EAS446lec16

EAS446lec16 - EAS 44600 Groundwater Hydrology Lecture 16...

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EAS 44600 Groundwater Hydrology Lecture 16: Solute Transport in Saturated Media Dr. Pengfei Zhang Introduction In this lecture we will discuss the transport of dissolved solutes in groundwater, the so-called mass transport or solute transport . The transport of colloidal-size particles in groundwater is much more complicated and beyond the scope of this course. There are two basic processes controlling the transport of solutes in porous media: diffusion and advection . Diffusion is the process by which a solute moves from areas of higher chemical potentials to areas of lower chemical potentials. This process is also known as molecular diffusion . Advection is the process by which dissolved solutes are carried along with the flowing groundwater. Diffusion For a one-dimensional system where the concentration of a solute ( C ) changes with time, Fick’s second law applies: 2 2 x C D t C d = (16-1) where C / t is the change in concentration over time, D d is the diffusion coefficient, and 2 C / x 2 is the second derivative of concentration with respect to transport distance. Values of D d for ions in water at 25 ° C can be found in Table 16-1. Table 16-1. Diffusion coefficients in water at 25 °C. Cations Anions H + 9.31 × 10 -9 m 2 /sec OH - 5.27 × 10 -9 m 2 /sec Na + 1.33 × 10 -9 m 2 /sec F - 1.46 × 10 -9 m 2 /sec K + 1.96 × 10 -9 m 2 /sec Cl - 2.03 × 10 -9 m 2 /sec Rb + 2.06
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This note was uploaded on 12/29/2010 for the course EAS 44600 taught by Professor Pengfeizhang during the Spring '10 term at CUNY City.

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EAS446lec16 - EAS 44600 Groundwater Hydrology Lecture 16...

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