Thermal diffusivity of heptane-isooctane mixtures

In this paper, we report on the measurement of the thermal diffusivity of heptane-isooctane mixtures in the liquid phase at room temperature and atmospheric pressure using the mode-mismatched dual-beam transient thermal lens technique. We found a good agreement between the thermal diffusivity values measured here directly and those determined indirectly in a previously published report. The most significant differences were observed at lower isooctane concentrations, being attributed to the effect of molecular London dispersive forces. We demonstrated that the behavior of the thermal diffusivity as a function of the relative mass fractions follows an empirical model for interacting binary mixtures, which not only accounts for deviations from the law of additivity in the thermal conductivity but also in the heat capacity per unit volume. The highest deviation from the linearity expected using the additivity rule was about 11 %, at a relative mass fraction of 50 wt %.