Thermal Engineering

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Experimental Analysis of Drying of Agricultural Product
(Addis Ababa University, 2004-09) Hagos, Berhane; Assefa, Abebayehu (PhD)
An experimental system set up has been developed to investigate the drying rate of the selected material, the drying air temperature and relative humidity and moisture content profiles developed with the food materials during forced convective air drying. The moisture content profile was determined by employing the technique of oven drying method. Embedded thermocouples were used to sense temperature at different locations, and the embedded digital relative humidity measuring instruments were used to sense the relative humidity and recording the values manually at different locations of the drying chamber. A data logger and a computer front end were implemented for data acquisition. Temperature, relative humidity, moisture and drying rate profiles are presented as function of the drying time. All profiles described the drying phenomena inside each trays of the drying chamber. The close relations of overall drying rate and profiles of moisture content, drying air temperature and relative humidity are discussed. Finally correlations are formulated from the experimental data to relate the drying parameters; drying air temperature, relative humidity, velocity, initial moisture content of material to be dried and drying time that predict the moisture content on wet basis.
Simulation of Modern Steam Power Plant
(Addis Ababa University, 2005-06) Hailu, Alemayehu; Assefa, Abebayehu (PhD)
The thesis describes a steam power plant simulator which has been developed using the MATLAB code. The simulation is important to study the behavior of the steam power plant system by means of a model, and the results obtained allow us to consider many different design possibilities as well as varieties operating conditions. Therefore, different designs may be evaluated so that an acceptable design can be chosen and safe levels may be established for the operating conditions. These results are also used for optimization of the plant. The basic considerations in the development of a mathematical model are first presented in the thesis, followed by a discussion of simulation of a steam power plant. Conservation equations and characteristic curves are used to model the component of the steam power plant. From these mathematical model equations, the component modules are developed using MATLAB code. Output parameters are obtained from input data to the component modules. The STEAM_POWER_PLANT_SIMULATION program is used to simulate the power plant system. In the program there are two main solvers. These are: the turbine-heater solver and boiler solver. The turbine-heater solver consists of the turbine and feed water heaters including the pumps and the condenser. The boiler solver has its own residue generator function and Jacobean generator function and then Newton-Raphson technique is used to solve a set of nonlinear algebraic equations.
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.
Energy Audit of Mekanissa Alcohol FactorY
(Addis Ababa University, 2009-01) G/Mariam, Samuel; Edessa, Dribssa (PhD)
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.
Modeling; Simulation and Performance Evaluation of Parabolic Trough Solar Collector Power Generation System
(Addis Ababa University, 2009-09) Mesfin, Mekuannint; Assefa, Abebayehu (PhD)
Parabolic troughs are one of the low cost solar electric power options available today and have significant potential for further cost reduction. Parabolic trough power plants use concentrated sunlight, in place of fossil fuels, to provide the thermal energy required to drive a conventional power plant. These plants use a large field of parabolic trough collectors which track the sun during the day and concentrate the solar radiation on a receiver tube located at the focus of the parabolic shaped mirrors. A heat transfer fluid passes through the receiver and is heated to temperatures required to generate steam and drive a conventional Rankine cycle steam power plant. In this thesis paper model of a parabolic trough power plant, taking into consideration the different losses associated with collection of the solar irradiance and other thermal losses is presented. MATLAB software is used to model the power plant at reference state and TRNSYS software is used to simulate the performance of the model at off design weather conditions. MATLAB modeling of the power plant is used to find the different reference values which are used as inputs for the TRNSYS modeling and simulation of the power plant. The reference values include the solar field area, the heat transfer fluid (HTF) and steam/water mass flow rates, overall heat transfer coefficients of the different heat exchangers, etc. The TRNSYS modeling and simulation are used to determine the net power, initial steam temperature, the inlet and outlet heat transfer fluid temperatures out of the solar field and steam and HTF mass flow rates in hourly basis for representative days of year 2001. The cost and financial analysis is made for the power plant. Solar Advisor Model is used to make this analysis under Addis Ababa weather condition. This analysis is used to determine the different costs associated with the power plant. The cash flow for the 30 years of operation of the power plant is also shown.
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.
