Effects of Inter-Particle Force on Particle Behavior and Heat Transfer around a Horizontal Tube in a Fluidized Bed

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The effects of cohesiveness and subsequent agglomeration of particles on the particle behavior and heat transfer characteristics around the horizontal tubes were experimentally studied. The inter-particle cohesive forces due to a liquid bridge were controlled by changing the humidity of the fluidizing air. The gross behavior of the fluidized bed with the cohesive particles was quantitatively evaluated by measuring the bed pressure drop and visual observation.Three kinds of experimental method were used to study the particle behavior and heat transfer characteristics around the horizontal tube. One of these is the simultaneous measurement of the particle behavior (void fraction and particle velocity) and the instantaneous local heat transfer coefficient at the same location on the tube surface. The other measuring methods are the visualization of the temperature and the particles on the tube surface from the inside of the tube using a micro-video camera. The temperature profiles around … More the heated tube were visualized by using thermosensitive liquid crystal sheet. And the heat transfer coefficient distributions were calculated from them by Newral network method. The behavior of the particles and the bubbles on the tube surface were visualized by throwing a laser light sheet from the inside.The obtained main results are summarized as following : When the inter-particle forces increased as the relative humidity of the fluidizing air increased, the void fraction around the tube became higher and the movements of the particles on the upper surface of the tube were suppressed, and consequently, the heat transfer coefficient around the tube became significantly lower. The decrease of overall average heat transfer coefficients around the tube by the increase of the inter-particle forces can be well correlated by using the channeling index which is estimated from the bed pressure drop. The new visualization method by throwing the laser light sheet from the inside of the tube was proposed and it can clearly distinguish the particles making contact with the tube surface from the bubble. Less