Determination of the apparent negative Soret coefficient of water-10% alcohol solutions by experimental and numerical methods in packed cells

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Abstract
This study presents two methods for measuring the Soret coefficient of water-alcohol mixtures (with a 10% mass fraction of alcohol: ethanol or propanol-2). These methods performed with porous packing are particularly adapted for apparent negative Soret coefficient determination (i.e. where the transport of the densest compound follows the thermal gradient inside the cell). The first method uses a flat-packed Soret cell operated under a downwards vertical thermal gradient; the second method uses a packed cylindrical thermodiffusion column (operated with an horizontal thermal gradient to yield the so-called coupling between thermodiffusion-convection) and thermogravitation. The porous packing is made of inert balls (ZrO 2 ). The porosity is about 38% and the intrinsic permeability 1.01 210 m10 m 2 or even 1.31 210 m10 m 2 . For each experiment, the time evolution of the alcohol fraction sampled at the top and bottom of the cells is checked against the numerical outputs of a thermodiffusion model: the METSOR code.

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