Heat transfer characteristics in the dense phase region of a pressurized fluidized bed

Heat transfer characteristics are complex, specifically in the dense phase region of fluidized beds. In this paper, the flow characteristics and the heat transfer coefficients of an immersed horizontal tube in a pressurized fluidized bed were examined. The digital image analysis technique was used to determine the emulsion phase fraction, contact time, the bubble frequency, and the fluidization number at different pressure. The bubble phase fraction and the contact time of the emulsion phase decreased with increasing pressure while the emulsion phase fraction and the bubble frequency increased. The fraction and the contact time of the emulsion phase decreased with increasing gas velocity while the bubble phase fraction and the bubble frequency increased. The average heat transfer coefficient increased with pressure and reached a maximum at the optimal fluidized gas velocity. At the same pressure and gas velocity, the smaller particle size led to a higher average heat transfer coefficient for Geldart B particles. A model of the average heat transfer coefficient was derived based on the emulsion phase fraction, contact time, and the Froude number. Copyright © 2020 Journal The Society of Chemical of Chemical Engineering Engineers, of Japan