume method. 2022-10-01T00:00:00Z