Effects of particle size and field orientation on the yield stress of magnetostabilized fluidized beds

Abstract

In this work, we present experimental measurements of the yield stress of gas-fluidized beds of magnetizable particles stabilized by an externally imposed magnetic field. Powder samples consist of spherical magnetite particles 35-65 μm in size. The magnetic field is applied in the bubbling regime and the gas velocity is decreased. At a critical gas velocity, particle chains that have formed due to attractive magnetostatic forces become jammed and the bed transits to a solidlike expanded state with a non-negligible yield stress. Our experimental setup allows us for taking measurements of the yield stress of the bed stabilized by a magnetic field oriented either in the vertical or horizontal direction (co-flow and cross-flow field configurations, respectively). In the cross-flow field configuration, the magnetic yield stress is increased with particle size. On the other hand, the magnetic yield stress is decreased in the co-flow field configuration as particle size is increased. This is interpreted as due to the dependence of the interparticle magnetostatic force on the interparticle contact angle with the field, which is, on average, affected by particle size in the jammed bed subjected to small consolidations.