An experimental investigation of variable density flow and mixing in homogeneous and heterogeneous media

Abstract

This study is an experimental investigation of variable density groundwater flow in homogeneous, layered and lenticular porous media. At the scale of the experiments the flow of dissolved mass in water depends upon both forced and free convection. In addition, density differences as low as 0.0008 g/cm3 (1000 mg/L NaCl) between a plume of dense water and ambient groundwater in a homogeneous medium produces gravitational instabilities at realistic groundwater velocities. These instabilities are manifest by lobe‐shaped protuberances that formed first along the bottom edge of the plume and later within the plume. As the density difference increases to 0.0015 g/cm3 (2000 mg/L NaCl), 0.0037 g/cm3 (5000 mg/L NaCl), or higher, this unstable mixing due to convective dispersion significantly alters the spreading process. In a layered medium, reductions in hydraulic conductivity of the order of half an order of magnitude or less can influence the flow of the dense plume. Dense water may accumulate along bedding interfaces, which when dipping can result in plume migration velocities larger than ambient groundwater velocities. In a lenticular medium the combination of convective dispersion and nonuniform flow due to heterogeneities result in relatively large dispersion. Scale considerations, further, indicate that convective dispersion may provide an important component of mixing at the field scale.

Effects of air injection on flow through porous media: Observations and analyses of laboratory‐scale processes

“…The concentration of the NaCl tracer was 500 mg/L above the NaCl background concentration in the tap water. This NaCl concentration was chosen to reduce density effects, yet provide reliable EC measurements [Schincariol and Schwartz, 1990;Silliman and Simpson, 1987]. In addition to the quantitative measurements, separate sets of experiments were conducted to visually inspect transport.…”

Viscous and gravitational contributions to mixing during vertical brine transport in water‐saturated porous media

“…These gravitational instabilities were studied by Lapwood [1948] for a heated fluid at the base of the porous medium and then by Wooding [1959] for solute-induced density differences. This earlier work was followed by the theoretical and experimental contributions of List [1965] on density-induced instabilities and then the extensive work that followed by Schincariol and Schwartz [1990] and Oostrom et al [1992]. These researchers selected experimental conditions where the brine-induced vertical velocity was generally much less than the horizontal velocity.…”

“…These researchers selected experimental conditions where the brine-induced vertical velocity was generally much less than the horizontal velocity. Most of List's experiments were conducted with U b /U x < 0.1, Schincariol and Schwartz [1990] adopted experimental conditions where U b /U x < 1.9. Oostrom et al [1992] experiments covered the range of 0.1 to 2.6 in U b /U x and they recognized the importance of this dimensionless velocity ratio.…”

Measurement of Degree of Saturation on Model Ground by Digital Image Processing

“…In hydrology and water resources, for example, image analysis methods have been valuable tools in tracing the movement of immiscible contaminants, such as oil and other non-aquaeous phase liquids (NAPL), in unsaturated heterogeneous porous media. For instance, Schincariol and Schwartz (1990) performed physical model studies to investigate the unstable behavior of aqueous phase plumes with densities larger than the ambient water by analysing photographs of the transport and ‰ow phenomena. Darnault et al (1998) developed a method where the intensity of transmitted light through a thin two-dimensional ‰ume was recorded and water saturation (in two-phase NAPL-water experiments) was correlated to the average hue (color) value of the pixels.…”