Solids behavior in dilute zone of a CFB riser under turbulent conditions

The behavior of the solid phase in the upper zone of a circulating fluidized bed riser was studied using a phase Doppler anemometer. Glass particles of mean diameter 107 μm and superficial gas velocities U_g covering the turbulent and the beginning of the fast fluidization regime were investigated. Three static bed heights were tested. Ascending and descending particles were found co-existing under all operating conditions tested, and at all measurement locations. Superficial gas velocity proved/happened to have a larger effect on descending particles at the wall and on ascending particles in the central region. Transversal particle velocities in both directions (toward the center and toward the wall) behaved relatively equivalently, with only slight difference observed at the wall. However, observation of the number of particles moving in either transversal direction showed a change in bed structure when increasing U_g. Furthermore, a balance was constantly observed between the core zone and the annulus zone where the mutual mass transfer between these two zones occurred continuously. Transition from a slow to a fast particle motion was accompanied by a transition to high levels of velocity fluctuations, and was found corresponding to the appearance of significant solid particle flow rate.     

Tunable diode laser measurement of pressure-induced shift coefficients of CO2 around 2.05 μm for Lidar application

Atmospheric carbon dioxide (CO₂) is one of the main contributors to the greenhouse effect. A global monitoring of CO₂ from space is foreseen as a key issue to quantify its sources and sinks at a regional scale and to better predict future levels of CO₂ and their effect on climate change. Differential Absorption Lidar (DiAL) is a promising and novel spectroscopic technique for remote sensing CO₂ spatial and temporal concentration distribution with a high level of accuracy. However, a precise knowledge of spectroscopic parameters of CO₂ molecular transitions and their dependence with temperature and pressure is required for reducing the uncertainty on DiAl measurements. Hence, to support remote sensing of carbon dioxide in the troposphere, we report on the accurate determination of air pressure-induced shift coefficients for eight absorption lines belonging to the R branch of (20⁰1)_III←(00⁰0)_I band of CO₂ at 2.05 μm. Purposely, a high-resolution tunable diode laser absorption spectrometer (TDLAS) coupled to a cryogenically cooled optical cell was implemented. From these measurements, we have further determined the temperature-dependencies of the air pressure-induced shift coefficients.     

Evidence of deep water penetration in silica during stress corrosion fracture

We measure the thickness of the heavy water layer trapped under the stress corrosion fracture surface of silica using neutron reflectivity experiments. We show that the penetration depth is 65-85 ?, suggesting the presence of a damaged zone of ～100 ? extending ahead of the crack tip during its propagation. This estimate of the size of the damaged zone is compatible with other recent results.     

Halogene

Ohne Zusammenfassung     

Experimental and Theoretical Study of Sprays Produced by Ultrasonic Atomisers

The atomisation of liquids by means of low-frequency ultrasonic atomisers results from unstable surface waves generated on the free surface of a thin liquid film. These unstable waves are obtained from the tuning of the amplitude and the frequency of an imposed oscillation. The thin liquid film develops as the liquid spreads over the atomising surface of the atomiser. This paper focuses on a systematic experimental analysis of the sprays produced by low-frequency ultrasonic atomisers. The thickness of the liquid film was measured and its effects on the drop diameter were studied together with the effects of both the liquid's physical properties and the ultrasonic atomiser's characteristics. The relationship between the mean drop diameter and the surface wave wavelength was accurately determined and introduced into a mathematical approach based on the maximum entropy formalism to predict the drop size distribution of the spray. Within the range of working conditions tested, the application of this formalism is successful and provides a procedure for the prediction of spray drop size distributions from calculations only.     

On a system of Klein-Gordon type equations with acoustic boundary conditions

We prove the existence, uniqueness and uniform stabilization of global solutions for a generalized system of Klein-Gordon type equations with acoustic boundary conditions on a portion of the boundary and the Dirichlet boundary condition on the rest.     

The use of PDE centres in the local RBF Hermitian method for 3D convective-diffusion problems

In this work an extension is proposed to the Local Hermitian Interpolation (LHI) method; a meshless numerical method based on interpolation with small and heavily overlapping radial basis function (RBF) systems. This extension to the LHI method uses interpolation functions which themselves satisfy the partial differential equation (PDE) to be solved. In this way, a much improved reconstruction of partial derivatives can be obtained, resulting in significantly improved accuracy in many cases.     

