Mechanical Design

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Biodiesel Production Optimization and Quality Assessment Using Jatropha Curcas Oil And Ethanol Alcohol
(Addis Ababa University, 2001) Demissie, Biniyam; Alemu, Demiss (PhD)
Concern over high transportation fuel costs, trade deficits, depleting resources, energy security, and mounting evidence of global climate change has led to re-investigation of fossil fuel alternatives. For this reason Ethiopian Ministry of Water and Energy has started promoting bio-energy as a means to transform the nation’s abundant renewable biomass resources into cost competitive, high power biofuels and products. Biodiesel offers one renewable fuel option that can be produced from non edible vegetable oil sources. Fortunately Ethiopia has many opportunities for biodiesel production. The country´s favorable climatic condition for the cultivation of non edible vegetable oil bearing plants and the abundance of ethanol alcohol produced from the byproduct of local sugar factories gave the country a great advantage in producing biodiesel and get a little relief from petroleum related problems. However, the effort made to introduce the technology and take the most out of it is so low to force policy makers and encourage local and foreign businessmen towards the production of biodiesel using local resources. Therefore this research tries to fill this gap. The main purpose of this research is therefore to develop a biodiesel production technique from Jatropha oil (Jatropha curcas Linnaeus) and a locally produced ethanol alcohol. Special attention was paid to the optimization of base-catalyzed transesterification for converting fatty acid ethyl ester (FAEE). The crude Jatropha oil used in the transesterification contained 5.01 mg KOH/g of acid and after neutralization it was possible to bring down the acid value to 1.35 mg KOH/g. Inorder to determine the optimum condition for tranestefication of Jatopha oil using ethanol and caustic soda as input, 16 experiments varyings ethanol-to-oil molar ratio (6:-9:1) and reaction temperature (55, 65, 70, and 78 oC). Reaction time, mixing intensity, and catalyst concentration was fixed to 3 hrs, 600 rpm, and 1.5 % by weight of the oil respectively. The optimum conditions found for transesterification were an ethanol-to-oil molar ratio of 9:1 and a reaction temperature of 70 0C. At the optimum condition obtained a FAEE conversion of 80 % v/v was achieved. The resulting Jatropha biodiesel has, a density of 0.86 g/ml, viscosity of 4.13 mm2/s, acid value of 0.71 mg KOH/g, and flash point of 173 0C satisfing ASTM D6751-02 and EN 14214 biodiesel standards. The production proces developed in this work will be used in production of a small scale plant withh capcity of 300 liter per day.
Biogas Production System Design for Condominium and its Feasibility
(Addis Ababa University, 2011-11) Gaddisa, Bekele; Alemu, Demiss (PhD)
The research is concerned with designing of Biogas Production System for Condominium and studying its Feasibility by crosschecking field survey and information from literatures. The field survey data support the opinion about the importance of constructing biogas plant for Condominium where the average family members’ number is five with average monthly energy cost for cooking is Birr 385 per family. The study indicates that at optimum condition 43.2 m3 day of biogas is obtained from the substrate collected from 10 blocks of Condominium. Based on present energy consumption, 43.2 m3 day biogas fulfills the cooking energy requirement for 43 households. If households use biogas instead of kerosene only, it can serve the cooking energy need for 115 households. Compressing biogas reduces storage requirements, concentrates energy content and increases pressure to the level needed to overcome resistance to gas flow. As the result of installing compressor for this system, 43.2m3 of biogas volume is stored in 7m3 of pressure vessel and the pressure increased to 11bar from 1.106bar. In this study, it was possible to see that the Biogas System Design for Condominium is financially as well as economically feasible as the NPV is positive and benefit cost ratio is greater than one. As financial analysis shows the 40 households will save annually Birr 121,175 or Birr 3,029 per family as a result of using biogas instead of other cooking energy sources & using biogas only instead of kerosene, the 115 households save Birr 1,067 per family per annual. This result is obtained if households construct a 96 m3 biogas plant with daily loading 1.5m3 of night soil in to digester
Computer Modeling and Simulation of Coal fired Cogeneration Power Plant
(Addis Ababa University, 2004-07) Tamirat, Yohannes; Alemu, Demiss (PhD)
This thesis describes a power plant simulator which has been developed using MATLAB code. The basis of the power plant modeled here is the design data of Coal-Phosphate Fertilizer Complex Project (COFCOP), and the type of boiler and turbine are taken as selected by the project. Therefore, the boiler modeled here is a circulating fluidized bed coal combustor type, and the turbine is an extraction condensing type at heat to power ratio. Conservation equations and characteristic curves are used to model each component of the 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. Simulation of systems, subsystems and components are accomplished using the Newton-Raphson technique. The total system of the power plant is simulated by a program called powerplant_main. In this program there are four basic solvers. These are: the turbine solver, the boiler solver, the water flow solver and the steam flow solver. Each solver has its own residue generator function and Jacobean generator function. The Gaussian elimination function is called by any solver during simulation. The power plant in COFCOP is still in design stage, and it cannot be used for program verification in this paper. Hence, a hypothetical power plant data is taken and the output of the simulation closely approximates the real case.
