Heats of transport in toluene-chlorobenzene-bromobenzene mixtures
Rowley, Richard L.
Master of Arts
The heat of transport is the transport property that characterizes the diffusion thermoeffect or Dufour effect, i.e., it relates the induced heat flux to an isothermal chemi cal potential gradient. It is formally defined as the ratio of heat flux to the mass flux under isothermal conditions. The heat of transport determined in binary liquid mixtures by Rowley and Home  constituted experimental verification of the Onsager heat-mass reciprocal relations. However, an attempt to simultaneously determine the two independent heats of transport in a ternary system by Platt  was not completely successful due to coupling of parameters. This work represents the determination of heats of trans port (Q1 and Q2) in ternary liquid systems. The composition and temperature dependence of the two independent heats of transport are determined experimentally. This in turn allows computation of the Onsager coefficients associated with ternary mixtures. The toluene-chlorobenzene-bromobenzene system was chosen because of diffusion data availability. A new experimental cell was designed to provide much more versatility in initial interface creation. Experiments involved measurement of temperature differences between two positions symmetric about the initial sharp diffusional interface as a function of time. Experimental data were fitted to the solution of the energy partial differential equation, which had been solved subject to experimentally imposed boundary conditions by a double perturbation technique, using Q1 and Q2 as adjustable parameters. The problem of coupled parameters was circumvented by using two data sets both at the same mean composition but with different initial composition gradients. The heats of transport in the toluene-chlorobenzene-bromobenzene system were fitted to a polynomial in composition and temperature as were the corresponding Onsager coefficients. The resultant expressions are valid in the range .1^w^<.6 (i=l,2), w^>.1, and 298.15 K<T <38.15 K where w1, w2, and w3 are weight fraction of toluene, chlorobenzene, bromobenzene respectively.