Existing millet threshers have not been performing up to expectation. Based on this, the physical properties of pearl millet grains were determined and used to design an axial-flow millet thresher. The length, width, thickness, geometric diameter, sphericity, surface area of the grains were found to decreased with decrease in moisture content of the grains from 11.6 to 7.8 %. The bulk and true densities of the grains were gotten as 0.73 and 1.14 kg m-3 respectively and the coefficient of friction of the grains on sheet metal and aluminium were obtained as 0.35 and 0.36 respectively. The thresher was made from locally available materials and evaluated at 3 levels of crop moisture content of 7.8, 9.7 and 10.3 % (dry basis), 4 levels of manual feed rates of 60, 90, 120 and 150 kg hr-1and 4 levels of cylinder speeds of 5.5, 7.3, 9.2 and 11.0 ms-1. The collected data were analyzed using analysis of variance and Duncan multiple range test. The thresher had 96.5 % and 95.2 % threshing and cleaning efficiencies respectively. The mechanical grain damage and scatter loss from the thresher were 2.65 % and 27.6 % respectively. The throughput capacity of 60 kg hr-1 was obtained at 9.7 % crop moisture content and 150 kg hr-1feed rate. The analysis of variance showed that for threshing efficiency, cleaning efficiency, grain mechanical damage, scatter loss and throughput, there was no significant difference at 1 % level of confidence in the interactions of the three independent variables. But the analysis showed that the main effects of crop moisture, cylinder speed and feed rate had high significant differences on each of the performance indices evaluated. The Duncan multiple range test showed that the best crop moisture content for threshing was 7.8 %. It yielded 38kg per hour throughput, 94.8 % threshing efficiency, 94.4 % cleaning efficiency and grains damage of 2.5 %. The highest feed rate (150 kg hr-1) and the two uppermost speeds gave best results.
1.1 Agriculture and the World Population
Food is a very important component of human existence. Agriculture plays a vital role in the sustenance and continuous existence of man and his domestic animals. With the world population of seven billion and growing at the rate of 1.1 % per annum (www.worldmeters.org),
there is the constant need to increase food production. The continuous increase in the world population would invariably increase the competition on food, land and other resources for agriculture (www.mapsofworld.com
). For example, lands that were once used for farming are now used for either residential building or some other non-agricultural based industries. This has led to the need to increase the use of technology in order to feed the ever increasing population and to make maximum use of available resources to feed the population.
Cereals and legumes are some of the essential and most consumed food by man (www.fao.org/docrep
). Cereals are widely consumed and utilized by man. They serve as raw materials for food and drug industries. This can be observed by the large metric tonnes of each of them reserved in silos and grains reserves world over (Mckee, 2011). Cereals are also used as animal feed and their stalks are as well useful to man in building temporary fence and as thatch for roofing of mud houses in villages (Mula et al.,
2009). Thus the importance of cereals to man cannot be over emphasized.
Millet is a kind of cereals that is widely grown in Africa and India. Millets are extremely important in the semi arid tropics of Africa and produced in 18.50 hectares by 28 countries covering 30 % of the continent (Obilana, 2007). According to DAFF (2011).