Thermal Engineering

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Browsing Thermal Engineering by Author "Alemu, Demiss (PhD)"

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    Design and Simulation of Sugar Juice Evaporator (Case study: Metehara Sugar Factory)
    (Addis Ababa University, 2015-04) Muleta, Kal id; Alemu, Demiss (PhD)
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    Design;Analysis and Optimization of Photovoltaic Thermal Collector and Storages Tank
    (Addis Ababa University, 2017-01) fisaha, Kifle; Alemu, Demiss (PhD)
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    Integration of Scheffler Concentrator and Thermal Storage Device for Indoor Injera Baking
    (Addis Ababa University, 2013-04) Yayeh, Melkamu; Alemu, Demiss (PhD)
    Women and children spend much of their time in collecting fire wood to cook Ethiopian common food item, Injera and they are the main groups exposed to smoke inhalation while cooking. Deforestation of biomass for cooking is damaging the rural household economy as well as contributing for local and global environment change; i.e. environmental pollution and health problems. The aim of the research work is to integrate Scheffler concentrator with thermal storage system via a secondary reflector for solar cooking to make cooking indoor convenient and avoid the problems that are caused due to carbon inhalation and deforestation. Thus, solar thermal powered Injera baking system is designed. The system consists of the primary concentrator (Scheffler), secondary reflector and thermal storage system with the cooking (pan) assembly. SolTrace software is used to model and simulate the Scheffler concentrator and secondary reflector. The solar power reaching the storage device is determined from the software. The storage device involves sensible heat storage mechanism with Hitec heat transfer salt as a storage medium. The heat retention capacity of the storage system is determined from heating and cooling curves generated by Ansys software modeling and simulation. Based on the results obtained, any convenient indoor cooking device shall be designed especially for rural areas where there is no grid connection; and the result of this research work will alleviate problems related to carbon inhalation and deforestation.
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    Investigation of Parabolic Dish Solar Concentrator for Local Areke Distillation
    (Addis Ababa University, 2015-03) Kassa, Adane; Alemu, Demiss (PhD)
    Areke is Ethiopian’s locally produced traditional fermented alcoholic liquor which is produced from difedif- mixture of milled gesho (Rhamnus Prinoides), finely ground and cooked/baked cereals, and water left for fermentation for nine to ten days, by the of process distillation. The heat required for the distillation process is obtained from burning firewood on inefficient three stone stoves. Energy inefficiency, greenhouse gas emission to the environment, human respiratory system diseases and deteriorating household economy are the major negative impacts that resulted from using biomass as energy source for local areke distillation. This thesis work presents the design and manufacturing of parabolic dish solar collector system for local areke distillation process as a substitute energy source instead of burning biomass and reports the test results of the system. In order to show design procedure; parabolic dish solar collector system with aperture diameter of 1.6m, depth of 0.4m and focal length of 0.4m was designed in full scale. The parabolic dish is designed for distillation of 24 liters of difedif to obtain 3 liters of areke with alcohol content of 44% per day (i.e. from 8:00AM to 5:00PM). One cycle of distillation takes on average 3 hours to obtain 1 liter of areke from 8 liters of difedif. However, the parabolic dish frame of aperture diameter of 1.2m, depth of 0.3m and focal length of 0.3m, which already exists in AAIT Mechanical workshop, with a little maintenance and modification was used for the test purpose. Aluminum foil laminated galvanized sheet is used as reflective surface for dish concentrator. The parabolic dish tracks the sun ray manually based on the shadow of pin on the edge of dish aperture. Especially made clay pot with capacity of 4 liters, and having effective surface area of 0.071m2 was used as absorber. 2.5 liters of difedif was used to conduct the test in three different days. The test result showed it was possible to obtain from 2.5 liters of difedif 0.25liters of areke with alcohol content of 44% and on the average it took 3 hours. And on average it took 1 hour and 15minutes to reach temperature of 70.4oC which is the boiling point temperature of alcohol in Addis Ababa at atmospheric pressure of 0.746atm, where the test was conducted. So, with appropriate design of solar energy distiller system for local areke distillation as an alternative source of energy showed promising results and has the potential to mitigate the negative impacts related to traditional areke distillation method.
