Navegando por Autor "Alves, Leonardo Santos de Brito"
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Item Accurate calculation of near-critical heat capacities CP and CV of argon using molecular dynamics.(2017) Nichele, Jakler; Oliveira, Alan Barros de; Alves, Leonardo Santos de Brito; Borges Júnior, ItamarMolecular dynamics (MD) employing the Lennard-Jones (LJ) interaction potentialwas used to compute the heat capacities of argon at constant volume CV and constant pressure CP near the critical point very close to the asymptotic region. The accurateMD calculation of critical divergenceswas shown to be related to a careful choice of the cutoff radius rc and the inclusion of long-range corrections in the LJ potential. The computed CP and CV values have very good agreement as compared to available NIST data. Furthermore, values of CV in a range of temperatures for which NIST data is not available could be computed. In the investigated range of temperatures, both CP and CVMD results were fitted to a simple mathematical expression based on an empirical model that describes the critical effectswhen the asymptotic models are not appropriate. The present approach is of general applicability and robust to compute thermophysical properties of fluids in the near-critical region.Item Molecular dynamics simulations of momentum and thermal diffusion properties of near-critical argon along isobars.(2016) Nichele, Jakler; Borges Júnior, Itamar; Oliveira, Alan Barros de; Alves, Leonardo Santos de BritoThree basic diffusion properties of argon – shear viscosity, bulk viscosity and thermal conductivity – were studied in the neighborhood of the critical point using molecular dynamics (MD) and the Lennard-Jones potential energy function. MD simulations were performed along the 1.0Pc and 1.2Pc isobars. Green-Kubo relations and a Lennard Jones pair potential were used. Four different sets of Lennard-Jones parameters were used. A comparison of computed shear viscosity and thermal conductivity values with data available from the National Institute of Standards and Technology (NIST) displayed a good agreement. Results for bulk viscosity indicated that values of this property cannot be neglected in this thermodynamic region, a result that violates the traditional and much-assumed Stokes hypothesis in classical fluid mechanics. Furthermore, it was shown that in the neighborhood of the critical region the bulk viscosity can have larger values than the shear viscosity.