Quantitative study of cluster growth in free-jet expansions of CO2 by Rayleigh and Raman scattering

The condensation produced in supersonic expansions of CO2 is studied quantitatively combining Rayleigh and Raman scattering. The cluster number density nc and the mean cluster size are obtained for five expansions with stagnation pressures P0=1-5 bars, and temperature T0=294 K, along axial and radial directions; nc and are determined from the condensation onset up to a terminal size, verifying the empirical law prop.P0^(2.23). A maximum growth rate d/dt approx.8x10(8) s^(-1) is estimated for the 5-bar expansion. The Raman spectra show a coexistence of solid and liquidlike phases in the jet, with a progressive transition from the liquid to the solid fraction as the clusters increase their size.Ministerio de Educación y Ciencia, Proyectos BFM2001-2276 y FIS2004-02576Peer reviewe

Nonequilibrium Processes in Supersonic Jets of N2, H2, and N2 + H2 Mixtures: (I) Zone of Silence

7 pages, 5 figures, 1 table.-- Printed version published Jul 30, 2009.Supporting information available at: http://pubs.acs.org/doi/suppl/10.1021/jp901700cNumber density and rotational temperature in the zone of silence of supersonic jets of N2, H2, and their mixtures N2 + 2H2 and 2N2 + H2, at p0 = 1 bar and T0 = 295 K, have been measured by Raman spectroscopy. Translational temperature in the jets has been derived from the experimental data assuming isentropic flow. The density along the jet axis decays at a rate depending on the composition of the expanded gas, which can be explained by the variation of its effective heat capacity ratio. Measurements across the jet axis do not support numerical off-axis density modeling from the literature. A strong nonequilibrium between the rotational degrees of freedom of both species is observed, even between the two spin species ortho-H2 and para-H2. From the corresponding rotational temperature data, a relationship between rotational cross sections for the inelastic collisions of the different species is established. In the expansions of the mixtures, an enrichment of N2 is measured on the axis, which is compared with the predictions from the theory of diffusive separation in jets.A. Ramos acknowledges CSIC for an I3P grant. This work has been supported by the Spanish Ministerio de Educación y Ciencia, research Project No. FIS2004-02576 and Project No. FIS2007-61430, and by the Comunidad de Madrid, Project No. S-0505/ESP /0237(ASTROCAM).Peer reviewe

Observation of crystallization slowdown in supercooled para-hydrogen and ortho-deuterium quantum liquid mixtures

We report a quantitative experimental study of the crystallization kinetics of supercooled quantum liquid mixtures of para-hydrogen (pH$_2$) and ortho-deuterium (oD$_2$) by high spatial resolution Raman spectroscopy of liquid microjets. We show that in a wide range of compositions the crystallization rate of the isotopic mixtures is significantly reduced with respect to that of the pure substances. To clarify this behavior we have performed path-integral simulations of the non-equilibrium pH$_2$-oD$_2$ liquid mixtures, revealing that differences in quantum delocalization between the two isotopic species translate into different effective particle sizes. Our results provide first experimental evidence for crystallization slowdown of quantum origin, offering a benchmark for theoretical studies of quantum behavior in supercooled liquids.Comment: 6 pages, 3 figure

Experimental and theoretical determination of rotational-translational state-to-state rate constants for N2:He collisions at low temperature (3<T<20 K)

10 pages, 7 figures.-- PACS nr.: 34.50.Fa.We present an experimental determination of state-to-state rotational–translational (RT) rate constants of N2:He collisions in the vibrational ground state as a function of temperature in the range 3<T<20 K. Raman spectroscopy in supersonic expansions of N2/He mixtures is used to determine the primary data that, together with the N2:N2 state-to-state RT rates previously determined [Ramos et al., Phys. Rev. A 66, 022702 (2002)], are needed to solve the master equation according to a procedure that does not impose any particular scaling law. We also report first principle calculations of the N2:He state-to-state RT rate constants performed using the full three-dimensional potential energy surface of Reid et al. [J. Chem. Phys. 107, 2329 (1997)], in the 3<T<300 K temperature range. The coupled-channel method, and the coupled-states approximation, were applied in the low (0–610 cm–1) and in the high (610–1500 cm–1) energy limits, respectively. A good agreement between theoretical and experimental results is found in the temperature range where comparison is possible.Thanks are due to the Spanish MCYT for financial support of the experimental part of this work (Research Project No. BFM2001-2276).Peer reviewe

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

Laboratory study of rate coefficients for H2O:He inelastic collisions between 20 and 120K

8 pags. ; 7 figs. ; 4 tabls. ; Supporting material: machine-readable tablesState-to-state rate coefficients for ortho-H2O:He and para-H2O:He inelastic collisions in the 20-120 K thermal range are investigated by means of an improved experimental procedure. This procedure is based on the use of a kinetic master equation (MEQ) which describes the evolution of populations of H2O rotational levels along a supersonic jet of H2O highly diluted in helium. The MEQ is expressed in terms of experimental observables and rate coefficients for H2O:He inelastic collisions. The primary experimental observables are the local number density and the populations of the rotational energy levels of H2O, quantities which are determined along the jet with unprecedented accuracy by means of Raman spectroscopy with high space resolution. Sets of rate coefficients from the literature and from present close-coupling calculations using two different potential energy surfaces (PESs) have been tested against the experiment. The Green et al. rate coefficients are up to 50% too low compared to the experiment, while most rates calculated here from the Hodges et al. PES and the Patkowski et al. PES are much closer to the experimental values. Experimental rates with an estimated accuracy on the order of 10% have been obtained for ortho-H2O:He and para-H2O:He inelastic collisions between 20 and 120 K by scaling and averaging the theoretical rates to the experiment. 2015. C The American Astronomical SocietyThis work has been supported by the Spanish Ministerios de Innovación (MICINN) and Economía y Competitividad (MINECO) through the research projects FIS2010-22064-C01, FIS2010-22064-C02, FIS2013-48275-C2-1-P, and FIS2013-48275-C2-2-P, and CONSOLIDER-ASTROMOL CSD2009-0038.Peer reviewe

Experimental and numerical investigation of an axisymmetric supersonic jet

21 pages, 10 figures, 2 tables.A comprehensive study of a steady axisymmetric supersonic jet of CO2, including experiment, theory, and numerical calculation, is presented. The experimental part, based on high-sensitivity Raman spectroscopy mapping, provides absolute density and rotational temperature maps covering the significant regions of the jet: the zone of silence, barrel shock, Mach disk, and subsonic region beyond the Mach disk. The interpretation is based on the quasi-gasdynamic (QGD) system of equations, and its generalization (QGDR) considering the translational–rotational breakdown of thermal equilibrium. QGD and QGDR systems of equations are solved numerically in terms of a finite-difference algorithm with the steady state attained as the limit of a time-evolving process. Numerical results show a good global agreement with experiment, and provide information on those quantities not measured in the experiment, like velocity field, Mach numbers, and pressures. According to the calculation the subsonic part of the jet, downstream of the Mach disk, encloses a low-velocity recirculation vortex ring.This research was supported by the Spanish Dirección General de Investigación Científica y Enseñanza Superior (DGICYES), Research Projects PB94{1526 and PB97{1203, and by the Fund for Fundamental Investigations of the Russian Academy of Sciences N 98-01-00155.Peer reviewe

HE-LHC: The High-Energy Large Hadron Collider – Future Circular Collider Conceptual Design Report Volume 4

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre-of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries