[en] In this doctoral thesis, the influence of operating conditions and thermophysical transport properties on the behaviour of falling film absorbers operating with the LiBr − H2O mixture in absorption technologies has been analysed. To this end, different numerical methodologies based on the Finite Volume Method (FVM) have been defined and evaluated. This work has made it possible to determine the influence of wettability properties on the hydrodynamic behaviour of the falling film flow in horizontal tubes by means of transient models. The range of applicability of the 2D and 3D models has also been studied, comparing the results with the solutions of the literature. The transient behaviour of the flow, as well as the evolution of the wetting area and the film thickness for different contact angles have been analysed by means of these models. The results have shown that the wettability properties have a great impact on these parameters and, therefore, must be considered in the studies of horizontal tube type falling films. Furthermore, different mathematical formulations and methodologies for studying the heat and mass transfer of falling film absorbers used in the literature have been compared, showing that the absorption varies depending on the chosen methodology. The selected methods were Fick and Higbie without imposing the mass fraction, assuming unidirectional diffusion at the interface. In the same way, the results of the models have been contrasted with experimental studies, with the Fick 1D method proving to be more reliable. Finally, the effect of thermodiffusion on the performance of falling film absorbers has been studied. For this purpose, the mass transfer caused by both concentration and temperature gradients has been considered. By means of the defined methodology, vapour absorption, temperature and mass fraction profiles have been examined for different operating conditions and thermodiffusion values. The results have shown that, as a result of the negative nature of the Soret effect of the LiBr − H2O mixture, thermodiffusion increases the absorption. Therefore, the use of fluids with a high absolute value of the negative thermodiffusion coefficient (DT) could improve the cost-effectiveness of absorption machines. However, it is essential to experimentally determine the DT coefficient of the mixture LiBr − H2O to quantify the real effect of the mass transfer mechanism under the temperature gradient on the absorber performance.

[eu] Doktorego tesi honetan LiBr − H2O nahastearekin xurgapen teknologietan lan egiten duten beheranzko film (falling film) motako xurgatzaileen portaeran lan baldintzek eta garraio propietate termofisikoek duten eragina aztertu da. Horretarako, hainbat zenbakizko metodologia definitu eta ebaluatu dira, bolumen finituen metodoan oinarrituta (ingelesez Finite Volume Method, FVM). Lan honi esker, bustigarritasun-propietateek hodi horizontaletako falling film fluxuaren portaera hidrodinamikoan duten eragina zehaztu ahal izan da, modelo iragankorren bidez. Era berean, 2D eta 3D ereduen aplikagarritasun-maila aztertu da, eta emaitzak bibliografiako lanekin alderatu dira. Modelo hauek erabiliz, fluxuaren portaera iragankorra aztertu da, baita bustitze-eremuaren bilakaera eta filmaren lodiera ere, ukipen-angelu desberdinetarako. Emaitzek erakutsi dute bustigarritasun-propietateek eragin handia dutela parametro horietan eta, beraz, kontuan hartu behar direla hodi horizontal motako falling film azterketetan. Honez gain, bibliografian erabilitako formulazio matematikoak eta falling film erako xurgatzaileen masa eta bero-transferentzia aztertzeko metodologia ezberdinak alderatu dira, xurgapena aukeratutako metodologiaren arabera aldatzen dela frogatuz. Hautatutako metodoak Fick eta Higbie izan dira, masa frakzioa inposatu gabe, eta faseartean norabide bakarreko difusioa gertatzen dela suposatuz. Era berean, modeloaren emaitzak lan esperimentalekin alderatu dira, Fick 1D metodoa fidagarriagoa dela frogatuz. Azkenik, termodifusioak falling film erako xurgatzaileen errendimenduan duen eragina aztertu da. Horretarako, kontzentrazio-gradienteek nahiz tenperaturagradienteek eragindako masa-transferentzia hartu da kontuan. Definitutako metodologiaren bidez, lurrunaren xurgapena eta filmaren tenperatura- eta masafrakzioaren profilak aztertu dira, hainbat lan-baldintza eta termodifusio balioetarako. Emaitzek agerian utzi dute, LiBr − H2O nahasketaren Soret efektuaren izaera negatiboa dela eta, termodifusioak xurgapena areagotzen duela. Beraz, termodifusio koefiziente (DT) negatiboaren balio absolutu handia duten fluidoak erabiltzeak xurgapen-makinen errentagarritasuna hobetu lezake. Hala ere, funtsezkoa da DT koefizientea esperimentalki zehaztea, tenperatura-gradientearen bidez ematen den masa-transferentziaren mekanismoak xurgatzaileen errendimenduan duen benetako eragina kuantifikatzeko.