BOUNDARY-LAYER MODELING OF GRANULAR FLOW IN THE TRANSVERSE PLANE OF APARTIALLY FILLED ROTATING CYLINDER

During the processing of particulate materials in rotary kilns and dri ers the transverse motion generated in the bed is the primary factor c ontrolling renewal of material at the exposed bed surface. The rate of surface renewal, in turn, determines the degree of material mixing an d the rate of heat transfer from the freeboard to the bed. An experime ntal campaign launched to investigate granular Flow behavior in a tran sverse plane of a rotary cylinder suggests that a continuum model base d on the constitutive equations developed for gravity flow in chutes m ay be adopted, in some particular cases, to describe flow in the shear (active) layer. A model is developed in which the dimensions of the s hear layer, the region near the Free surface, is assumed thin thereby permitting the governing equations to reduce to Prandtl's boundary lay er equations which are solved to obtain the depth and velocity profile s within the layer. Because the density at the free surface is discont inuous for the flow regimes of practical interest, the continuum assum ption breaks down at the free surface, hence, a stress-Free boundary c ondition has been avoided. In place of this a surface velocity constra int from the experimental campaign has been applied which, therefore, makes the model deficient in exploring the full potential of the bound ary layer analogy. Nevertheless, the appropriate velocity trends are p redicted well into the bed with the results comparing favorably with e xperimental data. (C) 1998 Published by Elsevier Science Ltd. All righ ts reserved.