Maximum Wall-to-Bed Heat Transfer in Fluidized Beds

Bock, H.

doi:10.1016/b978-0-08-028785-0.50021-6

Cited by 1 publication

(2 citation statements)

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“…They even proposed a correlation as a function of the excess gas velocity, but the procedure to obtain such expression was not explained. Also, as it was mentioned in the Introduction, Bock (1983) and Martin (l984a) analyzed independently experimental heat transfer rates in freely bubbling beds with models having a parameter clearly identifiable as the inverse of fw' By fitting the experimental data,fw turned out to be 0.33 and 0.38, respectively. These figures correspond to Np values much smaller than those expected from equation (l8a).…”

Section: Evaluation Of Parameters From Experiments In Freely Bubblingmentioning

confidence: 96%

“…This phenomenon, called Smoluchowski effect, can be predicted wth reasonable confidence. Bock (1983) presented a formulation including the Smoluchowski effect, but also an adjustable parameter related to the number of adjacent particles per unit area of the exchange surface, N p' The parameter was evaluated by fitting experimental data, and the associated values of N p turned out to be much lower than expected, for instance, from a cubic arrangement of particles (as reasonably assumed by Botterill et al, 1967). Although on a different basis, Martin (1984a) employed an approach similar to that of Bock. The last physical reason proposed to contribute to the thermal resistance at the wall is the effect of asperities on the particles and on the wall.…”

Section: Introductionmentioning

confidence: 98%

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Evaluation of Conductive Heat Transfer Mechanisms Between an Immersed Surface and the Adjacent Layer of Particles in Bubbling Fluidized Beds

Mazza¹,

Mariani²,

Barreto³

1997

Chemical Engineering Communications

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The evaluation of the heat transfer coefficient h w p between a heat exchanging surface immersed in a gas fluidized bed and the adjacent layer of dense phase particles is analyzed in this contribution. Gas convective and radiant effects are not included in the present analysis.The inclusion of h w p , or an equivalent formation, in mechanistic models describing heat transfer has been necessary because the sudden voidage variation close to the immersed wall restrains significantly the heat transfer rate. However, there is not at present a widely accepted expression to evaluate hwp'A precise formulation for h w p accounting for transient conduction inside .spherical particles, the Smoluchowski effect, the concentration of particles in the adjacent layer (N p) and an effective separation gap (to) is developed here.Although N p can be estimated, in principle, from experimental evidence in packed beds, and it is reasonably expected that to = 0, the analysis of experimental heat transfer rates in moving beds, packed beds, and bubbling fluidized beds indicate that values of h w p are, in general, smaller than expected from these assumptions. Appropriate values of to and N p are then estimated by fitting the experimental data. The probable effect of surface asperities is also discussed by analyzing a simplified geometrical model. It is concluded that the parameter to can be also effective to account for particle roughness, independently of thermal properties.

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Section: Evaluation Of Parameters From Experiments In Freely Bubblingmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 98%