Using Molecular-Level Simulations to Determine Diffusivities in the Classroom

We present work describing the practical use of molecular-level simulations to determine diffusivities in a course targeted at the general audience of first-year chemical engineering graduate students. We show how the simulation techniques can be used to directly complement traditional methods for obtaining diffusivities. Our philosophy is to provide a utilitarian tool that can be used in a manner analogous to existing techniques to obtain diffusion coefficients. The advantage of the simulation approach is that it will work in the absence of experimental data and can be easily applied to multicomponent mixtures with an arbitrary number of species. In the implementation of this work, we remain keenly aware of constraints due to time, computational resources, money, and target-audience qualifications, so that the implementation is feasible. We demonstrate that these simulations require only a few minutes to run on a contemporary (AMD Athlon 850 MHz) processor. In our approach we outline the basic steps necessary to obtain a transport diffusivity via molecular-level simulations. We also provide an example problem, where we compare the results of the simulation to the predictions from corresponding states and kinetic theory.