Thermal Engineering
Permanent URI for this collection
Browse
Recent Submissions
Item 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.Item 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.Item TRNSYS Modeling and Simulation of Solar Water Heating System for Addis Ababa University Technology Faculty Students Residence Hall(Addis Ababa University, 2011-01) Tsegaye Seyoum; Abebayehu Assefa (PhD)In this study, the transient performance of direct open-loop circulation active solar water heating system is computed using TRNSYS modeling and simulation software for flat-plate collector from the input of average annual climatic data of Addis Ababa and collector parameters. Typical daily hot water consumption for about 1000 students of Addis Ababa University, Technology Faculty was considered. The hot-water demand temperature (60 °C) is controlled by a conventional electrical/fuel auxiliary heater. The thesis focuses on simulation of solar water heating system and its economic analysis. The various design parameters are taken from the manufacturers and dealer companies of solar water heaters in Ethiopia and also from the world experience. The meteorological data for simulation was taken from SEWERA website found in a text and TMY format. The TRNSYS modeling and simulation are used to determine the outlet temperature of the solar collector and the daily contribution of the solar and the auxiliary heating system to the heating load. From the annual contribution of solar energy to the heating load and the estimated investment cost, the payback period of the heating system using two backup systems (i.e. fossil fuel or electricity auxiliary heating) was compared. The results obtained indicate that the payback period of the solar water heating system using furnace oil as backup heater is less than that of electricity, almost by half.Item Experimental Assessment of a Geothermal Still for Hot Spring Water Purification (A Case on Filwoha Hot Springs – Addis Ababa, Ethiopia)(Addis Ababa University, 2022-11) Kalkidan Minwyelet; Yilma Tadesse (PhD)The filwoha hot spring water is used for shower, hydro-therapy massage, sauna bath and steam bath services. Although the natural hot spring water provides such services it is not used as a drinking water. This is as a result of the concentration of parameters such as the total dissolved solid (TDS), the total alkalinity and the fluoride being above the standard requirements for a drinking water. In this research a geothermal still was manufactured and experimental tests were carried out at the Filwoha Spa Service Enterprise, Addis Ababa, Ethiopia. Geothermal still is an apparatus that uses the hot spring water both as a water to be treated and as an energy source that drive the geothermal still operation. The basin area of the geothermal still was and the glass cover tilt angle was fixed at . An L shaped condensate channel of is made to collect the distillate running down the inner surface of the inclined glass cover. To prevent any heat lose, the bottom and sides of the geothermal still was insulated with thick glass wool. The geothermal still construction was contained in a wooden frame of a trapezoidal shape. The geothermal still had an outlet pipe at the front, an inlet pipe at the back and another outlet pipe on the right side for the output discharge with each pipe having a diameter of . The experiment was performed at a water depth of . The operating flow rate for the geothermal still was between . The continues flow of the hot water across the geothermal still serves the purpose of maintaining the temperature of the water stored on the basin. Temperature readings of the parameters such as the basin water and the water vapor were recorded. The geothermal still was estimated to produce 8 liters of distillate output per day. Finally, the water quality analysis reports were prepared by Addis Ababa Water and Sewerage Authority (AAWSA) and Ethiopian Conformity Assessment Enterprise (ECAE) for the distillate samples collected from the geothermal still. The laboratory results showed that the concentration of the total dissolved solid (TDS), the total alkalinity and the fluoride was reduced to the acceptable level for a drinking water.Item Design and Simulation of Solar Powered Evaporative Cooler for Storage of Tomato(Addis Ababa University, 2024-07) Seniya Fedlu; Muaz Bedru (PhD)Post-harvest loss is one of the major problems that need great consideration to address challenge of food security. This issue is mostly common in Africa, especially in sub-Saharan Africa due to lack of electricity, high energy cost to income ratio and attempts to harnessing solar powered energy. However, Ethiopia is one of the high fruits and vegetables producing regions in Africa continent. But due to lack of proper storage around 20% of the harvested product gets spoiled since the region has a semi-arid climate condition which is unsuitable for storage of tomato. The safe storage temperature of tomato ranges between 18ºC to 22ºC. This temperature range can be achieved with refrigerators