Dynamic vertical forces working on a large object floating in gas-fluidized bed: Discrete particle simulation and Lagrangian measurement

In a number of practical applications of fluidized bed, large solid objects coexist with small bed materials and the prediction of large objects' motion in fluidized is quite important. In the present study, we investigate the dynamic vertical forces working on a large sphere floating in a three-dimensional bubbling gas-fluidized bed. Numerical results obtained by using Fictitious particle method (FPM) are directly compared in detail with experimental results obtained by a non-invasive Lagrangian sensor system which can directly measure forces working on a free-moving object. In the present condition, the sphere keeps on floating near the free surface of the bed during fluidization and it shows characteristic upward and downward motions. Time-series data of the dynamic vertical forces agrees reasonably well between the simulation and the experiment and its quasi-periodicity and intermittent occurrence of characteristic peaks are confirmed. The mean and standard deviation of the dynamic vertical forces show good agreements between the simulation and the experiment with some differences in distributions of the relative frequency. From the numerical results, we confirm that the fluctuation of forces is strongly related to the bubble motions and fluid force is more dominant for the floating and sinking motions of a sphere in a fluidized bed comparing to contact force. Dependency on the superficial gas velocity is also investigated and both the numerical and experimental results show the fluctuation intensity of the dynamic vertical forces becomes larger with the increase of superficial gas velocity.