Characterisation of airflow resistance of different moisture content wheat bulks mixed with different percentages and sizes of dockage

Airflow resistance is a key factor related to physical properties of grain bulks and is influenced by dockage size and its percentage. A cubic chamber with inner dimensions of 500 × 500 × 500 mm was employed to investigate the airflow resistance of wheat bulks mixed with varying sizes (≤1.1 mm, 1.1–2.0 mm, and ≥3.3 mm) and percentages of dockage (0, 1.0, 2.5, and 5.0 %), along with different moisture contents (14.5, 16.5, and 18.5 %), airflow velocities (1.1–6.6 m s⁻¹), and in both vertical and horizontal directions. The airflow resistance decreased with the reduced airflow velocity supplied by the fan, and the supplied airflow rate decreased with the increased airflow resistance. Fine materials (≤1.1 mm) mixed with the clean wheat led to 30–50 % increase of airflow resistance in both directions. Adding 1 % of dockage >3.3 mm (chaff) decreased the airflow resistance by ∼10 %, while adding dockage of 1.1–2 mm size (slightly smaller than wheat) did not result in airflow resistance change. Adding dockage with mixed size had an average 45.6 and 41.2 % increase of airflow resistance in horizontal and vertical directions, respectively. Airflow resistance in both clean and wheat mixture in the vertical direction was ∼50 % higher than that in the horizontal direction in any moisture content of wheat mixtures. This increased airflow resistance in the vertical direction was in the range of 10–117 %. The best regression equation was the Modified Haque model for predicting airflow resistances tested in this study.