and evaporative coolers. However, the cost of refrigeration system is very high compared to evaporative coolers and they also consume large amount of electric power for the same cooling effect. Thus, considering that there is no electrical coverage in the farming areas, a solar powered evaporative cooler would be more suitable for storage of tomato in the region. A direct evaporative cooler with a capacity of 100kg is designed and its performance is studied with simulation on ANSYS Fluent. The effect of varying the thickness of the cooling pad, inlet velocity and inlet temperature on the performance of the cooler is studied. Three pad thicknesses (50mm, 75mm and 100mm), inlet velocities of (0.5m/s, 1m/s, 1.5m/s, 2m/s and 2.5m/s) and inlet temperatures (25℃, 27℃, 29℃ and 33℃) are considered. The result shows that larger pad thickness has a higher temperature drop at the outlet compared to the pad with smaller thickness. The cooling capacity and cooling effectiveness also increases as the thickness of the pad increases because increasing the thickness of the pad increases the heat transfer area. Increasing the velocity of the air at the inlet increases the outlet temperature. Increasing the inlet velocity also increases the cooling capacity and cooling effectiveness since increasing the velocity increases the flow of air which favors the heat transfer. Optimum cooling conditions forItem Design and Experimental Investigation of Improved Hybrid Solar Dryer(Addis Ababa University, 2024-04) Helen Worku; Dino Adem (PhD); Sema Baye (Mr.) Co-AdvisorMaintaining 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.Item Modeling and Simulation of a Micro-Hydropower System for Rural Electrification [A Case Study of Temcha River, Ethiopia](Addis Ababa University, 2021-05) Getnet Belie; Tilahun Nigussie (PhD)As a fact, there is an imbalance of the electricity demand and supply in Ethiopia. Since the country has the potential for a micro-hydropower (MHP) system, development of the MHP system is an important technology to solve the problem of energy scarcity in the world. Therefore, the main objective of this study is to do modeling and simulation of a micro-hydropower system for rural electrification in the case of Temecha River, Ethiopia. The methodologies followed to finalize this study are: - Firstly, literature reviews section covers the theoretical framework and related work reviews on hydropower, specifically the MHP system. Secondly, the data collection and analysis section for yearly flow data was collected from Ethiopian Basins Development Authority and used to estimate the design flow rate. Thirdly, the modeling and simulation section of the research includes the design analysis of the system components and simulation of the system using MATLAB SIMULINK. Some of the SIMULINK results are power duration curve, flow duration curve, and others are included. The gross head and design flow rates are 7m and 0.7376m3/s, respectively considered for this research. Based on the preliminary analysis, the turbine selected for the site is a Kaplan turbine based on net head and design flow rate. As a result, the runner diameter, hub diameter, blade tip diameter, the net mechanical power output values are 354mm, 378mm, of 840mm, 82.5W respectively. The final electrical power output of the system is greater than the electricity demand amount of the selected site for 346 days of the year. In addition, the cost analysis has done via RETScreen software. The total estimated cost of the system is around $ 764,400 with that of the pay-back period is 7.2 years and the net present value is $ 1,446,858, which is positive. The value of the NPV indicates the feasibility of the system for the selected remote area to solve the scarcity of an electricity access. Finally, the overall outcomes of the study and the recommendation for future development of the system are covered.Item 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.Item Design, Modeling, and Analysis of A HAWT With A Passively Induced Morphing Blade(Addis Ababa University, 2023) Amare Adihena; Asfaw Beyene (PhD); Yilma Tadesse (PhD) Co AdvisorWind energy become a major form of energy in the past decades, which needs extensive research activities to improve power efficiency. Herein, a Palm tree-inspired morphing blade novel concept design is introduced to improve the power efficiency of conventional HAWTs. The rotor speed is regulated by a twist-augmented bending system and the blade restoration at low tip speed is performed by a spring-augmented pivot hinge system. The main objective of this research project is to design, a 3D model, and Analysis of a HAWT with a passively induced morphing blade. A NACA 4412 Applicable profiles is selected for the proposed morphing blade design. A knowledge-based design compatibility analysis (DCA) was investigated, indeed the design is compatible. The 3D model of the proposed morphing blade was done using CERO PTC 8, and ANSYS Fluent 2021R2 was used for the CFD analysis. The computational geometry was discretized in a