Abstract
The performance of grain augers, which are installed at high angles of elevation, is greatly affected by the high rotational or vortex motion imparted to the grain by the rotating screw. In a general study of auger performance characteristics recently carried out, it was shown that the losses in output resulting from the grain vortex motion are quite considerable. The present work has been aimed at studying the characteristics of grain vortex motion in order to permit a closer examination of the effect of this motion on auger performance.
In the first part of the investigation, a simplified theoretical analysis is presented which is based on the assumption that the grain behaves as a ‘semi-fluid’. With the aid of experimental data, it is shown that this assumption is approximately correct for the majority of vortices in which the relative motion between the grain layers is sufficient to cause agitation and prevent compaction. For a forced vortex in which there is no relative motion between the grain layers, the grain mass behaves more as a ‘solid’ than a ‘semi-fluid’.
In the second part of the investigation an analysis is made of the actual vortex motion in grain augers. It is shown that the vortex velocity distribution is a function of auger speed. A general expression is developed for the ‘critical’ speed of an auger at which reverse flow or slipping back of grain in the central region of the screw ceases. On the basis of the ‘critical’ speed analysis, an examination is made of the effect on performance of the size of the core diameter in relation to the outside diameter of the screw.
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