HR: 1340h
AN: H23D-1620    [Abstracts]
TI: MIXING-INDUCED PRECIPITATION: EXPERIMENTAL STUDY AND MULTI-SCALE NUMERICAL ANALYSIS
AU: Meakin, P
EM: paul.meakin@inl.gov
AF: Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415, United States
AU: * Tartakovsky, A M
EM: alexandre.tartakovsky@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, United States
AU: Redden, G
EM: george.redden@inl.gov
AF: Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415, United States
AU: Lichtner, P
EM: lichtner@lanl.gov
AF: Los Alamos National Laboratory, EES-6, MS D469, Los Alamos, NM 87545, United States
AU: Scheibe, T D
EM: tim.scheibe@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, United States
AB: Laboratory experiments and pore scale and continuum scale simulations were used to study mixing-induced precipitation. In the laboratory experiment, sodium carbonate and calcium chloride solutions were injected at equal rates along two different halves of a quasi two-dimensional flow cell filled with quartz sand. Carbonate precipitation occurred within the mixing interface in a zone with uniform width of less than 5 mm. Pore-scale smoothed particle hydrodynamics simulations were conducted to study the mechanism of precipitation layer formation. SPH simulations were able to reproduce the precipitation event observed in the experiment. The simulations also revealed the presence of large pore-scale concentration gradients. This, and the presence of sub-continuum scale features such as a precipitation layer with characteristic width on the order of the average sand grain diameter, indicate the absence of a clear scale separation required for the existence of local continuum advection-dispersion equations. Nevertheless, we found that an adaptive high-resolution model based on traditional advection-dispersion equations with grid sizes in the mixing zone smaller than the size of the sand grains can also reproduce the essential features of the experiment such as formation of a thin precipitate layer of uniform thickness. As an alternative to high-resolution simulations, we proposed a new form of homogeneous and heterogeneous reactions terms in the advection dispersion equation. These terms involve transport and mixing indices that account for a non-uniform concentration distribution and highly localized reactions. The proposed model approach estimates the pore-scale distribution of concentrations due to homogenous and heterogeneous reactions during mineral precipitation where conventional low-resolution advection-dispersion equations produced erroneous results.
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2007 Fall Meeting