Thermal Engineering

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Aerothermodynamics Analysis of Axial Flow Aircraft Gas Turbine Engine Compressor
(Addis Ababa University, 2009-10-05) Tilahun, Nigussie; Tesfaye, Dama (PhD)
The axial flow type compressor is one of the most common compressor types in use today. It finds its major application in large aircraft gas turbine engine like those that power today’s jet aircraft. Early axial flow aircraft engine compressors had pressure ratio of around 5:1 and require about 10 stages. Over the years the overall pressure ratios available exceed 30: 1 due to continued aerodynamic development that resulted in a steady increase in a stage pressure ratio with reduced number of stages. There has been in consequence a reduction in engine weight for a specific level of performance, which is particularly important for aircraft engines. These potential gains have now been fully realized as the result of intensive research into the Aero-thermodynamics Analysis of Axial Flow Aircraft Gas Turbine Engine Compressor. Therefore, careful design of compressor blading based on aero-thermodynamic theory, experiment and computational fluid dynamic (CFD) analysis is necessary not only to prevent useful losses but also to insure a minimum of stalling troubles. The complete analysis of this thesis is done to provide some part of design of an axial compressor suitable for a simple low-cost and low weight turbojet Aircraft Gas Turbine Engine Compressor by using different research work on the aero-thermodynamic analysis of the compressor. Details of CFD analysis on the models of the compressor, using a commercial software “FLUENT”, will be presented. The CFD simulation predictions were validated quantitatively against the experimental data and the theoretical (calculated values) were then used to obtain further insights into the characteristics of the flow behaviors. To calculate the work and power required by the compressor to sustain the flight, the blades of the compressor will be modeled, and the required equations will be developed. Finally a small scale computer program will be developed to calculate the power (work) required by the compressor and to determine other performance measuring parameters.
Analysis of Fluid Flow and Losses in Regenerative Flow Compressors Using Cfd
(Addis Ababa University, 2008-04) Te fe ri, Kas s a; Edessa, Dribssa (PhD)
Regenerative flow compressors are rotodynamic machines capable of producing high heads at very low flow rates. With comparable tip speed, they can produce heads equivalent to that of several centrifugal stages from a single rotor. They have found many applications for duties requiring high heads at low flow rates but the compression process is usually with very low efficiency which is their major drawback. Even though there are several factors that can be considered to improve the efficiency of these machines in this thesis various models will be developed with different blade and flow channel geometries to investigate their effect on performance. Details of CFD analysis on the models of the compressor, using a commercial software “FLUENT”, will be presented. And based on simulation results of the different models a blade and channel geometry that gives significant improvement on performance will be suggested.
[Application of Micro-Hydro Pv/Battery off- Grid Hybrid Energy System for Ethiopian Rural Area]
(Addis Ababa University, 2014-08) Tesfaye, Yohannes; Edessa, Dribssa (PhD)
Ethiopia is a developing country with a total access to electricity not exceeding 41% (in 2012) and the number of household connected to this access is 17%. About 85% of the population lives in places where access to electricity is less than 2%. The village for this study, Mogno Keshenbel Village (8.570N, 37.450E) has a total population of 4526 and 874 households (CSA, 2007, Guder Wereda Health Office). The village is about 68km from Guder substation; whicht makes the extension of the grid not yet practical and off grid electrification is the best option for the village. The community in the Mogno Keshenbel village uses Kerosene for lighting, water for milling and biomass for cooking and dry cells for radios. Nothing has been done so far in developing the renewable energy resources, such as small-scale hydro, solar and wind energy in the village. In this study, feasibility of micro hydro/PV/battery hybrid electric supply system to the village is analyzed using HOMER software (hybrid optimization model for electrical renewable) as optimization and sensitivity analysis tool. The logic behind HOMER selection is that it is proven and worldwide used for micro power design. Hydro potential of the village is analyzed by measuring the gross head of the river with the help of GPS (Geographical Position System) and stream flow data obtained from Ministry of Water, Irrigation and Energy and also Meteorological data of the village is collected from National Meteorological Agency of Ethiopia and NASA. Surface Metrology is used for the estimation of solar energy potentials. Electric load for the basic needs of the community, such as, for lighting, radio, television, ‘injera Mittad”, water pumps, milk processing and flour mills is estimated. One primary school and one health posts are also considered for the community. Additionally three Protestant churches and two Orthodox churches also considered. As a result, many feasible hybrid system combinations are generated, and accordingly, total net present cost (NPC) of the hybrid configuration and cost of energy (COE) for PV/ micro hydro/ battery hybrid system is $394,819 and $0.044/kWh, respectively, which is much lower than previously studied Micro hydro/wind hybrid system and PV/hydro/wind hybrid systems, and this value is less than the current grid price of Ethiopian ($0.06) [EPCO]. Index terms: Hybrid energy systems, Photovoltaic, Micro - hydro, off - grid system, HOMER
