Pore-Scale Investigation of the Effect of Incomplete Mixing on Bimolecular Reactions
EMSL Project ID
47585
Abstract
Incomplete mixing of solutes and spatial fluctuations in the concentration have been identified as a major cause of failure of deterministic effective models, such as deterministic dispersion-reaction equations, to accurately simulate mixing-controlled reactions. We propose an experimental study of the effect of spatial concentration fluctuations on the reaction of two solutes, A+B->C. In the absence of fluctuations, the classical diffusion-reaction equation predicts that concentrations of solutes decay as A = B ~ t^{-1}. Contrary to this, theoretical and numerical studies suggest that concentrations decay significantly slower. Recently we obtained exact analytical solutions for the purely diffusive system according to which the concentrations deviate from ~ t^{-1} to ~ t^{-d/4} behavior at characteristic transition time. We also derived analytical expressions for transition time as a function of Damkohler number, the coefficient of variation of the initial concentration and the size of the domain.A series of microfluidic experiments involving transport of two reactive solutes are proposed. The micromodels will be fabricated with newly purchased instrumentation in the EMSL clean room. The micromodels used in this study are two dimensional representations of porous media or channels etched into silicon waters. The new EMSL instrumentation allows us to fabricate structures with internal dimensions specified within 1 micron. Different micro- models will be designed and fabricated to investigate pure diffusion, transport in channels, and transport in porous media. Fluorescent microscopy will be used to determine intensity at selected locations as a function of time.
We will use experimental results to study validity of our and similar studies of diffusion-reaction systems. We expect that a non-uniform advection will significantly affect the scaling of the concentration with time. Furthermore, we hypothesis that classical advection-dispersion reaction equations will fail to accurately describe transport with mixing controlled reactions, because these equations disregard local concentration fluctuations. Currently we are developing several alternative reactive transport models and we will use the experimental results to study the accuracy and validity of these models.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2012-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Ling B, J Bao, M Oostrom, I Battiato, and AM Tartakovsky. 2017. "Modeling Variability in Porescale Multiphase Flow Experiments." Advances in Water Resources 1005:29-38. doi:10.1016/j.advwatres.2017.04.005
Tartakovsky AM, P de Anna, T Le Borgne, M Dentz, and D Bolster. 2013. "Flow Intermittency, Dispersion, and Correlated Continuous Time Random Walks in Porous Media." PNNL-SA-97279, Pacific Northwest National Laboratory, Richland, WA. [Unpublished]