Soret Coefficients of Organic Solutions Measured in the Microgravity SCM Experiment and by the Flow and Bénard Cells

Abstract

Soret coefficients of aqueous solutions of methyl, ethyl, isopropyl, and n-butyl alcohols and of solutions of methyl and ethyl alcohols in benzene have been measured in the Soret coefficient measurement (SCM) experiment under microgravity conditions on board the orbital platform EURECA at a mean temperature of 37.5 °C. These reference measurements will allow us to improve the understanding of the ground based results and to calibrate the ground based setup. This point is discussed with the values that we obtained by the flow cell technique and for systems that exhibited a hysteretic loop in the Schmidt-Milverton plots in the Be ´nard cell at a mean temperature of 37 °C.

Mass transport properties of the tetrahydronaphthalene/n-dodecane mixture measured by investigating non-equilibrium fluctuations

“…However, a much better theoretical and experimental understanding of the Soret effect is still needed in order to facilitate detailed predictions of the behavior of multi-component fluids. It is noteworthy that many studies of multi-component mixtures involve micro-gravity conditions in order to avoid convection, thus substantially complicating the experiments [21][22][23].…”

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

“…Although the effect itself has been known already for more than a century since the pioneering works of Ludwig [6] and Soret [7], the measurement of reliable data turned out to be rather difficult. Over time, a number of different experimental techniques have been developed, and even microgravity experiments have been performed [8] with the aim to circumvent problems arising from unwanted convection. Despite all these efforts, the experimental data basis is still rather small and often inconsistent when compared to diagonal transport properties, such as the isothermal diffusion coefficient.…”

“…A number of authors have measured the Soret coefficient, which shows an interesting sign change at an ethanol concentration of approximately 29 wt% [23,25,29]. Microgravity experiments have been performed, but no agreement with ground based measurements was achieved [8,30].…”

Soret Effect and Free Convection: A Way to Measure Soret Coefficients

“…And even in microgravity, the effect of g-jitters is, to our knowledge, not yet clearly established. Finally even if an experiment in microgravity is convection-free during all the duration of the flight (sometimes several months [7]), after the recovery of the experimental cell on earth, the accuracy on the Soret coefficient greatly rests on the accuracy of concentration measurements by some appropriate techniques such as density measurements, index of refraction measurements, or gas chromatography. And when dealing with volatile products, this could be the mean reason of large errors.…”

“…Clearly old techniques to detect e.g. the onset of convection, such as Schmidt-Milverton plots that are based on global measurements of heat fluxes, or Nusselt numbers, are inappropriate but remain still used [7]; they failed to produce acceptable values of Soret coefficients. Another approach is the so-called thermogravitational technique in which the coupling between thermal diffusion and convection may enhance the molecular separation, making the determination of the Soret coefficient even easier, see e.g.…”