Assessment of Feasibility of Wind Pumping For Village Water Supply and Irrigation in Ethiopia
(Addis Ababa University, 2010-11) Dejene, Assefa; Demiss, Alemu (PhD)
In this project three consecutive years wind speed data measured five times a day for more than thirteen stations from NMSA is used to predict the wind distribution pattern of the country. Based on the day time data, the most probable night time data is generated using appropriate software (HOMER), hence year round hourly data is generated for all stations along with statistical wind distribution model weibull shape and scale parameters. Based on the wind potential assessment, wind pumping feasibility is done for water supply and irrigation for a hypothetical model community at three different locations having similar topography as that of the representative sites. For pre determined daily water demand and varied water well depth, wind pump sizing is done for each application. Following the technical feasibility, economic analysis is done to compare with that of diesel pumping system. Cost analysis model is prepared using excel, in which system sizing and cost estimation are done. The life cycle cost, break even and unit water cost at different delivery head for pre determined daily flow rate is calculated based on given financial parameters for both systems. The unit water cost for wind pumping and diesel pumping at typical delivery head of 20m for mekele, Jijiga and Assosa are found as 5.66, 6.71 and 7.01birr/m 3 . In addition breakeven for wind pumping at typical delivery head of 20m occurs 1.9 years after the system becomes operational. Hence, the result shows that wind pumping is found to be more economical for water supply and irrigation than diesel pumping for stations having average wind speed 2.5m/s and above in the critical month. respectively, where as diesel pumping costs 25.10birr/m 3 In general at low hydraulic load wind pumping is best economical than diesel pumping for monthly average wind speed 2.5m/s and greater in the critical month. In this regard, the country wind potential assessment shows average monthly and annual wind speed above 2.5m/s is found extensively in Ethiopia, which strengthens the feasibility of wind pumping in the country.
Assessment of Thermal Stratification Impact in a Storage Tank on the Performance of PV/T and Hybrid PV/T-Heat Pump System using Computational Method
(Addis Ababa University, 2023-07) Mahder Dereb; Demiss Alemu (Assoc. Prof.)
In solar thermal systems, hot water storage tanks are employed to store the heat energy extracted from multiple energy sources and to balance the supply/demand of thermal energy requirements. One of the main challenges of these systems is the mixing of hot and cold water in the storage. Though several storage utilization methods were adopted, identifying the best approach to utilize the stored heat energy effectively and efficiently is still critical. Hence, this study has focused on modelling thermal stratification in a storage tank to assess its positive impact on the performance of existing hybrid PV/T and heat pump water heating system. One-dimensional multi-node model was simulated in MATLAB, with implicit finite-difference scheme, for evaluating temperature distribution and annual efficiencies of the system after the thermal stratification is applied. Details of the fluid flow stored in the stratified storage were studied in two dimensional CFD model using ANSYS Fluent. Both models were validated with experimental results from literature. Compared to the system with mixed storage, the stratified storage enhanced the annual solar fraction to 0.73. Thermal and overall efficiencies were also elevated with 14.8% and 15.6% respectively. Both the collector and storage heat losses were diminished with significant figures. Performance analysis was also done on geometrical parameters like H/D ratio, insulation, inlet locations, and operational conditions such as collector flow rates, heat removal factor and hourly hot water consumption fraction. The results of the CFD model showed that the temperature gradient differences in increasing storing time. Applying improved quality of model is still needed for simulating a better appropriate thermally stratified storage tank model in a solar thermal system technology.
CFD Analysis of Perforated Building Geometrical Characteristics Impact on Local Wind Environment
(Addis Ababa University, 2022-06) Anwar Endris; Wondwossen Bogale (Assoc. Prof.)
