Heat Transfer Intensification Mechanism of a Baffled Fluidized Bed Heat Exchanger

Abstract

Gas–solid fluidized bed heat exchangers are commonly applied to remove heat in highly exothermic processes. The heat transfer performance is related to hydrodynamics. Baffles, such as ring-type baffles, louver baffles, and packings, are widely applied to improve the hydrodynamics in a fluidized bed. In this study, a baffled fluidized bed heat exchanger was proposed to enhance the bed-to-surface heat transfer coefficient. The baffles are specially designed to intensify the contact characteristics between heat transfer tubes and fluidized bed medium. The hydrodynamics and heat transfer characteristics were compared between the conventional and the newly designed baffled heat exchanger to explore the intensification mechanism in dilute and dense fluidization regions. Proper arrangement of the baffles in the fluidized bed heat exchanger increases the time fraction of the particle packet as well as the solid holdup, which enhances the heat transfer coefficient in dilute region. For the dense region, the contact time between the packet and heat transfer surface is decreased in the baffled fluidized bed heat exchanger due to the reduced bubble size, increased bubble frequency, and enhanced radial movement of bubbles and particles. Therefore, the bed-to-surface heat transfer in the dense region is significantly intensified.