Radiative Heat Transfer in Circulating Fluidized Beds

1995 ◽  
Vol 117 (4) ◽  
pp. 963-968 ◽  
Author(s):  
Z. H. Fang ◽  
J. R. Grace ◽  
C. J. Lim
Keyword(s):  
Heat Transfer ◽  
Fluidized Beds ◽  
Radiative Heat ◽  
Circulating Fluidized Beds ◽  
Transfer Coefficients ◽  
Renewal Model ◽  
Cluster Transfer ◽  
Model Predictions ◽  
Dilute Suspension ◽  
Good Agreement

The radiation contributions to heat transfer in circulating fluidized beds are investigated based on a simple model involving clusters and dilute suspension. Local and length-averaged cluster transfer coefficients are derived based on a cluster renewal model with combined transient conduction and radiation. A three-component network is analyzed leading to a concise relation for the suspension-to-wall radiative transfer. Previous experimental data for heat transfer to a membrane wall with bed temperatures of 407 and 860°C (Wu et al., 1989) are in good agreement with model predictions.

Particle Motion in the Vicinity of the Wall of Circulating Fluidized Beds

2012 ◽  
Vol 614-615 ◽  
pp. 3-7
Author(s):  
Jian Hui Liu ◽  
Shuan Shi Fan ◽  
Dong Lai Xie
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Particle Motion ◽  
Fluidized Beds ◽  
High Density ◽  
Circulating Fluidized Beds ◽  
Low Density ◽  
Transfer Coefficients ◽  
Tube Heat Exchanger ◽  
Operation Conditions

High-density circulating fluidized beds (CFB) differ in several respects from low-density CFB systems. In high-density CFB risers, solids move upward throughout the entire riser cross-section, and the net downflow of particles at the wall, a commonly observed feature of fast fluidized beds, is absent. Hence there exists a transition regime from the low density to high density CFB where the net particle motion in the vicinity of the wall is changing from downwards to upwards. This was confirmed by experiments carried in a dual-loop high-density CFB facility with concentric-tube heat exchanger installed in the riser. Local suspension-to-wall heat transfer coefficient and suspension temperature distribution below and above the heat exchange section were measured. Experimental results elucidated that particles move both upwards and downwards in the vicinity of the wall for the operation conditions studied. This alternation of direction leads to higher heat transfer coefficients at both ends of the heat exchange.

scholarly journals Wall-to-Suspension Heat Transfer in a CFB Downcomer

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Huili Zhang ◽  
Jan Degrève ◽  
Raf Dewil ◽  
Jan Baeyens
Keyword(s):  
Heat Transfer ◽  
Fluidized Beds ◽  
Waste Heat ◽  
Circulation Rate ◽  
Circulating Fluidized Beds ◽  
Surface Renewal ◽  
Model Predictions ◽  
Heat Transfer System ◽  
And Storage ◽  
Model Expression

With the development of circulating fluidized beds (CFB) and dense upflow bubbling fluidized beds (UBFB) as chemical reactors, or in the capture and storage of solar or waste heat, the associated downcomer has been proposed as an additional heat transfer system. Whereas fundamental and applied research towards hydrodynamics has been carried out, few results have been reported on heat transfer in downcomers, even though it is an important element in their design and application. The wall-to-suspension heat transfer coefficient (HTC) was measured in the downcomer. The HTC increases linearly with the solids flux, till values of about 150 kg/m2 s. The increasing HTC with increasing solid circulation rate is reflected through a faster surface renewal by the downflow of the particle-gas suspension at the wall. The model predictions and experimental data are in very fair agreement, and the model expression can predict the influence of the dominant parameters of heat transfer geometry, solids circulation flow, and particle characteristics.

Analysis of the Heat Transfer Mechanism in High-Temperature Circulating Fluidized Beds by a Numerical Model

2002 ◽  
Vol 124 (1) ◽  
pp. 34-39 ◽  
Author(s):  
Qiao He ◽  
Franz Winter ◽  
Ji-Dong Lu
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Radiative Heat Transfer ◽  
Fluidized Beds ◽  
Radiative Heat ◽  
Total Heat ◽  
Circulating Fluidized Beds ◽  
Total Heat Transfer

A general numerical model is presented here to describe the complex fluid dynamics and the heat transfer process in high-temperature circulating fluidized beds (CFBs). The core-wall concept is used to describe the gas-solid flow in the dilute phase section of CFBs. The variation of the thickness of the wall layer along the height direction is considered in the fluid dynamic model in order to approach the practical conditions. Three components of heat transfer, i.e., the particle-convective heat transfer, the gas-convective heat transfer, and the radiative heat transfer, and their contributions to the total heat transfer coefficient are investigated. The influences of some operating parameters on the total heat transfer and its components are predicted. Detailed information about the mechanism of heat transfer is discussed. The radiative heat transfer accounts for about 30∼60% of the total heat transfer in high temperature CFBs. It gradually increases along the height direction of the furnace. When the contribution of particle convection increases, the contribution of gas convection decreases, and vice versa. Particle size shows a significant effect on the radiative heat transfer and the convective heat transfer. High bed and wall temperatures will primarily increase the radiative heat transfer.

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