With the need to achieve a net-zero goal in the architectural, construction, and engineering sector, there is a rapid growth in the use of passive building design to reduce buildings' carbon footprint. In this research field, replacing or incorporating ventilation systems with natural means has gained wide popularity across the world. To achieve natural cross ventilation in buildings, building perforation presented as a means of wind infiltration. The design of perforated building façades influenced by different architectural insights including cultural and economic motivations. This led to the introduction of unique geometrical features in urban areas. The literature on potential impact of these geometrical features on the local wind environment is still lacking. Hence, the presented study investigates the effect of geometrical features of building perforation on pedestrian level wind condition under different wind conditions. To achieve that, perforation design from existing building was. A lattice Boltzmann method with a detached eddy version of the K-omega-SST turbulence was model was used to conduct a transient CFD simulation for sensitivity study. The result indicates that different geometrical designs of the perforation can result in different near-faced wind conditions and pressure distribution on the faces despite having the same perforation ratio. The designs also exhibit wind amplification and deceleration effect depending on inflow wind conditions including its speed and direction. Different perforation design parameters have also an impact on the air flow pattern and speed inside the building. Therefore, the result indicates a need to characterize indoor activities for inclusion in comfort criteria and comfort analysis for open space cross-ventilated buildings.
CFD Based Design Optimization, Fabrication and Testing of A Micro Hydro Pelton Turbine
(Addis Ababa University, 2018-12) Tilahun, Nigussie; Edessa, Dribssa (PhD)
In areas where the supply of grid power is very difficult, utilisation of Micro hydro-power as renewable energy source is of great concern now a-days to eliminat extreme poverty around the world. These schemes can provide environmentally sustainable electricity and mechanical power to rural communities. For this purpose, selected types of micro hydro turbines need to be designed and developed depending up on the site locations. Thus, considering the potential of hydropower generation in Ethiopia, this research addresses the design, optimization, local manufacturing, and experimental test of a model of micro hydro Pelton turbine for one of the selected potential site (Indris River) in South West Shewa of Ethiopia to meet the requirements of the energy demands of the nearby village as a case study. Initially, the geometries to be compared (baseline design of the turbine) were done with the design guide lines and tested by developing numerical model using commercial CFD. Considerations are taken in designing the turbine with an effective post life recycling scheme in mind so that there will be minimum wastage of resources once the turbine is made redundant. CFD simulations using ANSYS-CFX were conducted, to optimize further the bucket shape in order to get a cost effective runner design. Additionally, consequences of variation in each design parameter were evaluated from the baseline design. The result of the study proposes some modifications in the baseline design. Through the analysis, a weight reduction of around 7.6% is achieved due to the modified runner design. Moreover, CFD was predicting a 3.9 % improvement of hydraulic efficiency. The optimization of number of buckets, length, depth and shape of the lip curve are the main design parameters for the achieved improvement in efficiency. It is then checked for structural safety with a more accurate method using ANSYS. At a later stage, the model was experimentally tested at the AAIT Lab to have a tangible confirmation of efficiency at variable operational conditions. The experimental results confirmed a 2.8% improvement in efficiency. This prediction was validated for the modified runner design used in the simulation using the same head and flow rate conditions as for the baseline design. Overall, the comparative results with CFD were satisfactory and in line with the theory, and verifying the turbine model design effectiveness which will be useful for implementation of rural electrification projects.
Computational and Experimental Analysis of Ice Thermal Storage with Solar Refrigerator
(Addis Ababa University, 2020-06) Kamil, Nuredin; Yilma, Tadesse (PhD)
In rural areas of Ethiopia the grid electricity supply coverage is very low, which is about 2%. As result of this dairy product preservation before supply to local market is difficult especially for night time collected milk. However, utilization of direct coupled PV powered solar refrigerator incorporated with Ice thermal storage able to preserve the products until market. The use of Ice thermal storage can avoid the use of solar batteries. The study includes the design, manufacture the prototype and experimental testing and computational modeling of PV powered solar refrigerator. As a case study Adama city Ethiopia is selected for the experimental test, the solar radiation of the site is analyzed. The minimum daily average solar radiation is determined at a month of August which is . To preserve 5L milk, MT3.5DC compressor and 140W PV panel are selected. The operating point of compressor is obtained and the minimum solar radiation required for the solar refrigerator is Computational simulations using ANSYS-Fluent is conducted to determine the amount of ice produced as a thermal storage for night time preservation and the average temperature of waterice during solidification process. The system produced nearly 1kg solid ice with a mean temperature of . During night time which is the discharging process of the ice the milk got chilled from and maintained this temperature for more than 12hours. Then, the model is manufactured and tested for its performance. During the experimental test solar radiation was simulated virtually with DC power supply due to frequent intermittent nature of the radiation. From the experiment, it was observed that the average water-ice temperature was -12.5 o C. In the discharging process the milk temperature was reduced from 310K to 274K within 12 hours. Also, the milk temperature is reached to a range of to with in 4hours duration and satisfies the FAO standard. CFD simulation was validated by experimental test, with 6% maximum deviation.