well-structured fine tetrahedral cell with the recommended skewness <0.95 and orthogonal quality >0.1. The CFD analysis was based on the simplified Reynolds Averaged Navier Stokes (RANS) governing equations with a steady-state Spalart-allmaras turbulence viscous model. From the CFD simulation results, the average power produced at an annual mean wind speed was 870 KW. In addition, the linear relationship between the theoretical (analytical), and CFD simulation results of power coefficient (Cp), Tip speed, and produced power, shows a very strong correlation. To compare the Annual Energy production (AEP), a conventional SANY SE7715 wind turbine installed in the Adama II wind farm project with the same operating conditions and partial design specifications was taken as a reference site. Using the software-based analysis results, the AEP of the newly introduced morphing blade at annual mean wind speed is 7.62 GWh. Likewise, the average AEP of the reference site as per the prior researcher’s investigation is 5.59 GWh. which is about 570 GWh gross AEP for the total 102 sets. This indicates the AEP of the novel morphing ability wind turbine design is 36.4 % higher than the reference site. Finally, the detailed design of the inner structures of the palm tree-inspired morphing blade, detailed structural load analysis, prototype, and experimental investigations are part of the future work.Item Potential Assessment, Techno-Economic Feasibility Study and Modeling of a Micro Hydropower Plant to Power the Street Light Using Akaki River(Addis Ababa University, 2023-10) Ezra Girmachew; Tilahun Nigussie (PhD)Ethiopia, one of the east African nations, has an abundance hydroelectric resource potential due to the abundant water resources in the country. However, in recent years, demand for electricity has grown, especially in urban areas. Therefore, it is essential to make optimum use of the national resources for the improvement of electrical energy. The main objective of this thesis is modeling, simulation, assessment of potential, and techno-economic viability of a micro-hydropower system for the electrification of street lighting in the case of Big Akaki River in Ethiopia. The approach used to achieve the objective involves understanding the fundamental operating principle and reviewing prior works, which are done as part of the literature review. The yearly flow data was collected from Ethiopia's office of water, irrigation, and energy and the head data obtained from GPS visualizer. Next based on these data modeling and selection of scheme components including techno economic viability of the system using RETScreen and MATLAB SIMULINK was done. Moreover, Flow duration curve, turbine efficiency curve, Power duration curve, from RETScreen and hydropower simulation from MATLAB SIMULINK results are included. For this research the gross head of 2.8m and design flow rates of 0.459m3/s, were considered. Based on the net head and design flow rate, Kaplan turbine was selected for this study. Consequently, the design parameters like the turbine speed, runner discharge diameter, specific speed and the net mechanical output was found to be 568.3rpm, 390mm, 515.5rpm and 7.41KW respectively. All in all, the systems water to wire efficiency of 53.13% was optimized to be greater than the demand at the selected area for street light. For the cost of the study, RETScreen software was applied also used to estimate total cost of the system to be $275,400, with a pay-back period of 15.6 years and an overall positive net present value of $30,779 overall.Item Design and Optimization of Solar Thermal Vapor Absorption Refrigeration System Integrated With Phase Change Material for Cold Room Application(Addis Ababa University, 2023-06) Firehiwot Matewose; Demiss Alemu (PhD); Demiss Molawerk (Mr.) Co -AdvisorNow a day many cooling systems are used in order to keep the food product in the conditioned room. For this cooling effect, mostly conventional compression refrigeration system is applicable which has high-energy consumption and the working fluid of it that is HFCC causes the environmental degradation and ozone layer depilation. Using renewable energy is a promise-able technology to solve the above problem but its energy source is not pretty much. For energy of low quality source absorption-based cooling system is compatible what if it requires energy storage system. This thesis emphasizes optimizing the vapor absorption refrigeration system of performance 7.772 kW. Material that undergoes phase change (PCM) is combined utilizing solar thermal energy to provide cooling capacity, allowing the system to function at night as a backup thermal energy storage system. The cooling load was calculated for 6500 kg of fish is to be stored in 4x2x2.5 m size of the room. By using ASPEN plus software, the vapor absorption refrigeration for this load was optimized and modeled. Ammonia, which is created by distilling an ammonia-water (NH3-H2O) solution in the generator, serves as the refrigerant for the VAR system. The obtained Coefficient of