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Research Papers: Forced Convection

Heat Transfer to Flat Strips Immersed in a Fluidized Bed

[+] Author and Article Information
Christopher Penny, Dennis Rosero, David Naylor

Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, ON, M5B 2K3, Canada

Jacob Friedman1

Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, ON, M5B 2K3, Canadajfriedman@ryerson.ca

1

Corresponding author.

J. Heat Transfer 133(7), 071703 (Mar 30, 2011) (7 pages) doi:10.1115/1.4003530 History: Received January 07, 2010; Revised January 26, 2011; Published March 30, 2011; Online March 30, 2011

Heat transfer to objects immersed in a fluidized bed has been studied extensively across a relatively large range of geometries, though most work has looked at cylinders, a geometry important in power generation fluidized bed applications. As the power generation industry has been the primary stimulant to fluidized bed heat transfer research, very little information is available regarding geometries significant in heat treating applications. In this work, heat transfer to thin flat strips immersed in a fluidized bed is examined. This geometry is important in the steel strap manufacturing industry where many manufacturers use environmentally damaging molten lead baths to heat-treat their product. In order to determine the feasibility of a fluidized bed heat treating system as an alternative to the more hazardous lead-based process, an experimental investigation has been conducted in which Nusselt number data for flat strips with widths in the range of 6.35–25.4 mm are obtained using a laboratory-scale fluidized bed (310 mm diameter). Aluminum oxide sand particles in the range of dp=145330μm (50–90 grit) are used as the fluidized media within the fluidized operating range from 0.15Gmf to approximately 10Gmf. The strip orientation angle θo was also varied to establish the position from which maximum heat transfer is obtained. It was found that a decrease in particle diameter, an increase in fluidizing rate, and an increase in sample diameter resulted in an increase in Nusselt number. It was also observed that for the smaller samples tested, a maximum Nusselt number plateau was reached, at approximately G/Gmf=2.5. Finally, it was shown that an increase in θo (from 0 deg to 90 deg) resulted in an increase in Nusselt number. A correlation for the maximum Nusselt number was developed, providing excellent agreement within ±15%.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 3

Energy balance of element of width dx

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Figure 4

Temperature distribution for a 9.53 mm sample oriented at 0 deg in a bed of 203 μm particles

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Figure 5

Experimental Nusselt number versus G/Gmf for all flat strip sample sizes at 0 deg orientation in 70 grit sand: (a) 6.35 mm, (b) 9.53 mm, (c) 12.7 mm, and (d) 25.4 mm

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Figure 6

Experimental Nusselt number versus G/Gmf for all flat strip sample sizes at 90 deg orientation in 70 grit sand: (a) 6.35 mm, (b) 9.53 mm, (c) 12.7 mm, and (d) 25.4 mm

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Figure 7

Experimental Nusselt number versus G/Gmf for ws=12.70 mm flat strip sample in 70 grit sand for all orientations

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Figure 8

Mean Nusselt number versus particle size for all flat strip samples oriented at 45 deg

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Figure 9

Calculated Nusselt number (Eq. 23) versus experimental Nusselt number for all data

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Figure 1

Schematic cross section of fluidized bed column and sample

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Figure 2

Inside terminal assembly

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