Tef (Eragrostistef (Zucc.) Trotter) on the Basis of its Engineering (Physical and Mechanical) Properties

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Addis Ababa University


Tef (Eragrostis tef (Zucc.) Trotter) is a typical crop growing in most areas of Ethiopia, ranking first in area coverage and second in cereal production. Threshing of tef is often done by animal trampling which commonly causes quality and quantity loss. Consequently, improving the threshing technique is a priority which requires research intervention. The objective of the current research project was to investigate the theoretical and experimental of threshing mechanisms for designing tef threshing unit on the basis of its physical and mechanical properties. The physical and mechanical properties of tef namely: diameter, length, modulus of elasticity, shear strength and flexural rigidity were determined. Four major varieties [Local, DzCr-438- (Kora), Dz-Cr-387/RIL-355 (Quncho) and Dz-01-1880 (Guduru)] were considerd for the research. The test varieties were harvested by sickles with a minimum height of cutting 1-1.5 cm from the ground. The panicles were separated from the stem and the stem was divided in three equal lengths. The segments’ physical sizes were measured and coded. Texture Analyzer and Universal Testing Machine were used for measuring their mechanical properties. The factors considered were moisture content, diameter and thickness of the tefs’ stem. Experimental data were analyzed using analysis of variance (ANOVA) linear modeling correlated with multi linear modeling. The means were compared with different range tests and graph construction in R i386.3.0.1 software. The results indicated that among the tef varieties the minimum and maximum values of modulus of elasticity were 1.03 and 3.88 Gpa at moisture levels of 5.5% and 19.70% at upper and bottom positions for Kora and Guduru varieties respectively. The maximum modulus of elasticity and shear strength of tefs’ stem were applied to determine the power requirements of the threshing unit. Then designing and manufacturing of the threshing units were performed following the standard design procedures. After manufacturing the newly developed threshing unit and establishing the test stands, the design effect of the SG-2000 model and the newly developed (closed type concave and drum) threshing units were evaluated. The three variables: threshing capacity, cleaning efficiency and separation efficiency on feed rate and drum speed with three levels 275, 325 and 400kg.hr and 900, 1000 and 1200 rpm respectively. Experimental data were analyzed using analysis of variance (ANOVA) non-linear modeling, correlated with polynomial modeling and spearman methods. The means were compared with different range tests and graph construction and analysis in R i386.3.0.1, ANSYS 2015 and MATLAB 2014a software’s were used. The test result revealed that the newly developed (cylindrical type concave) has significant difference under 99% of confidence interval on separation and cleaning efficiency over SG-2000 (the open type concave). The maximum threshing capacities were found to be 70.88 and 52.11 kg.hr -1 -1 for newly developed and SG-2000 threshing units respectively. Further, the research compared the design effect along the concave length of two threshing units. The mean values of the cleaning and separation efficiencies were 24.85% and 35.92%; and 85.66% and 93.34% for SG-2000 and newly developed threshing units respectively. Upon comparison of the two threshing units, the mean values of performance increment for newly developed over SG-2000 threshing units were 7.8%, 44.54% and 9.5%. The maximum value increments were 36.4%, 56.19% and 15.4% in capacity, cleaning efficiency and separation efficiency respectively. The effective threshing zone was determined, based on the result it is recommended to minimize the length of both threshing units with respect to the existing features. MATLAB 2014a software was used for the evaluation and graphical representation of modeling and simulation. Under mathematical and computational modeling and simulation, the result showed that best fit in optimization of the performance evaluations parameters of tef threshing unit. Therefore, the technology is recommended to promote to the end users. It can improve the cleaning efficiency of tef threshing mechanisms; increase the quality of tef and the drudgery of farmers. To perform closer to 100 % cleaning efficiency, it is recommended to have additional sieves.



Cleaning Efficiency, Concave, Design, Drum, Separation Efficiency, Tef, Threshing Unit, Trampling