Modeling, Simulation and Performance Evaluation of Central Receiver System Power Plant with Thermal Storage
(Addis Ababa University, 2010-09) Bedru, Muaz; Assefa, Abebayehu (PhD)
Solar Central Tower systems have a single receiver placed on top of a tower surrounded by hundreds of mirrors (heliostats) which follow the apparent motion of the sun in the sky and which re-direct and focus the sunlight onto the receiver. The key elements of a solar tower system are the heliostats:- provided with a two-axis tracking system, the receiver, the steam generation system and the storage system. A fluid circulates through the receiver, collecting thermal energy at high temperatures, and flows to an insulated storage tank. Steam for the 10 MW turbines is made as needed by pumping the hot fluid to a heat exchanger. The receiver and energy storage fluid is a commercial molten potassium and sodium nitrate mixture. The number of heliostats will vary according to the particular receiver‟s thermal cycle and the heliostat design. The power plant analyzed in this paper has a capacity of generating 10MW electric power. The power cycle was modeled using EES to obtain the state point variables such as conductances of the heat exchangers, mass flow rates of steam and HTF, enthalpies, temperatures, pressures etc… at specified state points for steady state operation of the plant. These state point variables are used as reference inputs and/or parameters during system simulation using TRNSYS. The CRS was modeled in TRNSYS simulation studio using existing TRNSYS 16.0 components most of which are from STEC library release 3.0 packages. The CRS financial and economic analysis as well as different system component size and number was optimized using SAM. Without the incorporation of thermal storage, 788 heliostats with 97m2 area satisfies the power demand specified for this research but the addition of thermal storage increases the number of heliostats to 1200 with significant increase in initial system cost and decrease in levelized energy cost. A six hour capacity two tank thermal storage is incorporated with the power plant in order to avoid power transient during low and high DNI, to have power when there is no sunlight, to increase the capacity factor and to minimize the levelized cost of energy. The addition of a thermal storage extends the power plant operation to 16 hours with 13 hours of constant 10MW net electrical power output for a clear sunny day. The SAM analysis reveals that the ii addition of thermal storage in the system significantly increase the investment cost from $58,072,837.73 to $76,781,394.61 with minimizing effect of LCOE from 33.02 to 26.79 cents/kWh and increasing capacity factor from 17.3 to 30.0%
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%.
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.
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.
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.
Modeling Simulation and Performance Evaluation of Parabolic Dish Solar Power Plant
(Addis Ababa University, 2011-01) Aklilu, Tesfaye; Abebayehu, Assefa (PhD)
A solar parabolic dish electric power generation system is one option for a high temperature solar concentrator that is capable to achieve a high system performance. This results from the fact that it combines an excellent concentrator, a very efficient cavity receiver and a high performance heat engine. The Stirling dish system produces electricity using concentrated solar thermal energy to drive a Stirling engine. The system utilizes a parabolic mirror equipped with dual-axis tracking to concentrate solar radiation onto a thermal receiver integrated in the Stirling engine. The receiver consists of a heat exchanger designed to transfer the absorbed solar energy to the working fluid, typically, hydrogen. The Stirling engine then converts the absorbed thermal energy to mechanical power by expanding the gas in a piston-cylinder in a manner similar to a gas or diesel engine. The linear motion is converted to a rotary motion to turn a generator to produce electricity. The electrical output of the system is proportional to the size of the reflector, its optical losses and the efficiencies of the Stirling engine and the generator. This thesis outlines the theory and models for the collector, receiver, and Stirling engine, the parasitic power. An energy prediction model was created for solar Stirling dish systems to predict the location dependent long term performance of these systems. The model analyzes the performance of the parabolic mirror, receiver, Stirling engine, and the parasitic power consumption to predict the net power produced. The power plant analyzed in this paper has a capacity of generating 10MW electric power. The performance prediction models were implemented in EES and TRNSYS and include location dependent properties that affect the performance based on the direct normal insolation, ambient temperature, density of air (altitude), sun elevation angle, and the wind speed. The cost and financial analysis is made for the Dish System. Solar Advisor Model is used to make this analysis under Kombolcha weather condition. This analysis is used to determine the different costs associated with the power plant. The cash flow for the 30 years of operation of the power plant is also shown. I
The Impact of Foreign Direct Investment (FDI) on Technology Transfer
(Addis Ababa University, 2011-10) Yared, Lemma; Daniel, Kitaw (PhD); Gulelat, Gatew (Mr.)
