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SUMMARY:Solutal Convection in Porous Media - Prof Marc Hesse\, University 
 of Texas
DTSTART:20210225T113000Z
DTEND:20210225T123000Z
UID:TALK156850@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:Solutal convection in porous media is thought to be controlled
  by the molecular Rayleigh number\, Ram\, the ratio of the buoyant driving
  force over dissipation by molecular diffusion. The mass flux should incre
 ase linearly with Ram\nand the finger spacing should decrease as Ram. Inst
 ead\, our experiments show that the flux levels off at large Ram and the f
 inger spacing increases with Ram.\nHere we show that the convective patter
 n is controlled by a dispersive Rayleigh number\, Rad\, balancing buoyancy
  and dispersion. Increasing the bead size of the porous medium increases R
 am but decreases Rad and hence coarsens the\npattern. While the flux is pr
 edominantly controlled by Ram\, the anisotropy of mechanical dispersion le
 ads to an asymmetry in the pattern that limits the flux at large bead size
 s.\n\nNumerical simulations at the Darcy scale reproduce both the trend in
  the convective pattern and quantitative fluxes of the pore-scale results\
 , only adjusting anisotropy of mechanical dispersion. Our simulations show
  the flux recovers\na linear scaling with reduced coefficient as dispersio
 n becomes dominant\, consistent with the recent laboratory experiments. Ho
 wever\, sub-linear flux scaling\narises either in a transitional regime wh
 ere diffusion and dispersion are comparable or if grains become too coarse
 . In this case\, the pore-scale simulations show that convective up- and d
 ownwellings arise in individual pores. This leads\nto additional mixing no
 t accounted for in Fickian dispersion model on the Darcy scale. The buoyan
 cy-driven pore-scale mixing observed here therefore has different characte
 ristics from mixing processes in pressure-driven flows and requires\na new
  approach to upscale them to the Darcy scale.\n
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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