Date: 5-9 December 2011
Place: San Francisco
The poster presentation at the 2011 American Geophysical Union Fall Meeting by Nick Engdahl was among the top. Nick teamed up with Dr. Graham Fogg, Professor of Land Air Water Resources and Sr Investigator in Project 1, presented "Direct upscaling of kinetically controlled reactive transport with mobile-immobile mass transfer" at the conference meeting last year in San Francisco. Nick was awarded the 2011 Outstanding Student Paper Award. 4,638 students requested to be judged for the OSPA and only 149 students were awarded.
Engdahl, N.B. and Fogg, G.E. (2011), Direct upscaling of kinetically controlled reactive transport with mobile-immobile mass transfer, poster, American Geophysical Union Fall Meeting 2011, San Francisco, CA, H31E-1209
Mass transfer processes are known to strongly influence the migration of passive tracers and contaminants through porous media but the effect of such processes in reactive transport systems has not been studied as thoroughly as the passive case. Mobile-immobile diffusion can delay solute arrival times and prolong tailing of tracers which will affect the extent of mixing and the apparent reaction rates within the transport domain. This study investigates some of the most basic effects that mass transfer processes will have on several variations of a reactive transport system and evaluates the observed behavior of the system at multiple scales using highly resolved numerical models. In particular, we consider the importance of correctly accounting for the portion of the domain within which reactions are able to occur. The “reactive domain” may include the entire model or only the mobile or immobile portions of the model depending on the type of porous media and the type of reactions being considered (product formation, degradation, decay, etc…). The simulations are based on the Lattice-Boltzmann method and allow explicit modeling of multi-component flow, mobile advective-diffusive transport, immobile diffusive transport, and kinetically controlled reactions at the pore-scale where the physics of each process are well understood. The models can also include solutes with different diffusivities, grain interiors with a continuum of immobile porosities, and solutes can be selectively allowed or prohibited from the immobile domain. The pore-scale models of multi-domain reactive transport are then upscaled in a variety of ways to determine local volume averages of the concentration, reaction rate, mobile and immobile mass fractions, and the extent of mixing as well as the ensemble averaged and effective parameter equivalents of these quantities. This approach allows the physical distributions within the model domain and their moments to be related to the upscaled model parameters without requiring any assumptions about the form of the distributions or the nature of the media. An important aspect of the current study is that it focuses on reactions similar to kinetically controlled degradation while previous work has mostly considered precipitation-dissolution reactions. Overall, it is clear that mass transfer processes can strongly affect reactive transport systems but also that proper identification of the “reactive domain” of each solute is very important when attempting to construct upscaled reactive transport models.