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Onset of natural convection induced by bottom–up transient mass diffusion in porous media

✍ Scribed by Ka-Kheng Tan; Yee-Wan Tan; Thomas S.Y. Choong

Publisher
Elsevier Science
Year
2009
Tongue
English
Weight
858 KB
Volume
191
Category
Article
ISSN
0032-5910

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✦ Synopsis

The theory of convection induced by transient mass diffusion in porous media is advanced and verified by computational fluid dynamics (CFD) simulation. A theory of the onset of buoyancy convection and a new transient Rayleigh number were derived. 2D time-dependent simulations were conducted for bottom-up diffusion of methane gas in a porous medium pre-saturated with air. Sand particles with diameter ranged from 0.003 to 0.006 m were used as the porous media. The average maximum transient Rayleigh number for the onset of convection in the simulations was found to be 29.7, which was quite close to the theoretical value of 27.1. The critical times, critical depths of gas penetration and wavelengths were predicted accurately. It was found that the mass transfer may be driven by simultaneous diffusion and buoyancy convection after the onset. The rate of mass transfer for the convection phase was over three times that of pure diffusion.

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## Boundary layer thickness ratio This paper deals with the study of the buoyancy induced heat and mass transfer from a slender body of revolution embedded in a saturated porous medium. The study has reported the important case of a cylinder with linear temperature and concentration distributions.