[en] The thermodiffusion phenomenon in liquid mixtures describes the induction of a concentration gradient subjected to a temperature gradient due to the cross-coupling effect of heat and mass transfer. In recent years, this phenomenon has aroused great interest in the scientific community due to its potential in a broad field of applications. However, in the case of multicomponent mixtures, in the absence of experimental data, the underlying transport mechanisms are still unknown. Thus, the present doctoral thesis focuses on thermodiffusion experiments in multi-component, namely, ternary mixtures related to the Diffusion Coefficients Measurements in ternary mIXtures (DCMIX) project, an international collaboration between the European Space Agency and several research teams. The project aims to establish a reliable set of reference data for the validation and calibration of present and future ground laboratory measurements and prediction models. In this framework, transport properties such as thermodiffusion, molecular diffusion and Soret coefficients have been determined over several ternary systems. Four different experimental techniques have been used during the course of this work. The thermogravitational columns allowed to determine thermodiffusion coefficients of both binary and ternary mixtures from steady-state measurements. Components unsteadystate tracking, in addition, enabled determining the molecular diffusion coefficient in binary mixtures, and the effective diffusion in ternary mixtures. Molecular diffusion coefficients of both binary and ternary mixtures were determined by the Sliding Symmetric Tubes technique. Moreover, during an international stay, diffusion and Soret coefficients of binary and ternary mixtures were determined by the Optical Beam Deflection (OBD) technique in the Physikalisches Institut of Universität Bayreuth (Germany), while microgravity experiments of the fourth campaign of the DCMIX project were performed by the Selectable Optical Diagnostic Instrument, SODI installed inside the ISS. The DCMIX1 mixture, THN|IBB|nC12 at a mass composition of 0.80|0.10|0.10 was used to adapt the two-laser Mach-Zehnder interferometer (473.0 and 632.8 nm) into a threelaser one (473.0, 543.0 and 632.8 nm). The unsteady-state analysis was tested in the thermogravitational micro-column to determine the effective diffusion coefficient of ternary mixtures by the quasi-binary approach. Also, the effect of the suitability of the light sources was tested during steady-state concentration separation to determine the thermodiffusion coefficients. The stability during a thermodiffusion experiment by the Thermogravitational Technique was tested at four different ternary mixtures of DCMIX2 system Tol|Meth|CH. Experimental results were discussed with numerical and analytical models where the role of cross-diffusion coefficients was considered on the thermogravitational behaviour. Apart from hydrocarbon mixtures, thermodiffusion, molecular diffusion and Soret coefficients of the aqueous mixture from DCMIX3, TEG|H2O|EtOH were determined at a mean temperature of 30 °C and compared to OBD and microgravity experiments. Given the attraction of fullerene, and the lack of properties of nanofluids in the literature, thermodiffusion, molecular diffusion and Soret coefficients were analysed over the ternary system C60|THN|Tol, tested in orbit during DCMIX4. The properties of this mixture were analysed at four different temperatures, 20 °C, 25 °C, 30 °C and 35 °C, thus determining the dependence on the average temperature. The results obtained in the Fluid Mechanics laboratory of MGEP-MU and SODI were compared with those measured in other terrestrial laboratories by Optical Digital Interferometry (ODI) and Optical Beam Deflection techniques. Experiments in OBD also enabled to study transport properties of the fullerene in five aromatic solvents: methylnaphthalene, toluene, o-xylene, m-xylene and p-xylene. In this study, the effect of the number of cycles and methyl groups of the molecular structures were analysed on the thermodiffusive behaviour. Last, the hydrocarbon ternary system MN|Tol|nC10 was studied in a transversal and integral manner, from different mass compositions of the ternary system to their corresponding binary mixtures over the entire concentration range. Thermodiffusion, molecular diffusion and Soret coefficients were determined for 15 binary subsystems and their combinations into 10 ternary mixtures by different thermogravitational columns and the Sliding Symmetric Tubes. This work has advanced the knowledge of the relation between the transport properties of binary and ternary mixtures. In summary, this PhD thesis provides important experimental data on the properties of binary and ternary mixtures using different techniques (convective and non-convective) and under different gravity conditions to feed the literature with new reference data, providing an added value towards the understanding of transport mechanisms in multicomponent mixtures.

