One of the aerodynamic characteristics of lentil is its terminal velocity. In order to determinate the terminal velocity, was designed a vertical wind tunnel. It was fabricated based on existing methods and standards. For decreasing the non-uniformity of airflow in the vertical wind column, was used a honey comb test area with 5 mesh screens. So, a wind tunnel nozzle was designed and fabricated using Morel method with the aim of increasing airflow rate and decreasing losses due to mesh screens. The height and section area of tunnel were 1.425 m and 0.1 × 0.1 m2, respectively. The pressure loss values were calculated at different parts of tunnel and then, the required power of tunnel was determined. In this study, lentil grains of Kimia and Gachsaran varieties were separated at three groups based on their size (small, medium and large). Then, the terminal velocity was measured at 5 levels of moisture content (8, 12, 16, 20 and 24% (w.b.)) for each group. The results showed that Kimia and Gachsaran variety had the highest (7.204 m·s–1) and the lowest (6.987 m·s–1) terminal velocity, respectively. The mean value of terminal velocity increased linearly from 6.751 to 7.396 m·s–1 by increasing the moisture content from 8 to 24% (w.b.). Also, by increasing the grains dimension from small to large, the terminal velocity increased from 6.345 to 7.792 m·s–1.
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