Computerized Activity Based Costing System for process industries, A Case Study On Zemilli Paint Factory
(Addis Ababa University, 2006-11) Gizaw, Mesfin; Alemu, Demiss (PhD)
There is increasing evidence that external and internal pressures are being placed upon companies to acknowledge, characterize and analyses environmental issues, impacts and costs. It has been becoming crucial that companies will increasingly be faced with responsibilities extending outside the factory gate to point of sale and beyond. Companies will need to adopt a life cycle perspective into the decision-making framework, to support managements' decisions regarding the environmental impacts and costs of activities and products. The manufacturing and process sector has suffered from poor management systems for a long time. In process industries, the need for better cost management systems arises from efficiency problems and lack of resources. With activity-based costing, the processes and the costs of activities become more transparent than earlier. ABC has highlighted that true understanding of what it costs to provide products/services is at the same time a tool for better management. It helps to better understand and serve as guides in any business process improvement initiatives, and to subject resources to its efficient usage. In a nutshell, it helps to make more effective business process improvement at more transparent cost. This study is an illustration to point out required changes that could be made during the activity-based costing process in Zemilli paint factory. It shows the benefits and advantages that have come true because of the ABC-process and discuss the problems connected to this process. The ABC-process consists of two phases. The phases and their outcomes are described in chapter four preceded by the basic principle of ABC in chapter three of this study. The first chapter of the thesis dedicated to introduction, background, the importance, objective and the general outline of the paper. The second chapter of the thesis gives the existing condition of process industries in Ethiopia considering specific attention to Zemilli paint factory. While the third chapter of the thesis is fully dedicated to literature survey and Computerized Activity Based Costing System for process industries, A Case Study On Zemilli Paint Factory. ______________________________________________________________________________________ ___________________________________________________________________________ Addis Ababa University, School of Graduate Studies, Department of Mechanical Engineering ix followed by chapter four which gives emphasis to problem formulation and the Activity Based Costing model developed to the factory. The thesis is wind up by including chapter five with outline information to the developed visual basic programming using ABC principles. Finally a conclusion and recommendation is drawn out from the executions of the study in chapter six. The most concrete result of the whole process is a database with visual basic programming working on ABC-model. The model can be used as a tool of daily management. It has been used to find out the costs of each activity and operation. This has enhanced the cost awareness of the unit. The model can also be used for simulation. It can be used to find out the profitability of the operation of the factory.
