Characterizing Particle-Wall Contact Behavior and Fluctuations in Gravity-Driven Dense Granular Flows in Cylindrical Tubes Using DEM

The primary objective of the paper is to observe and characterize the flow attributes of gravity-driven dry granular media in vertical cylindrical tubes. Particle packing fractions of ∼60% were the prime focus in the current study as the targeted application is the use of dense particulate media as heat transfer fluids (HTF). Experimental and computational studies were previously conducted to understand the influence of different geometrical parameters on the flow physics [1], [2]. Flowrate, particulate velocity, and packing fraction profiles were studied for different inertial numbers and preliminary observations were made about the corresponding regimes. However, flow characteristics that could have a direct implication on the heat transfer behavior remained unexplored. Hence, the current effort serves as an extension of our previous studies. The three-dimensional computer simulations were conducted by implementing the Discrete Element Method (DEM) for the Lagrangian modelling of particles. Hertz-Mindilin models were used for the soft-particle formulations of inter-particulate contacts. Since the particle contact behavior plays an important role in the conduction heat transfer of these regimes [3], the particle-wall residence times and near-wall packing fractions are studied in the current work. Particle fluctuations, which lead to flow agitation that effect heat transfer [4] are also studied. It was observed that the intermittent nature of the flow resulted in the propagation of wave-like structures in the upstream direction. The characteristics of this phenomenon and its possible influence on the heat transfer physics is also discussed.