Performance was 0.7, this is a typical performance for a vapor-absorbing system. The power source of VAR system was solar based heat energy where solar radiation is under Hawassa weather conditions. This solar thermal heat energy supplied for 6 hours for VAR system and the remaining 18hrs is provided by PCM storage system. The size of the CPC collector was 28.26 m2. Additionally, the system's performance is examined in MATLAB integrating with ASPEN plus software. The charging and discharging temperature variation with respect to time for thermal storage is 3.5 and 9.5 hours for minimum solar radiation and 1.5 and 15.5 hours for maximum solar radiation respectivelyItem 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.Item Numerical Investigation on Charging Discharging of a PCM Using PV and Thermal Oil for Injera Baking Application.(Addis Ababa University, 2023-06) Meseret Alemu; Abdulkadir Aman (PhD); Gashaw Getent (Mr.) Co AdvisorMillions of Ethiopians rely on bio mass, charcoal, and animal dung to supply their energy demands. All of this energy is used to bake injera, more than 50%. This traditional biomass based baking has an impact on women's and children's he alth, energy, and ability to attend school. Due to its abundant and readily accessible renewable energy source, solar energy had been considered to be a good alternative for cooking. However, because of its intermittent nature, there is a mismatch between the load and the solar energy that is available for the baking purpose, so a thermal storage system that provides the necessary energy has been integrated. T his study investigates th e thermal characteristic of the charging and discharge processes and main heat transfer processes in the injera baking system with PV which was integrated with the thermal storage system T his study was conducted beginning with review ing related papers, system design, data collection and data analysis in addition, performed m athematical and numerical model s and numerical simulation was conducted using a finite difference computational model for the thermal storages that was PCM and thermal oil The thermal oil was used to store energy and to transfer heat, furthermore, the dev eloped computational models are analyzed using MA TLAB programming software. F rom the numerical simulation result by using solar radiation data of Addis Ababa showed that the thermal storage has the capacity to store about 3 3 MJ during charging using const ant heat flux which was from the PV The amount of energy discharged from the PCM was 13.1 MJ and from the thermia oil was 3 .5 0 MJ by using natural convection heat transfer and the discharging and overall efficiency of the system w ere about 50.2 and 46.67 respectively. Also, the baking pan surface temperature stayed between 220 o c and 1 46.4 o c for about three hours . T his result was compared with different papers and it can be concluded that the numerical ly investigated solar powered Injera baking integrated with thermal storage showed a promising result.Item Experimental Investigation of Solid-Liquid Separator and Solar Tunnel Dryer for a Biogas Digestate(Addis Ababa University, 2023-06) Tesfamichael Awoke; Wondwossen Bogale (PhD)Through the 20th century, higher energy demand, fossil fuel depletion, environmental pollution problems and waste management requirements led the development of biogas production technology. However, the biogas plant's slurry/digestate, causes significant environmental issues since it pollutes the soil, water, and air through the release of phosphate and nitrate gases. With the use of mechanical and thermal treatments, digested biogas waste is suitable for use as fertilizer or a soil amendment. In order to use biogas digestate as fertilizer, to minimize environmental pollution and to store and transport it securely and conveniently; liquid components must first be separated mechanically by presses (solid-liquid separator) and then thermally by vaporization (dryer). This study examines the fundamental design of the screw type solid-liquid separator and solar tunnel dryer, manufacturing and laboratory investigations, as well as characterize both the solid and the liquid portions’ suitability from the mechanical and thermal parameters such as the portions’ final moisture content. By using both the separator and dryer, the moisture content (the liquid fraction) of the fresh biogas digestate is able to reduce from 75% to 5% ( from 75% to 40% using the separator and from 40% to 5% using the solar dryer). The separator has a capacity of separating 7.5m3 of digestate at 8 hours and the dryer has the capacity to dry 2m3 of digestate at a drying time of 3 days, 7-8 hr. per day at the experimentation site Addis Ababa, 8.9806° N, 38.7578° E. Both the separator and dryer has a cost of approximately 35,000 ETB.Item Design and Simulation of Institutional Solar-powered Cookstove Using Thermal Storage System(Addis Ababa University, 2023-06) Tihun Birhanu; Abdulkadir Aman (PhD); Kamil Dino, (PhD)The world's demand for energy is rising quickly, yet