Computational Fluid Dynamics and Experimental Analysis of a Self-Aspirated Domestic Biogas Cook Stove with a Two-layer Porous Radiant Burner to Improve the Performance of Conventional Burner
(Addis Ababa University, 2023-06) Yared Yalew; Kamil Dino (PhD)
To meet the requirements of increased thermal efficiency and reduced pollutant emissions of a conventional burner biogas cookstoves, a porous radiant burner (PRB) is added to these conventional burners. The porous radiant burner operates on an excess enthalpy approach, which asserts that recirculates the lost heat from hot combustion products to incoming fuel-air mixture. However, to achieve this excess enthalpy combustion with high reactant velocity, these porous burners employ compressed air, which requires an additional compressor. This thesis aims to investigate the performance of a naturally aspirated domestic biogas stove with a double-layer porous radiant burner cookstove. In the present work, the porous radiant burner comprising silicon carbide (SiC) and cast iron is investigated via numerical and experimental analysis. In the numerical analysis, the geometry of the existing porous radiant burner cookstove is modified with new features such as an orifice and slots (for air entrance) to get higher reactant velocity and lower pressure drop without using an external compressor. Then, the experimental investigation follow-up to evaluate the performance of the new naturally aspirated porous radiant burner, and compared it with the existing conventional burner. The numerical results indicate that naturally aspirated porous radiant burner has a better pressure distribution and higher reactant velocity than the existing burner and it can be operate without external pumping . The experimental results show that the naturally aspirated PRB has improved thermal efficiency in the range of 51-59%, reduced carbon monoxide (CO) and nitric oxides (NOx) pollutant emissions in the range of 41-55 and 4-10 parts per million at gas flow rates of 6-8 liters per minute, respectively. The new self-aspirated porous radiant burner biogas cook stove has 3.5% improved efficiency, 79.4% CO, and 28.7% NOx lower pollutant emissions compared to conventional burner cookstoves. Finally, this self-aspirated porous radiant burner biogas stove will have better efficiency if the best thermal resisting material is used and utilizes the biogas at a pressure greater than the atmospheric pressure.
Computational Modeling and Performance Analysis of Solar Thermal Storage Integrated with Parabolic Solar Concentrator for Cooking Application
(Addis Ababa University, 2020-06) Dejene, Kebede; Demiss, Alemu (PhD); Yilma, Tadesse (PhD)
Cooking using biomass, which is commonly practiced in developing countries, causes rampant deforestation and exposure to hazardous emission. Hence, the utilization of solar energy for cooking can be used as solution to mitigate both problems . As solar radiation is not available at every hour of the day, thermal storage is essential for availing thermal energy at the required time of use. Therefore, this work investigates the long term efficiency of the solar cooker with a parabolic concentrating collector integrated with thermal storage using a 1D finite-difference computational model was developed under the actual cooking condition. For two type thermal storages, that is sensible pebble bed thermal storage and PCM thermal storage with air as heat transfer fluid, computational modeles are developed using MATLAB programming environment. In both case, the results of the computational models were verified using xperimental test results available in articles published in reputable journals. In first case, a cook stove of packed pebble bed thermal storage having 0.3m diameter and 0.9m height was simulated for actual charging and cooking condition using solar radiations of Addis Ababa and Semera. The simulation resulted in thermal storage capacity of 40.1 MJ during a clear day and 12.85 MJ energy during cloudy day for Addis Ababa, and 60.3 MJ and 29.47 MJ of thermal storage for clear and cloudy day of Semera, respectively. The overall cooking efficiencies of the cookstove are 30% and 22.08% under Addis Ababa climate condition and 36.6% and 31.1% under Semera climate condition for the day of the highest and the lowest solar radiation respectively using forced convection. Hence, it can be concluded that solar concentrating cookers with pebble bed thermal storage can have an overall cooking efficiency between 22% and 30% on a clear sky day when the Sun is overhead in tropical areas. Where as for PCM thermal storage, the thermal storage capacities of 47.42 MJ and 14.59 MJ and the overall cooking efficiencies of 53.62% and 44.10% were obtained for the day of the highest and the lowest solar radiation of Addis Ababa, respectively. For highest and lowest radaition day of Semera , the thermal stoarge capacity was 65.36MJ and 38.98MJ and the overall cooking efficiencies were 51.45% and 53.16%, respectively.
