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.