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Optimization of a buoyancy chimney with a heated ribbed wall

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Abstract

Heat and mass transfer in natural convection vertical channels was investigated by means of two-dimensional CFD simulations aided by optimization algorithms. The channel was immersed in air, enclosed between an adiabatic smooth wall and an isothermally heated ribbed wall. The ribs were perpendicular to the fluid flow and their height, width, pitch, thermal conductivity and lateral wall inclination were variable. Also the smooth heated wall channel was studied and compared with the ribbed one. The existence of an optimal channel width for a given channel height and rib geometry was shown. A sensitivity analysis was carried out for the ribbed and the smooth channels. Optimization was applied to the ribbed channel problem in order to maximize the heat and the mass transfer through a multi-objective genetic algorithm. It was found that the presence of the ribs penalizes the channel performance so that no ribbed channel over-performed the smooth one.

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Abbreviations

A r :

channel aspect ratio

A wet :

wetted area (m2)

H :

channel height (m)

H′:

non-dimensional channel height

H 0 :

reference channel height (m)

\({\dot{M}}\) :

mass flow rate (g/s)

M′:

non-dimensional mass flow rate

Nu :

Nusselt number

Nu x :

local Nusselt number

\({\dot{Q}}\) :

channel heat transfer rate (W)

Ra :

Rayleigh number

R h :

rib height (m)

R n :

ribs number

R p :

rib pitch (m)

R w :

rib crest width (m)

S :

channel width (m)

c p :

fluid specific heat at constant pressure (J/(kg K))

g :

gravitational acceleration (m/s2)

h :

local heat transfer coefficient (W/(m2 K))

h av :

average heat transfer coefficient (W/(m2 K))

s :

heated wall curvilinear abscissa measured from the channel inlet (m)

u ref :

reference velocity (m/s)

x :

vertical abscissa measured from the channel inlet (m)

ΔT :

ribbed wall to ambient temperature difference (K)

ΔT′:

non-dimensional temperature difference

ΔT 0 :

reference ribbed wall to ambient temperature difference (K)

α:

rib lateral wall inclination (deg)

β:

fluid thermal expansion coefficient (1/K)

λ:

rib thermal conductivity (W/(m K))

λfl :

fluid thermal conductivity (W/(m K))

μ:

fluid dynamic viscosity (kg/(m s))

ρ:

fluid density (kg/m3)

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Acknowledgments

Financial support for this research was provided by MIUR, PRIN 2005, Grant No. 2005094817. Thanks to Prof. E. Nobile (University of Trieste) and G. Tanda (University of Genova), for the scientific support. Technical support by ES.TEC.O. Srl, Trieste, italy, is gratefully acknowledged.

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Authors and Affiliations

  1. DIMeC-Università degli Studi di Modena e Reggio Emilia, via Vignolese 905/b, 41100, Modena, Italy

    Marco Cavazzuti & Mauro A. Corticelli

Authors
  1. Marco Cavazzuti
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  2. Mauro A. Corticelli
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Correspondence to Mauro A. Corticelli.

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Cavazzuti, M., Corticelli, M.A. Optimization of a buoyancy chimney with a heated ribbed wall. Heat Mass Transfer 44, 421–435 (2008). https://doi.org/10.1007/s00231-007-0255-6

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  • DOI: https://doi.org/10.1007/s00231-007-0255-6

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