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Hoppers are commonly used devices for handling and storing granular materials. Despite their common use and deceptivelysimple design, hoppers have a number of problems associated with them, including funnel flows, choking, bridging, and flooding.
Some funnel flows are characterized by stagnant regions of material near the walls of the hopper. The first material into the hopper rests close to the hopper walls and is the last to leave. This contrasts with mass flow, where all of the material flows from the hopper simultaneously and the first material into the hopper is the first to leave. Funnel flow problems include
- materials that degrade or change properties over time
- large velocity gradients resulting in segregation
- generated dust, which can increase the possibility of explosion
An extreme version of funnel flow is a rathole, where only a small region of the material discharges from the hopper.
Other common problems are bridging and flooding. Bridging occurs when a stable arch of material forms -- supporting the weight of the material above it. The result is stoppage of flow, which can only be restarted by collapsing the arch of material. Once the bridge collapses, a sudden surge or flood of material attempts to leave the hopper. Bridging and flooding result in inconsistent flows, which may affect processes both upstream and downstream of the hopper.
Visualization and Animation of Hopper Flow Output
The Hopper Flow Discharge tool generates a state file describing the particle positions in the hopper over time. Screenshot #1 above shows a portion of the state file generated by the tool for the default parameters (click thumbnail to enlarge). The BenchmarkHopperMovie attached under Supporting Documents was produced by the ParticleVis visualization software using the generated state file as input.
Any state file produced by the Hopper Flow Discharge tool can be be downloaded to your machine from the output screen of the tool following tool execution. The ParticleVis software can be downloaded to your machine from the pharmaHUB resources page.