Computer-Aided Aerodynamic and Structural Design of Horizontal-Axis Wind Turbine Blades
(Addis Ababa University, 2009-06) Biadgo, Mulugeta; Tesfaye, Tamrat (phD)
Designing horizontal-axis wind turbine (HAWT) blades to achieve satisfactory levels of performance starts with knowledge of the aerodynamic forces acting on the blades. In this thesis, HAWT blade design is studied first from the aspect of aerodynamic view and the basic principles of the aerodynamic behaviors of HAWTs are investigated. Second the structural design which consists of the blade material selection and the determination of structural cross section, FEM analysis is done using CATIA V5 R16 and ANSYS 10. The displacement, Von Mises and Principal stress results are determined, these results shows that ANSYS is more conservative than CATIA in FEM analysis. Blade-element momentum theory (BEM) known as also strip theory, which is the current mainstay of aerodynamic design and analysis of HAWT blades, is used for HAWT blade design in this thesis. BLADE DESIGN PROGRAM which is a user-interface computer program for HAWT blade design is written. It gives blade geometry parameters (chord-length and twist distributions) and design conditions (design tip-speed ratio, design power coefficient and rotor diameter) for the following inputs; power required from a turbine, number of blades, design wind velocity and blade profile type (airfoil type). The program can be used by anyone who may not be intimately concerned with the concepts of blade design procedure and the results taken from the program can be used for further studies.
Cost-of-energy Optimization of 3D Printed Small-scale Wind Turbine Blades
(Addis Ababa University, 2024-06) Abraham Kassahun; Wondwossen Bogale (PhD)
Human-induced climate change is an urgent challenge that necessitates the adoption of renewable energy sources. Wind energy conversion proves to be a promising option, with the horizontal axis wind turbines being identified as the most efficient and mature technology. While large turbines have been widely explored, there is a need for small-scale power solutions – notably in Ethiopia given its low electrification rate. The optimization of wind turbines is a well researched topic, but cost-of-energy optimization has been a challenge due to the difficulty in modeling the cost of traditional wind turbine manufacturing techniques. This research explores the use of 3D printing cost models to optimize energy costs in small-scale wind turbine blades. The cost involved in 3d printing a small wind turbine blade are explored. The cost of each activity in the process is modeled and a total cost estimate is stipulated. A linear relationship was found between the volume of the blade and the turbine cost. This relationship was used in the cost-of-energy optimization of the blade. A python code utilizing a genetic algorithm and a blade element momentum analysis model is written and utilized to obtain a cost-of-energy optimized design. The design variables chosen for optimization are the design wind speed, the tip-speed ratio and the airfoils used. The wind distribution was taken to be that of Addis Ababa. The results indicate the great potential of direct cost-of-energy optimization. A cost of energy of 0.67 $/KWh is obtained for the design which is better than the Skystream 3.7 wind turbine for our location. Sensitivity analysis is also performed by varying the design variables. The objective was found to be much more sensitive to the tip-speed ratio than the design wind speed.
Design and CFD Analysis of a Micro Kaplan Turbine Runner
(Addis Ababa University, 2018-06-06) Getachew, Tikue; Edessa, Dribssa (PhD)
Utilization of Micro hydro power as renewable energy source is giving great attention now a days. This micro hydropower energy can be obtained from potential hydro sites with sufficient water discharge and pressure head. Depending upon the sites, water turbines are designed and manufactured to avail hydropower energy. Low head turbines are widely used on run of rivers and they classified under reaction turbines. They operate at higher flow rate, smaller head and faster rotational speed, thus being more compact than other types of machines. With the increasing cost of energy and the high demand of green energy, the micro hydro Kaplan power plants gain special attention. The development of micro hydro Kaplan power plants on large scale will generate enough energy for the rural community and are being economically profitable. They comprise runner and draft tube and the efficiency of hydro Kaplan reaction turbine is significantly affected by the performance runner. In this present work focused on the design and CFD analysis of a micro Kaplan runner for selected potential site called Denkaka village which is located in Oromia Region, Ethiopia. This runner design and performance improvement is prime concern. In this research, size of the runner was determined using formulas depend on the site data of 3.125m gross head and 0.6m3⁄s fluid flow rate. Geometrical parameters (Dtip =0.4m, Dhub=0.15m, nmax=26��−1 and net power capacity is 14.7 kW) are to be determined. Different tools were used to run simulations. These include XFLR5 soft-ware to determine NACA2412 coordinate pointes of blade profile, Solid work used to make solid 3D model of the runner and ANYS CFX to do its volumetric meshing, fluid flow simulation, for numerical flow analysis and to evaluate the hydraulic performance of the runner. The complete flow pattern is numerically simulated using k-�� model. Simulations have been carried out by varying fluid flow rate and runner speed of the turbine. Research results show 14.7kW of net hydraulic power output and 91.6% hydraulic efficiency were generated. Also as obtained from the pressure contour analysis, there is maximum at the leading edge and then decreases towards the trailing edge. The results obtained from flow simulations were found to be in accordance with turbine characteristics curves. The comparison shows that there is close similarities between present and Dr. Ruchi Khare work.
