A heat transfer model for tubes immersed in gas fluidized beds

Chandran, R. Sreekumari Bharat; Chen, J. C.

doi:10.1002/aic.690310211

Cited by 31 publications

(18 citation statements)

References 41 publications

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“…. In this study, we use the general model of Kunii and Smith to calculate k pa , that is

k_{pa} = k_{normalg} true[ε_{pa} + \frac{true(1 - ε_{pa} true)}{ϕ_{normalk} + 2 k_{normalg} / 3 k_{normals}} true]

where ϕ k is given by

ϕ_{normalk} = 0.305 {true(\frac{k_{normals}}{k_{normalg}} true)}^{- 0.25} for 1 \leq \frac{k_{normals}}{k_{normalg}} \leq 1000

…”

Section: Resultsmentioning

confidence: 99%

Systematic study on heat transfer and surface hydrodynamics of a vertical heat tube in a fluidized bed of FCC particles

Yao

Zhang

et al. 2014

AIChE Journal

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Bed-to-wall heat transfer properties of a vertical heat tube in a fluidized bed of fine fluid catalytic cracking (FCC) particles are measured systematically using a specially designed heat tube. Two important surface hydrodynamic parameters, i.e. the packet fraction (d pa ) and mean packet residence time (s pa ) based on the packet renewal theory, are determined by an optical fiber probe and a data processing method. The experimental results successfully reveal the axial and radial profiles of heat-transfer coefficient, the effects of superficial gas velocity, and static bed height on heat-transfer coefficient, most of which can be explained successfully by the measured s pa , an indicator of packet renewal frequency. s pa is found to play a more dominant role than d pa on bed-to-wall heat transfer. With a fitted correction factor, the modified Mickley and Fairbanks model is able to predict the heat-transfer coefficients with enough accuracy based on the determined packet parameters. Figure 23. Effect of static bed height on heat-transfer coefficients.

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“…. In this study, we use the general model of Kunii and Smith to calculate k pa , that is

k_{pa} = k_{normalg} true[ε_{pa} + \frac{true(1 - ε_{pa} true)}{ϕ_{normalk} + 2 k_{normalg} / 3 k_{normals}} true]

where ϕ k is given by

ϕ_{normalk} = 0.305 {true(\frac{k_{normals}}{k_{normalg}} true)}^{- 0.25} for 1 \leq \frac{k_{normals}}{k_{normalg}} \leq 1000

…”

Section: Resultsmentioning

confidence: 99%

Systematic study on heat transfer and surface hydrodynamics of a vertical heat tube in a fluidized bed of FCC particles

Yao

Zhang

et al. 2014

AIChE Journal

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“…18 The authors evaluated h B from experimental values of the total coefficient h by subtracting the solid and gas contributions in the dense phase. For estimating the bubble-phase heat transfer coefficient h B , the gas convective contribution (h c,B ) resulting from the own void plus the so called through flow, and the radiant contribution (h rad,B ) from the exchange between the surface and the solid particle at the bubble boundary should be considered.…”

Section: Evaluation Of Heat Exchange With the Bubble Phasementioning

confidence: 99%

Computational fluid dynamics simulations of heat transfer between the dense‐phase of a high‐temperature fluidized bed and an immersed surface

2011

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The transient process of heat transfer between a high‐temperature emulsion packet and the wall of an immersed surface is simulated using computational fluid dynamics (CFD). From these simulations, the total heat transfer coefficient and its radiant contribution due to the emulsion (dense) phase are evaluated. The results are compared with experimental data (Ozkaynak et al., “An experimental investigation of radiant heat transfer in high temperature fluidized beds,” in Fluidization IV, 1983:371–378) and with predicted values from the generalized heterogeneous model (GHM), (Mazza et al., “Evaluation of overall heat transfer rates between bubbling fluidized beds and immersed surfaces,” Chem Eng Commun., 1997;162:125–149). The CFD simulations are in good agreement with both, experimental data and theoretical GHM predictions and provide a reliable way to quantify the studied heat transfer process. Also, the GHM is validated as a practical tool to this end. © 2011 American Institute of Chemical Engineers AIChE J, 58: 412–426, 2012

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“…There exist two distinct approaches (Mickley and Fairbanks, 1955;Botterill and Williams, 1963) for the prediction of the heat transfer coefficient. Many investigators have subsequently suggested modifications to the basic models cited above so as to achieve good agreement with experimental data (Saxena and Gabor, 1981;Chandran and Chen, 1985).…”

Section: Influence Of the Wall On Transient Conductionmentioning

confidence: 99%

Influence of the wall on transient conduction into packed media

Chandran

Chen

1985

AIChE Journal

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Surfaces immersed in moving packed beds and fluidized beds frequently experience a "renewal" type of contact with packed media. If there is heat transfer during surface renewal, it can be modeled as a transient conduction process provided the contribution due to thermal radiation is negligible. There exist two distinct approaches (Mickley and Fairbanks, 1955;Botterill and Williams, 1963) for the prediction of the heat transfer coefficient. Many investigators have subsequently suggested modifications to the basic models cited above so as to achieve good agreement with experimental data (Saxena and Gabor, 1981;Chandran and Chen, 1985).A review of the literature indicated that the model developed by Kubie and Broughton (1975) exhibits satisfactory agreement with experimental data without the use of empirical parameters. However, the model requires a numerical solution and that detracts it from use for design purposes. From an application standpoint, it is desirable to develop a simple closed-form relation for the heat transfer coefficient; such a relation is derived in this note. ANALYSISConsider a disperse system comprising a gas-solid medium with a close-packed matrix of solid particles and stationary gas that comes into contact with a surface at a different temperature for a certain duration. For the case of negligible radiant contribution, heat transfer occurs by unsteady state conduction. In formulating the problem, it is important to (i) account for the influence of the surface or wall on the local packing, and (ii) recognize the heterogeneity of the two-phase medium. The property boundary layer concept introduced by Kubie and Broughton (1975) is used here to account for the wall effect. This translates into the voidage variation shown in Figure 1. The heterogeneous nature of the disperse system, however, is more difficult to deal with. Hence as a first approximation, the stochastic behavior of multiple particles is treated as pseudo-homogeneous in this work.For constant wall temperature, with the usual assumptions, the governing equations for transient conduction into the disperse system can be written in normalized form as: Equations 1 and 2 were obtained by using the relation proposed by Kubie and Broughton (1975) subject to

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A heat transfer model for tubes immersed in gas fluidized beds

Cited by 31 publications

References 41 publications

Systematic study on heat transfer and surface hydrodynamics of a vertical heat tube in a fluidized bed of FCC particles

Systematic study on heat transfer and surface hydrodynamics of a vertical heat tube in a fluidized bed of FCC particles

Computational fluid dynamics simulations of heat transfer between the dense‐phase of a high‐temperature fluidized bed and an immersed surface

Influence of the wall on transient conduction into packed media

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