Wide scale range structure in polyelectrolyte-protein dense complexes: where Sans meets freeze-fracture microscopy

We show in this paper how the combination of SANS and freeze-fracture electron microscopy (FFEM) is a powerful tool to picture the structure of very turbid sample liquids at spatial scales lying from a few A to several microns. In a given range of chain size and species concentrations, primary complexes in the shape of globules are observed by both techniques. SANS allows a precise quantitation of size, inner structure, and composition of these globules, as well as aggregated structure of the globules at larger scales, which is fractal-like, with a Hausdorff dimension 2.1 characteristic of Reaction Limited Aggregation (RCLA). The existence of aggregates is seen by FFEM, but most of all FFEM shows the lack of any further structure at larger scale, up to the micrometer size.     

Comparison of interfacial electron transfer through carboxylate and phosphonate anchoring groups

The effects of anchoring groups on electron injection from adsorbate to nanocrystalline thin films were investigated by comparing injection kinetics through carboxylate versus phosphonate groups to TiO2 and SnO2. In the first pair of molecules, Re(LA)(CO)3Cl (ReC1A) and Re(Lp)(CO)3Cl (ReC1P), [LA=2,2'-bipyridine-4,4'-bis-CH2-COOH, Lp=2,2'-bipyridine-4,4'-bis-CH2-PO3H2], the anchoring groups were insulated from the bipyridine ligand by a CH2 group. In the second pair of molecules, Ru(dcbpyH2)2(NCS)2 (RuN3) and Ru(bpbpyH2)2(NCS)2 (RuN3P), [dcbpy=2,2'-bipyridine-4,4'-biscarboxylic acid, bpbpy=2,2'-bipyridine-4,4'-bisphosphonic acid], the anchoring groups were directly connected to the bipyridine ligands. The injection kinetics, as measured by subpicosecond IR absorption spectroscopy, showed that electron injection rates from ReC1P to both TiO2 and SnO2 were faster than those from ReC1A. The injection rates from RuN3 and RuN3P to SnO2 films were similar. On TiO2, the injection kinetics from RuN3 and RuN3P were biphasic: carboxylate group enhances the rate of the <100 fs component, but reduces the rate of the slower components. To provide insight into the effect of the anchoring groups, the electronic structures of Re-bipyridyl-Ti model clusters containing carboxylate and phosphonate anchoring groups and with and without a CH2 spacer were computed using density functional theory. With the CH2 spacer, the phosphonate group led to a stronger electronic coupling between bpy and Ti center than the carboxylate group, which accounted for the faster injection from ReC1P than ReC1A. When the anchoring groups were directly connected to the bpy ligand without the CH2 spacer, such as in RuN3 and RuN3P, their effects were 2-fold: the carboxylate group enhanced the electronic coupling of bpy pi* with TiO2 and lowered the energy of the bpy orbital. How these competing factors led to different effects on TiO2 and SnO2 and on different components of the biphasic injection kinetics were discussed.     

A technical study on the Spraytec performances: influence of multiple light scattering and multi-modal drop-size distribution measurements

The present paper reports an experimental investigation on the performance of the Spraytec, the recent particle sizer commercialized by Malvern Instruments, Malvern, UK. As with the previous Malvern particle sizers, the Spraytec provides a volume-based drop-size distribution from the analysis of a diffraction pattern resulting from the interaction between a spray and a laser beam. This work focuses on the behavior of the Spraytec in two different situations. First, the influence of multiple scattering caused by the measurement of large and spatially inhomogeneous sprays is investigated. Second, a test of multi-modal drop-size distribution measurement is conducted. Contrary to the previous Malvern instrument, Spraytec's mathematical inversion procedure includes a patented multiple-scattering algorithm that allows measurements of very high concentrated sprays. This algorithm is tested here for large and inhomogeneous sprays for which multiple light scattering affects the measurement. The results show that the Spraytec algorithm cannot satisfactorily correct the measurements in this specific situation. It was also observed that the use of this algorithm is prohibited in the absence of multiple light scattering. In the second part of the study, a test of multi-modal drop-size distribution measurement is conducted. For the investigated situations it was found that the Malvern Spraytec is reliable in measuring such spray drop-size distributions.