Design and CFD Analysis of Thermal Energy Storage Using Pcm for Cooking Application
(Addis Ababa University, 2020-06) Mengesha, Alemu; Demiss, Alemu (PhD)
Nowadays there is a serious need for the development of the alternative, appropriate, cheap method of energy use of cooking. In Ethiopia, the majority of the population depends on biomass for cooking applications. However, to avoid this drawback, alternative energy is needed. Hence,the overall purpose of this paper deals with the design and analysis of thermal energy storage using solar salt combnation of 60%NaNO3 and 40%KNO so as to avoid enrgy demand and supply problem. It provides a high energy storage density at a constant temperature which corresponds to the phase transition of phase change material (PCM). At the time of energy available from the solar source, a PCM energy storage technology is selected and designed which will be used for later cooking application.The basic design of the study was using steel materials as a tank (shell) for thermal energy sorage, copper tube encapsulated with PCM material. Heat transfer fluid(air) was selected for the model. In addition, two-dimensional Governing equations like continuity, momentum, and energy were discretized by using the finite volume method (FVM). Thus, all the transient 2D numerical simulations during the charging and discharging process were carried out using the commercial software CFDANSYS Fluent 17.2.As a result,a charging efficiency (70.1%) and discharging efficiency(36.9 %) was obtaind during simulation of thermal energy storage unit by using different mass flow rate. It was observed that the energy stored during charging (30096.47 KJ) and the discharged energy(83454.83KJ) were possibliy used for cooking.This energies were found to be a suitablel design for an indoor cooking application.
Design and Development of a Solar Powered Cooling System to Harness Potable Water from Humid Air (A case study in Semi-Arid zones of Ethiopia)
(Addis Ababa University, 2019-05-14) Gudeta, Wegissa; Abdulkadir, A. Hassen (PhD)
Water shortage is very noticeable in semi-arid parts of Ethiopia where there is hardly any freshwater source at all. Currently, the most interesting method of getting sustainable alternative potable water by harvesting humid from air is continuously under research around the globe. This study was to quantify water from humid air as one of alternative sources using a solar energy prototype targeting semi-arid zone where predominantly pastoralists are living. This paper presents collection of humid air as sand bed introduced to atmosphere at night and a solar thermal regenerative process during day time then extract water from the system. The main objective of this thesis is to design and manufacture the prototype. The experimental setup consists of composite materials: calcium chloride and river sand as well as the glass box enhancing of capturing moisture from air and facilitate regenerative process. It is obvious that semi-arid has a hot temperature in day time, whereas sand bed is actually cooled at night. Hence, the two windows on the prototype introduce the ambient humid air to pass on the sand bed where the humidity will start adsorb. Whereas the solar glass box is exposed to solar radiation and internal temperature become increase where the evaporation and condensation has begun, the water drops will slide over the inner surface of solar glass and finally collected into the jar through the condensate trough. Due to weather climates similarity of Yabello and Adama, testing was done at Wind Farm Electrical Station -1, Adama. The result of one day experiment showed that moisture was collect on the sand bed during night and evaporation also successfully collected on the inner surface of the glass. Testing has been performed after good preparation at Adama wind farm Electric station-1for day and result shows that promising because water condensation on inner surface noticed. But, the numerical result and experimental result did not agree. Low production rate may be the consequence of air leakage, low of humidity amount in the air and low solar radiation intensity. After observing the test result for the effectiveness of the prototype further modification is recommended.
