Numerical Analysis of Radiative Effects on Natural Convection in Vertical Convergent and Symmetrically Heated Channels

ABSTRACT

Natural convection in a convergent channel with finite-thickness principal walls at uniform heat flux is investigated numerically. Heat conduction in the walls and the effects of walls emissivity are taken into account. Laminar two-dimensional steady-state conditions are assumed. Results in terms of wall dimensionless temperature profiles as a function of convergence angle, channel spacing, and heat flux are given for various values of wall emissivity. Wall temperatures decrease significantly, passing from δ = 0° to 2° at the lowest channel spacing. Streamlines and temperature fields show a recirculating region in the channel for large values of L _w/b _min and for δ equal to 5° and 10°. Correlations between Nusselt numbers and Rayleigh numbers are proposed. Dimensionless parameters are in the following ranges: 4.4 ≤ Ra′_bmin ≤ 1.5 × 10⁵, 10 ≤ L _w /b _min ≤ 58, 0.0 ≤ ϵ ≤ 1.0, and 0° ≤ δ ≤ 10°. Numerical predictions are in very good agreement with experimental data.

This work was supported by Ministero dell'Istruzione, dell'Università e della Ricerca with a 2003–2005 Progetto di Ricerca d'Interesse Nazionale grant and Seconda Università degli Studi di Napoli with 2003 and 2005 research grants.

Notes

UWT: Uniform Wall Temperature.

UWHF: Uniform Wall Heat Flux.