Articles written in Sadhana

    • Non-reactive solute transport modelling with time-dependent dispersion through stratified porous media


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      We present a numerical solution of the mobile–immobile model (MIM) with time-dependent dispersion coefficient to simulate solute transport through heterogeneous porous media. Observed experimental data of non-reactive solute transport through hydraulically coupled stratified porous media have been simulated using asymptotic and linear time-dependent dispersion functions. Non-Gaussian breakthrough curves comprising long tails are simulated well with the MIM incorporating asymptotic time-dependent dispersion model.The system is under the strong influence of physical nonequilibrium, which is evident by variable mass transfer coefficient estimated at different down-gradient distances. Asymptotic time-dependent functions are capable of capturing the rising limb of the solution phase breakthrough curves with improved accuracy, whereas tailing part simulation capabilities are similar for both asymptotic and linear time-dependent dispersion functions. Further, the temporal moment analysis demonstrated increased spreading, variance for linear dispersion model ascompared with asymptotic dispersion model. It is also observed that the first-order mass transfer coefficient varies inversely with travel distance from the input source. It can be concluded from the study that MIM with time-dependent dispersion function is simpler yet sensitive to account for medium’s heterogeneity in a better manner even for small observation distances from the source.

    • Application of temporal moments to interpret solute transport with time-dependent dispersion


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      Temporal moments of solute transport through porous media are calculated to analyze the time average spatial distribution of solute plume. Simulation of spatially and temporally distributed breakthrough curves (BTCs) is computationally rigorous and lacking the explanation about overall plume evolution within porous media. However, temporal moment provides an attractive and simple solution to study the plume behavior. In this study, temporal moments are presented to interpret solute plume behavior in heterogeneous porous media such as hydraulically coupled stratified porous media with different time-dependent dispersion models. Governing equations of solute transport have been solved numerically using Crank-Nicolson scheme,and further solute concentration data has been utilized to calculate moments of solute concentration using numerical integration. The effect of various parameters such as mass-transfer coefficient, pore-water velocity, time-dependent dispersion coefficients, and porosity of mobile region on the transport of solute has been studied through sensitivity analyses. Temporal moment analysis revealed that the mass recovery, mean residence time,and variance are sensitive to the estimated parameters. Numerical results suggested that the asymptotic timedependentdispersion function with mobile–immobile model represents the plume spreading through heterogeneous porous media in a more realistic manner

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