Buoyancy-driven flow in fluid-saturated porous media near a bounding surface

Buoyancy-driven convective heat transfer from a vertical flat surface that bounds fluid-saturated porous medium is experimentally studied. An analysis has shown that the dispersion, caused by tortuous pore-scale flow field, can be a significant term in the transport of energy from the wall. The present experiments suggest possible dependence of thermal dispersion on pore-scale Peclet number in the range approximately from 1 to 103. However, the magnitudes are smaller than those obtained for homogeneous porous media reported in the literature.; Porous media are made of packed spherical beads with the primary interstitial fluid of water. The bead materials with similar or dissimilar thermal conductivities to that of water allow examination of the effects of conductive heat transfer. Wall temperature is employed as a noninvasive measurement technique based on the idea that the variation in time and location is an indication of flow field developing adjacent to the wall. This technique minimizes high-frequency noise commonly observed in data taken in such a medium.; Steady state results show that heat transfer can be explained by a Darcy-based model. The model assumes a velocity slip at the boundary and has no thermal dispersion. The factors contributing to this phenomenon include the thinning of the velocity boundary layer due to flow which is restricted by shear stresses from the stationary solid matrix, and an increase in effective thermal conductivity due to usually higher thermal conductivity of solid than that of fluid.; The dispersion coefficient increases with Peclet number for the steel and polyethylene cases although the magnitudes are generally lower than those reported in the literature for homogeneous media. The small magnitudes may be because of high local porosity near the wall, which causes flow paths to be less tortuous than those away from the wall. Transient profiles agree with those from conjugate analyses and confirm that the thermal conductivity of a porous medium as seen by the wall is that of the fluid phase material. This is because of high local porosity near the wall and also the fact that the stagnant conductivity is a relatively weak function of solid-to-fluid conductivity ratio.