1 research outputs found
Experiments on microjets of undercooled liquid hydrogen
28th International Symposium on Rarefied Gas Dynamics 2012 (2012). AIP Conf. Proc.; 9 pags. ; 7 figs. ; 1 tab. ; PACS: 67.63.Cd, 33.20.Fb, 64.60.My, 64.70.dg, 47.60.KzNovel experiments on liquid microjets (filaments) of hydrogen and deuterium, carried out at the Laboratory of
Molecular Fluid Dynamics of the IEM, are reported. These filaments, less than 10 microns in diameter, are an ideal medium
to produce highly undercooled liquid samples and to investigate the homogeneous solidification process, free from wall
effects. The filaments exit from cryogenic capillary nozzles into a vacuum chamber, to cool down very fast by surface evaporation. Finite size radius leads to a temperature gradient across the filament, determined by thermal conductivity, and, possibly, to a velocity gradient as well. The filaments are monitored by laser shadowgraphy, and analyzed by means of high performance Raman spectroscopy. Real-time measurements in the rotational and vibrational spectral regions reveal the structure and temperature along the filaments, allowing to track the crystal growth process. The high spatial resolution of Raman spectroscopy allows observing in situ the structural changes of the liquid microjets, with a time resolution of ∼ 10
ns. The filaments of pure para-H2 can be cooled down to 9 K (65% of its melting point at 13.8 K), while staying liquid,
before eventually solidifying into a metastable polymorph. Crystallization kinetics revealed a growth rate of 33 cm/s, much higher than expected for a thermally activated process. The time and spatial control attained in these experiments offers new opportunities for investigating the processes of nonequilibrium phase transformations in undercooled fluids, as well as the propagation of liquid jets into a rarefied gas media. © 2012 American Institute of PhysicsThis work has been supported by the the Spanish Ministerio de Ciencia e Innovacion, through grants FIS2007-61430, FIS2010-22064-C02-01, and HD2008-0068, by the Helmholtz Gemeinschaft, through grant VH-NG-331, and by the German academic exchange service (DAAD) under reference Nr. 50025171.Peer reviewe