Evaluation of a new wind tunnel with expanding corners

A new low-speed, closed-circuit, closed-test-section wind tunnel, called BLT, has been designed and built at KTH. The turbulence intensity in the test section is <0.04%, the total pressure variation is <±0.1% and the temperature variation is <±0.07°C over the cross-sectional area. The concept of expanding corners with an expansion ratio of 1.32 first investigated by Lindgren et al. in 1998, has been implemented successfully with a two-dimensional total pressure loss coefficient of 0.047 at a chord Reynolds number of 200,000. It is comparable to or even better than the values found in most wind tunnels using nonexpanding corners. The findings in this study prove the usefulness of expanding corners to achieve a compact wind tunnel circuit design without compromising the flow quality.     

Reynolds Number Effects on Statistics and Structure of an Isothermal Reacting Turbulent Wall-Jet

Three-dimensional direct numerical simulation (DNS) is used to investigate the effects of changing the Reynolds number on dynamics of a reacting turbulent wall-jet. The flow is compressible and a single-step isothermal global reaction is considered. At the inlet, fuel and oxidizer enter the domain separately in a non-premixed manner. In this study, the bulk Reynolds number of the flow, in terms of the inlet quantities, varies from Re = 2000 to Re = 6000, which results in a comparable change in friction Reynolds numbers. The DNS database in Pouransari et al. (Phys. Fluids 23(085104), 2011) is used for the lower Reynolds number case and for the higher Reynolds number case, a new DNS is performed. One of the main objectives of this study is to compare the influences of changing the Reynolds number of the isothermal flow with the heat-release effects caused by the chemical reaction, that we studied earlier in Pouransari et al. (Int. J. Heat Fluid Flows 40, 65–80, 2013). While, both turbulent and flame structures become finer at the higher Reynolds number, the effect of decreasing the Reynolds number and adding the combustion heat release are compared with each other and found to be similar for some aspects of the flow, but are not always the same.     

Improved models for the phase behaviour of hydrogen fluoride: chain and ring aggregates in the SAFT approach and the AEOS model

Hydrogen fluoride presents one of the strongest hydrogen bonds known. Ring aggregates exist both in the vapour and liquid phases at low temperatures resulting in an anomalously high low-temperature vapour pressure. The effect of ring-like aggregates on the vapour—liquid phase equilibria of associating fluids is studied within the framework of the statistical associating fluid theory (SAFT) and in the chemical model of Lencka and Anderko (AEOS). The SAFT approach incorporates separate contributions to describe chain formation, association (hydrogen bonding), and long range dispersion forces. The treatment of the association interactions stems from the thermodynamic perturbation theory of Wertheim. At the first level of approximation the contribution of ring-like aggregates is neglected and only chain- and treelike structures are treated. In this work an earlier extension of the approach to incorporate ring aggregates is used to model the phase behaviour of hydrogen fluoride. The chemical model of Lencka and Anderko for associating fluids is also considered together with a modification that takes into account the formation of ring aggregates. Vapour pressures and coexistence densities are examined together with heats of vapourization, and the calculations are compared with experimental data.     

Electron spin resonance studies of 199HgH, 201HgH, 199HgD and 201HgD isolated in neon and argon matrices at 4K: an electronic structure investigation

Various isotopomers of the mercury hydride radical (HgH) have been generated in a microwave discharge and trapped in neon and argon matrices at 4 K for electron spin resonance (ESR) investigations. Both the dipolar (A_dip) and isotropic (A_iso) components of the nuclear hyperfine interactions have been directly measured for ¹⁹⁹Hg, ²⁰¹Hg, H and D. Electronic structure information for HgH in its X²Σ ground state obtained from the hyperfine data is compared with theoretical results from several different computational methods. The hyperfine interactions in HgH are unusually large with A_iso(¹⁹⁹Hg) = 6859(3), A_dip(¹⁹⁹Hg) = 446(3), A_iso(H) = 730(2) and A_dip(H) = 0(2) MHz. A standard analysis of the hyperfine interactions demonstrates the need for a more in-depth theoretical treatment of HgH that should include relativistic effects. An interesting shift in spin density is observed when deuterium replaces hydrogen in HgH. The decreased spin density on deuterium, which was demonstrated in earlier studies, can now be more fully investigated since these new measurements confirm an associated increase in spin density on mercury     

The Structure of a Lyotropic Liquid Crystalline Phase that Orients in a Magnetic Field

Abstract

The structure of a lyotropic liquid crystalline phase with positive diamagnetic anisotropy (type I), that spontaneously orients in a magnetic field has been studied by means of water NMR quadrupole splittings, NMR diffusion and polarized absorption spectroscopy. It is concluded that this phase is built up of long rodlike aggregates. A preliminary study of a sample with negative diamagnetic anisotropy (type II) shows that this phase probably consists of lamellar aggregates. It is suggested that these phases are suitable as orientation matrices for studies of chromophores with polarized light spectroscopy.     

Discrete Polynuclear Growth and Determinantal Processes

We consider a discrete polynuclear growth (PNG) process and prove a functional limit theorem for its convergence to the Airy process. This generalizes previous results by Prähofer and Spohn. The result enables us to express the F ₁ GOE Tracy- Widom distribution in terms of the Airy process. We also show some results, and give a conjecture, about the transversal fluctuations in a point to line last passage percolation problem. Furthermore we discuss a rather general class of measures given by products of determinants and show that these measures have determinantal correlation functions.     

Preparation of iron oxide nanocrystals by surfactant-free or oleic acid-assisted thermal decomposition of a Fe(III) alkoxide

A new non-hydrolytic, alkoxide-based route was developed to synthesize iron oxide nanocrystals. Surfactant-free thermal decomposition of the iron 2-methoxy-ethoxide precursors results in the formation of uniform iron oxide nanocrystals with an average size of 5.6 nm. Transmission electron microscope study shows that the nanocrystals are protected against aggregation by a repulsive surface layer, probably originating from the alkoxy-alkoxide ligands. Addition of oleic acid resulted in monodisperse nanocrystals with an average size of 4 nm. Mössbauer analysis confirmed that the nanocrystals mainly consisted of maghemite. Analysis of the magnetic hysteresis loop measurements and the zero field and field cooled measurements displayed an excellent fit to established theories for single-domain superparamagnetic nanocrystals and the size of the magnetic domains correlated well to the crystallite size obtained from transmission electron microscope.