Heat transfer from an immersed tube in a pulsating fluidized bed

Abstract

Heat transfer from an immersed tube in a pulsating fluidized bed was investigated computationally using an Eulerian-Eulerian approach. The relation between solids volume fraction distribution and heat transfer coefficient (HTC) was analyzed and the effects of temperature of the immersed tube, pulsation frequency, inlet superficial velocity and pulsation amplitude on heat transfer behaviors were studied. An interesting deflection phenomenon was observed in the presence of pulsation whereby particles that were heated by the immersed tube were transported away by the air in a circular pattern, giving rise to plume trails in the particle temperature distribution. At lower frequency of pulsation, air entering the fluidized bed formed larger bubbles and this led to lower heat transfer rates. At a higher inlet superficial velocity, higher convective heat transfer rates were achieved and the phenomenon of particle renewal at the surface of the immersed tube was enhanced in the presence of pulsation. Within the range of operating conditions considered in this study, heat transfer efficiency was higher in the presence of pulsation of inlet air flow. The best heat transfer performance was observed at high pulsation frequency (8 Hz) where smaller bubbles were formed in the fluidized bed and high inlet superficial velocity (U/Umf = 1.725) where rates of convective heat transfer were higher and the effect of particle renewal was stronger. This points towards the possibility of utilizing pulsed fluidization as an effective means of improving heat transfer rates in fluidized bed systems.