Turbulent bubble suspensions and crystal growth in microgravity. Drop tower experiments and numerical simulations

• Autores: Pau Bitlloch Puigvert
• Directores de la Tesis: Josep Xavier Ruiz Martí (dir. tes.), Jaume Casademunt i Viader (dir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2012
• Idioma: inglés
• Tribunal Calificador de la Tesis: Michael Ewald Dreyer (presid.), Jordi Ortin Rull (secret.), Ricard Gonzalez Cinca (voc.)
• Materias:
  • Física
    • Física de fluidos
  • Ciencias de la tierra y del espacio
    • Ciencias del espacio
• Enlaces
  • Tesis en acceso abierto en:  TDX  Dipòsit Digital de la UB 
• Resumen

  • 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.