Thermal Engineering

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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.
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 Advisor
Wind 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.
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.
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 -Advisor
Now 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 respectively
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.
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 Advisor
Millions 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.
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.
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.
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.
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.
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%.
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.
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.
Mathematical Modeling and Simulation of Mixed Mode Natural Convection Solar Dryer for Green Banana Flour Production
(Addis Ababa University, 2021) Betelihem, Zemedkun; Kamil, Dino (PhD)
Fruit drying is one of fruit preservation technique so as to increase shelf life of the produces and reduce food losses. Open air is an old and usual way of drying systems, it consumes a lot of time and also other problems related with contamination. It also consumes bigger space. Solar dryer uses direct solar energy in a better way to produce great amount of heat by using different means, such as, solar air heater and drying chamber with many compartments to handle more products in a good air circulation, only consuming small space. The main objective of this thesis work is to design, model and simulate a natural convection mixed mode solar greenhouse dryer integrated with solar air collector (SAC) for drying of green banana. The dryer consists of an arc roof structure covered with polyethylene plastic on a concrete floor. Solar air collector tilted at an angle of 21⁰ is connected with the greenhouse. To investigate the drying performances of the mixed mode natural convection solar greenhouse dryer, dynamic model of heat and mass transfer was developed and thin layer drying model was selected and this system of non-linear partial differential equations was solved numerically using MATLAB/Simulink software. Comparative study on the performance of the green house dryer with and without SAC was conducted with software simulation. The result showed that the maximum air temperature, maximum product temperature, and maximum cover temperature, without and with solar air collector are found to be 33℃, 46℃, and 78℃ and, 34℃, 54℃, and 79℃ respectively. The moisture ratio of green banana reduced from 1.58 % (db) to 0.2 % (db) within 3 days. Effect of wind speed on the drying performance was also simulated and as a result wind speed has inverse effect on the drying temperature. Therefore, the designed greenhouse solar dryer with solar air heater has a good performance for drying of fruits within a reduced time span and better quality.
Mitigating Condensate Recovery Problem for Boiler Feed Water in Wonji/ Shoa Sugar Factory
(Addis Ababa University, 2021-03) Hanfato, Haile; Wondwossen, Bogale (PhD)
Today the competitiveness of sugar industry is dependent on the efficiency of the factory. The major contributor for the efficiency is the energy performance of the plant as sugar factory is one of intensive energy demanding manufacturing sector. Usually clarifications, evaporation, pan Boiling, and crystallization sections of sugar factory use most of thermal energy of the steam to concentrate and crystallize. In addition to run the factory without interruption continuous and sufficient supply of feed water is important. However, boilers of most sugar factories in Ethiopia are unable to supply enough steam for their respective factory operation purposes besides their electric power generation are not even self-sufficient rather they need external power supply to run the factory like Wonji shoa Sugar factory due to different reasons; one of the reasons is shortage of condensate to the Boiler as feed water. This is mainly known when exhaust steam supplied to first effect evaporator and clear juice heater is recovered only 87.5 % of it. 6.1 t/h or 146.4 tons per day hot Condensate is lost. That is 146.4 tons or 149,082 liters of treated heated water is required per day. Therefore, thermal energy performance of the factory can be improved by increasing the amount of condensate recovered and this is accomplished by avoiding intermittent crushing, reducing down times, crushing different cane varieties together, regular inspection and maintenance of leakages on steam-condensate lines and mainly manage exhaust steam temperature delivered to first effect evaporator and clear juice heater by controlling the amount of de-superheating water. Therefore, Boiler stoppage because of the drop of over flow level of hot well tank as the result of low condensate recovery will be reduced to zero. Consequently, the performance of the Boiler steam generation will be improved by 5%, and the loss of condensate will be minimized to zero so that avoiding downtime will help the factory to save about 7,400,000 birr per day and minimizing condensate loss helps the factory to save 4,621,543.4 birr per day. Totally the factory can save 12,021,543.4 birr per day.
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.
