Flow and Clogging of Submerged Hoppers
| When |
Nov 22, 2016
from 10:45 to 12:00 |
|---|---|
| Where | Centre Blaise Pascal |
| Attendees |
Juha Koivisto |
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In accord with the Beverloo equation the flow rate of granular material from a hopper is constant, irrespective of the filling height. In this talk two situations are compared: a case of dry non-cohesive grains and a case where the entire hopper is submerged under water. The experimental setup consists of a cylindrical flat bottomed hopper with a centered orifice at the bottom. The diameter of the hopper varies from 50 to 200 mm while the orifice has values from 3 to 10 mm. The grains are spherical polydisperse glass beads with 0.9-1.1 mm diameter.
The most noticeable difference between the two cases is that in the submerged case, the flow rate clearly depends on the filling height. However, the behavior is rather counterintuitive: The flow rate increases as the filling height decreases. For pure fluids the flow rate decreases as the filling height decreases as it is set by the hydrostatic pressure. Similar behavior is now discovered in the dry case, but the rate increase is much smaller and is merely just before the hopper runs out of grains. Previous studies have only reported the final decrease of flow rate, and disregarded it as a boundary effect. For small orifice sizes the hopper clogs.It is found that the qualitative behavior is the same in both submerged and dry cases while only quantitative behavior changes. This indicates that the interstitial medium does not affect the geometry of the clogging process, just the dynamics.