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RESEARCH PAPERS: Natural and Mixed Convection

Experimental Investigation of Natural Convection in an Asymmetrically Heated Vertical Channel with an Asymmetric Chimney

[+] Author and Article Information
Oronzio Manca, Marilena Musto, Vincenzo Naso

DIAM-Dipartimento di Ingegneria Aerospaziale e Meccanica,  Seconda Università degli Studi di Napoli, Real Casa dell’Annunziata, Via Roma, 29, 81031 Aversa (CE), ItalyDETEC-Dipartimento di Energetica, Termofluidodinamica applicata e Condizionamenti ambientali, Università degli Studi di Napoli Federico II, Piazzale Tecchio, 80, 80125, Napoli, Italy

J. Heat Transfer 127(8), 888-896 (Mar 15, 2005) (9 pages) doi:10.1115/1.1928909 History: Received March 02, 2004; Revised March 15, 2005

An experimental investigation on air natural convection, in a vertical channel asymmetrically heated at uniform heat flux, with downstream unheated parallel extensions, is carried out. One extension is coplanar to the unheated channel wall and the distance between the extensions is equal to or greater than the channel gap (geometrically asymmetric chimney). Experiments are performed with different values of the wall heat flux, aspect ratio (Lhb), extension ratio (LLh) and expansion ratio (Bb). For the largest value of the aspect ratio (Lhb=10), the adiabatic extensions improve the thermal performance in terms of lower maximum wall temperature of the channel. Optimal configurations of the system with asymmetrical chimney are detected. Flow visualization shows a cold inflow in the channel-chimney system that penetrates down below the channel exit section. Maximum wall temperatures and channel Nusselt numbers are correlated to the channel Rayleigh number, Ra*, and to the geometrical parameters, in the ranges 3.0×102Ra*Bb1.0105, 1.0Bb3.0 and 1.0LLh4.0 with Lhb=5.0 and 10.0.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of the experimental apparatus: (a) test section and heated wall; (b) visualization arrangement; and (c) position of thermocouples on the channel walls (all dimensions are in mm)

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Figure 2

Wall temperature rise versus the axial coordinate, for Lh∕b=5.0 and qΩ=300Wm−2 and various B∕b values: (a) L∕Lh=1.5; (b) L∕Lh=2.0; (c) L∕Lh=3.0; and (d) L∕Lh=4.0

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Figure 3

Wall temperature rise versus the axial coordinate, for Lh∕b=10.0 and qΩ=300Wm−2 and various B∕b values: (a) L∕Lh=1.5; (b) L∕Lh=2.0; (c) L∕Lh=3.0; and (d) L∕Lh=4.0

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Figure 4

Ratio of the maximum wall temperature rise above the ambient air in a channel without the adiabatic expansion ratio, for Lh∕b=5.0 and different L∕Lh: (a) qΩ=100Wm−2; (b) qΩ=300Wm−2; and (c) qΩ=450Wm−2

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Figure 5

Ratio of the maximum wall temperature rise above the ambient air in a channel without the adiabatic expansion ratio, for Lh∕b=10.0 and different L∕Lh: (a) qΩ=100Wm−2; (b) qΩ=300Wm−2; and (c) qΩ=450Wm−2

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Figure 6

Comparison between wall temperature rise profiles along axial coordinate in a channel with a geometrically symmetric extension from (18) and geometrically asymmetric extension from present data, for qΩ=300Wm−2, Lh∕b=10, and various B∕b values: (a) L∕Lh=2.0; (b) L∕Lh=3.0; and (c) L∕Lh=4.0

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Figure 7

Flow visualization in a system with an asymmetric chimney, qΩ=300Wm−2, Lh∕b=5.0, B∕b=2.5, and L∕Lh=1.5. Smoke inflow: (a) at the channel inlet of the heated side; (b) at the channel inlet of the unheated side; and (c) at the channel outlet on the heated side.

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Figure 8

Flow visualization in a system with a symmetric chimney, qΩ=300Wm−2, Lh∕b=5, and L∕Lh=1.5: (a) B∕b=2.0; and (b) B∕b=4.0

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Figure 9

Dimensionless wall temperature versus the channel Rayleigh number multiplied by the expansion ratio for Lh∕b=5.0 and 10: (a) L∕Lh=1.5 and (b) L∕Lh=4.0

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Figure 10

Dimensionless wall temperature versus the channel Rayleigh number multiplied by the expansion ratio for Lh∕b=5.0 and 10

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Figure 11

Channel Nusselt number versus the channel Rayleigh number multiplied by the expansion ratio for Lh∕b=5.0 and 10

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