Berlin 2018 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

CPP: Fachverband Chemische Physik und Polymerphysik

CPP 37: Focus: Smart Hydrogels and Hydrogel Based Devices II - organized by Gerald Gerlach, Walter Richtering and Thomas Hellweg

CPP 37.11: Vortrag

Mittwoch, 14. März 2018, 12:45–13:00, C 130

Silo outflow of soft frictionless hydrogel spheres — •Ahmed Ashour¹, Torsten Trittel¹, Tamás Börzsönyi², and Ralf Stannarius¹ — ¹Institute of Experimental Physics, Otto von Guericke University, Magdeburg, Germany — ²Institute for Solid State Physics and Optics, Wigner Research Center for Physics, Hungarian Academy of Sciences, Budapest, Hungary

The outflow of hard grains with different shapes and types in 2D and 3D silos has been extensively studied. The availability of incompressible but deformable hydrogels in recent years opened the door to study the effects of softness and nearly zero friction on the outflow of grains from silos with small aperture under the influence of gravity. We conduct a quasi-2D silo experiment with hydrogel spheres. This material shows new qualitative and quantitative features as compared to hard grains: The silo does not clog even when the orifice size is only slightly larger than two spheres in diameter. By decreasing the orifice size below two sphere diameters, intermittency of the flow rapidly increases, followed by a permanently clogged state. The soft spheres clog at a certain container fill height, unlike hard grains which flow out practically independent of the container fill level. The Janssen effect, a saturation of the pressure in a silo with fill height, is obviously ineffective for the soft frictionless material, the pressure at the silo bottom increases linearly with fill height (hydrostatic). On the other hand Beverloo's equation that describes the mass flow rate remains valid. Another important difference to hard grain silo discharge is that above a certain height respective to the orifice, the spheres above move in plug flow.