Abstract
The knowledge of the aerodynamic characteristics of tef grains and chaff (floating velocity, aerodynamic resistance coefficient) is significant for the construction and operation of machines, which treat substances with air flow and in all cases when substances are moved in the air. Terminal velocity and drag coefficient of tef grain and straw materials (Kuncho variety) have been experimentally measured by suspending the particles in an air stream. The effects of moisture content of tef grain, node position and length of straw on terminal velocity were studied. The results showed that moisture content have significant effects (p<0.01) on terminal velocity. By increasing moisture content from 7.3 to 25.94 % (w.b.), its terminal velocity increased linearly from 2.98 to 3.87 m/s. Drag coefficient of the tef grain decrease from 0.77 to 0.59 as moisture content increase from 7.3 to 25.94 %. The terminal velocity of the straws with different node positions (node free, end node, and middle node) and lengths (1 to 10 cm) were also measured. Keywords: Aerodynamic properties, terminal velocity, drag coefficient, tef, straw, node DOI : 10.7176/CER/11-3-05 Publication date : April 30 th 2019
Highlights
One of the economical cereal crops in Ethiopia is tef
The initial moisture content of the tef grain was found and in order to be able to measure the effect of moisture content on terminal velocity, the grain was rewetted by adding a calculated amount of water according to equation 1
Effect of moisture content on Terminal Velocity and Drag Coefficient Terminal velocity and drag coefficient were linearly related to moisture content as indicated in equations Table 1
Summary
One of the economical cereal crops in Ethiopia is tef. It is indigenous to the country, and is a fundamental part of the culture, tradition, and food security of the people. This crop is gaining international recognition and acceptance, and is a means of foreign currency earning in addition to its value as food and industrial crop at home. Tef accounts for about a quarter of the total cereal production and is highly economical food grain in Ethiopia. 6 million households grow tef and it is the dominant cereal crop in 30 of the 83 high-potential agricultural woredas (Bekabil et al, 2011). The grain, after grinding and fermentation of the dough, is used to make a thin flat pan cake called ‘injera” (Eleni, 2001)
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