Design and Experimental Investigation of Improved Hybrid Solar Dryer
(Addis Ababa University, 2024-04) Helen Worku; Dino Adem (PhD); Sema Baye (Mr.) Co-Advisor
Maintaining consistent and optimal temperature for a particular food item can be challenging when using solar food dryers, particularly when solar radiation levels are low. This issue can be mitigated by using an Improved Hybrid Solar Dryer, which has been specifically designed to address these challenges. The dryer has been experimentally investigated and compared to traditional open-air sun drying methods for drying red chilies in Addis Ababa, Ethiopia. To thoroughly analyze its performance, the system's output was measured by turning the heater on and off within the dryer for different days. The dimensions of the dryers were: 2m collector length, 2𝑚2 collector area , 2.5m height of the drying chamber from the leg of the dryer to the top of chimney, A drying chamber with a length of 1 meter and a width of 1 meter was used. Each tray had an area of 0.7 square meters. The heating element had a size of 200 watts, the fan 18 watts, and the PV cell size was 4 PV modules, each with a capacity of 55 watts. Using the Improved Hybrid Solar Dryer, it took 26 hours to reach the desired moisture content of 11% from an initial moisture content of 91% on a wet basis. In comparison, open-air sun drying achieved only a 35% moisture content on a wet basis at the same 26-hour mark. The average drying rates, average collector efficiency, and average drying efficiency of the Improved Hybrid Solar Dryer with heater to reach the desired moisture content of 11% (on a wet basis) were are 0.035892 𝑘𝑔/ℎ𝑟 , 62.3%, and 27% respectively while the average drying rate of open-air sun drying was 0.00612 𝑘𝑔/ℎ𝑟.
Design and Experimental Investigation of Savonius Wind Turbine with Air Jet mechanism
(Addis Ababa University, 2021-02) Balcha, Tola; Abdulkadir, A. Hassen (PhD)
The Savonius wind turbine is a type of wind turbine with a vertical axis that operates on the aerodynamic drag principle. It has potential to be developed as it has great advantages, such as simplicity in design and construction, full-capacity operation and production of energy in areas with low wind potential. However, because of its low performance compared to other turbines, the turbine is rarely used. The low efficiency of the turbine is due to the negative torque generated with this turbine. Several researchers have worked to reduce the negative torque generated by this turbine in a variety of ways. Most of them, however, are achieved by limiting the Omni-directional properties of this turbine, which is its main advantage and feature. In this work, we have developed a new feature called the air jet mechanism to reduce the negative torque of the turbine without omitting its Omni-directional properties. The air jet mechanisms have been developed with the capacity to receive wind from all directions and direct it to the useful area of the turbine blade. Due to its geometrical characteristics, the air jet mechanism also works as a venture to increase the speed of the incoming wind. In order to observe their size influence, three different sizes of air jet mechanisms are developed and labeled as longer air jet mechanism, medium air jet mechanism and shorter air jet mechanism and successively positioned around the conventional two-blade Savonius wind turbine with a diameter of 0.4 m and an aspect ratio of 1.5. The performance test of this specified turbine was performed in the laboratory by adding three different size air jet mechanisms around it and without air jet mechanisms (i.e. the bare turbine alone). The performance of the Savonius wind turbine tested under each air jet mechanism is compared with that of the bare Savonius wind turbine tested under the same conditions. When measured with a longer air jet mechanism at a tip speed ratio of 0.4, the power coefficient of the stated Savonius wind turbine increased from 0.05 to 0.11. The results of the investigation showed that an air jet mechanism could increase the efficiency of the conventional two-blade Savonius wind turbine without omitting the wind reception property from all directions.
Design and Experimental Investigation of Solar Cooker with Thermal Energy Storage
(Addis Ababa University, 2018-11) Muluken, Biadgelegn; Abdulkadir, Aman (PhD)
Cooking is the major necessity for people all over the world. It accounts for a major share of energy consumption in developing countries. Therefore, there is a critical need for the development of alternative and affordable methods of cooking. Solar cooking is a novel and eco-friendly method of harnessing sun’s energy. Solar cookers can be of a great use in saving fuel and enabling in eco-friendly cooking of food. Solar energy is available during daytime only and also intermittent. So, thermal storage is important for indoor solar cooking requirements and will ensure continuity of service, reduce the use of conventional energy, and give a reasonable cooking time compared with conventional cooking. The solar cooker designed for this study is1.5 aperture area of compound parabolic dish concentrator integrated with thermal storage media (1.5litter of oil and 0.74kg of rock) as an absorber (area of 0.4 )to increase the duration of the effective energy storage period without tracking and utilize thermal energy for night cooking. The overall system is designed with an assumption to cook 1kg of rice in 45minutes requiring power of 522W which is obtained from the stored energy from the sun. Therefore, the numerical simulation, experimental test, and validation of the two results are done. An absorber with thermal storage is simulated by COMSOL software to show temperature distribution. As it is shown in the simulation section, the temperature of TES could reach365K after 6hours. Where as in the experimental result, due to so many losses the energy reduced in some extent and it reaches 354K. Even if it has low energy, it can cook the required food by placing TES in the insulated tank during discharging. Therefore, there were deviations between experiment and simulation because the model did not account the basic losses and frustration of solar radiation in case of numerical simulation. The model of the TES system was validated with experimental results and a brief reason was found between experiment and simulation for the charging cycle. The discharging of TES is started after it is lifted from solar collector and it is placed on the insulated tank and loaded by pot with water. This is maximum temperature of water reached after 40 minutes is 355K (82℃).
