Experimental Investigation of a Concentrating Solar Fryer with Heat Storage
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Today many of the solar cookers available in the market are direct cookers, without storage, and they are used for low to medium temperature cooking purposes. In this dissertation, experiments of heat collection, transportation and storage have been carried out using parabolic dish concentrators, steam as heat carrier and phase change material (PCM) as heat storage respectively. The design of the system has been focused to meet the demand for high temperature heat storage, in an economical, safe, robust and simplified way. The stored heat has mainly been tested for Injera baking purpose, the national food of Ethiopia, which requires intensive energy. Most households eat Injera three to four times per day. Injera needs a heat supply in the range of 180-220°C and more than 85% of Ethiopians use biomass fuel to bake this food. A nitrate salt mixture (solar salt) that has a melting point in this range of temperature was therefore selected as PCM media in this research. The research starts by developing two polar mounted parabolic dish concentrators that are suitable to closed loop self-circulation heat transportation. The first system was placed at NTNU and was coupled to an aluminum block heat storage that has PCM cavities and steam channels. This system was tested for natural and artificial heat source charging. The stored heat was tested for egg frying and water boiling. The second system, at Mekelle University, was coupled to Injera baking clay plate, which has an Imbedded coiled stainless steel steam pipe as a heating element. This system demonstrated an indirect solar Injera baking at about 160°C. However, the heating up time and the baking time interval were very long 3 hours and about 15 minutes respectively. The steam based solar Injera baking result has led to a new research line on Injera baking process and a review of its actual baking temperature. Therefore, Injera baking was tested on three different stove materials regarding its baking time, temperature and Injera quality on different baking surface temperatures. These experiments have identified the possibility of Injera baking as low as 120°C surface temperatures and the ordinary stove design can then be modified to save about 50% of its energy consumption. Another system was tested for alternative way of using solar energy indirectly. In this system, the high intensity solar radiation from the receiver’s of a double reflector parabolic dish concentrator was transported onto an absorber using a light guide. The system was designed for short distance radiation transportation and water was boiled in an experimental case. A third version of a heat storage was designed with conducting fines coupling a coiled top plate with a solar salt bed in a container below. Two units were made and tested at NTNU and Mekelle University. Injera baking tests were carried out on the top plate of the heat storage. Injera baking on a fully charged storage shows shorter baking times compared to conventional electric stoves. The system was demonstrated to the public and the Injeras baked on it and a solar cooked Ethiopian stews were served as a free lunch to the participants at Mekelle university. This was the first complete solar prepared Ethiopian food in the history of solar research in Ethiopia.
Består avPaper 1: Tesfay, Asfafaw H; Kahsay, Mulu Bayray; Nydal, Ole Jørgen. Solar Powered Heat Storage for Injera Baking in Ethiopia. Energy Procedia 2014 ;Volum 57. s. 1603-1612 http://dx.doi.org/ 10.1016/j.egypro.2014.10.152 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
Paper 2: Tesfay, Asfafaw H; Kahsay, Mulu Byray Kahsay. Nydal, Ole Jørgen Design and development of solar thermal Injera baking: steam based direct baking Energy Procedia, volume 57, pp. 2946 – 2955, 2014 http://dx.doi.org/10.1016/j.egypro.2014.10.330 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
Paper 3: Asfafaw H Tesfay, Ole Jorgen Nydal, and Mulu Bayray Kahsay Energy Consumption Assessment of Injera: A Strategy for Energy-Efficient Stove Designs in Ethiopia.
Paper 4: Asfafaw H. Tesfay, Getachew M. Derese, Chimango Mvula, Ole J. Nydal and Mulu B. Kahsay. Experimental Investigation of Optical Pipe as a Means of Radiation Transfer for Solar Thermal Applications
Paper 5: Asfafaw H Tesfay, Mulu Bayray Kahsay, Ole J. Nydal Charging-discharging of a household size PCM storage
Paper 6: Asfafaw H Tesfay, Mulu Bayray Kahsay, Ole J. Nydal Storage integrated solar stove: A case of solar Injera baking in Ethiopia, IEEE GHTC, IEEE proceeding, 659-666, 2014. Is not included due to copyright. Available at http://dx.doi.org/10.1109/GHTC.2014.6970353
Paper 7: Mahmud, Anwar Mustefa; Kahsay, Mulu Bayray; Tesfay, Asfafaw H; Hagos, Ftwi Yohannes; Gebray, Petros; Kelele, Hailay Kiros; Gebrehiwot, Kindeya; Bauer, Hans; Deckers, Seppe; Baerdemaeker, Josse De; Driesen, Johan. Solar Energy Resource Assessment of the Geba Catchment, Northern Ethiopia. Energy Procedia 2014 ;Volum 57. s. 1266-1274 http://dx.doi.org/ 10.1016/j.egypro.2014.10.116 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
Paper 8: Mulu B. Kahsay, John Paintin, Anwar Mustefa, Asfafaw Haileselassie, Meseret Tesfay, Biniam Gebray. Theoretical and Experimental Comparison of Box Solar Cookers with and without Internal Reflector. Energy Procedia, volume 57, 1613–1622, 2014. http://dx.doi.org/ 10.1016/j.egypro.2014.10.153 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license