Da. Nield, ESTIMATION OF AN EFFECTIVE RAYLEIGH NUMBER FOR CONVECTION IN A VERTICALLY INHOMOGENEOUS POROUS-MEDIUM OR CLEAR FLUID, International journal of heat and fluid flow, 15(4), 1994, pp. 337-340
The concept of an effective Rayleigh number (for a clear fluid), or ef
fective Rayleigh-Darcy number (for a porous medium), is introduced in
the context of convection in a vertically inhomogeneous horizontal lay
er. Estimates for this quantity, based on mean values of the physical
quantities, are proposed. These estimates are compared with known, acc
urate results.