资源环境科技发展态势分析平台

Analysis of reactive transport in natural and engineered porous media has benefited from the concept of mixing ratios, in particular as a basis for mathematical separation of transport and reactions processes. General use of solute age has also been recently explored as a way to describe solute mass transfer and/or as a proxy for reaction extent. Age here is defined as exposure‐time to the flow field. Pairing these concepts we develop mixing ratio models that are structured on age. One‐dimensional transport is cast in terms of age‐structured mixing ratios in general and compared with conventional formulations of mixing ratio models, demonstrating that age is often a more natural independent variable than absolute time. Using this modeling framework we then apply age‐structured mixing ratios to the problem of mixing‐limited reactive transport in one‐dimension by explicitly considering unmixed and mixed phases. In order to address mixing limitations under the entirety of transport including the pre‐asymptotic dispersion timeframe, we use the same age variable to define the dispersion coefficient value in a local‐formulation of transport. Establishing an age‐dependent dispersion coefficient allows simulation of the whole transport time including both pre‐asymptotic and asymptotic dispersion conditions with one model. In our application we explore use of this modeling approach to both synthetic pre‐asymptotic data and experimental asymptotic data pertaining to one famous experiment.