Technology has gaining importance as vital factor for competitiveness in the world economy. Technology transfer through Foreign Direct Investment (FDI) has become the predominant channel of technology transfer. FDI can have important technological spillovers in host economies, especially if it takes a joint-venture form subject to local control. Technology transfer has been a subject of considerable interest to many groups, such as policymakers, international funding agencies, and business executives, due to close relationship between technology transfer and economic growth. It has aroused the interest of academic researchers. Despite all this attention, however, the concept and mechanism of technology transfer remains vague, controversial, and inadequately operationalised. Unfortunately, due to the need for capital and/or absence of appropriate national technology policies, most host developing countries focus on maximizing the quantity of their FDI inflow, while underestimating the importance of appropriateness of technologies transferred through FDI. However, competitive technology has become a basic prerequisite for economic development and growth, and developing countries like Ethiopia should try to achieve best possible technological gains from FDI. Using a firm-level survey, this study examines effects of FDI on local metal and engineering firms. The survey indicates that technological inflow through FDI is an important conduit in promoting local firms to upgrade and to be competitive in national as well as international market. However, the local technological capability to adopt the technology, the collaboration between foreign based companies and local firms, and the national technology policy are very weak to benefit from FDI. The study also explores the possible contributing factors related to foreign technology transfer, such as domestic competition and linkages (training and consultancy, employee movement, etc). The experience of newly developing countries is reviewed with regard to FDI and technology transfer and the gaps are identified and analyzed. To address the problem the researcher proposes policy implications and framework by putting the contributors to effectively transfer technologies from FDI.
Quality Management Practices, the Case of Harar Brewery Share Company
(Addis Ababa University, 2011-11) Negalegn, Alemu; Daniel, Kitaw (PhD); Birhanu, Beshah (Mr.) Co-Advisor
In today‟s tight competitive market, quality is becoming a single competitive dimension in different parts of the world. Several quality management practices have been implemented in several organizations to produce quality product and to deliver quality service. The Ethiopian manufacturing industries are facing different problems in becoming competent in this intense global competition. Poor quality management practice is one of the major causes which forced to be weak in the international market. There are very few local companies which tried to implement different quality management practice like ISO 900 quality management system, ISO 14000 environmental management system and HACCP systems to bring better organizational performance. But these companies couldn‟t achieve the envisioned result due to ineffective implementation of these quality management systems. Among the local companies Harar Brewery Share Company (HBSC) implemented the three quality management practices interactively and achieved the benefits of implementing those practices. HBSC, the Ethiopian Quality Award winner in 2009, has better implemented the ISO 9000:2000 QMS, ISO 14001:2004 and HACCP interactively and as a result the financial performance of the company has been improved, the company reduced the process variation and factory standards have been met, about 5,000,000 birr has been saved annually by utilizing resources efficiently, the skill level of the employees have been increased so that becoming productive, customer satisfaction is being growing, the company has been building good images in the society and ultimately the HBSC laid the foundation for the next movement towards achieving total organizational involvement on quality. In bringing these achievements, HBSC faced several challenges and employed strong effort in curving those challenges to the truck of practicing quality management. From the experience of HBSC, it can be observed that if the efforts of quality management have been practiced effectively and interactively, tangible outcomes can be registered. The lessons HBSC left for other local manufacturers is that it can be possible to achieve better performance by implementing ISO 9000, EMS and HACCP effectively with high commitment. Therefore, other manufacturers should implement these systems and gain the benefit of practicing them.
