Heat Transfer in Rotary Drums Via Conduction, Convection, and Radiation

Granules are the second-most used substance after water [1] in many industries like the food, pharmaceutical, ceramics, and construction industries. Granular processing consumes roughly ten percent of the worldÕs energy [2]. Granules, however, donÕt behave like conventional solids, liquids, or gases, which makes them difficult to model. Thus, there is a great need for research in optimization of these processes to save energy and resources. Rotary drums are often used for granular processing including milling, heating, cooling, mixing, granulation, and more. However, heat transfer in rotary drums can be inefficient, leading to wasted energy. Valuable resources can be saved by developing more accurate models for the heat transfer in rotary drum applications to granular processing.

This research focuses on understanding the heat transfer mechanisms in the granular bed, inside a rotary drum, via conduction, convection, and radiation. Experiments will be performed using silica beads in a stainless steel drum to investigate the effect of drum rotation rate, granular fill level, and inlet air flow rate on heat transfer between the drum wall and granular bed. Silica is a common catalyst and most industrial drums are stainless steel, so this research represents common industrial applications.

Granular processes can be modeled using discrete element method (DEM) simulations by inputting particle physical properties such as density, viscosity, and thermal conductivity. The graduate student leading this research has modeled conduction in a rotary drum and is working on the models for convection and radiation. These models must be validated by experimental data in order to prove their accuracy, which will be the focus of this specific study.

Once the simulations and validations have been accomplished, experimental results will be compared to simulated results in order to examine the validity of the simulations and the models can be applied to quantify all three modes of heat transfer and study which modes dominate under varying operating conditions. The results can be used to optimize rotary drum efficiency in larger-scale industrial applications.

References

[1] Andreotti et al., Granular Media: Between Fluid and Solid, 2013.

[2] Duran, Sands, Powders, and Grains: An Introduction to the Physics of Granular Materials, 2000.