Convective roll patterns in vertically vibrated beds of granules

This paper describes dynamic transition of convection motions of granules under vertical vibrations. The granule motion of one convection mode, which has been studied by many authors, is downward along the vertical side walls and upward in the middle forming a heap. Tile present study focuses on the granule motion of the other convection mode that occurs in rectangular containers: granules move upward along the vertical side walls, anti downwards in the middle forming a valley. This latter convection mode is stable enough to yield multiple pairs of convection rolls, The number of convection rolls is strongly dependent on the vibrational acceleration, granular size, and tu a lesser extent on frequency, given the bed height and width. The critical vibrational acceleration, where a transition occurs between the two convection modes, is dependent on the bed height but not on the bed width in the range investigated (100-200 mm). In the case of large granules (mean diameter (d) over bar greater than or equal to 0.78 mm) a chaotic state (where convective motion of granules ceases to exist) is found to appear in between the two convection modes mentioned above.