(81a) Heat Transfer in a Rotary Drum

Rotary drums deliver high heat and mass transfer rates, making them extensively useful for powder mixing and heating processes in metallurgical, cement, mining, pharmaceutical, detergent and other particulate processing applications. However, these processes are very difficult to model and operate because of the complex behavior affected by the particle parameters and process conditions such as particle size and distribution, shape, composition, fill level, rotation rate, and operating temperature. The current experimental research is focused on understand the heating mechanisms by conduction and radiation at high temperatures (>600⁰C) and studying the effects of particle size distribution, fill level, and relatively low rotation rate (<10rpm). This work also serves to bridge the gap in the literature for experimental data and validating simulation-based research.

Experiments are performed using 2 mm diameter silica beads to investigate the granular flow and heat transfer by conduction and radiation inside a 6-inch diameter and 3-inch-long stainless-steel rotary drum. The drum is attached to two 10-inch titanium wheels, hence preventing the direct contact of the drum wall with the rollers. One end of the drum is closed using a transparent quartz window, capable of handling high temperatures. Another end of the drum is closed using a sapphire window, compatible with an IR camera, specifically chosen to obtain a high transmittance to the infrared light. The drum walls are maintained at a desired high temperature using NI-Cr resistive wires and a PID controller. The particle bed temperature evolution is recorded on the IR camera, which is used to determine the average particle bed temperature over time and calculate the wall-to-particle heat transfer coefficient.