Design and Manufacture of Laboratory Model for Solar Powered Injera Baking Oven
(Addis Ababa University, 2011-11) Mesele, Mekonnen; Alemu, Demiss (PhD)
Currently millions of people around the world rely on wood as a source of fuel for cooking. Although this situation not only pertains to impoverished rural communities, it is within these communities and in industrializing countries that mostly occurs. The burning of wood in open fires is causing a number of health problems but is also deteriorating for the rural household economy as well as for the local and global environment. Injera is the stable bread in Ethiopia; it is perhaps consumed by almost all Ethiopian people on a daily basis. Biomass fuel can consist of either wood, crop residues, or dried animal dung. Using these energy sources can result in negative effects such as deforestation, environmental pollution, and health problem. Women and children are the main groups exposed to the indoor smoke produced while cooking. The overall aim of this thesis project is to use solar powered injera baking oven, so as to avoid the problems that are caused due to burning of fossil fuels and to assure the environmental sustainability. In this project a laboratory model for solar powered injera baking oven system is designed and manufactured; the laboratory model consists of the oil storage and heating tank, the piping and pumping system, the baking pan assembly, and supporting frame and legs as its main components. The system uses electrical heater to heat the heat transfer oil (shell thermia B) to the required temperature, and then the heated oil is pumped to the baking pan assembly to heat the pan surface and re-circulates in the system using an electrical driven pump. To protect heat loss; ash insulation system for the heat transfer oil gallery, the oil storage and heating tank and fiber glass insulation for the piping lines are used. During the experimental test a temperature of about 215oC on the baking pan surface is achieved and injera is baked on this surface. To increase the heating up time of the pan surface, the pan supporting plate should be a high thermal conductivity material.
Design of Energy Efficient Buildings for Hot Areas of Ethiopia With Respect to Air Conditioning
(Addis Ababa University, 2004-10) W/abzgi, Teklay; Alemu, Demiss (PhD)
This thesis is intended to identify the design improvements of buildings that can be made for the hot region of Ethiopia. A detail literature survey is done on design improvements and those that can be most suitable and economical are suggested. A case study of two different buildings in Gode (one of the hottest area in Ethiopia) was conducted using building energy simulation software to quantify the energy saving from some of the design improvement measures such as using insulation in roof or ceiling and in walls, window glazing and shadings, and orientation. The simulation result verifies that using 75mm insulation in roof or ceilings give a better saving and most economical when the building has small glazing area with respect to the wall size and lower internal cooling load. And when the building has large glazing area using either internal or external window shading is the best way to reduce the annual energy cost of the building and 50mm roof insulation is most economical. In addition to the above results the relation between insulation and different conditions of cooling load in a building is verified. This result shows that when internal load and solar load through window are dominating insulation can have a negative impact to cooling load.
Heat Transfer Analysis During the Process of Injera Baking by Finite Element Method
(Addis Ababa University, 2011-11) Getenet, Gashaw; Alemu, Demiss (PhD)
The main objective of this study was the modeling and simulation of the heat transfer during the process of injera baking. In doing these, mathematical models and finite element formulations for baking pan and injera during baking was developed. In this study, thermo physical properties of injera were studied analytically and were used for the temperature profile prediction using the numerical model. The main properties of interest were specific heat capacity, thermal conductivity, and density. The mathematical model of injera during baking employs the coupled partial differential equations proposed by Luikov. Resulting system of non linear partial differential equations in time and two space dimensions were reduced to algebraic system by applying the finite element numerical method. The fundamental two-dimensional axisymmetric transient finite element model with triangular elements to predict the heat transfer for the baking pan and heat and mass transfer that occur during baking of injera was solved using the Finite Element Method by MATLAB. The backward difference time stepping technique was used for the transient analysis. The simulation was done in terms of temperature profile during heat up, and cyclic injera baking. Simulation was carried out for four different input heated oil temperatures (250, 275, 300, and 325° ) and for four different electric power sources (1.867, 2.2, 2.5, and 3 ). Two types of baking pans (clay and ceramic) with different thicknesses were investigated. Experiments on conventional clay baking pan were conducted to measure heat up time, and mass balance of batter and injera. The heat up time obtained from simulation was compared with experimental test; from the comparison a relatively good agreement was obtained. The energy utilization and efficiency of electric baking pans were determined based on the amount of energy baking pans use in a baking session for a given power input. A relatively better efficiency was obtained for 10 thick clay and 8 thick ceramic baking pans with a power source of 2.5 . While the 10 pan was not practically realized, the 8 ceramic pan manufactured by Tabor ceramic factory is currently under study. Key Words: Finite element method, Injera, Heat and Mass Transfer, Simulation, Efficiency.
