Circulating fluidized beds heat transfer

Measurements of heat transfer in circulating fluidized beds require use of very small heat transfer probes, in order to reduce the interference to the flow field. The dimensions of the heat transfer surface may significantly affect the heat transfer coefficient at any radial position in the riser. All the treatment of circulating fluidized bed heat transfer described is based on a small dimension for the heat transfer surface. The heat transfer coefficient decreases asymptotically with an increase in the vertical dimension of the heat transfer surface [Bi et al., 1990]. It can be stated that the large dimensions of the heat transfer surface... 

L. Glicksman, Circulating Fluidized Bed Heat Transfer, in Circulating Fluidized Bed Technology II, R Basu and J. F. Large eds., Pergamon Press, Oxford, 1988. 

Glicksman LR. Circulating fluidized bed heat transfer. In Basu P, Large JF, eds. Circulating Fluidized Bed Technology 11. Oxford Pergamon Press, 1988,... 

Noymer, P. D., Hyre, M. R., and Glicksman, L. R., The Influence of Bed Diameter on Hydrodynamics and Heat Transfer in Circulating Fluidized Beds, Fluidization and Fluid-Particle Systems, AIChE, pp. 86-90 (1995)... 

Another parametric effect is the apparent dependence of the heat transfer coefficient on the physical size of the heat transfer surface. Figure 24, from Burki et al. (1993), graphically illustrates this parametric effect by showing that the effective heat transfer coefficient can vary by several hundred percent with different vertical lengths of the heat transfer surface, for circulating fluidized beds of approximately the same particle diameter and suspension density. This size effect significantly contributed to confusion in the technical community since experimental measurements by inves-... 

Burki, V., Hirschberg, B., Tuzla, K., and Chen, J. C., Thermal Development for Heat Transfer in Circulating Fluidized Beds, ALChE Annual Meeting, (1993)... 

Ebert, T., Glicksman, L., and Lints, M., Determination of Particle and Gas Convective Heat Transfer Components in Circulating Fluidized Bed, Chem. Eng. Sci., 48 2179-2188 (1993)... 

Grace, J., Heat Transfer in Circulating Fluidized Beds, Cir. Fluid. Bed Tech., 63-81 (1986)... 

Lints, M. C., and Glicksman, L. R., Parameters Governing Particle-to-Wall Heat Transfer in a Circulating Fluidized Bed, Circ. Fluid. Bed Tech. IV, 297-304 (19923)... 

Palchonok, G. I., Breitholz, C., Anderson, B. A., and Lechner, B., Heat Transfer in the Boundary Layer of a Circulating Fluidized Bed Boiler, Fluidization... 

Silva, E. M. V., Ferreira, M. C., and Freire, J. T., Mean Voidage Measurements and Fluid Dynamics Analysis in a Circulating Fluidized Bed with a Spouted Bed Type Solids F eeding System, Proc. of2nd European Thermal-Sciences and 14th UIT National Heat Transfer Conference, Rome (1996)... 

The mechanism of heat transfer in circulating fluidized beds is described in this section. Effects of the operating variables on the local and overall heat transfer coefficients are discussed. 

The suspension-to-wall surface heat transfer mechanism in a circulating fluidized bed (see Chapter 10) comprises various modes, including conduction due to particle clusters on the surface or particles falling along the walls, thermal radiation, and convection due to... 

In circulating fluidized beds, the clusters move randomly. Some clusters are swept from the surface, while others stay on the surface. Thus, the heat transfer between the surface and clusters occurs via unsteady heat conduction with a variable contact time. This part of heat transfer due to cluster movement represents the main part of particle convective heat transfer. Heat transfer is also due to gas flow which covers the surface (or a part of surface). This part of heat transfer corresponds to the gas convective component. 

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