Granular Matter (2011) 13:713–721 DOI 10.1007/s10035-011-0293-0 ORIGINAL PAPER Numerical and experimental study of a spherical particle ﬂow in a cylindrical tube under vacuum conditions Simon Vanmaercke · Engelbert Tijskens · Gert Van den Eynde · Yann Bartosiewicz Received: 23 May 2011 / Published online: 1 November 2011 © Springer-Verlag 2011 Abstract The paper aims at developing a validated model that can accurately predict the ﬂow of a particulate material. This model will serve as a virtual design tool for the design of a novel passive safety system for nuclear reactors. Therefore an experimental setup consisting of a vertical glass tube is ﬁlled with 500 ± 30 μm spherical glass particles. The experi- ment is then placed in a vacuum and the particles are released by opening a valve. The velocity of the particles is recorded during their fall at three different heights using a non invasive optical tracking technique with an original implementation. The same experiment is then simulated using the Discrete Element Method and results are compared. A good agree- ment between the simulation and the experiment was found. The sensitivity of the simulation to a change in the contact stiffness, dynamic Coulomb coefﬁcient of friction and tan- gential contact force model was investigated. The inﬂuence of the initial position of the simulated particles on the packing factor was shown to be very important. Finally the experi- ment proved to be extremely sensitive to a perturbation of the outﬂow section of the tube, something that was predicted by the simulations. Keywords Discrete Element Method · Vacuum · Pulsating ﬂow · Validation · Sensitivity analysis S. Vanmaercke (B ) · G. Van den Eynde SCK.CEN, 200 Boeretang, 2400 Mol, Belgium e-mail: svanmaer@sckcen.be E. Tijskens Katholieke Universiteit Leuven, 30 Kasteelpark Arenberg, 3001 Heverlee, Belgium Y. Bartosiewicz Université Catholique de Louvain, Institude of Mechanics, Materials and Civil Engineering, 2 Place du Levant, 1348 Louvain-la-Neuve, Belgium 1 Introduction The ﬂow of spherical particles in a cylindrical tube was studied because of its possible use in a secondary safety shut- down system of future nuclear reactors [1]. For this applica- tion small neutron absorbing spheres are placed on top of the actual reactor core and kept there during normal opera- tion by means of a metallic seal. In case of an accident, the temperature of the reactor will increase, leading to a melting of the seal and releasing the absorber spheres into the active core region. This is illustrated in Fig. 1 where several simula- tion snapshots are shown during the melt of the metallic seal. The neutron absorbing particles, have a very high melting point, and therefore melt of the absorber particles is not con- sidered.The absorber spheres will then absorb a significant portion of the neutrons, and stop the chain reaction. For this application complete understanding of the ﬂow behavior is crucial. Therefore a validated model that can accurately pre- dict the ﬂow of a particulate material is needed. This model will serve as a virtual design tool for the design of a novel passive safety system for nuclear reactors. The absorber particle ﬂow should be repeatable and robust in order to have a highly reliable safety system. In a ﬁrst instance the particle ﬂow is studied in detail without the inter- action of the metallic seal, to fully validate the geometry and the contact force model used in the simulations. In this work, the DEM simulations are done using DEMeter [2] 1 , a general purpose software for particle based simulations. Experiments in air have initially been done both with “open top” tubes and with closed tubes. Because both results were drastically dif- ferent it was clear that the air resistance is not a negligible parameter for this simulation. Therefore experiments have been conducted in vacuum to exclude the inﬂuence of air 1 http://dem-research-group.com. 123