Behaviour of a curtain of particles falling through a horizontally-flowing gas stream

With a view to an application in heat recovery from hot gases, the fluid dynamics of a curtain of particles falling in a horizontal gas stream was studied. Air with a uniform velocity profile flowed through a duct with cross-section of 0.15 × 0.60 m. A stream of sand particles, with a mean diameter of 204 μm and density of 2640 kg/m3, was fed into the duct from above to form a curtain across the entire width of the duct. The particle flowrates ranged from 0.031 to 0.047 kg/s. The inlet particle curtain thickness in the direction of the gas flow ranged from 0.02 to 0.10 m, and the horizontal air velocity was varied from zero to 1.2 m/s. In an experimental study, the trajectory of the particle curtain was tracked using high-speed video camera and the velocity profile of the air downstream of the curtain was measured using a pitot tube. The fluid dynamic behaviour of the particle curtain was analysed using a Eulerian–Eulerian computational fluid dynamics (CFD) model that is capable of predicting the complete flow fields of the gas and particles. Also, a simple single particle model was used to predict the particle velocity at the centerline and trajectories of the leading and trailing edges of the particle curtains falling in a horizontal air flow. Good agreement was found between the experiments and the CFD model predictions. However, predictions from the simple single particle model were less satisfactory due primarily to the non-uniform gas flow found in practice, compared to the assumed uniform flow.