SELECTED PHYSICAL AND MECHANICAL PROPERTIES OF COWPEA AS RELATED TO MECHANICAL THRESHING OF THE ENTIRE PLANT SHOOT
SELECTED PHYSICAL AND MECHANICAL PROPERTIES OF COWPEA AS RELATED TO MECHANICAL THRESHING OF THE ENTIRE PLANT SHOOT
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Date
1988-11
Authors
UBA NWUBA, EPHRAIM IFEANYI
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Abstract
To eliminate pod-picking, it has become necessary to
replace the conventional cowpea (Vigna unguiculata (L.)
Unlp) pod thresher with whole shoot thresher.
This research work deals with selected physical and
mechanical properties of cowpea stalk, pod and grain, as
related to the mechanical threshing of the entire cowpea
shoot. In the study it was found that the cowpea varieties
differed significantly in their grain size which ranged
from G.35 to 9.18mm in length; and the suitability of the
varieties to whole shoot threshing decreased with the grain
size. The mechanical properties of the cowpea stalk were
found to increase with decrease in moisture content and
increase in the rate of loading. The mean stalk elastic
modulus and crushing/bending strength at 25mm/min rate
of loading were 30.4 MPa and 5.10MPa respectively, in
radial compression; and 4l70MPa and 38.6MPa respectively,
in simple bending at about 8% moisture content, wet basis
(MC,wb), the moisture level at which the stalk became
more brittle. The minimum force of 7.25 to 29N required
to crack the dry pod was very low when compared to grain
and stalk. While the elastic modulus,of grain in uniaxial
compression (mean 454MPa at 7.5% MC, wb) was independent
of variety and grain size.
The IAR cowpea pod thresher was tested for whole shoot
threshing and was redesigned. It was confirmed that the
stalk moisture content of about 8% wb was very suitable for
Whole shoot threshing, although threshing at
slightly higher moistures would be possible. The
crushing and breaking energy requirements of single
stalk of cowpea at 8% MC, wb, were 0-00393 and
0.109 J respectively, while the threshing energy
requirement of the whole shoot thresher was estimated
as 139 J at 45Om/min cylinder speed.
Finally, an air flow rate of 16m2/min was found
to be adequate for pneumatic cleaning of threshed
whole shoot cowpea,
Description
A thesis submitted to the Postgraduate School,
Ahmadu Bello University, in partial
fulfilment of the requirements
for the degree of
Doctor of Philosophy
Department of Agricultural Engineering
Faculty of Engineering
Ahmadu Bello University
November, 1988
Keywords
PHYSICAL AND MECHANICAL PROPERTIES,, ENTIRE PLANT SHOOT, COWPEA AS RELATED,, MECHANICAL THRESHING,