Heats of transport in binary liquid mixtures
The diffusion thermoeffect or the heat flux induced by an isothermal chemical potential gradient can be characterized by the heat of transport; the ratio of the heat flux to the mass flux under isothermal conditions. The heat of transport, Q, for the carbon tetrachloridecyclohexane system was measured by Rowley and Home (198) and the ternary heats of transport, and Q2, were studied by Platt, Vongvanich, Fowler, and Rowley (1982) for the toluene-chlorobenzene-bromobenzene system. In this work, the binary heat of transport, Q, is determined for the toluene-chlorobenzene, chlorobenzene-bromobenzene, and toluenebromobenzene systems. The effect of temperature and composition on the binary heat of transport is examined and the Onsager and thermal diffusion coefficients calculated from Q. In addition, a qualitative view of the relationship between the ternary heats of transport of Platt, et al., and the binary heats of transport of this work is presented. The binary heats of transport are determined experimentally, using the boundary sharpening cell of Platt, Vongvanich, and Rowley (1982) by fitting experimentally measured temperature differences to the solution of the energy partial differential equation subject to appropriate boundary conditions. The composition dependence of the heat of transport, Onsager coefficient, and thermal diffusion coefficient are reported for the toluenechlorobenzene and chlorobenzene-bromobenzene systems at 298.15 K and 38.15 K and for the toluene-bromobenzene system at 38.15 K. The study of the relationship between the binary and ternary heats of transport indicate that there is indeed a definite relationship between the toluene-chlorobenzene-bromobenzene system and corresponding binaries, at least near the binary limits of the ternary system.
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