Tef (Eragrostistef (Zucc.) Trotter) on the Basis of its Engineering (Physical and Mechanical) Properties
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Date
2020-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
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.
Description
Keywords
Cleaning Efficiency, Concave, Design, Drum, Separation Efficiency, Tef, Threshing Unit, Trampling