Heat transfer in freeboard region of fluidized beds
This research involved the study of heat transfer and fluid mechanic characteristics around a horizontal tube in the freeboard region of fluidized beds. Heat transfer coefficients were experimetnally measured for different bed temperatures, particle sizes, gas flow rates, and tube elevations in the freeboard region of air fluidized beds at atmospheric pressure. Local heat transfer coefficients were found to vary significantly with angular position around the tube. Average heat transfer coefficients were found to decrease with increasing freeboard tube elevation and approach the values for gas convection plus radiation for any given gas velocity. For a fixed tube elevation, heat transfer coefficients generally increased with increasing gas velocity and with high particle entrainment they can approach the magnitudes found for immersed tubes. Heat transfer coefficients were also found to increase with increasing bed temperature. It was concluded that this increase is partly due to increase of radiative heat transfer and partly due to change of thermal properties of the fluidizing gas and particles. To investigate the fluid mechanic behavior of gas and particles around a freeboard tube, transient particle tube contacts were measured with a special capacitance probe in room temperature experiments. The results indicated that the tube surface experiences alternating dense and lean phase contacts. Quantitative information for local characteristics was obtained from the capacitance signals and used to develop a phenomenological model for prediction of the heat transfer coefficients around freeboard tubes. The packet renewal theory was modified to account for the dense phase heat transfer and a new model was suggested for the lean phase heat transfer. Finally, an empirical freeboard heat transfer correlation was developed from functional analysis of the freeboard heat transfer data using nondimensional groups representing gas velocity and tube elevation.
- Research Organization:
- Lehigh Univ., Bethlehem, PA (USA). Inst. of Thermo-Fluid Engineering and Science
- DOE Contract Number:
- FG22-80PC30214
- OSTI ID:
- 5249686
- Report Number(s):
- DOE/PC/30214-T7; ON: DE84004615
- Resource Relation:
- Other Information: Portions are illegible in microfiche products. Original copy available until stock is exhausted
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
FLUIDIZED-BED COMBUSTORS
HEAT TRANSFER
CORRELATIONS
EXPERIMENTAL DATA
GLASS
LIMESTONE
MATHEMATICAL MODELS
SILICA
TEMPERATURE DEPENDENCE
TRANSIENTS
VELOCITY
VOID FRACTION
CARBONATE ROCKS
CHALCOGENIDES
COMBUSTORS
DATA
ENERGY TRANSFER
INFORMATION
MINERALS
NUMERICAL DATA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
ROCKS
SEDIMENTARY ROCKS
SILICON COMPOUNDS
SILICON OXIDES
421000* - Engineering- Combustion Systems