Effect of particle size distribution on heat transfer in bubbling fluidized beds applied in thermochemical energy storage

The aim of the present work is to characterize the effect of particle size changes from cycling of the thermochemical energy storage material CaO/Ca(OH)₂ on fluidizability and wall-to-bed heat transfer coefficients in the fluidized bed. Materials replicated from previous storage cyclization experiments are experimentally investigated in an ambient fluidization test rig. Differential pressure measurement and a horizontally immersed heat transfer probe are used to characterize fluidizability and wall-to-bed heat transfer between immersed cylinder and bed material. Sauter mean diameters of the replicated particle size distributions range from 27 µm to 282 µm. Particle size distributions with Sauter mean diameters significantly smaller than approximately 50 µm were found to be difficult to fluidize due to excessive channeling, resulting in low heat transfer coefficients. In this case, fluidization quality and heat transfer is enhanced for higher gas velocities. Fluidizable particle size distributions ranged from Sauter mean diameters of 48 µm to 282 µm. Measured heat transfer coefficients show little dependency on the particle size. Observed maximum heat transfer coefficients range from 344 W m⁻² K⁻¹ to 350 W m⁻² K⁻¹.