Enhanced bed–wall heat transfer in narrow-channel fluidized beds with extended surfaces for particle solar receivers

Concentrating solar power (CSP) coupled with high-temperature, thermal energy storage (TES) offers a promising solution for dispatchable solar electricity with high-efficiency thermal power plants at firing temperatures above 700 ° C . High-temperature TES with oxide particles for CSP requires a receiver that can effectively heat particles without exceeding temperature limits of receiver structural materials. Indirect particle receivers with confining walls benefit from high wall heat transfer coefficients that reduce the temperature difference between irradiated receiver walls and particle-bed temperatures. Bubbling particle fluidization in smooth-wall narrow channel beds can provide high heat transfer coefficients such that solar receivers with angled cavity walls can sustain high normal solar fluxes above 200 kW m −2 , but bed–wall heat transfer still remains the critical thermal resistance. This study investigates the impact of incorporating extended surfaces (U-shaped fins) in narrow-channel, counterflow fluidized beds to enhance the bed–wall heat transfer coefficient. Experimental results show that bubbling fluidized beds with fin walls can achieve effective bed–wall heat transfer coefficients over 2500 W m − 2 K − 1 at 400 ° C for particles with mean diameter ≈ 225 μ m and over 1500 W m − 2 K − 1 for larger particles with mean diameter ≈ 408 μ m. Such high effective heat transfer coefficients occur at relatively low upward gas velocities and are largely insensitive to the downward particle mass flux. These values represent more than a two-fold improvement compared to smooth-wall fluidized beds. The effectiveness of internal fin walls in enhancing bed–wall heat transfer offers a pathway to lower the size and material costs of indirect particle receivers. • Bubbling bed–wall effective heat transfer coefficients can exceed 2500 W m − 2 K − 1 with extended surfaces. • Bed–wall effective heat transfer coefficients with extended surfaces vary little with particle mass flux. • Classic fin analysis using smooth-wall heat transfer coefficients tracks heat transfer trends with extended surfaces.