Juliusz Dąbrowa

Interdiffusion: Consistency of Darken's and Onsager's Methods

The Nernst-Planck flux formula is used in Darkens method to obtain the interdiffusion fluxes. The effective interdiffusion potentials, derived for the independent components in the system, allow obtaining the symmetrical matrix of the interdiffusion coefficients. The transport coefficients for 2, 3 and r-component system are presented. Interpretation of obtained matrixes in the light of Onsagers theory of irreversible thermodynamics is shown. Equation for the entropy production in the interdiffusion process is displayed. The presented approach allows calculation of entropy production during interdiffusion, as well as formulating Onsagers phenomenological coefficients for the interdiffusion in an explicit form, a form which is directly correlated with the mobilities of the atoms present in the system.

Dispersion in cylindrical channels on the laminar flow at low Fourier numbers

A numerical solution of the uniform dispersion model in cylindrical channels at low Fourier numbers is presented. The presented setup allowed to eliminate experimental non-idealities interfering the laminar flow. Double-humped responses measured in a flow injection system with impedance detection agreed with those predicted by theory. Simulated concentration profiles as well as flow injection analysis (FIA) responses show the predictive and descriptive power of the numerical approach. A strong dependence of peak shapes on Fourier numbers, at its low values, makes the approach suitable for determination of diffusion coefficients. In the work, the uniform dispersion model coupled with the Levenberg-Marquardt method of optimization allowed to determine the salt diffusion coefficient for KCl, NaCl, KMnO4 and CuSO4 in water. The determined values (1.83, 1.53, 1.57 and 0.90)×10(-9)m(2)s(-1), respectively, agree well with the literature data.