Natural convection experiments about a finite-length cylindrical heat source in a liquid-saturated porous medium

Convective heat transfer in liquid-saturated porous media was investigated utilizing a geometry and hydrodynamic/thermal boundary condition, relevant to the problem of nuclear waste isolation in geologic repositories. The transient and steady state thermal fields were measured throughout an annular region bounded by vertical, coaxial cylinders. The inner cylinder was comprised of a finite length heat source, supported above and below by insulating sections; the outer cylinder was maintained at a constant temperature. An overlying liquid layer was used to impose a permeable upper surface boundary condition; this layer was maintained at a constant temperature equal to that of the outer cylinder. All properties of the porous medium, including porosity, permeability, and effective thermal conductivity were measured. It is shown that steady state heater surface temperatures (at constant heater power) increases with increasing vertical distance due to the buoyantly driven upflow. The measured steady state radial temperature drop across the annulus was found to systematically depart from the finite length cylinder conduction solution as heater power was increased. Comparisons between measured results and numerical predictions obtained using the finite element code MARIAH showed very good agreement.