Non-invasive measurement of floating–sinking motion of a large object in a gas–solid fluidized bed

A Lagrangian sensor system has been established to non-invasively measure both the vertical position and dynamic force acting on itself. It consists of a 3-axis acceleration sensor, a 3-axis magnetometer, a microcontroller, a wireless module, batteries, and external electromagnetic coils. In this study, we applied the system to a free-moving coarse object in a gas–solid fluidized bed. The floating and sinking motions of the object in the fluidized bed are essentially caused by differences between its density and the apparent density of the fluidized media. However, the object sometimes shows strange behavior under the influence of variance in the fluidization state. We measured the temporal change of the upward force acting on the object as well as the vertical position, which is invisible from the outside. The experimental results indicate that the force acting on the object differs significantly between the floating and sinking states and is greatly complicated by interference with rising bubbles in the fluidized bed. The probability density of the vertical position of the object shows that its motion is explained not only by hydrostatic effects, but also by inhomogeneity of the fluidization state in the bed.