[1] Experiments were completed in a laboratory-scale, porous media tank to study the transport patterns of a saltwater wedge in a freshwater aquifer. Three types of experiments were performed to develop: (1) steady state salt-wedge data observed under different hydraulic gradient conditions; (2) transient salt-wedge data observed under intruding-wedge conditions; and (3) transient salt-wedge data observed under receding-wedge conditions. Furthermore, flux measurements were made to quantify the flow characteristics of three distinct steady state experiments. The saltwater intrusion model SEAWAT was used to simulate these data sets. The model results along with the experimental data are presented as benchmark problems for testing density-coupled groundwater flow models. A worthiness analysis was completed to test the sensitivity of these experimental problems to density-coupling effects. The results of our analysis show that the proposed benchmark is a more robust alternative to the traditional Henry problem. These new experimental data sets can be used to assess the performance of saltwater intrusion models under both steady state and transient conditions.Citation: Goswami, R. R., and T. P. Clement (2007), Laboratory-scale investigation of saltwater intrusion dynamics, Water Resour.
Zero-valent iron nanoparticles (INP) were synthesized and stabilized using poly acrylic acid (PAA) to yield stabilized INP (S-INP). A two-dimensional physical model was used to study the fate and transport of the INP and S-INP in porous media under saturated, steady-state flow conditions. Transport data for a nonreactive tracer, INP, and S-INP were collected under similar flow conditions. The results show that unstabilized INP cannot be transported into groundwater systems. On the other hand, the S-INP can be transported like a tracer without significant retardation. However, the S-INP plume migrated downward as it moved horizontally in the physical model, indicating that small density gradients have significant influence on two-dimensional transport. The variable-density groundwater flow model SEAWAT was used to model the observed density-driven transport patterns. This is the first time a two-dimensional transport data set is reported for demonstrating the multidimensional transport characteristics of nanoparticles. The data shows the importance of density effects, which cannot be fully discerned using one-dimensional, column experiments. Finally, we also demonstrate that the numerical model SEAWAT can be used to predict the density-driven transport characteristics of S-INP in groundwater aquifers.
We computationally investigate the dynamics of a self-propelled Janus probe in crowded environments. The crowding is caused by the presence of viscoelastic polymers or non- viscoelastic disconnected monomers. Our simulations...
In this work, we have considered the crystallisation behaviour of supercooled water in the presence of surface defects of varying size (surface fraction, α from 1 to 0.5). Ice nucleation on Ag exposed β-AgI (0001 plane) surface is investigated by molecular dynamics simulation at a temperature of 240 K. For systems with α > 0.67, the surface layers crystallise within 150 ns. In the system with defects, we observe two distinct stacking patterns in the layers near the surface and find that systems with AA stacking cause a monotonic decrease in the early nucleation dynamics with an increase in defect size.Where AB stacking (α = 0.833) is observed, the effect of the defect is diminished and the dynamics are similar to the plain AgI surface. This is supported by the variation in the orientational dynamics, hydrogen bond network stability, and tetrahedrality with respect to the defects. We quantify results in terms of the network topology using double-diamond cages (DDCs) and hexagonal cages (HCs). The configurations of the initially formed layers of ice strongly affect the subsequent growth even at long timescales. We assert that the retarded ice growth due to defects can be explained by the relative increase in DDCs with respect to HCs.
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