Diffusion thermoeffect in ternary liquid mixtures
Platt, Gerald Edwin
Rowley, Richard L.
Master of Science
The diffusion thermoeffect or Dufour effect, a heat flux induced by an isothermal chemical potential gradient, is usually characterized by the heat of transport. The heat of transport is defined as the ratio of the heat flux to the mass flux under isothermal conditions. Although heats of transport have been measured in binary liquid mixtures, no direct measurements have been made in ternary nonelectrolyte liquid mixtures. In this work, the two independent heats of transport for toluene-chlorobenzene-bromobenzene mixtures at 25°C were determined at various compositions using a withdrawable liquid gate cell. Values were obtained by fitting calculated to measured temperature differences via a weighted non-linear least squares fitting routine using heats of transport as adjustable parameters. Experimental temperature differences were measured at points symmetric about the initial diffusion interface. The diffusion thermoeffect can be described mathematically by the hydrodynamic equations into which fluxes, obtained using methods of nonequilibrium thermodynamics, have been substituted. The resulting set of coupled differential equations were solved using a perturbation scheme for the composition and temperature profiles as functions of time. Initial and boundary conditions used corresponded closely to the experimental configuration. In addition to heats of transport, the Onsager coefficients were determined. The effect of a third component on ternary solution thermal diffusion experiments was evaluated using Onsager reciprocity.