Using a physical model to determine the hydrodynamic dispersion coefficient of a solution through a horizontal sand column
Le Anh Tuan1 and Guido Wyseure2
1College of Environment and Natural Resources, Can Tho University, Vietnam
2Laboratory for Land and Water Management, Faculty of Biosciences Engineering, Catholic University of Leuven, Belgium
Received 9 November 2018; accepted 12 January 2019
Miscible displacement can be understood as a physical process in a porous medium whereby two or more fluids fully dissolve into each other when a fluid mixes and goes into the pore space occupied by other fluids without the existence of an interface. A physical model was made in Can Tho University, which included an electrical current system connecting nine groups of four-electrode probes for measuring the electrical conductivity of a potassium chloride solution flowing through a horizontal sand column placed in a firm frame. The experiments were performed with different volumetric flow rates and three types of sand (fine, medium and coarse). The breakthrough curves were analysed, and then the hydrodynamic dispersion coefficients were calculated. The hydrodynamic dispersion coefficient was one of the hydraulic and solute transport parameters used to design a constructed subsurface flow wetland. The research proves that the flows were laminar, and that mechanical dispersions dominated over molecular diffusions and that the dispersions were large enough to cause combined mixing and flowing processes.
Keywords: breakthrough curves, electrical conductivity, four-electrode probes, hydrodynamic dispersion coefficients, physical model.