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Design, fabrication and
performance of a motorized cowpea thresher for Nigerian
small-scale farmers
S. V. Irtwange
Department of
Agricultural and Environmental Engineering, University of
Agriculture, Makurdi, Nigeria. E-mail:
svirtwange@yahoo.com
.Tel: +2348035885567.
Accepted 2 November, 2009 |
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Based on
the results of measurements of moisture content of grains,
cowpea grain and pod sizes, grain-pod ratio, angle of
friction of grains and some information from literature, a
motorized cowpea thresher using a star-shaped beater to
which beater belts were attached was designed and locally
built. Five varieties of cowpea, K59, Ife-Brown, IT84E-124,
Ife-Bimpe and TVX 715 which are fairly representative of the
most popular varieties in Nigeria were selected for the
measurement of design parameters. The statistical design
used in studying the effect of variety on length, width,
thickness, equivalent diameter, sphericity, pod weight and
grain-pod ratio with 30 replications, moisture content with
3 replications and angle of friction with 5 replications was
complete randomized design (CRD). The moisture content for
the grain varieties ranged from 11.06 to 12.02% w.b while
the size and shape measurement parameters namely; length,
width, thickness, equivalent diameter and sphericity ranged
from 8.22 to 10mm, 6.04 to 6.83 mm, 4.36 to 5.38 mm, 6.00 to
7.09 mm and 0.71 to 0.79 respectively for grains. For the
pods, the length, width and thickness ranged from 124.78 to
194.93 mm, 7.28 to 9.15 mm and 5.27 to 7.86 mm respectively.
The pod weight and grain-pod ratios ranged from 1.96 to 3.39
and 0.75 to 0.86 respectively for all the varieties tested
while the angle of friction of grains on mild steel ranged
from 23.6 to 26.6o. The results of
the study as indicated by analysis of variance (ANOVA) show
that there is highly significant effect (P ≤ 0.01) of
variety on all the grains and pods measurement parameters
except angle of friction where non-significance was
observed. Skewness and kurtosis analysis indicates that the
frequency distribution curves for grains and pods
measurement parameters generally approximated those of the
normal distribution. Based on the optimum machine
parameters, the machine throughput was determined to be
101.19, 110.86, 74.33, 75.81 and 102.09 kg grains/hour for
K59, Ife-Brown, IT84E-124, Ife-Bimpe and TVX 715
respectively. Preliminary performance evaluation tests
carried out on the fabricated thresher using IT84E-124 as
the test material at recommended beater and fan speeds of
500 rpm and 1400 rpm respectively indicated average
threshing efficiency of 96.29%, percentage damage of 3.55%
and percentage threshed and undamaged grains of 92.74%. A
cleaning efficiency and loss of 95.60 and 3.71% respectively
was observed indicating that with the use of a star-shaped
beater, drudgery and cost can be reduced to a minimum and
yet achieving good quality products.
Key words:
Design, fabrication, thresher, cowpea, performance
evaluation.
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