(81b) Scale-up of Heat Transfer for Rotary Drums with Baffles

Granular materials and powders often require thermal treatment in the food, mineral, pharmaceutical and chemical industries. Rotating drums (kilns) are common devices for the thermal treatment of particulate systems. Developing a better understanding of heat transfer in rotary drums can improve the quality of the product as well as save on energy and material costs. For good product quality, it is often necessary to raise the temperature of the particles uniformly. Although studies have demonstrated the effectiveness and importance of baffles/flights in decreasing the heating time and improving the final product uniformity, many questions about the use of baffles still remain. Understanding the relationship between particle properties and rotary drum operating conditions on the heating time is important for predicting processing time in real-world applications. Simulations using the discrete element method (DEM) were carried out as a means of better understanding the role of baffles in regulating heat transfer. The operating conditions were altered by adjusting the following variables: particle fill level, drum size, baffle size, number of baffles, and the speed of rotation. Furthermore, the effect of material parameters was investigated by varying the size and thermal conductivity of the particles. The results demonstrate how fill level as well as the number and size of baffles play an important role in the heat transfer process. Significant improvements were noted by increasing the number and size of the baffles. The effectiveness of baffles varied as a function of fill level and rotational speed, showing a correlation between these variables. In this work, we also introduced an appropriate characteristic time for baffles that helped us to develop an empirical relationship capable of predicting the average temperature of particle beds.