Improvement of Maintenance Management System A Case Study on Walia Intercity Bus Service Enterprise
(Addis Ababa University, 2007-07) Tadele, Teklehaimanot; Alemu, Demiss (PhD)
This thesis seeks to provide a greater depth into the exploration of the subject “Vehicle Maintenance Management System” (VMMS). It is found that improved maintenance helps to increase revenues of a firm by increasing vehicle or equipment performance and availability. Most importantly, firms must have maintenance policies and strategies so that the whole firm will be directed in the same direction to reduce equipment down time. The purpose of this thesis is to improve the existing maintenance management system and maintenance efficiency of the enterprise under consideration. The establishment of effective and efficient maintenance management system is the mechanism by which controllable costs are reduced and equipment availability is increased. Controllable costs are the costs incurred due to improper decision during purchasing process by selecting incompatible and cheap price items with out considering reliability and maintainability, and costs incurred due to poor maintenance management system practiced during operation. Thus, the main objective of this thesis is to examine the existing maintenance of Walia Intercity Bus Service Enterprise (WIBSE) and recommend better maintenance management system that enhances vehicle availability with reasonable maintenance cost. The author believes upon implementation of the recommended maintenance management system, availability of vehicles for transportation and useful life are expected to increase due to minimizing of down time and abuse.
Large Scale Application of Solar Water Heating System in Ethiopia
(Addis Ababa University, 2007-07) Bekele, Addisu; Alemu, Demiss (PhD)
In this thesis the investigation of the possible use of solar energy for large scale water heating system is conducted for the following sites in Ethiopia: Addis Ababa Tannery, Dire Tannery, Modjo Tannery, and Jimma Hospital. The thesis focuses on simulation of large-scale solar water heating system and its economic analysis. Transient performance of the system is computed using a numerical heat transfer model of a single glass cover flat plate collector solar water heater with riser and header type active system. The various design parameters are gathered from the inside country solar water heater manufacturers and dealer companies and also from the world experience. The meteorological data for simulation was prepared by taking the average of five years starting from 2001 - 2005. From the annual contribution of solar energy to the heating load and the estimated investment cost, the unit solar energy cost and the pay back period of the system for each case were calculated. The result obtained indicates that the unit solar energy cost for all cases are less than that of unit cost of fuel heating. Hence the solar energy is the viable alternative source of energy for large-scale water heating systems in Ethiopia
“Modeling and Simulation of Solar Evaporative Crystallization of Lake Brine” (The Case of Lake Abijata/Salla)
(Addis Ababa University, 2006-07) Kore, Silashi; Alemu, Demiss (PhD)
Abijata Lake water constitutes the raw material for the production of salt in solar salt works. The salts are: Industrial salts------Sodium carbonate (Na2CO3) Edible salt-----------Sodium chloride (NaCl) The concentration of the Lake water through solar evaporation results in the successive crystallization of less soluble salts (Na2CO3, NaHCO3) first, followed by NaCl. Salt work uses the empirical Baume (OBe) Scale, to measure the concentration of the brines. According to that scale the Lake water concentration is 4.22 OBe (specific gravity of 1.03).The crystallization of Trona (Na2CO3.NaHCO3.2H2O) begins at 26.13 OBe (specific gravity of 1.22) and sodium chloride (NaCl) crystallize at 39.16 OBe (specific gravity of 1.37) Solar crystallization Processes Producing salt from the lake water involves the selective recovery of pure Trona (Na2CO3.NaHCO3.2H2O) and sodium chloride (NaCl), free of other soluble or non-soluble salts and other substances. To this end, an appropriate quantity of Lake Water is concentrated through natural evaporation, which leads to the fractional crystallization of all salts contained: a process based on their varying solubility. The basic step in the processes of salt recovery from the Lake water was made with the division of the evaporation basins in to two: The first basin, usually called nurse pond (pre-concentration pond), was used for the production of saturated brine, which was feed in to second basin, usually called crystallizer. What basically elevates Salt works to ecosystem is the fact for Lake Water to be concentrated up to the point salt crystallization. 90% of its salt content has to be evaporate, thus requires a vast surface. For this reason ponds (pre-concentration ponds) take up 90% of the salt work area. Crystallizers take up approximately 10% of the salt work area. Crystallizes take up the remaining 10% of the area. These basins are especially designed ix and have their bottom leveled and concentrated, aiming to facilitate and optimize the collection of salt with machinery. The first pond of the salt work is feed with Lake Water (raw material) usually via pumping. As the lake water flows along the pond, its concentration raises continuously through natural evaporation. The evaporation (concentration) of brine is achieved by exposure to solar radiation and with the help of the prevailing microclimate in the area, especially the winds, rainfall, air temperature and humidity and duration of sunshine. So an increasing salinity (concentration) gradient is created throughout the ponds of the salt works with a simultaneous and continuous reduction of the volume of Lake Water, which initially entered the system of ponds. This is the physicochemical process of salt production.
