The mechanics of moving vertical fluidized systems: III. Application to cocurrent countergravity



Previous studies in this laboratory have verified the assumption of a single fundamental relation between void fraction and slip velocity for counter-current flow and batch fluidization of solid rigid particles in water. The present investigation was undertaken to test the applicability of a generalized theoretical analysis to the case of cocurrent counter-gravity flow.

The cocurrent countergravity flow and batch fluidization of two ideal fluidized systems were studied experimentally in a 1 in. diameter column. The systems were 0.0184 in. diameter glass spheres-water and 0.00396 in. diameter glass spheres-water. Holdup, pressure drop, and fluid and particle velocities were measured for the cocurrent counter-gravity flow experiments. Holdup and fluid velocity were measured for the batch fluidization runs.

Calculated slip velocities for cocurrent counter-gravity flow and batch fluidization gave a single curve when plotted against holdup. It is therefore concluded that the experimental results support the validity of the basic assumption for the cocurrent countergravity flow of liquid-solid systems.

The experimental data for cocurrent countergravity flow are in excellent agreement with the operating diagram (holdup as a function of fluid and particle velocities) for cocurrent countergravity flow determined from the holdup-slip velocity relationship obtained from the batch fluidization experiments. Stable operation in the cocurrent counter gravity flow region where the fluid velocity is less than the single particle transport velocity is possible provided there is mechanical support for the solids and the solids flow rate is controlled at the bottom of the column. The application of the theory to the prediction of behaviour in compound cocurrent countergravity flow fluidized systems is demonstrated.