An experimental procedure to estimate tube erosion rates in bubbling fluidised beds

• Erosion rate of a tube in a cold model fluidised bed was investigated.
• The overall erosion rate is well interpreted by the existing model.
• A new experimental procedure was developed to estimate the erosion rate profile.
• The erosion rate is proportional to the bubble frequency and the wake length.

We studied the erosion rate of a horizontal plaster tube in a cold-model bubbling fluidised bed of 510 μm glass beads at different fluidisation velocities and at ambient pressure and temperature. To this end, we developed a new experimental procedure based on the cyclic immersion of a cylindrical probe in a bed kept at incipient fluidisation (U = 1.03 Umf) and we compared the obtained results with those achieved during experiments with the same probe immersed at a fixed position inside the fluidised bed operated in bubbling regime. The new procedure was meant to simulate the impact of the bubbles wake with the probe, providing a simplified physical model for erosion in the bed. We also interpreted the experimental results in light of existing models to describe the overall erosion rate. The analysis of data indicated a clear correlation among surface erosion and bubble wake dynamics. Besides, the new procedure provided a way to address the angular profile of tube erosion caused by the exposure to the wake of a single rising bubble. Once multiplied by the product between bubble frequency and wake length, these data allow reconstructing the angular erosion rate profiles in the range of the fluidisation velocity investigated. This result finds confirmation in the analysis of the pertinent literature concerning the drag coefficients of a horizontal tube immersed in dense and dilute granular flows.

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