An analysis of a mixed convection associated with thermal heating in contaminated porous media

• Published in: The Science of the total environment 2014-11, Vol.499, p.7-17
• Main Authors: Krol, Magdalena M., Johnson, Richard L., Sleep, Brent E.
• Format: Article
• Language: English
• Subjects: Applied sciences; Buoyancy; Buoyancy ratio; Contaminant transport; Contaminants; Convection; Density; Exact sciences and technology; Global environmental pollution; Groundwater - chemistry; Heating; Models, Chemical; Peclet number; Permeability; Pollution; Porosity; Porous media; Rayleigh number; Soil (material); Soil - chemistry; Soil Pollutants - analysis; Soil Pollutants - chemistry; Thermal remediation; Transport
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2014.08.028

The occurrence of subsurface buoyant flow during thermal remediation was investigated using a two dimensional electro-thermal model (ETM). The model incorporated electrical current flow associated with electrical resistance heating, energy and mass transport, and density dependent water flow. The model was used to examine the effects of heating on sixteen subsurface scenarios with different applied groundwater fluxes and soil permeabilities. The results were analyzed in terms of the ratio of Rayleigh to thermal Peclet numbers (the buoyancy ratio). It was found that when the buoyancy number was greater than unity and the soil permeability greater than 10−12m2, buoyant flow and contaminant transport were significant. The effects of low permeability layers and electrode placement on heat and mass transport were also investigated. Heating under a clay layer led to flow stagnation zones resulting in the accumulation of contaminant mass and transport into the low permeability layer. The results of this study can be used to develop dimensionless number-based guidelines for site management during subsurface thermal activities. •Subsurface buoyant flow occurring during thermal remediation is modeled.•Buoyancy ratio is derived in terms of permeability, temperature, and gradient.•Heated subsurface flow is grouped into 3 types, allowing for site characterization.•Buoyant flow occurring under clay layers can lead to mass accumulation.•Stagnation zone under clay layers can lead to mass transport into the clay layer.