Natural convection experiments about a finite-length cylindrical heat source in a liquid-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 the problem of 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, 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. Experimental results obtained in this effort showed steady-state heater surface temperatures (at constant heater power) to increase 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, thereby contributing to the qualification of this code for repository-design applications. 13 references