[en] In this thesis the study of thermogravitational effect at high-pressure and free media has been developed, with which the thermo-hydrodynamic behavior and the experimental determination of transport properties can be deepen, especially the thermal diffusion coefficient of liquid and liquefied mixtures. The experimental results under high pressure obtained by means of the new thermogravitational installation are of great interest for the developing and adjusting of numerical and theoretical models applied for predicting and optimizing the exploration and exploitation of oil wells. This installation is up to today, the only facility at international scale that can analyze experimentally the thermogravitational effect in terms of pressure. This thesis focuses on the design, construction and validation of a new thermogravitational column able to work at high pressure, up to 500 bar. Together with this, the necessary devices and the procedures to operate at high pressure, for filling the column with the fluid and extracting the samples for evaluation, complying with safety regulations have been designed. To design the column has been paid particular attention to its critical features and functions that were known from previous experience in using this technique at atmospheric pressure and the revision of the state of art. The developed thermogravitational column's configuration is cylindrical, and its dimensions are: height 500 mm, 1 mm gap width, 5 ports for sample extraction evenly distributed along the column, and radius curvature of 0.99. Once the thermogravitational column was validated at atmospheric pressure with the liquid mixtures that were studied in the Benchmark of FONTAINEUBLEAU and after checking that it operates within the validity limits of the FJO theory, the installation has been used to determine the thermal diffusion coefficient of binary mixtures of n-alkanes at atmospheric pressure and various different concentrations. From this work we can conclude that the thermodiffusion coefficient of mixtures of n-alkanes has a linear dependence with its mass fraction. This result allows a quantitative determination of DT values, from the knowledge of viscosity and thermal expansion coefficient of analyzed mixture. For the experimental determination of the thermodiffusion coefficient of IBB-nC12, IBB-nC12, and THN-IBB mixtures at average temperature of 25 °C and pressures between 20-200 bar, first, the values of thermophysical properties of the mixture and the density gradient along the column at stationary state were experimentally measured. The results obtained showed that DT coefficient decreases with pressure and fits well to a line, at least, for the three studied mixtures. This dependence of thermodiffusion coefficient with pressure is mainly due to the viscosity variation with pressure. As it was found for binary mixtures of n-alkanes at atmospheric pressure for the mixtures studied in the Benchmark (THN-IBB and IBB-nC12) the thermal diffusion coefficient is proportional to the ratio of thermal expansion coefficient and dynamic viscosity DT ~ a/N.

[eu] Doktorego-tesi honetan ingurune aske eta presio altuetarako termograbitazio-efektua garatu da, honek portaera termohidrodinamikoan eta garraio-propietateak determinatzeko prozedura esperimentalean gehiago sakontzeko aukera ekainiko du, bereziki, difusio-termiko koefizientea nahaste likidoetan zein likidotuetan. Termograbitazio-instalazio berriarekin lortutako emaitza esperimentalak interes handia du petrolio-putzuen arakatze eta ustiatze optimizaziorako erabilitako zenbakizko kodeen garapenerako eta doikuntzarako. Hau da, orain arte, mundu mailan esperimentalki termograbitazio-efektua presiopean azter dezakeen instalazio bakarra. Tesi honetako lanaren ardatz nagusia 500 barretaraino lan egiteko prestatutako termograbitazio-zutabe berri bat diseinatzea, eraikitzea eta baliozkotzea izan da. Honekin batera, presio altuetara lan egiteko gailuak eta fluidoak kargatzeko eta aztertzeko laginak lortzeko prozedurak ere diseinatu dira. Zutabea diseinatzerakoan arreta berezia jarri da beronek behar dituen funtzio eta ezaugarri kritikoetan, guzti hau aurretik zutabearekin presio atmosferikoan lan egitetik dugun esperientziatik eta gaur egungo egoeraren errebisiotik lortu dugu. Garatutako termograbitazio-zutabea zilindrikoa da, ondoko dimentsioduna, altuera 500 mm; tartearen zabalera 1 mm-koa; fluido laginak lortzeko zutabearen altueran zehar 5 harbide berdinbanatu ditu eta bere kurbadura-erradioa 0,99koa. Behin termograbitazio-zutabea presio atmosferikoan FONTAINEUBLEU benchmarkean erabilitako nahasteekin baliozkotuta eta FJO teoriaren baliotasun esparru barruan ondo lan egiten duela egiaztatuta, instalazio berria presio atmosferikoan n-alkanoen nahaste bitarren termodifusio koefizientea determinatzeko erabili da. Azterketa honetatik ondoriozta dezakegu n-alkano nahasteen termodifusio-koefizientearen eta masa-frakzioaren artean dependentzia lineala dagoela. Emaitza honekin DT balioak determinatu ditzakegu, soilik aztertu nahi dugun nahastearen biskositate eta hedapen-koefiziente termikoa ezagututa. IBB-nC12, THN-IBB eta THN-nC12 nahaste likidoen termodifusiokoefizienteak esperimentalki determinatzeko, 25 °C-tako batazbesteko tenperaturara eta 20-200 barretako presio tartean, baldintza hauetan nahasteen propietate termofisikoak eta zutabearen altueran zehar sortutako dentsitate gradientea esperimentalki neurtzen dira. Lortutako emaitzetatik ondorioztatzen da DT koefizientea presioarekin txikitzen dela eta berau, aztertutako hiru nahasteentzat, zuzen batera ondo doitzen dela. Presio atmosferikorako nalkanoen nahaste bitarrentzat aurkitu moduan, Benchmarkeko THN-IBB eta nC12-IBB nahasteentzat termodifusio-koefizientea proportzionala dela, nahastearen biskozitate-dinamiko eta hedadura-koefiziente termikoaren zatidurari DT ~ a/N.