Aerodynamic Properties of Tef Grain and Straw Material
ARTICLE IN PRESS
BIOSYSTEMS ENGINEERING
98 (2007) 304 – 309
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/issn/15375110
Research Paper: PH—Postharvest Technology
Aerodynamic properties of tef grain and straw material
A.D. ZewduÃ
Food Science & Postharvest Technology, Alemaya University, P.O. Box 49, Ethiopia
ar t ic l e i n f o
Article history: Received 15 January 2007 Accepted 1 August 2007 Available online 20 September 2007
Terminal velocities were measured for both tef (Eragrostis tef (Zucc.) Trotter) grains and straws using the suspension velocity method. The terminal velocity of tef grains increased linearly from 3.08 to 3.96 m sÀ1 with increase in moisture content from 6.5% to 30.1% wet basis (w.b.). Straws with different lengths, node-free, with a node in the middle, and with a node at the end were tested for their terminal velocities. Straws with nodes had higher terminal velocities compared with node free. Straws with a node at the end had the highest terminal velocity (5.4 m sÀ1 for 10-cm-long straws). Terminal velocity decreased from 3.69 to 2.13 and 3.08 to 1.70 m sÀ1 for middle-node and node-free straws, respectively, but for end-node straws the terminal velocity showed gradual increase from 3.32 to 5.40 m sÀ1 as the length of straw increased from 1 to 10 cm. The drag coefficients for grain and resistance tally obtained terminal velocities. Tef grains drag coefficient decreased from 0.83 to 0.65 with increase in moisture content from 6.5% to 30.1%. Node-free straws exhibited higher resistance coefficients and end-node straws the lowest. & 2007 IAgrE. Published by Elsevier Ltd. All rights reserved. coefficient (drag coefficient  frontal area) for straw were calculated from the experimen-
1.
Introduction
Tef (Eragrostis tef (Zucc.) Trotter) is an important cereal crop indigenous to Ethiopia, constituting about 20% of cereal production of the country (Bultosa & Taylor, 2004). Countries such as
BIOSYSTEMS ENGINEERING
98 (2007) 304 – 309
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/issn/15375110
Research Paper: PH—Postharvest Technology
Aerodynamic properties of tef grain and straw material
A.D. ZewduÃ
Food Science & Postharvest Technology, Alemaya University, P.O. Box 49, Ethiopia
ar t ic l e i n f o
Article history: Received 15 January 2007 Accepted 1 August 2007 Available online 20 September 2007
Terminal velocities were measured for both tef (Eragrostis tef (Zucc.) Trotter) grains and straws using the suspension velocity method. The terminal velocity of tef grains increased linearly from 3.08 to 3.96 m sÀ1 with increase in moisture content from 6.5% to 30.1% wet basis (w.b.). Straws with different lengths, node-free, with a node in the middle, and with a node at the end were tested for their terminal velocities. Straws with nodes had higher terminal velocities compared with node free. Straws with a node at the end had the highest terminal velocity (5.4 m sÀ1 for 10-cm-long straws). Terminal velocity decreased from 3.69 to 2.13 and 3.08 to 1.70 m sÀ1 for middle-node and node-free straws, respectively, but for end-node straws the terminal velocity showed gradual increase from 3.32 to 5.40 m sÀ1 as the length of straw increased from 1 to 10 cm. The drag coefficients for grain and resistance tally obtained terminal velocities. Tef grains drag coefficient decreased from 0.83 to 0.65 with increase in moisture content from 6.5% to 30.1%. Node-free straws exhibited higher resistance coefficients and end-node straws the lowest. & 2007 IAgrE. Published by Elsevier Ltd. All rights reserved. coefficient (drag coefficient  frontal area) for straw were calculated from the experimen-
1.
Introduction
Tef (Eragrostis tef (Zucc.) Trotter) is an important cereal crop indigenous to Ethiopia, constituting about 20% of cereal production of the country (Bultosa & Taylor, 2004). Countries such as