(71h) Quantitative Study of Conduction and Convection Heat Transfer Mechanisms in a Rotary Drum

Granular materials undergo process steps that include transportation, drying, heating and chemical or physical conversion. In several instances, these materials need to be heated or cooled during processing, and rotary drums (kilns) are the most commonly used process equipment for this purpose. It is not always possible to conduct experiments using different materials and consider all process conditions to study the thermal mechanisms due to the inherent complexity of these processes. Therefore, computational modeling and simulations have been extensively used to understand the heat transfer mechanisms in rotary drums. This work focuses on understanding the heat transfer mechanisms in the granular bed inside a rotating drum, using both simulations and experiments.

Experiments are performed using 4 mm diameter silica particles to investigate the granular flow and heat transfer mechanisms inside a 3-inch radius and 3-inch long stainless-steel rotary drum. The drum rides on two titanium wheels, precluding the direct contact of the drum wall with the rollers. One side of the drum is closed with a transparent quartz window, which can handle high temperatures. Another side of the drum is closed with a sapphire window, compatible with an IR camera, specifically chosen to give a high transmittance to the infrared light. The setup is designed to handle up to 1000⁰ C, making it possible to study all modes of heat transfer via conduction, convection, and radiation. The wall of the drum is maintained at a desired high temperature using heat guns placed around the drum. A drum tumbler is used to a rotate the drum, and the temperature evolution in the particle bed is recorded using Omega thermocouples and a mid-wave infrared (MWIR) camera. The conduction and convection modes of heat transfer are quantified under varying operation conditions to establish a keen understanding of the heat transport. For this, both experiments and CFD-DEM (using MFIX-DEM, an open-source multi-solver suite) simulation techniques are used to analyze the thermal behavior.