On the validity of the Onsager reciprocal relations for simultaneous heat transfer and multi-component diffusion

In this work, the validity of the Onsager reciprocal relations (ORR) for the heat transfer and multi-component diffusion case in the presence of external forces is re-examined. It is shown that the ORR are necessarily fulfilled for this process even if the quasi-equilibrium postulate is applied. Moreover, it is shown that the resistance coefficients for this case are uniquely defined. It is believed that this work could contribute to the further understanding of the ORR.