The student Antton Sanjuan Esnaola obtained an EXCELLENT CUM LAUDE with mention INTERNATIONAL DOCTORATE

The student Antton Sanjuan Esnaola obtained an EXCELLENT CUM LAUDE with mention INTERNATIONAL DOCTORATE

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• Thesis title: Mecanismos de transporte en mezclas multicomponentes: desarrollo analítico, numérico y experimental en diferentes regímenes

Court:

• Presidency: Werner Köhler (University of Bayreuth)
• Vocal: Mohamed Najib Ouarzazi (University of Lille)
• Vocal: Juan Felipe Torres (Australian National University)
• Vocal: Estela Lapeira Azcue (Mondragon Unibertsitatea)
• Secretary: Ane Errarte Yarza (Mondragon Unibertsitatea)

Abstract:

This doctoral thesis provides a comprehensive study of transport mechanisms in binary and multicomponent liquid systems under different operating regimes. To this end, analytical, numerical, and experimental methodologies have been combined to characterize the thermogravitational behavior and thermophysical properties of solutions of different nature.

The numerical and experimental analysis carried out has made it possible to delimit the range of validity of the FJO theory, demonstrating its ability to reproduce species separation in both steady and transient regimes, although restricted to moderate values of the dimensionless parameters  and . In particular, its validity has been verified in the transient regime for  200 and in the steady regime up to values on the order of  1000. Furthermore, the study of the parameter  has confirmed the classical equilibrium limit  2.00, while proposing a more restrictive condition for the transient regime,  1.00.

Regarding thermogravitational behavior, the developed three-dimensional analytical formulation, supported by numerical simulations and experimental validation, demonstrates that for high values of , steady-state species separation increases as the transverse confinement  of the cavity decreases. This result highlights the key role of transverse diffusion in systems with moderate confinement, which is absent in the classical limit , allowing the proposal of a universal correlation for separation as a function of  and .

In addition, thermogravitational stability in solutions with negative thermodiffusion coefficients has been investigated through three-dimensional linear theory, simulations, and experimental work. The results show that transverse confinement acts as a stabilization mechanism capable of suppressing convective currents induced by adverse density gradients, in contrast to the instability predicted by two-dimensional analyses. Critical values of , dependent on , have been identified, defining the conditions under which these mixtures can be stabilized in cartesian cavities.

In parallel, the combined use of convective and non-convective experimental techniques under both terrestrial and microgravity conditions has enabled the determination of thermophysical properties and transport coefficients in complex systems. In this context, the characterization of the polymer solution Ps|Tol from the DCMIX4 project has been completed, and the Ps|Ch mixture has been analyzed under equivalent conditions. Additionally, experimental data obtained under microgravity conditions have been processed and analyzed.

Furthermore, as a result of a research stay at the University of Bayreuth, a characterization of binary mixtures of alcohols in Tol and MN has been carried out, identifying trends as a function of chain length, temperature, and sign changes in the  and  coefficients.

Finally, the analysis methodology proposed by Prof. Bou-Ali and Prof. Platten has been extended to enable the determination of concentrations in quaternary mixtures through measurements of density, refractive index, and speed of sound. This has made it possible to obtain thermodiffusion coefficients in systems composed of MN|THN|IBB|C₁₂. Moreover, the traceability between thermodiffusion coefficients of binary, ternary, and quaternary systems has been demonstrated, extending correlations that allow the prediction of thermodiffusion coefficients in multicomponent mixtures.

Overall, this thesis provides new experimental and numerical methodologies, predictive correlations, and original experimental data that significantly contribute to the understanding of mass transport phenomena in non-equilibrium multicomponent systems, expanding the available knowledge and providing useful tools for their analysis and modeling

This doctoral thesis provides a comprehensive study of transport mechanisms in binary and multicomponent liquid systems under different operating regimes. To this end, analytical, numerical, and experimental methodologies have been combined to characterize the thermogravitational behavior and thermophysical properties of solutions of different nature.

The numerical and experimental analysis carried out has made it possible to delimit the range of validity of the FJO theory, demonstrating its ability to reproduce species separation in both steady and transient regimes, although restricted to moderate values of the dimensionless parameters  and . In particular, its validity has been verified in the transient regime for  200 and in the steady regime up to values on the order of  1000. Furthermore, the study of the parameter  has confirmed the classical equilibrium limit  2.00, while proposing a more restrictive condition for the transient regime,  1.00.

Regarding thermogravitational behavior, the developed three-dimensional analytical formulation, supported by numerical simulations and experimental validation, demonstrates that for high values of , steady-state species separation increases as the transverse confinement  of the cavity decreases. This result highlights the key role of transverse diffusion in systems with moderate confinement, which is absent in the classical limit , allowing the proposal of a universal correlation for separation as a function of  and .

In addition, thermogravitational stability in solutions with negative thermodiffusion coefficients has been investigated through three-dimensional linear theory, simulations, and experimental work. The results show that transverse confinement acts as a stabilization mechanism capable of suppressing convective currents induced by adverse density gradients, in contrast to the instability predicted by two-dimensional analyses. Critical values of , dependent on , have been identified, defining the conditions under which these mixtures can be stabilized in cartesian cavities.

In parallel, the combined use of convective and non-convective experimental techniques under both terrestrial and microgravity conditions has enabled the determination of thermophysical properties and transport coefficients in complex systems. In this context, the characterization of the polymer solution Ps|Tol from the DCMIX4 project has been completed, and the Ps|Ch mixture has been analyzed under equivalent conditions. Additionally, experimental data obtained under microgravity conditions have been processed and analyzed.

Furthermore, as a result of a research stay at the University of Bayreuth, a characterization of binary mixtures of alcohols in Tol and MN has been carried out, identifying trends as a function of chain length, temperature, and sign changes in the  and  coefficients.

Finally, the analysis methodology proposed by Prof. Bou-Ali and Prof. Platten has been extended to enable the determination of concentrations in quaternary mixtures through measurements of density, refractive index, and speed of sound. This has made it possible to obtain thermodiffusion coefficients in systems composed of MN|THN|IBB|C₁₂. Moreover, the traceability between thermodiffusion coefficients of binary, ternary, and quaternary systems has been demonstrated, extending correlations that allow the prediction of thermodiffusion coefficients in multicomponent mixtures.

Overall, this thesis provides new experimental and numerical methodologies, predictive correlations, and original experimental data that significantly contribute to the understanding of mass transport phenomena in non-equilibrium multicomponent systems, expanding the available knowledge and providing useful tools for their analysis and modeling.