Comparison of the Energetics of Vertical and Horizontal Air Channels of Grain Cleaning Machines
DOI:
https://doi.org/10.32515/2414-3820.2026.56.224-232Keywords:
pneumatic separation, aspiration channel, terminal velocity, floating coefficient, energy intensity, grain cleaning machineAbstract
The purpose of the article is to compare, on a common physical basis, the energy performance of the two principal air-channel arrangements used in grain cleaning machines – the vertical aspiration channel, in which the air stream rises against gravity, and the horizontal (inclined) blowing channel, in which the air stream crosses the falling grain. The comparison is made for an equivalent separation task in order to reveal which arrangement is inherently more energy-efficient and why.
Both channels separate the grain mixture by the aerodynamic properties of its components, primarily the terminal (floating) velocity. Starting from the equation of motion of a particle in an air stream, with the drag force expressed through the floating coefficient, the steady states for both orientations were obtained. In the vertical channel the working air velocity must approach the terminal velocity of the boundary component (about 6–8 m/s), since light impurities are carried upward only when the air velocity exceeds their floating velocity, while sound grain falls under gravity; in addition, the air performs work against gravity to remove the light fraction. In the horizontal channel the vertical transport of the material is provided by gravity, and the air merely deflects the particles horizontally, so a substantially lower velocity (about 3–4 m/s) is sufficient. Since the fan power scales as the cube of the air velocity, this difference in required velocity is strongly amplified in energy consumption. A worked numerical example for an equivalent task gives a fan-power ratio of about 8.5 in favour of the horizontal arrangement, confirmed by the cubic law and supported by trajectory and velocity-relaxation analysis.
It is concluded that the vertical aspiration channel is energetically the more expensive arrangement, mainly because its working velocity is fixed near the terminal velocity and because the air lifts the light fraction against gravity, whereas the horizontal channel exploits gravity for vertical transport and therefore consumes several times less energy (by an estimate, 5–9 times). The advantage of the vertical channel that justifies its dominance in practice is the sharper separation governed by a single parameter and its compactness. The principal levers of energy saving are regulation of the air velocity and a closed-loop air circuit. Further research should experimentally verify the obtained energy relationships and optimise combined vertical–horizontal schemes.
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