Energy Saving and Fuel Switching Opportunities in Tabor Ceramic Products Share Company
(Addis Ababa University, 2011-12) Mebratu, Markos; Demiss, Alemu (PhD)
Ceramics is defined as inorganic, non-metallic materials those are consolidated and acquire their desired properties under the application of heat. This application of heat in practice takes place inside high-temperature kilns, usually for long period of time making ceramics energy intensive industry. Tabor Ceramic Products Share Company is traditional ceramic manufacturing and energy intensive industry as it produces tiles, sanitary ware and tableware products. It is the only ceramics producing company in Ethiopia located in southern part of the country in Hawasa town. Due to high energy cost from total production cost and using highly inefficient kilns and other energy using equipments the company is in financial crisis. The growing need for ceramic products due to development of the country, increasing fuel cost from time to time and well known energy saving practices in European and Asian ceramic industries which can be easily adapted to our countries ceramic plant as well as the fact that the company is in real need of ways which can reduce its energy cost have necessitated this study. Several energy saving opportunities in the tabor ceramics factory are obtained by this research and can be directly implemented in the factory. It is tried to classify some of energy saving options based on cost of implementing them and this is done by estimating the capital cost and annual cost of operation as well as saving that could be achieved by implementing the saving option and by calculating the payback period of the measures. The result of the current research has showed that more saving can be achieved by investing more on identified energy saving opportunities. Actually it is not to deny that there are no cost energy saving options that can increase the profitability of the company if implemented and priority should be given to these saving measures. Energy saving measures identified by the current research like reducing thermal mass of existing kiln cars, installing new modern low thermal mass kiln cars, recovering waste heat from cooling zone of tunnel kilns especially from glost kiln, installing high speed burners in kilns, avoiding dummy firing in tunnel kilns, reducing loss of products at each step of production, applying monitoring and targeting system etc can be implemented with low cost there by resulting in huge energy saving which can pay back the investment cost in less than two years time, for most of them the payback period being below one year. But above all the energy saving opportunity that can make tabor ceramics factory competent in local as well as in world market by greatly reducing its specific energy consumption i.e. energy consumed to produce one ton of ceramic products, is introducing the technology of single fast firing by installing roller kiln for tiles production. This measure will require substantial investment cost and change in process and the reward will be very high; saving of about 50% with payback period of below three years. Finally by considering the technology and trained man power availability of the country it is discovered that it is possible to save energy equivalent to at least 424,429liters of kerosene or about 6million birr [kerosene cost 14birr per liter when this research is done] annually. The major fuel switching opportunities identified by current research and to be applied in Tabor Ceramics Factory are mainly focused on switching to cheaper fuels that can be obtained within Ethiopia thereby saving the foreign currency the country expends to import petroleum fuels. According to the researcher this can be achieved by using Ethiopian coal as fuel in spry drier which currently uses gasoil, effectively recovering heat from cooling zones of kilns to supply heat required for drying sanitary wares to save fuel used in boilers to produce hot water for mentioned purpose, and as there is plan that Ethiopia will be commercially producing natural gas in coming six years it is wise decision to switch fuel of kilns from current kerosene to natural gas. This will have multi-benefit as experiences from developed countries shows that they have already done this measure because natural gas is environmentally friendly fuel than other solid and liquid fuels and in our case it will save foreign currency for fuel of kilns when produced in Ethiopia.
Modeling and Performance Evaluation of a Simple Reactive Muffler of Vehicles Using CFD
(Addis Ababa University, 2012-01) Dessalegn, Abera; Edessa, Dribssa (PhD)
One of the components in the exhaust system of vehicle is muffler. The purpose of the muffler is to reduce the exhaust noise produced by the engine. The main objective of this study is modeling performance evaluation of a simple reactive muffler of vehicles using CFD. Simple expansion chamber muffler has been modeled numerically using Computational Flu id Dynamics (CFD) in order to determine its acoustic response. The CFD model consists of an ax isymmetric grid with a single period sinusoid of suitable amplitude and duration imposed at the inlet boundary. The time history of the acoustic pressure and par ticle velocity is recorded at two points, one point in the inlet pipe and the other point in the outlet pipe. These time histories a re Fourier transformed and the Transmission Loss (TL) of the muffler is calculated. The mean flow has also been considered. The mean flow model of the muffler is done using finer mesh and with a suitable inlet velocity applied at the inlet boundary and the pressure drop across the muffler is found. The performa nce of the muffler is evaluated based on Transmission Loss, Insertion Loss and Backpressure. The simulation of the muffler was carried out using FLUENT software package. GAMBIT was used to create a mesh and to define the boundary condition of the required object, which is ready and analyzed by FLUENT. The version used is FLUENT 6.3.26. The solver implemented was an axisymmetric, segregated implicit solver with second order implicit time stepping. Second order upwin discretization was used for the density, momentum, energy, turbulent kinetic energy and turbule dissipation rate equations. PISO pressure velocity coupling is used. The k - for closure. The working fluid was air with the density modeled assuming an ideal gas. The bounda conditions consist of a velocity inlet, a pressure outlet and a series of walls. The CFD results are compared with numerical results. Transmissions Loss vs. frequency curves are analyzed. Expansion chamber mufflers have been widely studied and results show that the larger the expan ratio the greater the Transmission Loss. It is a good practice to design a muffler to work best in the frequency range where the engine has the highest sound energy.