conventional energy supplies are also declining. Future energy demands must thus be supplied and increased securely and efficiently. One of the most pressing issues of the twenty-first century is the sustainable production and use of renewable energy. A dependable supply of clean, affordable energy for everybody must be addressed. Because of that, this study determined if a solar-powered institutional cook stove with thermal energy storage that uses commercial SHELL THERMIA OIL B as the heat transfer medium as well as 40% KNO3+60% NaNO3 potassium nitrate salt (Solar Salt) as PCM for institutional food preparing was feasible. A mixture of 41L HTF (bulk temperatures up to 320ºC, and film temperature up to 340ºC) and 42 sealed copper tubes (Internal diameter 62.611 mm, 2 mm thickness 300 mm height) carrying a total of 60 kg of PCM (melting point range of 210-220°C and the Latent heat fusion 108.67 KJ/Kg)is used to store heat. The HTF was filled in the storage compartment to cover the copper tubes and is assumed to fit within cylinder jackets that wrap around the tubes and also operate as a heat transfer medium. A heater having 4500 W and 220 V input power from photovoltaic system with temperature control device is immersed inside storage during the charging phase. The ANSYS software is used to simulate the proposed model's thermal storage unit's transient behavior. ANSYS Workbench was utilized in a step-by-step fashion to model the process. A pressure-based solver was employed for melting/solidification processes, and for pressure-velocity coupling, the Semi-implicit pressure-linked equation technique was used. Grid independence assessment is also performed in order to choose the ideal grid size with the best solution and the lowest computing cost. The thermal storage's performance was assessed utilizing constant heat flux. The developed model's numerical study was solved numerically using an enthalpy-porosity approach and validated against experimental data. The results demonstrated that the CFD simulation using ANSYS Fluent for the stove was appropriately validated. Based on the simulation results, a performance investigation was carried out. The thermal storage was able to store 53.5MJ of energy in 3.8889 hours of charging time. The overall cooking, charging, and discharging efficiencies were 61.46%, 71.52%, and 85.62%, respectively. In the case of a convective heat transfer coefficient of 244 W/m2 K, the phase change material and heat transfer fluid demonstrated good heat retention of 5 h. Finally, the results indicate expanding the application of solar cooking at the institutional level is visible.Item Design, Simulation, Manufacturing and Testing of a Low-Cost Tube Type Direct Solar Oven(Addis Ababa University, 2022-04) Yonael, Tesfaye; Kamil, Dino (PhD)Ethiopia is rated as number four country in the world for solar cooking potential by the Solar Cookers International (SCI) in 2020. The country had an estimate of 24,200,000 people who live in areas that have good solar cooking power potential but with fuel scarcity. Shortage of electrical coverage in most parts of the country has led to high biomass dependency for energy demand. The household baking accounting for more than half of this energy, the country faces a great deforestation scale of around 200,000ha per year. Indoor pollution and hard labor of women and children are also results of this situation. Thus, this research focuses on designing, simulating, manufacturing and testing of a tube type direct solar oven which is low cost and easy to manufacture at the local markets of Ethiopia. The tube type direct solar oven is designed to bake 1kg of bread dough. It has a cylindrical oven inside an air tight transparent tube that acts as an insulation for the oven. For low cost and ease of fabrication the air tight transparent outer cover is a square prism made of 4 plastic (acrylic) plates. The solar oven is made of light materials which are easy to find locally. Thus, it has the advantage of being portable and affordable. Simulation of the solar ray’s trajectory using COMSOL Multiphysics showed that all the incidence rays falling on the parabolic trough will reflect back on to the receiver for a 0º incidence angle. And the bread baking simulation using COMSOL took 35min to bake 1kg of bread dough which is 5minutes longer than the analytical design. Tests conducted on the manufactured solar oven showed that the standard cooking power of the solar oven at 700W/m 3 2 is 98W. The actual bread baking time of the oven was longer than the designed and simulated results due to quality in manufacturing and quality of materials used. But the economic analysis showed that the tube type direct solar oven is al low-cost effective baking tool with a short payback period resulting in an initial investment of $100 and a maximum payback period of 4months and 24days. Thus, the tube type direct solar oven is an easy to manufacture, easy to use low-cost direct solar oven that has a potential of being widely accepted by the Ethiopian society for its economic and