HEAT, MASS AND EROSION RATES BETWEEN BUBBLING FLUIDIZED BEDS AND IMMERSED SURFACES

Several industrial applications of fluidization technology consider the presence of surfaces immersed in bubbling fluidized beds. For example, tube banks in bed boilers, tubular membranes to enhance specific chemical reactions and food pieces to be freezed or dehydrated. Moreover, surface treatments, as hardening, coating or chemical vapor depositions, can be reliably carried out in fluidized beds. The surface-to-bed heat, mass and erosion rates control the actual efficiency as well as the velocity of the aforementioned industrial processes, and this explains the paramount importance of experimental and modeling studies to support a reliable design and operation of industrial processes. The fluid dynamic field around the immersed surface presents different peculiarities respect to the average characteristics of the fluidized bed. These peculiarities are responsible for the actual values of the mass and heat transfer between the surfaces and the fluidized beds. Similarly, they governed the momentum transfer, whose main aspect is the surface erosion caused by the impacts with the fluidized particles. This chapter aims to analyze the transport phenomena among surfaces immersed in fluidized beds in light of the most recent experimental and modeling results reported in literature. The main goal of this contribution is to shed light on the characteristics of each transport phenomena and to point out the real analogies among them