Design and Manufacturing of Solar Injera Dryer
(Addis Ababa University, 2020-10) Senay, Teshome; Abdulkadir, Aman (PhD); Kamil, Dino (PhD)
About two-third of Ethiopian diet consists of injera, which has a strong cultural significance and high nutritional value, as it is rich in fibre, amino acids, calcium, iron and most importantly it is gluten-free. Injera is dried and prepared in times of food scarcity or for commercial and household usage. The objective of this thesis was to design and evaluate a mixed-mode natural convection solar injera dryer with unique vertical air distribution unite with 20 injera drying capacity. Three dimensional simulation of unloaded solar dryer was developed to simulate the performance of the modified mixed mode solar dryer using the computational fluid dynamics (CFD) software ANSYS FLUENT for month of July and April by solving the governing equations describing the unsteady fluid flow. Dual-band discrete ordinates (DO) radiation model, Species transport model and shear stress transport (SST) k-omega (k-ꙍ) turbulence models were employed. The dimensions of the dryer were: 2 m, 2 m , 1.4 m, 2.2 m, 1.5 m and 1 m for collector length, collector area, height of the vertical air distributer channel, the height of the drying chamber, length and width of the drying chamber respectively. 2 C above the ambient throughout the drying period. The overall temperature distribution through the drying trays shows a uniform temperature distribution. The average velocity and mass flow rate through the drying trays were found to be 0.1 m/s and 0.061 kg/s respectively and both were uniformly distributed through the drying trays. There was a pressure gradient through the drying tray, which helps to maintain the airflow through the dryer. The simulation result indicated the collector outlet temperature was 10 o From the experimental result, it was clear that the modified mixed mode drier performance was higher by 19% when compared with other similar mixed mode drier. In addition, the temperatures of the drying air inside the drier was found to be more than 5 C from the ambient temperatures. A uniform temperatures distribution was noticed through the drier, this is the result of the vertical air distributer channel, which was newly developed and integrated through the drying chamber, and the collector and drying efficiency of the drier were found to be 30% and 15.25% respectively. The drying rate of the drier was 2.634*10 o kg/s and the Verma thin layerdrying model fits best for injera drying based on the X -5 . The experimental result was compared with the simulation result and the simulated temperature result showed an average overestimation on drying chamber by -1.5% and underestimation on collector outlet by 1.6 %.
Design and Optimization of Solar Powered Micro-Refrigerator at Dire Dawa Shinile
(AAU, 2017-10) Mohammed, Abrasha; Yilma, Tadesse (PhD)
Energy is one of the key factor for development of the country, and it can be gained from different sources, but some of these sources are not environmentally friendly, expensive and difficult to transport; like fossil fuel. The best option to solve these problems is use solar energy, wind energy and etc. Ethiopia has huge potential for solar energy because it is located close to the equator. Refrigerator is one of the essential tools used in daily. Especially refrigerator is very required for the people who live in desert area for cooling water. The people living in grid connected system use electric powered refrigerator for cooling water, but people living in desert off-grid area can't get electric powered refrigerator. Therefore this problem would be solved when they use solar powered refrigerator. In this work Dire Dawa shinile is study area of this thesis and it located at 9.68° latitude and 41.85° Longitude. One of the major drawbacks of solar refrigerator technology has been the large battery systems that were required to store the sun’s energy for use during the night and cloudy periods. These batteries have a relatively short life time and replacements are expensive. In this work solar power refrigerator optimization is eliminates the expensive energy storage batteries and use ice storage tank instead of battery. PV sizing for solar powered refrigerator is depending on power requirement of compressor by using PVsyst software. The Freeze water in ice storage tank by using the sun's energy which operate compressor of refrigerator and then by using these ice storage to cooling water drink, during solar energy couldn't drive compressor. The net capacity of the refrigerator use for cooling water is 33L and an ice storage of 1kg, is able to maintain 6 liter of water drink temperature below 5℃ as comfortable for drink. The initial cost of solar powered refrigerator is 13,266birr and this cost would be obtain after one year. Solar powered refrigerator system can be reliably used at where the local grid is not continuously available where as refrigeration need is critical.

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