Gas-to-particle heat transfer

The heat transfer behavior in a spouted bed (see 9.8) is different from that in dense-phase and circulating fluidized bed systems as a result of the inherent differences in their flow structures. The spouted bed is represented by a flow structure that can be characterized by two regions the annulus and the central spouting region (see Chapter 9). The heat transfers in these two regions are usually modeled separately. For the central spouting region, the correlation of Rowe and Claxton (1965) can be used for Repf 1,000 

Substituting the corresponding values for the spouted bed into Eqs. (12.32), (12.68), and (12.69) reveals that the distance required for the gas to travel to achieve a thermal equilibrium with the solids in the annulus region is on the order of magnitude of centimeters, while this distance in the spout region is one or two orders of magnitude larger. 

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Integration of Eq. (6) for S02 in Table V estimates the conversion achieved. Simulation of periodic symmetrical switching between a reactant mixture and air gave an estimate of 99.4% at 12 min after the switch to the S03/S02 reactant mixture in reasonable agreement with the overall conversion of 98.8% measured by Briggs et al. (1977). With respect to model sensitivity, it was found that bed midpoint temperature was sensitive to the wall and gas to particle heat transfer coefficients. An extensive study of sensitivity, however, was not undertaken. 

Gas to liquids (GTL) conversion, 15 217 Gas-to-particle heat transfer, 11 809 Gas Transmission and Distribution Piping, 19 480... 

Schofield and Glikin estimated the heat-transfer coefficient by using the correlation given by McAdams (1954), which correlates data for gas-to-particle heat transfer in air to about 20 percent over a range of Reynolds numbers (Rep, defined in the previous section) between 17 and 70,000 ... 

Investigator Type of correlation Phases involved Region associated Rowe and Claxton [82] Gas-to-particle heat transfer coefficient Gas-solid Central spouting region... 

The heat transfer behavior in a spouted bed is different from that in the dense-phase or circulating fluidized bed system due to the inherent differences in their flow structures. The gas-to-particle heat transfer coefficient in the annulus region is usually an order of magnitude higher than that in the central spout region. The bed-to-surface heat transfer coefficient reaches a maximum at the spout-annulus interface and also increases with the particle diameter. 

Gas to particle heat transfer coefficients are t3q>ically small, of the order of 5-20 W m K. However, because of the very large heat transfer surface area provided by a mass of small particles (1 m of 100 pm particles has a surface area of 60 000 m ), the heat transfer between gas and particles is rarely limiting in fluid bed heat transfer. One of the most commonly used correlations for gas-particle heat transfer coefficient is that of Kunii and Levenspiel (1969) ... 

In general, the average gas-to-particle heat transfer coefficients for ISDs are much higher than those in classical dryers that operate under similar hydrodynamic regimes. For example, when the heat... 

Although not discernible in Fig. 4.16, the parameters Ho and x were varied in the experiments. In contrast, the diameter D of the upper, cylindrical part of the apparatus was constant, and consequently dimensionless representation is the only justification for the appearance of this quantity in the correlation. The Schmidt number was also constant, and has been incorporated in the pre-factor of Eq. 4.21. The values of the pre-factor, a, and of the exponents, m, p, and q, which are listed in Tab. 4.6, depend on whether the Sherwood numbers shall be used in combination with the CSTR or with the PFR assumption in order to calculate particle-to-gas mass transfer in the unit. Nusselt numbers for gas-to-particle heat transfer can be obtained by analogy. To this purpose, the pre-factor should be split to... 

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