This article investigates the influence of diffusion-thermo effect on transient free convective heat and mass transfer flow in a channel bounded by two infinite vertical parallel plates. Fully developed laminar flow is considered when the boundaries are subjected to symmetric concentration and thermal input. The Dufour effect is taken into consideration. The velocity, temperature, and concentration profiles are obtained analytically using the Laplace transforms technique and used to compute the shear stress, Nusselt number, and mass flux. During the course of computation, it was found that transient solution at large time coincides with steady-state solution derived separately. Diffusion-thermo (Dufour effect) is observed to create an anomalous situation in temperature and velocity profiles for small Prandtl numbers. There is also flow reversal for a small Dufour number and negative values of the sustentation parameter $(N)$. At steady-state, there is neither heat nor mass transfer between the fluid and the plates.

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