[eu] Termodifusioaren fenomenoak deskribatzen du tenperatura gradiente baten menpeko nahasketetan induzitzen den kontzentrazio gradientea zeina bero eta masa transferentziaren akoplamendu-gurutzatuaren ondorioz sortzen den. Azken urteotan, fenomeno horrek interes handia piztu du zientzialarien komunitatean, erabilgarritasun potentzial zabala baitu askotariko eremuetan. Alabaina, osagai anitzeko nahasketetan, datu esperimentalen faltan, oraindik ere ez dira argitu garraiorako barne mekanismoak. Horiek horrela izanik, doktore-tesi honek osagai anitzeko termodifusio esperimentuak ditu ardatz; zehazki, Diffusion Coefficients Measuremets in ternary miXtures (DCMIX) proiektuari lotutako hiru osagaiko nahasketak. Proiektuak berak Europako Espazio Agentziaren eta ikerketa talde ugariren arteko elkarlana du oinarri eta egungo eta etorkizuneko Lurreko neurketen eta aurresate ereduen balioztatzerako eta kalibraziorako erreferentziazko datu fidagarriak ezartzea helburu. Marko horren baitan, hainbat sistema hirutarren garraio propietateak zehaztu dira, hala nola, termodifusioa, difusio-molekularra eta Soret koefizienteak. Horretarako, lau teknika esperimental baliatu dira lan honetan zehar. Termograbitazio zutabeek termodifusio koefizientea zehaztu ahal izatea ahalbidetu dute nahasketa bitar zein hirutarretan, egoera egonkorraren analisiaren bitartez. Halaber, nahasketa bitarren difusio-molekular koefizientea eta nahasketa hirutarren difusio efektiboa ere zehaztu dira, egoera ezegonkorrean sistemari egin zaion jarraipenaren bidez. Hala nahasketa bitarretan, nola hirutarretan, difusio koefizientea Tutu Simetriko Irristakorren teknika baliatuta neurtu da. Bayreutheko Unibertsitateko (Alemania) Physikalisches Instituten eginiko nazioarteko egonaldian, difusio-molekular eta Soret koefizienteak Uhin Optikoen Deflexio (OBD) bidez determinatu ziren, nahasketa bitar zein hirutarretan. Horiez gainera, DCMIX proiektuaren laugarren kanpainan hainbat termodifusio esperimentu garatu ziren mikrograbitatean, Nazioarteko Espazio Estazioko Diagnostikorako Instrumentu Optiko Hautagarria (SODI) baliatuta. DCMIX1eko, THN|IBB|nC12 0.80|0.10|0.10 masa konposizioa duen erreferentziazko sistema baliatu da Mach-Zehnder interferometroa bi argi-iturritatik (473.0 eta 632.8 nm) hiru laserrekora (473.0, 543.0 eta 632.8 nm) egokitzeko. Horren baitan, alde batetik, egoera ezegonkorraren analisiaren bitartez nahasketaren difusio efektiboa neurtu da termograbitazio mikro-zutabean, analisi kuasi-bitarrean hurbilpena eginda; bestetik, argiiturrien eragina ikertu da termodifusio koefizienteen zehaztapenean. Zutabe termograbitazionaletan egindako esperimentuetan nahasketa hirutarren egonkortasuna egiaztatu da, DCMIX2 misioko Tol|Meth|CH sisteman oinarritutako lau nahasketa hirutarretan. Esperimentuen emaitzak eredu numeriko eta analitikoetan oinarriturik eztabaidatu dira, difusio-gurutzatuak portaera termograbitazionalean duen eragina aintzatetsita. Hidrokarburo nahasketez harago, DCMIX3 kanpainako, TEG|H2O|EtOH, nahasketa akuosoaren termodifusio, difusio-molekular eta Soret koefizienteak zehaztu dira, batez besteko 30 °C-ko tenperaturan eta emaitzak OBD eta mikrograbitatean eginiko esperimentuekin alderatu. Fullerenoak duen erakargarritasunak eta literaturan nanofluidoen garraio propietateen gaineko hutsuneak eraginda, termodifusio, difusio-molekular eta Soret koefizienteak analizatu dira, C60|THN|Tol sistema hirutarraren baitan, orbitan, DCMIX proiektuan. Nahasketa horren propietateak lau tenperaturatan ikertu dira: 20 °C, 25 °C, 30 °C eta 35 °C. Era horretara determinatu dira propietate horien menpekotasunak batez besteko tenperaturarekiko. MGEP-MUko Fluidoen Mekanikako laborategian eta SODIn eskuratutako emaitzak Interferometria Optiko Digitala (ODI) eta Uhin Optikoen Deflexioa baliatzen duten beste laborategien emaitzekin alderatu ziren. Gainera, OBD teknikak fullerenoaren garraio propietateak aztertzea ahalbidetu du bost disolbatzaile aromatikotan: metilnaftalenoa, toluenoa, o-xilenoa, m-xilenoa eta p-xilenoa. Ikerketa honetan, molekulen zikloen kopuruak eta egituretako metilo taldeek termodifusioaren jokabidean duten eragina aztertu da. Azkenik, MN|Tol|nC10 hidrokarburo hirutarren sistema ikertu da era transbertsalean eta integralean, sistema hirutarraren hainbat kontzentraziotatik azpisistemak osatzen dituzten nahasketa bitarretara, hauen kontzentrazio eremu osoa ikertuz. Termodifusioa, difusio-molekularra eta Soret koefizienteak zehaztu dira 15 azpi-sistema bitarretan eta 10 nahasketa hirutarretan, termograbitazio zutabeen eta Tutu Simetriko Irristakorren bitartez. Lan honen bidez, nahasketa bitar eta hirutarren arteko garraio propietateen korrelazioa egiaztatu da. Laburbilduz, doktore-tesi honek osagai anitzeko nahasketen garraio propietateen datu esperimental garrantzitsuak eskaintzen ditu hainbat teknika (konbektiboak eta ezkonbektiboak) grabitate eremu ezberdinetan erabiliz. Bibliografia erreferentziazko datu berriez elikatzen du, osagai anitzeko nahasketen garraio mekanismoen ezagutzan ekarpen berriak eginaz.