A Petri net Approach to Bottling Line Modeling and Performance Analysis: A Case Study on Meta Abo Brewery Share Company
(Addis Ababa University, 2004-10) Lakew, Mesfin; Alemu, Demiss (PhD)
Increasing global competition has made many business leaders and policy makers turn their attention to such critical issues as productivity and quality. Businesses seek new approaches to production processes and manufacturing techniques and explore new boundaries of technology. One of the frequently prescribed remedies for the problem of decreased productivity and declining quality is the automation of factories. To achieve strategic benefits of automation in line with improved quality, greater flexibility, and cost reduction, firms must carefully manage the implementation of their techniques. In the light of the above, because of capital intensive and complex nature of automated manufacturing system (AMS), the design and operation of these systems require modeling and analysis in order to select the optimal design alternative and operational policy. Besides, errors in the modeling process can substantially contribute to the development time and cost. Therefore, special attention should be paid to the correctness of the models that are used at all planning levels. Petri nets as a graphical and mathematical tool provide a uniform environment for modeling, formal analysis and design of manufacturing systems. This study therefore, focuses on both traditional analysis of manufacturing system after setting key performance factors and the application of Petri nets in modeling and analysis of an AMS. It also includes a comprehensive review of xvi Petri nets and manufacturing system in view of Petri nets application domain. ith the view to give more emphasis in the practical and realistic industrial application of Petri nets, particularly in modeling and analysis of AMS, a case study on an existing manufacturing firm was carried. In this regard, Meta Abo Brewery S. Co (MABSCo) is believed to serve as a model. Above all, the success of Petri nets and related technologies can be greatly achieved only when more industrial engineers and designers use them together with other techniques in system development and operation. The author, being an industrial engineer, develop the sample model attributed to the bottling line of MABSCo through a careful study of relevant literatures, systematic data collection, and after systematic survey of the plant, particularly the bottling line. Further research in the future that includes other classes of Petri nets is also proposed to make the study more complete.
Transint Analysis of Cooling Load of a Single Zone Building
(Addis Ababa University, 2004-10) Fantu, Korbaga; Alemu, Demiss (PhD)
Cooling load calculation is the major work performed in the air-conditioning system design. This should be performed as accurately as possible to reduce over design or under design of the system. Some of the factors that influence results of cooling load are heat gain through wall and glass, infiltration of atmospheric air, ventilation, appliances load, and occupancy. The objective of this thesis is to develop a user-friendly program that can easily calculate space-cooling load of a single zone system taking some of the basic inputs like latitude, longitude time zone, building materials and other metrological data of the location. This thesis uses finite difference method for computation of transient heat conduction through the wall and roof. Implicit finite difference method is chosen for its stability.. To make the developed program more friendly, number of commonly used construction materials with their thermal properties are inbuilt in the program. Infiltration effect in the total cooling load is also discussed in detail. Various experimental data and graphs are used for determining the infiltration rate. Heat gain through window is calculated by taking solar heat gain coefficients (SHGC) of the various combinations of glass used. Various types of glass and glass combination with their thermal properties are also inbuilt in the program. The components of heat gain are finally categorized under convective and radiant portion. The convective portions are taken as cooling load. The radiant portions are changed to viii cooling load by multiplying them with radiant time factors. Beside the project uses number of assumptions proposed by ASHRAE for its calculation of heat gain and cooling load. All the above-mentioned influencing factors of cooling load calculation are dealt in-depth in the thesis in chapter 3 4 5 and 6. The results found are verified with results found in other literatures. Finally cooling load of an actual building in Gode is computed using the developed program.

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