Gas interchange between bubble and emulsion phases in a 2D fluidized bed as revealed by two-fluid model simulations

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Using two-fluid model simulations, the present work aims at characterizing the interchange due to gas advection between the emulsion phase and bubbles in fully bubbling beds of Geldart group B particles that are fluidized with air. In the studied beds the bubbles are slow, which means that the advection transport of gas through the bubble boundary is the main mechanism of gas interchange. In an initial verification step, the pressure distribution and the gas interchange coefficient for isolated bubbles obtained in the two-fluid simulation are compared with the classical potential flow theory of fluidized beds, providing concordant results. In a second step, the work analyzes the gas interchange in fully bubbling beds and the effects of the superficial velocity, bed height, and particle diameter on the interchange coefficient and the crossflow ratio. The results indicate that both the interchange coefficient and the crossflow ratio in bubbling beds are about two times those predicted by the potential theory of isolated bubbles. A corrected model for the gas interchange is proposed based on the introduction of the gas throughflow into the classical potential flow theory. As a consequence, the gas interchange coefficient in the corrected model is a function of the superficial gas velocity instead of the minimum fluidization velocity.
Fluidized bed, CFD, Gas interchange, Bubble, Throughflow
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Chemical Engineering Journal 215–216 (2013) 15 January, pp. 479–490