Heat Transfer in Clustered Gas-Solids Flows

At sufficient mass loading, gas-solids flows exhibit strong two-way coupling where the dynamic evolution of the particles is intimately linked to a carrier gas. This strongly-coupled case can give rise to large-scale coherent structures in the particulate phase (clusters), which effectively ‘de-mix’ the underlying flow. Inhomogeneous particle distributions can lead to significantly reduced heat transfer due to poor gas-solids contact. Here, we utilize a volume-filtered Eulerian-Lagrangian (EL) method to examine the role of clustering on heat transfer. Specifically, the role of particle structuring on the thermal developmental length scale in a riser is quantified through a novel two-step simulation approach. The degree of particle clustering is first established with cold flow simulations of cluster-induced turbulence (CIT). At statistical steady-state, CIT outputs are fed into a secondary simulation with a defined particle-fluid thermal gradient. Thus, the thermal conditions in the second simulation evolve over the length of the riser and allow the effect of clustering on the thermal development length scale to be rigorously quantified.