Natural convection experiments with a finite-length, vertical, cylindrical heat source in a water-saturated porous medium

An experimental effort is under way to investigate convective heat transfer in liquid-saturated porous media utilizing a geometry, and hydrodynamic/thermal boundary conditions, relevant to nuclear waste isolation in geologic repositories. In the present work, measurements were made of the transient and steady-state thermal fields throughout an annular region bounded by vertical, coaxal 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. Results obtained in this effort showed steady-state heater surface temperatures (at constant heater power) to increase with increasing vertical distance due to buoyancy-driven upflow. The measured steady-state radial temperature drop across the annulus w3as found to systematically depart from the finite-length-cylinder conduction solution as heater power was increased, consistent with the presence of increased convective-energy transport. Comparisons between measured results and numerical predictions obtained using the finite element code MARIAH showed good agreement, thereby contributing to the qualification of this code for repository-design applications