Fluid mechanics and heat transfer in fluidized beds

Abstract

Heat transfer between submerged surfaces and gas-fluidized beds depends on fluid mechanics and particle dynamics. Therefore, reliable prediction of the heat transfer coefficient must be based on the observation of particle motion towards and from solid surfaces. Experiments with luminescent particles reveal a rather broad particle residence time distribution at solid surfaces. This broad residence time distribution gives rise to a smearing-out effect of the two different heat transfer mechanisms, namely particle convective and gas convective, respectively. Well-defined residence times can be realized by means of a rudimentary variant of fluidized bed heat transfer in the form of moving bed heat transfer. Experimental and theoretical results obtained from moving bed heat transfer allow the sound modeling of the two “pure” mechanisms (particle convective and gas convective). A predictive equation is derived which may be seen as a safe interpolation between the two extremes. The comparison with a large number of experiments proves the reliability of the prediction with respect to any feature of fluidized bed heat transfer.