Hopper flow, models

The intermediate hopper acts as a storage balancing the inventory change. Evidently there is essentially no inlet and outlet effect, inasmuch as the voidage curves taper off into their respective asymptotic values for both the top and bottom sections of the fast column. This simple boundary condition facilitates flow modeling and the solution of the hydrodynamic equations. It should also be noted that the acceleration zone for the materials tested is too short to call for consideration. 

The models that have evolved for dense phase conveying are not numerous but they do take different approaches considering various forces acting on the material being conveyed. One of the first applications of dense phase conveying could be considered to be that of Janssen [5] in his analysis of bin and hopper flow. The downward flow in... 

A large one-sixth-scale model of the unloader hopper was selected so that flow patterns in the enclosure could be evaluated.Smoke was used to simulate the behavior of the lime dust in the enclosure. The lime drop from the clamshell was simulated by releasing coarse sand, thus modeling the flow patterns caused by the volume displacement and the air entrainment. The effects of local wind speed and direction on the enclosure were also simulated. 

Conclusions concerning the causes of the fugitive emissions were developed from extensive model testing. The emissions escaped from the enclosure by direct plume trajectory and wind flow patterns. Lime dropped into the back of the grizzly creates a plume towards the front of the enclosure, whereas a drop near the front produces a plume to the rear. The plume is caused by the rapid displacement of air and dust from the hopper. 

Eq. (8.24), and the modified Mohr-Coulomb yield (or failure) criterion, Eq. (8.27). It should be noted that other yield criteria, such as the von Mises criterion, are used to model the flow of bulk solids in hoppers, and more conditions may need to be imposed, such as the Levy flow rule, in order to close the system of equations [Cleaver and Nedderman, 1993],... 

We now follow the modeling approach outlined for the melt extrusion process. We assume steady state conditions and a given mass flow rate then, starting from the hopper, where initial conditions are known, calculations are made in finite steps, ending up at the die, with extrudate pressure, mean temperature, and solids content. If the flow rate at these conditions does not match that of the die, or if the calculations break down for some reason (e.g., insufficient solids conveying), calculations are repeated at a new mass flow rate. 

A history of hopper and feed screw designs showed that each design evolved to facilitate and improve powder flow to the compactor feed screw conveyance system. Feed hopper designs depicted in Fig. 4 show designs incorporated in older compactor models [examples (A)-(C)]. Dehont et al. described the powder compaction feeding systems that were in use up to 1989. ... 

Prediction of gas solid flow fields, in processes such as pneumatic transport lines, risers, fluidised-bed reactors, hoppers and precipitators are crucial to the operation of most process plants. Up to now, the inability to accurately model these interactions has limited the role that simulation could play in improving operations. In recent years, CFD software developers have focused on this area to develop new modelling methods that can simulate gas-liquid-solid flows to a much higher level of reliability. As a result, process industry... 

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