Stability analysis under thermogravitational effect

Abstract

In the present work, an interferometric unsteady analysis of the thermogravitational technique was for the first time attempted in a paralelepipedic microcolumn using binary mixtures with negative Soret coefficients. In particular, water/ethanol and toluene/methanol were considered, as they have significantly different thermophysical properties and relaxation times. Experiments were run with different temperature gradients in order to understand their impact on the stability of separation. Experimental results were compared with theoretical ones, predicted by Fury-Jones-Onsager theory, and by OpenFOAM 3D numerical simulations. Correlations between the separation and the flow in the third dimension perpendicular to the thermal gradient of the thermogravitational microcolumn were analysed. Numerical simulations were also conducted in traditional cylindrical columns in order to compare the results with those previously reported. In these cases, the impact on separation stability was correlated with the azimuthal component of velocity. Thus, in both configurations, the disturbing convective current, always generated in the direction perpendicular to the thermal gradient applied, was shown to be vital for flow stability analysis.