environmental advantages.Item Design, Manufacturing and Performance Evaluation of Modified Solar Bubble Dryer for Pepper-Vegetable Crop(Addis Ababa University, 2021-10) Mengistu, Zelalem; Kamil, Dino (PhD)Capsicum (Red pepper) is a spice type plant having major role in Ethiopians daily dish and plays an important role in the national economy. On average 79% of pepper production goes to market and this results employment for urban and rural workers. For anyone who produces fruit or vegetables on a commercial basis, one of the most serious challenges is getting their products to market and selling before it spoils. The objective of this study was to design and manufacture modified solar bubble dryer to minimize and overcome the post-harvest loss of pepper vegetable crop. The experimental result showed that the efficiency of the dryer and the mass flow rate was found to be 22.6%, 3.53 x10−4kg s⁄. In addition to this the modified solar bubble dryer is portable, easy to operate and can also be used to dry any kind of vegetable. It reduces the moisture content of the pepper from about 71% to its safe storage condition of 13% in 20 hours of operation. This result was achieved within five days of experiment for four hours per day at a drying rate of 0.1 kg hr⁄. It was observed that, the modified solar bubble drier performance was 10% greater than other similar drier, and the drying time is 20% lower than that of open sun dryer. It was also observed that a uniform temperatures distribution was noticed through the drier and the temperature inside the drying chamber was greater than that of ambient temperature by an average of 3 to 5°C. Therefore, it is recommended that the modular feature of the solar bubble dryer is an option to dry vegetables to reduce the alarming rate of postharvest losses in the country.Item Design, Manufacturing and Experimental Investigation of Pico-Power Hydrokinetic Turbine(Addis Ababa University, 2021-09) Teklemariam, Tadesse; Abdulkadir, Aman (PhD)Ethiopia has plenty of rivers and groundwater sources in the countryside which have the potential to generate electricity from Pico up to Mega power. There is a hydrokinetic turbine technology to generate green energy using river flow water. The gap is to interact with this technology and energy resource of water. The cost of imported equipment for this technology is expensive as well as the available equipment is mostly for large-scale hydropower energy conversion technology projects. This study aims to design, manufacture locally available material and experimental investigation of Pico power hydrokinetic turbine to grasp energy from the river water resource. The hydrokinetic turbine is the systems class of “zero-head” hydropower whereby energy is extracted from the kinetic energy of flowing water, similar to wind turbines, rather than the potential energy of falling water. The method to do this research includes optimizing the geometry of the turbine blade and force analysis of the blade using Ansys software. The blade was manufactured with a 3D printer and the mechanical components were manufactured in the workshop of the school of mechanical and industrial engineering. The test was conducted in four setups at different water velocities. The results are AC RMS value of 11.33Amp and RMS value of voltage 6.89volt respectively with the motor revolution of 486.75 rpm. The power coming from the experiment showed that it is sensitive to current and they have the same sinusoidal pattern plotting the results within each interval of seconds. The net power can be obtained from the turbine was 128.37 watts. The efficiency of the turbine is 51.48%.Item Modeling & Simulation of Small-scale Biodiesel Plant and Design of Excess Ethanol Recovery System(Addis Ababa University, 2019-03) Girma, Demeke; Demis, Alemu (PhD)Rising world fuel prices, the growing demand for energy, depletion in fossil fuel, and concerns about global warming are the key factors driving the increasing interest in renewable energy sources and in biofuels in particular that can be used as an alternative fuel in CI engines. The aim of this study was modeling and simulation of the small-scale biodiesel plant under construction at Addis Ababa institute of technology and design of excess ethanol recovery mechanism for the plant. Experimentally determined reaction conditions (Reaction temperature 80OC, Ethanol to Oil molar ratio 9:1, catalyst concentration 1% w/w, reaction time 3.5Hours) for optimal Biodiesel production were used for the design of the plant. Aspen Plus software version8.4 was used for the simulation of the Transesterification. The simulation was done by initially determining the reaction kinetics of the Transesterification process from a biodiesel yield vs time graph obtained from a defended thesis titled “Emission and Performance Characteristics of Jatropha Ethyl Ester and its blends with Diesel Fuel in a C.I. Engine” done by Haymanot Baynesagn at Addis Ababa institute of technology from which the reaction conditions for the plant design are taken. From the