A new method is introduced to measure the thermal diffusion coefficient, based on moiré deflectometry. The soret coefficient of sucrose-water solution of 10% is measured. A cell containing the homogeneous solution of sucrose and water solution is placed in a moiré deflectometry system. Using a water cooling system, the two end of the cell is held on different temperatures  and . This causes a linear temperature gradient inside the solution and a mass transfer occurred from one side to other side. A concentration gradient is also occurred over time, which causes mass transfer in opposite direction. Finally these two phenomena reach to equilibrium and the net mass transfer gets zero. By cutting off the temperature difference, first, the temperature gradient, and then the concentration gradient, disappears, and causes the displacement of moiré fringes. The moiré fringes deflections are used to measure the refractive index gradient inside the cell and then the soret coefficient is derived.

Keywords: Moiré deflectometry, Soret coefficient, Temperature gradient.

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