Design and performance of a countersunk screen in a maize cleaning device

To increase the probability of particle penetration and decrease grain loss in maize cleaning devices, a countersunk screen was designed to enable particles move towards screen holes. The factors affecting the tendency of particles to penetrate screen holes and the various behaviours of particles penetrating screen holes were analysed by numerical simulation using couples computational fluid dynamics and the discrete element method (CFD-DEM). Simulations of a threshed maize mixture moving in a typical cleaning device were carried. An airflow of 12.8 m s−1 and the direction angle of 25° was utilised. Among the three kinds of arrangements of screen holes investigated, cleaning performance of a countersunk screen with H-type arrangement of screen holes was the best. The impact angle of particles on the screen was influenced by the airflow direction angle, and the speed of maize particles was the main factor influencing probability of penetration of particles. Screening efficiency was the best at an airflow velocity of 11.2 m s−1. As the angle of the sidewall around screen hole increased from 40° to 60°, the tendency of grains to penetrate the screen holes was enhanced. Grains slipping along the sidewall penetrated the countersunk screen hole with high efficiency, reducing inefficient impacts. The screening efficiency of cleaning device with countersunk screen was 35.20% greater than that with the similar standard round-hole screen.