What are the angle of repose, the angle of fall, and the angle of difference?

The angle of repose refers to the angle between the sloping side of a powder cone and the horizontal plane after the powder particles freely fall onto a horizontal plane under specific conditions. The angle of repose is a significant indicator of powder flowability. The smaller the angle of repose is, the better the flowability will be. It is generally assumed that the angle of friction and the angle of repose are approximately equal. For some materials, such as sorghum, the magnitudes of the two angles can be different.

The angle of fall is the decreased angle obtained after the angle of repose has been measured, and the powder pile is subjected to regular mechanical vibrations. During the vibration, the particles slide down the powder pile along the sloping surface, resulting in a decreased tilt angle which is called the angle of fall.

The angle of difference is calculated by subtracting the angle of fall from the angle of repose. The angle of difference is one of several parameters that can be used to evaluate powder floodability. The larger the angle of difference is, the better the floodability will be.

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