Design and Manufacturing of Solar Injera Dryer

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Addis Ababa University


About two-third of Ethiopian diet consists of injera, which has a strong cultural significance and high nutritional value, as it is rich in fibre, amino acids, calcium, iron and most importantly it is gluten-free. Injera is dried and prepared in times of food scarcity or for commercial and household usage. The objective of this thesis was to design and evaluate a mixed-mode natural convection solar injera dryer with unique vertical air distribution unite with 20 injera drying capacity. Three dimensional simulation of unloaded solar dryer was developed to simulate the performance of the modified mixed mode solar dryer using the computational fluid dynamics (CFD) software ANSYS FLUENT for month of July and April by solving the governing equations describing the unsteady fluid flow. Dual-band discrete ordinates (DO) radiation model, Species transport model and shear stress transport (SST) k-omega (k-ꙍ) turbulence models were employed. The dimensions of the dryer were: 2 m, 2 m , 1.4 m, 2.2 m, 1.5 m and 1 m for collector length, collector area, height of the vertical air distributer channel, the height of the drying chamber, length and width of the drying chamber respectively. 2 C above the ambient throughout the drying period. The overall temperature distribution through the drying trays shows a uniform temperature distribution. The average velocity and mass flow rate through the drying trays were found to be 0.1 m/s and 0.061 kg/s respectively and both were uniformly distributed through the drying trays. There was a pressure gradient through the drying tray, which helps to maintain the airflow through the dryer. The simulation result indicated the collector outlet temperature was 10 o From the experimental result, it was clear that the modified mixed mode drier performance was higher by 19% when compared with other similar mixed mode drier. In addition, the temperatures of the drying air inside the drier was found to be more than 5 C from the ambient temperatures. A uniform temperatures distribution was noticed through the drier, this is the result of the vertical air distributer channel, which was newly developed and integrated through the drying chamber, and the collector and drying efficiency of the drier were found to be 30% and 15.25% respectively. The drying rate of the drier was 2.634*10 o kg/s and the Verma thin layerdrying model fits best for injera drying based on the X -5 . The experimental result was compared with the simulation result and the simulated temperature result showed an average overestimation on drying chamber by -1.5% and underestimation on collector outlet by 1.6 %.



Solar drier, Mixed mode drier, Injera, Simulation, Vertical air distributer channel