Impacts of Pulsed Fluidization on Heat Transfer and Bubble Hydrodynamics in Bubbling Fluidized Beds

Mild bubbling fluidization can achieve bed-wall heat transfer coefficients hT,w, > 1000 W m-2 K-1 in narrow-channel fluidized beds [1]. The high bed-wall heat transfer due to fluidization provides a means for using oxide particles as the heat transfer media in large-scale, high-temperature thermal energy storage (TES) systems. For next-generation concentrating solar power plants with thermal energy storage (CSP-TES), particle fluidization can decrease the size of primary particle heat exchangers for the thermal power cycle and can lower bed-wall temperature differences within indirect particle-receivers. Pulsing of the fluidizing gas flow has been considered to further increase heat transfer by mitigating bubble agglomeration and particle clumping [2-4] and thereby reduce the cost of heat transfer components for CSP-TES systems. This study explores the impact of pulsed fluidization on bed-wall heat transfer and flow dynamics in narrow-channel fluidizing bed passages characteristic of proposed designs for particle heat exchangers and indirect receivers. The results show that pulsing the fluidizing gas with a 50% duty cycle does not improve heat transfer coefficients but does limit gas bubble growth over the height of the narrow-channel fluidized bed (0.27 m in height). Reduced bubble sizes improve flow homogeneity and decrease particle mixing, which can improve particle receiver and HX performance within CSP-TES.