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    Performance Analysis and Reliablity Testing of a Ceramic Bake Ware for an Electric Injera Baking Stove
    (Addis Ababa University, 2015-04) Ambaw, Garedew; Alemu, Demiss (PhD)
    In this study, the suitability and reliability of a ceramic bake ware based electric stove (CBWBES) for injera baking application were assessed experimentally and a mathematical model of the coupled heat and mass transfer of the baking process was developed and solved using Finite Element (FE) method. MATLAB code was used to perform the FE analysis, which is then used to estimate the performance of the CBWBES for different numbers of baking cycles. The FE model was first validated using experimental data obtained from field testing of the performance of the CBWBES. The reliability of the CBWBES was investigated for its thermal shock resistance by subjecting the mitad in cycles of baking, and heating and cooling tests from (180 to 210 oC). Regarding the suitability of the new ceramic mitad While; two injera baked at mitad top surface temperature of 210oc Shows poor product quality formation 10 injera baked at a reduced temperature of 147 to 150oc Shows its suitability for the intended application. The CBWBES passed 12 cycles „of injera baking and 6 heating and air cooling cycles without the occurrence of deep cracks in the body. The 10 injera produced before the advent of the cracks was in good quality, with an excellent bottom crest formation and porous top surface structure. The total energy intensity of the new CBWBES was calculated and becomes 1.96 MJ/kg.; which is comparably close to the value of the conventional clay stove, which is 1.79 MJ/kg. The higher thermal inertia of the new CBWBES yields longer heat up times and longer times to recover the baking surface temperature once injera is baked; this was mainly attributed to the increased thickness of the bake ware used for the present test. The heat up time obtained experimentally closely matched with the simulation result with an error of less than 10 %., and the simulation shows about 82 % efficiency can be realizable by reducing the thickness to 8mm for 20 cycles of injera baking, even though the absence of suitable production process in manufacturing the ceramic mitad affects its quality for baking application; based on the results obtained it could be concluded that the CBWBES can be a very good substitute for conventional clay bake wares both for energy efficiency and good quality of product formation provided that a reduction in the heating up time is achieved in the new ceramic bake ware.
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    Specifying Air Conditioning Requirements for Commercial Buildings of Ethiopia
    (Addis Ababa University, 2014-04) Worku, Jemal; Alemu, Demiss (PhD)
    Having Conditioned air is a non questionable comfort issue for both commercial and residential buildings. To do so there should be a specified air condition requirements for air conditioning design so that the required comfort will effectively be attained. Specifying the local or national air conditioning requirements is the only way to effectively attain the human comfort while constructing any building. The main intension of this paper is to specify the air conditioning requirements based on local or national data. Mainly the cooling load in w/m2 which is the main parameter for AC design is determined for representative areas of Ethiopia using the HAP software. These selected representative areas are at different temperature zones. These are Addis Ababa for moderate temperature, Bahir-Dar for warm temperature, Dire-Dawa for hot temperature, and Semera for very hot temperature. While doing this paper first the weather data for the selected areas of Ethiopia are collected from the National Metrology Agency. Also the architectural data or floor plans are gathered for each representative room types. Then all the data are entered in to the soft ware and analyzed by keeping some parameters like relative humidity as a checking point for comfort conditions. Finally the main AC design parameters are specified. Mainly the cooling load in w/m2 for all representative areas of the country is specified for rooms of various applications. The results show that the air conditioning design for commercial buildings depend on many factors. These are geographical locations, orientation of the building, types of applications to which the building is used for, number of population, the floor to which the room is located and the material to which the building is made. In general it is observed that north oriented buildings have lower cooling load in relative to other orientations. And the cooling load is specified for based on north orientation. And also other parameters have their own effect on the effective design of the room from AC perspective. Hence it is recommended for the air conditioning designers of the commercial building to use these local or national standards in which the above factors are considered and to have an effective air conditioning system.