Measurement of the Soret, diffusion, and thermal diffusion coefficients of three binary organic benchmark mixtures and of ethanol–water mixtures using a beam deflection technique

Abstract

We have measured the Soret (S _T ), diffusion (D), and thermal diffusion (D _T ) coefficients of three binary mixtures of dodecane (DD), isobutylbenzene (IB) and 1,2,3,4-tetrahydronaphthalene (TH) for a concentration of 50 wt% at a temperature of 25°C by means of an optical beam deflection cell. This relevant experimental technique was still missing from a recent benchmark campaign for the measurement of the Soret effect. The measured coefficients agree to within a few percent (10% for S _T , D of TH/IB) with the proposed benchmark values. A detailed analysis of the measurement process of the beam deflection cell, which allows for an elegant extension to include temperature gradients within the windows, is given, and improved benchmark values are suggested. In addition, ethanol–water mixtures have been investigated very carefully over a broad concentration and temperature range. Comparison with data of Kolodner and Wiegand gives a generally good agreement with some systematic deviations. Contrary to theoretical predictions, we have not been able to identify a second sign change of S _T at high ethanol concentrations.

Keywords:

• diffusion
• thermal diffusion
• Soret effect

Acknowledgements

We thank R. Piazza for his hospitality and help with the beam deflection setup, A. Krekhov for assistance with the numerical analysis, and S. Hartmann for TDFRS measurements. This work was supported by Deutsche Forschungsgemeinschaft (DFG) (Ko 1541/5-2).