Page 202 - gas transport in porous media

Khanafer and Vafai
196
for double-diffusive convection in a fluid-filled rectangular cavity. The generalized
model covered the entire range from Darcy flow to free fluid flow. Numerical pre-
dictions by the model indicate that the flow pattern as well as heat and mass transfer
is profoundly influenced by the buoyancy ratio. Also non-Darcy effects on flow,
heat, and mass transfer become significant when the Rayleigh or Darcy numbers are
large. The Sherwood and Nusselt numbers were found to be sensitive to bed porosity
variation in the non-Darcy regime.
Later on, the same authors (1997b) analyzed double-diffusive natural convection in
fluid saturated porous medium using a generalized porous medium model for a Prandtl
number of Pr = 1.0. One of the vertical walls of the porous cavity considered was
subject to convective heat and mass transfer conditions. It was shown that heat and
mass transfer rates were sensitive to the applied mass transfer coefficient in both the
Darcy and non-Darcy flow regimes. It was also observed that the Sherwood number
approaches a constant value as the solutal Biot number increases.
The problem of coupled heat and mass transfer by natural convection from a ver-
tical, semi-infinite flat plate embedded in an air saturated porous medium in the
presence of an external magnetic field and internal heat generation or absorption was
formulated by Chamkha and Khaled (2000). The plate surface was maintained at con-
stant temperature or constant heat flux and was permeable to allow for possible fluid
wall suction or blowing. Useful correlations containing various physical parameters
for both isothermal and isoflux walls were reported in that study.

REFERENCES
Horizontal Surface

J.D. Chang and P. Cheng, Matched asymptotic expansions for free convection about an imperme-
able horizontal surface in a porous medium, Int. J. Heat Mass Transfer, vol. 26, pp. 163–174
(1983).
P. Cheng, Geothermal heat transfer, in W.M. Rohsenow, J.P. Hartnett, and E.N. Ganic (eds.), Handbook of
Heat Transfer Applications, 2nd ed., Chap. 11, McGraw-Hill, NY (1985).
D. Lesnic, D.B. Ingham and I. Pop. Conjugate free convection from a horizontal surface in a porous
medium. Zeitschrift fur Angewandte Mathematik und Mechanik, vol. 75, pp. 715–722 (1995).
D. Lesnic and I. Pop, Free convection in a porous medium adjacent to horizontal surfaces. Zeitschrift fur
Angewandte Mathematik und Mechanik, vol. 78, pp. 197–205 (1998).
D.A. Nield and A. Bejan, Convection in Porous Media, Springer-Verlag, NY (1992).
I. Pop and R.S.R. Gorla, Horizontal boundary-layer natural convection in a porous medium saturated with
a gas, Transport In Porous Media, vol. 6, pp. 159–171 (1991).
D.A. Rees and D.S. Riley, Free convection above a near horizontal semi-infinite heated surface embedded
in a saturated porous medium, Int. J. Heat Mass Transfer, vol. 28, pp. 183–190 (1985).
D.A.S. Rees, The effect of inertia on free convection from a horizontal surface embedded in a porous
medium, Int. J. Heat Mass Transfer, vol. 39, pp. 3425–3430 (1996).
D.A.S. Rees and K. Vafai, Darcy-Brinkman free convection from a heated horizontal surface, Numerical
Heat Transfer, Part A, vol. 35, pp. 191–204 (1999).