Bubbles trapped in a fluidized bed: Trajectories and contact area.

Area of Science:

• Fluid mechanics
• Granular physics
• Multiphase flow

Background:

• Understanding bubble dynamics in granular systems is crucial for industrial processes.
• Confined granular layers with ascending gas flow present complex multiphase interactions.

Purpose of the Study:

• To investigate bubble dynamics within a confined granular layer subjected to an upward gas flow.
• To quantify the impact of gas flow rate and grain size on trapped air volume, bubble size, and three-phase contact area.

Main Methods:

• Experimental investigation of bubble behavior in a stationary fluidized granular layer.
• Systematic variation of gas injection flow rate and grain diameter.
• Quantification of air volume, bubble size, and three-phase contact area.

Main Results:

• A central fluidized zone with a parabolic shape was observed.
• Bubbles either remained stationary or were entrained downwards and captured by the central air channel.
• Trapped air volume fraction remained constant (2%-3%) across varied flow rates and grain sizes.
• Normalized gas-liquid-solid contact area decreased with increasing gas flow rate.

Conclusions:

• Bubble behavior is dependent on their initial location relative to the fluidized zone.
• The counter-intuitive decrease in contact area with flow rate has potential implications for industrial applications.
• The findings provide insights into gas-solid-liquid interactions in granular systems.