Experimental study of heat transfer and transport properties of granular material in indirectly heated rotary drums

The study of heat transfer in granular flows has extensive applications. This paper reports an experimental investigation of the heat transfer behavior in an indirectly heated rotary drum system with granular materials of various sizes. In this study, various particle motion behaviors were generated by applying inertial forces at different rotation speeds, and noncontact infrared thermography and particle tracking velocimetry were employed to quantify the thermal temperature and velocity distribution characteristics within the system. In addition, the heat transfer coefficient between the granular bed and the heated wall was determined using thermal balance equations, and the self-diffusion coefficient, which describes the diffusive motion of particles, was obtained by analyzing the random fluctuations of the particles. The results demonstrate that smaller particle sizes and increased rotation speed facilitate thermal temperature increase. Furthermore, a positive linear correlation between the heat transfer coefficient and the self-diffusion coefficient was observed, which implies that the forced thermal convection is a significant mechanism in enhancing the heat transfer behavior of granular systems.