Thermal Analysis, Design and Experimental Investigation of Parabolic Trough Solar Collector
(Addis Ababa University, 2012-02) Yidnekachew, Messele; Abebayehu, Assefa (PhD)
Experimental Study of Biomass Gasification in a Downdraft Gasifier Using Different Feedstocks
(Addis Ababa University, 2012-02-19) Henok, Mekonnen; Abebayehu, Assefa (PhD)
The primary interest of this research work is to study the gasification properties of different biomass feedstock materials which are easily available in Ethiopia. An overview of biomass is discussed in this paper so as to have a clue what chemical composition does a biomass material can have and its implication of energy conversion. The different types of conversion processes are also covered in order to show the possible ways that energy can be extracted from biomass and to compare their merits and demerits relative to gasification. A precise theoretical overview of gasification is dealt which has laid a very starting ground for what is done in the simulation and experimental works. Experimental investigation is an irreplaceable tool to get a very meaningful finding in this research even though simulation can give a good guidance and a pre insight. Simulation work alone can be misleading since many simplifying assumptions were taken in order to make it possible to simulate the very complicated thermo-chemical process inside the gasifier and also the still unclearly phenomenon of tar formation. Both simulation and experimental work are undertaken in this research. A Matlab program is used to simulate the effects of moisture content and equivalence ratio on the constituent gas composition of the produced gas. An algorithm based on a thermodynamic model with certain simplifying assumptions is used so that the Matlab program will not miss the physical outlook of the modeled gasification process. Tables and figures are generated which are suitable to see the effects of different parameters on the final output of the gasification process. An experimental investigation is undertaken using different feedstock materials. The experiments are being carried out for some selected biomass materials which are charcoal, sawdust, coffee husk and a mixture of sawdust and coffee husk. The effects of moisture content and equivalence ratio on the final syngas composition are studied. The amount and nature of tar produced while gasifying the different feedstock is also examined. A comparison of the simulation and experimental works is done and it was reasoned out what effects the deviation of the experimental result from that of the simulation work. It was also attempted to compare the simulation and experimental results with those in literatures. At the end recommendations and suggestion of future works are presented concerning the work of this research.
Fluid Flow Analysis and Performance Prediction Of A Radial Fan Using CFD
(Addis Ababa University, 2012-06) Tesfaye, Kebede; Edessa, Dribssa (PhD); Abdulkadir, Aman (Mr.) Co-Advisor
Centrifugal fans are machine for moving a gas, such as air, by accelerating it radially outward in an impeller to a surrounding casing. They are often used in heating and ventilation and air condition system (HVAC). But, the efficiency of the fan can still be improved by studying their detail performance characteristics and modifying their geometry. In this thesis, at first step, an experimental study is conducted to investigate the performance characteristics of forward curved centrifugal fan by varying its volume flow rate. From the performance characteristics of a base machine which were plotted based on the test result, the performance of the fan increases as the flow rate of the working fluid increases from zero to design flow rate of the fan. Beyond its design point, the performance of the fan starts to drop. Next, a two dimensional (2D), steady state, incompressible, turbulent flow field inside fan models have been analyzed numerically. During numerical simulation, from all types of k-ε and k-ω turbulence models, the appropriate turbulence model is selected based on their agreement with the experimental result. Details of CFD analysis are done on the effects of shaft speed and blade numbers. From the CFD analysis, a best improvement of 4.05% in efficiency has been attained at 49 blade number. But the analysis done on the shaft speed resulted in the flow rate and outlet total pressure enhancement with direct proportion to input power and shaft speed.

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