Fluidization of Size Segregating Binary Mixture

Fluidization of a mixture of bi-disperse particles is often characterized by initial and final fluidization velocities. Both conditions are typically determined following the conventional method based on the behaviour of the bed pressure drop vs the superficial gas velocity. In early days, manometers were used for measuring bed pressure drop. Later with piezoelectric devices, the fluctuations in the pressure-drop in a fluidized bed is more accurately captured. In addition, visualization of the bed, albeit peripheral, helps in understanding the physical structure of the bed. The fluctuations in the bed pressure drop vs the superficial gas velocity plot and the physical configuration of the bed suggest possible existence of multiple characteristic points in a fluidized bed of mixture. The objective of the current work is to understand the fluidization and de-fluidization process of a binary mixture using simultaneous measurement of pressure drop and video imaging of the bed.

Particles of two different mean diameters, both from Geldart B group, are selected for experiment. Particles of different diameters are coloured differently for clear demarcation.

Experiments were performed in a transparent glass column for visualization. Videos of the bed were captured using a DSLR (Nikon D5200) camera. A pressure transmitter (AFRISO DMU11D) was used to measure the pressure drop. Data were collected using the National Instrument’s data acquisition system (NI 9219). The extracted images from the videos were analysed using `ImageJ’ software.

Experiments were performed for different bed configurations. Intermediate configurations and characteristic points depend on the initial condition of the bed. Different phenomena such as vertical and azimuth segregation and square slug formation are observed depending on the initial condition; however, the final configuration after the complete fluidization - de-fluidization process is independent of the initial bed condition.