No description available.

No description available.

Light intensity distribution studies in the heterogeneous photocatalytic reactors were carried out successfully with potassium ferrioxalate chemical actinometry, reproducible light intensity estimates of the irradiation source were obtained. The increased light intensity in the reactor system increased the absorption as determined by actinometry. It was found that reflectivity was a dependent variable but mesh opening area was an independent variable. The photocatalytic mineralization of dichoroacetic acid DCAA, in the presence of TiO2 immobilized on a plate in an externally irradiated bubble column photoreactor had been investigated. The mass transfer and activity evaluation were measured. It was found that increasing the catalyst thickness, increased the photoactivity until it reaches the optimum loading, further loading increase caused the reaction rate to remain constant. This phenomenon was observed with increased lamp power (intensity) and initial solute concentration. However, the catalyst activity was not influenced by the increasing concentration of dissolved oxygen. The reaction rate for DCAA photomineralization was expressed using the Langmuir-Hinsheldwood model.

Light intensity distribution studies in the heterogeneous photocatalytic reactors were carried out successfully with potassium ferrioxalate chemical actinometry, reproducible light intensity estimates of the irradiation source were obtained. The increased light intensity in the reactor system increased the absorption as determined by actinometry. It was found that reflectivity was a dependent variable but mesh opening area was an independent variable. The photocatalytic mineralization of dichoroacetic acid DCAA, in the presence of TiO2 immobilized on a plate in an externally irradiated bubble column photoreactor had been investigated. The mass transfer and activity evaluation were measured. It was found that increasing the catalyst thickness, increased the photoactivity until it reaches the optimum loading, further loading increase caused the reaction rate to remain constant. This phenomenon was observed with increased lamp power (intensity) and initial solute concentration. However, the catalyst activity was not influenced by the increasing concentration of dissolved oxygen. The reaction rate for DCAA photomineralization was expressed using the Langmuir-Hinsheldwood model.

No description available.

No description available.

No description available.

We study the formation and spreading of a turbulent jet of bubbles in microgravity. This has been analyzed from the recordings obtained in previous experimental campaigns of microgravity. Results have been compared with a simplified model of passive bubbles, in which bubbles are advected by the mean flow and dispersed due to the local degree of turbulence at each point of the jet. Thanks to the expertise obtained with this part of the thesis, we have designed and built a new experiment that has been used 36 times in the 4.7 s drop tower of ZARM (“Center of Applied Space Technology and Microgravity”) in Bremen. With this experiment we have obtained, for the first time in history, a monodisperse suspension of bubbles, within a turbulent flow, in microgravity. From the resulting measures we have characterized the relaxation time of pseudo-turbulence (previously generated due to the effect of buoyancy forces upon the injected bubbles in normal gravity conditions). We have also studied the interaction between bubbles and the turbulent medium. Results have been compared with Lattice-Boltzmann simulations of the flow. On the other hand, we have also studied the impact of residual gravitational vibrations (known as g-jitters) upon the quality of semiconductors solidified in microgravity. The quality of the resulting crystals has been studied from the analysis of the inhomogeneities in their dopant concentration. This study has been based entirely on simulations, but g-jitters have been modeled from acceleration signals measured in real space missions. / En la present tesi s’estudia, en primer lloc, la formació d’un doll turbulent de bombolles en condicions de microgravetat. Aquest ha sigut analitzat a partir del tractament de les gravacions obtingudes per altres investigadors en experiments de microgravetat. Els resultats s’han comparat amb un model simplificat de bombolles passives, en el que aquestes són arrossegades pel flux mitjà i, simultàniament, són dispersades degut al grau local de turbulència a cada punt. Gràcies a la experiència obtinguda en aquest anàlisi, s’ha dissenyat un nou experiment que ha sigut utilitzat en 36 llançaments de la torre de caiguda de 4.7 segons del ZARM (“Centre de Tecnologia Espacial Aplicada i Microgravetat”) a Bremen. Amb aquest experiment s’ha aconseguit, per primera vegada a la història, una suspensió monodispersa de bombolles, en el sí d’un flux turbulent, en condicions de microgravetat. A partir dels resultats obtinguts, s’ha caracteritzat per primera vegada el temps de relaxació de la pseudo-turulència (generada prèviament degut a l’efecte de les forces de flotació sobre les bombolles injectades en gravetat normal). També s’ha estudiat l’efecte causat per les bombolles en el medi turbulent. Els resultats han sigut comparats amb simulacions realitzades mitjançant el model de Lattice-Boltzmann. Per altra banda, s’ha estudiat també l’efecte que tenen les vibracions gravitatòries residuals sobre la qualitat de semiconductors solidificats en microgravetat. S’ha analitzat la qualitat dels cristalls resultants a partir de l’estudi de les inhomogeneïtats en la concentració de dopant. Aquest estudi ha sigut realitzat íntegrament a base de simulacions, però s’han establert els paràmetres dominants del soroll gravitatori a partir de valors mesurats en missions espacials reals.