Bed‐to‐wall heat transfer in a downer reactor

Abstract

The effects of superficial gas velocity (0.5 to 4.5 d s ) , solid circulating rate (0 to 40 kg/m2.s), suspension density (0 to 19 kg/m3) and particle sizes (83, 103, 163,236 pm) on the bed-to-wall heat transfer coefficient have been determined in a downer reactor (0.1 m I.D. x 3.5 m high). Bed-to-wall heat transfer coefficient increases with increasing suspension density. The heat transfer coefficient by gas convection played a significant role, especially at lower solid circulation rates or suspension densities and larger particle sizes. At a given particle suspension density in the downer reactor, the heat transfer coefficient increases with decreasing particle size. A model is proposed to predict the bed-to-wall heat transfer coefficient in a downer reactor.Les effets de la vitesse de gaz superficielle (de 0,s a 4,s d s ) , de la vitesse de circulation des solides (0 a 40 kg/m2.s), de la masse volumique de suspension (0 a 19 kg/m3) et de la taille des particules (83, 103, 163, 236 pm) sur le coefficient de transfert de chaleur lit-paroi, ont ete determines dam un reacteur a colonne descendante (0,l m de diametre interieur x 3,5 m de hauteur). Le coefficient de transfert de chaleur lit-paroi augmente avec la masse volumique des suspensions. Le coefficient de transfert de chaleur par convection du gaz joue un r d e significatif, en particulier a de faibles vitesses de circulation des solides ou masses volumiques des suspensions et avec des tailles de particules larges. Pour une masse volumique de suspensions de particules donnee dans le reacteur a colonne descendante, le coefficient de transfert de chaleur augmente avec la diminution de la taille des particules. On propose un modele afin de predire le coefficient de transfert de chaleur lit-paroi dans un reacteur a colonne descendante.

Cluster and Bed-to-wall Heat Transfer Characteristics in a Dual Circulating Fluidized Bed

“…In CFBs, the total heat transfer coefficient ( h t ) would be the sum of three individual components, which are gas convection ( h gc ), particle convection ( h pc ), and radiation ( h r ). Although there are some doubts about the additive nature of these components, the overall heat transfer coefficient can be approximated as ,,, h normalt = h normalc + h normalr = h gc + h pc + h normalr where the radiative component can be neglected at room temperature . Therefore, the heat transfer coefficient ( h c ) in this study might be sum of gas ( h gc ) and particle convection ( h pc ) components.…”