Effect of particle size and sand inventory on wall-to-bed heat transfer characteristics of circulating fluidized bed riser

The present paper describes a numerical study on the steady state wall-to-bed heat transfer characteristics of circulating fluidized bed (CFB) riser of cross section 0.15 m x 0.15 m and height 2.85 (m). 3-D CFD simulations for heat transfer characteristics were carried out for heated portion (heater) of 0.15 (m) width and 0.60 (m) height. Heater was placed 0.60 (m) above the distributor plate which is the lower splash region of CFB. For modeling and simulation, CFD code Fluent - version 6.3.26 has been used. Modeling and meshing were done with Gambit software - version 2.4.6. The wall of heater was maintained at the constant heat flux q″ = 1000 (W/m²). RNG k-ε model was used for turbulence modeling. Mixture model and Gidaspow model for phase interaction were used for the simulation of two phase flow (air + sand mixture flow) and Gidaspow model found to be more accurate model further simulations. Results obtained were compared for distribution of bed (air + sand mixture) temperature across the heater and local heat transfer coefficient along the height of the heater for two sand inventories (4 kg and 7 kg) and six particle sizes falling in the range of Geldart B type particles (60 μm, 100 μm, 160 μm, 260 μm, 360 μm, 460 μm). Results obtained through CFD simulations were compared with available literatures and experimental results which were obtained from available CFB setup of IIT Guwahati.