Repose definitions

The angle of internal friction, a, is defined as the equilibrium angle between flowing particles and bulk or stationary solids in a bin. Figure 4 illustrates the definition. The angle of internal friction is greater than the angle of repose. 

All the preceding particulate handling steps are affected by the unique properties of all particulates, including polymeric particulates while they may behave in a fluidlike fashion when they are dry, fluidized and above 100 pm, they also exhibit solidlike behavior, because of the solid-solid interparticle and particle-vessel friction coefficients. The simplest and most common example of the hermaphroditic solid/ fluidlike nature of particulates is the pouring of particulates out of a container (fluidlike behavior) onto a flat surface, whereupon they assume a stable-mount, solidlike behavior, shown in Fig. 4.2. This particulate mount supports shear stresses without flowing and, thus by definition, it is a solid. The angle of repose, shown below, reflects the static equilibrium between unconfined loose particulates. 

There are two main definitions of the angle of repose as follows. 

The one-phase stability criteria are posed in terms of g " in (8.4.5) and (8.4.6), but before we use those criteria to test for stability, it will prove more convenient to repose them in terms of the fugacity. We can rewrite (8.4.5) and (8.4.6) in terms of fugacities by combining the definition otg (3.7.38) with the integrated definition of the fugacity in (4.3.12). Then (8.4.5) requires that stable phases have... 

Bulk materials that are composed of fine particulate constituents are much more sensitive to the influence of the void gas, as changes of volume are resisted by the rate at which the gas can progress through the interstices of the mass. As a result, the repose conditions are very dependent upon the conditions of slope formation, as is the density condition to which they settle. Such materials do not have a specific angle of repose , either in filling or discharge conditions, and it is misleading to ascribe a definitive... 

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