Transition from Mixed to Forced Convection for Opposing Vertical Flows in Liquid-Saturated Porous Media

Abstract

Mixed convection phenomena can occur within liquid dominated geothermal reservoirs due to interactions of injected flows, or groundwater flows, with the buoyancy induced fluid motion. This problem was studied experimentally and numerically for the case of opposing flows a out a vertical heat source in a liquid saturated porous medium. The ratio of the Rayleigh number (Ra) to the Peclet number (Pe) was identified as the nondimensional parameter which characterizes the relative influence of buoyancy driven to pressure gradient driven fluid motion. The transition from mixed to forced convection was numerically determined to be (Ra/Pe) = -0.5, where the minus sign denotes superimposed downflow. Agreement between measured and predicted thermal field results showed that the finite element code of Gartling and Hickox (1982, a,b) can be used to model low temperature (single phase) geothermal reservoirs throughout the natural, mixed, and forced convection regimes.