Impact of low-temperature electrical resistance heating on subsurface flow and transport

The effects of subboiling electrical resistance heating (ERH) on subsurface flow and transport were examined in a series of two-dimensional tank experiments, with temperatures reaching 50C. To analyze the experiments and determine the dominant mechanisms affecting flow and transport, a fully coupled two-dimensional finite difference electrothermal model was developed to simulate electrical current flow, temperature-dependent fluid flow, and mass transport. The model incorporates temperature-dependent equations for density, viscosity, diffusion coefficient, and electrical conductivity, capturing the nonisothermal processes dominant in the subsurface. The model was validated with laboratory-scale experiments in which voltage distribution, instantaneous electrical power, temperature, and tracer transport were measured. Tracer experiments and transport modeling indicated that temperature-induced buoyant flow and contaminant movement could be significant when applying ERH in the subsurface, even at 50C. A sensitivity study was performed to assess the impact of including temperature-dependent properties such as water density, viscosity, and electrical conductivity. A change in water density of 1.3% (at 50C) resulted in buoyant flow and increased velocity through the heated zone, indicating that heating contaminated zones to 50C can have a large impact on mass transport. Temperature-dependent electrical conductivity had a direct impact on ERH power consumption as well as the time to reach desired temperatures.