biodiesel yield vs time graph, the amount of biodiesel obtained at a point of 30 min interval time for temperatures of 60OC, 70OC, 80OC and 90OC was calculated. Then, the amount (in gram, mole & litter) and concentration of other components in the reaction process at every time interval for the specified temperatures were calculated. From the determined concentration values, the integrated form of the transesterification reaction was plotted so that from slope of the plot, the forward and reverse rate constants determined. The Arrhenius equation is an equation that shows the dependency of the rate constant on temperature. Thus, the natural logarithm of the rate constants determined for the specified temperatures above was plotted against the invers of the temperatures and from the slope of which the kinetic parameters; Activation Energy and Frequency factor (input parameters to the simulation) determined as; for forward reaction Eaf= 25.769KJ/mol and Frequency factor Af = 60.26/min and for the revers reaction Eab= 22.934KJ/mol and Frequency factor Ab=4.69/min. Aspen software consists of property database for lots of materials. However, Triglyceride oils such as Jatropha oil have not been yet added to the database. Thus, it was a must to select a similar material from the existing once to represent Triglyceride oils. Triolein oil is the mostly selected model to represent Triglyceride oil. Accordingly, the transesterification reaction was modeled with Triolein in place of Triglyceride and the simulation done. The simulation result obtained was 91.4% yield of biodiesel which was higher than the experimentally determined value of 85.24%. As the Transesterification reaction is a reversible, excess alcohol is normally added to force the reaction towards the forward. Thus, after the completion of the reaction the amount of alcohol being consumed in the reaction is much lower and much amount to remain unreacted that is termed as excess alcohol. The amount of ethanol that remains unreacted at the end of transesterification reaction was nearly 73%. If this excess amount of ethanol is left uncollected and reused, the process cannot be economical. Thus, inclusion of a mechanism for recovering of excess ethanol in a transesterification process is mandatory. For biodiesel production plant of higher capacity, distillation column is the mostly used alcohol recovery system. However, a reflux condenser is used for smaller production capacity of plant. In this paper, a design of vertical helical coil heat exchanger with dimensions of height 510mm, Shell Diameter 285mm, copper tube of Ø7.94mm (5/16 inch) with coil pitch of 17mm was designed for use as reflux condenser.Item Modelling the Heat Transfer during the Solidification of a Sand-casting Process by using Finite Element Method: The Case of "Akaki Basic Metal Industry"(Addis Ababa University, 2021-09) Biniyam, Mulugeta; Demiss, Alemu (PhD)Even though sand-casting process is one of the oldest techniques to produce different products, the method is known as process of uncertainty since it is difficult to control process parameter and identify the real cause for defects associated to the process. Most defects encountered during casting identifies after the process is completed and then it leads to remelting and wastage of material, time and manpower. Currently modern casting foundries utilizes a significant effort to understand the underlying physics involved in solidification casting process to and to model casting process. However, local foundries used floor trial method to eliminate casting defects that leads to less productivity and decrease competitiveness in the market. The main purpose of this study is to numerically model the solidification heat transfer during sand-casting process in case of Akaki Basic Metal Industry (ABMI). The model employs finite element method (FEM) utilizing fixed mesh technique. Computational simulation of the problem modeled using ANSYS software. Three cases selected from the foundry, casting of ash cleaner door and manhole cover by grey cast iron and casting of aluminum flywheel. The actual density of sand mold measured experimentally using analytical balance as 2506 kg/m3. The simulation of a two-dimensional transient thermal analysis result shows the temperature distribution, heat flux distribution and nodal values. The result of the simulation depicts the total solidification times are 2249, 177, and 133 seconds for case 1, case, 2 and case 3 simulation. Besides parametric study analysis was performed to investigate the effect of mold size, pouring temperature and mold property on the cooling of solidification. Validation of results with experimental literature shows a good agreement with experimental literature data. The study result can be an input to the foundry for controlling process parameters without performing actual casting in the floor. The study recommends that local foundries could give attention in using numerical models to predict the casting process in order to increase their productivity and competitiveness.