The student Ane Errarte Yarza obtained an OUTSTANDING CUM LAUDE qualification with 'INTERNATIONAL DOCTORATE' mention

The student Ane Errarte Yarza obtained an OUTSTANDING CUM LAUDE qualification with 'INTERNATIONAL DOCTORATE' mention

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Thesis title: Analysis of transport mechanisms in multicomponent liquid mixtures and nanofluids in ground laboratories and microgravity

Court:

• Chairmanship: Carlos Santamaría Salazar (UPV/EHU)
• Vocal: Valentica Shevtsova (Mondragon Unibertsitatea)
• Vocal: Werner Köhler (University of Bayreuth)
• Vocal: José Javier Ruiz Martí (Universidad Rovira i Virgili)
• Secretary: Miren Larrañaga Serna (Mondragon Unibertsitatea)

Abstract:

The phenomenon of thermodiffusion describes the induction of a gradient of concentrations within a mixture subject to a temperature gradient, due to the cross-coupling of heat and mass transfer. In recent years, this phenomenon has attracted considerable interest in the scientific community because of its potential usefulness in various fields. However, in the absence of experimental data, the internal transport mechanisms in multicomponent mixtures are unknown, and therefore, this doctoral thesis focuses on the analysis of the phenomenon of thermodiffusion in multicomponent mixtures; Specifically, in ternary mixtures within the Diffusion Coefficients Measuremets in ternary miXtures (DCMIX) project, which is based on the collaboration between the European Space Agency and several international research groups, and aims to establish a set of reliable reference data for the validation and calibration of measurements and prediction models under terrestrial conditions.

Several experimental techniques, such as the Thermogravitational technique, the Sliding Symmetric Tube technique, the Optical Beam Deflection technique and the Selectable Optical Diagnostic Instrument, which operates inside the International Space Station, have been used to determine transport properties, including thermodiffusion, molecular diffusion and the Soret coefficient.

In the established framework, the transport properties of various ternary systems aligned with the DCMIX project have been determined. The DCMIX1 reference system THN|IBB|nC12 with a mass composition of 0.80|0.10|0.10|0.10 was used to adapt the Mach-Zehnder interferometer from two light sources (473.0 and 632.8 nm) to a three-laser system (473.0, 543.0 and 632.8 nm). During the thermodiffusion experiments, the stability for the thermogravitational technique has been tested for four ternary mixtures based on the Tol|Meth|CH system of the DCMIX2 mission. In addition to the hydrocarbon mixtures, the thermodiffusion, molecular diffusion and Soret coefficients of the aqueous mixture of DCMIX3 TEG|H2O|EtOH at an average temperature of 30 °C have been determined. Given the attractiveness of fullerene, and the gap in the literature on the transport properties of nanofluids, the thermodiffusion, molecular diffusion and Soret coefficient within the on-orbit C60|THN|Tol ternary system have been analysed during the DCMIX4 mission. Likewise, during the international stay at the Physikalisches Institut of the Universität Bayreuth (Germany), the transport properties of fullerene in five aromatic solvents: methylnaphthalene, toluene, o-xylene, m-xylene and p-xylene have been determined using the Deflective Optical Wave technique. In this study, the influence of the number of rings and the methyl groups of the molecules on the diffusion coefficients has been analysed. Finally, the ternary system of the hydrocarbons MN|Tol|nC10 has been analysed from different concentrations of the ternary system to their corresponding binary mixtures over the whole concentration range.

In summary, this PhD thesis provides significant experimental data on the properties of binary and ternary mixtures using convective and non-convective techniques and under different weightlessness conditions to feed the literature with new reference data, providing added value towards the understanding of transport mechanisms in multicomponent mixtures.