Tef (eragrostistef (zucc.) Trotter) On The Basis Of Its Engineering (physical And Mechanical) Properties

Tef (Eragrostis tef (Zucc.) Trotter) is a typical crop growing in most areas of Ethiopia, rankingrnfirst in area coverage and second in cereal production. Threshing of tef is often done by animalrntrampling which commonly causes quality and quantity loss. Consequently, improving thernthreshing technique is a priority which requires research intervention. The objective of therncurrent research project was to investigate the theoretical and experimental of threshingrnmechanisms for designing tef threshing unit on the basis of its physical and mechanicalrnproperties. The physical and mechanical properties of tef namely: diameter, length, modulus ofrnelasticity, shear strength and flexural rigidity were determined. Four major varieties [Local, DzCr-438-rn(Kora),rnDz-Cr-387/RIL-355rn(Quncho)rnandrnDz-01-1880rn(Guduru)]rnwerernconsiderdrnforrnthernrnresearch.rnTherntestrnvarietiesrnwerernharvestedrnbyrnsicklesrnwithrnarnminimumrnheightrnofrncuttingrn1-1.5rncmrnrnfromrnthernground.rnThernpaniclesrnwerernseparatedrnfromrnthernstemrnandrnthernstemrnrnwas divided in threernequal lengths. The segments’ physical sizes were measured and coded. Texture Analyzer andrnUniversal Testing Machine were used for measuring their mechanical properties. The factorsrnconsidered were moisture content, diameter and thickness of the tefs’ stem. Experimental datarnwere analyzed using analysis of variance (ANOVA) linear modeling correlated with multi linearrnmodeling. The means were compared with different range tests and graph construction in Rrni386.3.0.1 software. The results indicated that among the tef varieties the minimum andrnmaximum values of modulus of elasticity were 1.03 and 3.88 Gpa at moisture levels of 5.5%rnand 19.70% at upper and bottom positions for Kora and Guduru varieties respectively. Thernmaximum modulus of elasticity and shear strength of tefs’ stem were applied to determine thernpower requirements of the threshing unit. Then designing and manufacturing of the threshingrnunits were performed following the standard design procedures. After manufacturing the newlyrndeveloped threshing unit and establishing the test stands, the design effect of the SG-2000 modelrnand the newly developed (closed type concave and drum) threshing units were evaluated. Thernthree variables: threshing capacity, cleaning efficiency and separation efficiency on feed rate andrndrum speed with three levels 275, 325 and 400kg.hrrn and 900, 1000 and 1200 rpm respectively.rnExperimental data were analyzed using analysis of variance (ANOVA) non-linear modeling,rncorrelated with polynomial modeling and spearman methods. The means were compared withrndifferent range tests and graph construction and analysis in R i386.3.0.1, ANSYS 2015 andrnMATLAB 2014a software’s were used. The test result revealed that the newly developedrn(cylindrical type concave) has significant difference under 99% of confidence interval onrnseparation and cleaning efficiency over SG-2000 (the open type concave). The maximumrnthreshing capacities were found to be 70.88 and 52.11 kg.hrrn-1rn-1 rnfor newly developed and SG-2000 threshing units respectively. Further, the research compared the design effect along the concavernlength of two threshing units. The mean values of the cleaning and separation efficiencies werern24.85% and 35.92%; and 85.66% and 93.34% for SG-2000 and newly developed threshing unitsrnrespectively. Upon comparison of the two threshing units, the mean values of performancernincrement for newly developed over SG-2000 threshing units were 7.8%, 44.54% and 9.5%. Thernmaximum value increments were 36.4%, 56.19% and 15.4% in capacity, cleaning efficiency andrnseparation efficiency respectively. The effective threshing zone was determined, based on thernresult it is recommended to minimize the length of both threshing units with respect to thernexisting features. MATLAB 2014a software was used for the evaluation and graphicalrnrepresentation of modeling and simulation. Under mathematical and computational modeling andrnsimulation, the result showed that best fit in optimization of the performance evaluationsrnparameters of tef threshing unit. Therefore, the technology is recommended to promote to the endrnusers. It can improve the cleaning efficiency of tef threshing mechanisms; increase the quality ofrntef and the drudgery of farmers. To perform closer to 100 % cleaning efficiency, it isrnrecommended to have additional sieves.

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