Design, Construction and Testing of Solar Egg Incubator with Thermal Storage System
(Addis Ababa University, 2020-12) Sintayehu, Bekele; Abdulkadir, Aman (PhD)
Incubation is a process by which birds hatch their eggs and develop the embryo within their egg in to young off-spring. In Ethiopia where most of the population live in rural areas where there is no access to grid provided electricity, the method of hatching used were restricted to natural incubation in which the mother hen or broody hen provide the necessary condition for the development of embryo to fully developed offspring. But this is inefficient technique in terms’ of production number, since the mother hen can produce limited amount of young offspring (from 10-12 per cycle). So to solve the problem associated poultry industry hatching method, in this research design, construction and testing of solar poultry egg incubator for hatching chicken egg which can be used in rural areas of the country is discussed. The system has solar thermal collector integrated with low power photovoltaic panel. It uses solar thermal energy to heat air inside solar collector. Air is pressurized from the environment to the solar collector by the inlet fan and gain heat inside the air chamber. The heated air from the collector flow to the incubation chamber due to pressure difference created between them by the inlet fan. Heat exchange process takes place inside the incubation chamber from the hot air to the egg maintaining the egg at 37.80c and 60% the optimum temperature and relative humidity required for incubation respectively. The machine has incubation capacity of 80 egg per on incubation cycle (21 days). The amount of heat energy needed for the incubation of the specified amount of egg is 185w. Total collector area of is used for utilization of the required amount of energy. Thermal energy storage system using paraffin wax as a thermal mass. It is used to store thermal energy needed for the time direct solar radiation is not available. 20kg of paraffin wax is used as a thermal storage material and the volume of thermal storage container is to replace the amount of 80w lost energy in the form of heat from the incubator box during the time direct solar radiation is not available.
Improvement of Energy Efficiency of Addis Ababa Bottle & Glass Share Company
(Addis Ababa University, 2010-09-20) Eshetu, Wondimu; Tesfaye, Dama (PhD)
Addis Ababa Bottle & Glass Share Company purchases furnace oil and electricity from National Oil Company (NOC) and Ethiopia Electric Power Corporation respectively to satisfy its primary energy demand. The prices of a liter of furnace oil and a kWh of electricity are 9.49Birr and 0.5778 Birr respectively. The objective of the thesis is to suggest cost effective measures to improve the efficiency of energy use. The scope is to identify energy conservation opportunities to reduce energy costs and prepare an energy & documentation to implement cost effective energy utilization changes. The methods employed to achieve the objectives of the research are: Literature review, Preliminary data collection of the company, Inspection of company energy consuming systems and equipment, Perform desktop analysis, Identify feasible Energy Conservation Opportunities (ECOs), Perform technical feasibility of the identified (ECOs), Perform economic analysis of the identified (ECOs), Prepare list of recommended energy conservation measures (ECOs) & Prepare action plan. To evaluate the performance analysis of these major energy consuming systems, different data were collected by using portable instruments, the instruments installed on major energy systems, nameplate and referring to company log sheet and record book. The instruments are: Portable Combustion Analyzer (PCA) analyze combustion air, Infrared and dual K contact thermometer measure the surface temperature, Tape meter measure the length of the object & Vernier's calliper measure the internal pipe diameter. Using these data pre-energy audit analyses on heating value of furnace oil, combustion property of the furnace and some of the results obtained including NCV of furnace oil is 39262.6kJ/kg & the excess air in the furnace is 136% . To conclude that using standard methods the energy balance was conducted to determine the first law efficiency of the furnace and the corresponding energy Sankey diagram. The first low efficiency of the furnace on heat balance method is found to be 42%.
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.
Enhancing Power Generation Capacity of Metahara Sugar Factory
(Addis Ababa University, 2011-01) Tatek, Zewdie; Edessa, Dribssa (PhD)
When sugar cane is crushed and the juice separated for crystallization, the remaining dry matter - called bagasse - is burnt in furnace to provide thermal energy. The thermal energy from the combustion of bagasse is used to generate steam which is utilized to drive the power turbines, the mill turbines and for the processes in the plant. Currently, all Ethiopian sugar mills are using bagasse to generate electricity through their cogeneration power plant for self sufficiency and to light the nearby villages only. But many foreign sugar mills are producing and selling electricity from excess bagasse, leaves, trashes of sugar cane in addition to self sufficiency. Metahara Sugar Factory, one of the sugar mills in Ethiopia, fortunately has the potential to use the excess bagasse, which is currently 17.2% of the total bagasse produced, to generate more electric power and earn additional money by selling the power through the national grid or using the power for its own irrigation pump stations. The above figure is determined at the current moisture % bagasse, 50.04%, and average evaporation cofficient, 1.998. But it increases to 30.23% if the moisture % bagasse is lower to 45% and the evaporation cofficient is improved on average to 2.39 by implementing different energy saving opportunities. A total annual savings of more than 14,844,094.19 Birr can be achieved through the use of the excess bagasse. This thesis has assessed the energy resource in Metahara Sugar Factory and determined the steam generation efficiency of the plant. It has also forwarded possible measures to enhance the electric power generation capacity based on measurements, collected data and foreign sugar factories experience.

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