Le cyclone réacteur IV: Mesure de l'efficacité des transferts de chaleur entre les parois et les phases gazeuse et solide

The purpose of the present paper is the experimental study of different mechanisms of heat transfer for both gas and the solid phases inside a cyclone reactor. The measurements are based on the study of the outlet temperature of the gas and of the particles as a function of the inlet Reynolds number (385–11 000), of the wall temperature (630–1150 K), of the nature of the carrier gas (air, argon, CO₂, (helium) and of the particles (sand, bronze), and of the particle size (radius of particles from 0.1 to 0.5 × 10⁻³ m). It is shown that the particles are heated mainly during their contact with the heated wall and that the efficiency of the wall-particle and wall-carrier gas transfers decrease when the solid flow rate increases. Simple scale-up relationships are proposed to represent the extent of these two mechanisms as a function of operating conditions.     

Elastic properties of materials by pulsed neutron powder diffraction

We describe the use of pulsed neutron powder diffraction to measure the mean-square thermal displacements of atoms in polycrystalline materials at various temperatures. Data for aluminum, Pu_0.95Al_0.05, Ce_0.90Th_0.10, titanium, hafnium and CeRh₃B₂ are presented. A simple Debye model accounts for the observations, and a Debye temperature Θ_DW can be extracted from the data. Θ_DW is atom-specific and anisotropic, and is related to the elastic constants of the material. This technique provides a means of obtaining information on the elastic behavior of materials for which the traditional methods are not applicable.     

Local environment and dynamic characteristics of the 119Sn(II) and 119Sn(IV) Mössbauer probes on the surface of Cr2O3 exposed to hydrogen sulfide atmosphere

Tin dopant located on the surface of Cr₂O₃ crystallites interacts easily, at room temperature, with adsorbed H₂S molecules. Contrary to the initial oxygen-surrounded tin species, the resulting Sn(II) and Sn(IV) sulfur-surrounded entities exhibit no spin polarization, at least down to 4.6 K, which shows that they are more distant from the magnetically ordered oxide substrate. Additionally, their thermal vibration amplitudes are greater than in oxygen-surrounding, which denotes a weaker bonding of the tin within the H₂S adsorbed layer. Moreover, for Sn(II), sufficiently large quadrupole splitting allows the Goldanski-Karyagin effect to be seen. Thermal vibration amplitudes of Sn(II) are then found to be greater in the plane of the three neighbouring sulfur atoms than in the perpendicular direction.     

Low-temperature deposition and crystallization of RuO2/TiO2 on cotton fabric for efficient solar photocatalytic degradation of o-toluidine

A green low-temperature deposition and crystallization method was developed to uniformly coat RuO₂/TiO₂ nanocomposite onto cotton fabrics for efficient solar photocatalysis. The sequential growth of anatase TiO₂ and rutile RuO₂ on the surface of the cotton was confirmed by XRD, Raman and XPS characterizations. After the deposition of RuO₂, the optical properties of RuO₂/TiO₂/Cotton revealed better visible light absorption and higher charge mobility, and XPS spectra showed that the peaks of Ti 2p_3/2 and O 1 s shifted towards the lower binding energies due to the interfacial charge transfer at the robust RuO₂/TiO₂ mediated with Ti–O–Ru bonding. The photocatalytic performances of the RuO₂/TiO₂/Cotton were evaluated towards the photodegradation of o-toluidine (o-TD), an aromatic amine widely used in the chemical industry. Compared with TiO₂/Cotton, RuO₂/TiO₂/Cotton exhibited a remarkable improvement in the photocatalytic activity. The presence of RuO₂ on the surface of TiO₂/Cotton narrowed the band gap and improved the absorption of visible light. Moreover, the successful formation of a robust heterogeneous interface between TiO₂ and RuO₂ suppressed the charge carrier (e^–/h⁺) recombination effectively. With the RuO₂/TiO₂ coating chemically bound to the cotton fibers, RuO₂/TiO₂/Cotton delivered long-term stability in photocatalytic activity and high mechanical durability even after 20 washing times. Our facile and scalable synthesis strategy paved a universal route to efficient immobilization of visible-light-responsible TiO₂-based photocatalysts on the low-heat-resistant substrates for various applications.

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An interval-parameter fuzzy two-stage stochastic program for water resources management under uncertainty

This study presents an interval-parameter fuzzy two-stage stochastic programming (IFTSP) method for the planning of water-resources-management systems under uncertainty. The model is derived by incorporating the concepts of interval-parameter and fuzzy programming techniques within a two-stage stochastic optimization framework. The approach has two major advantages in comparison to other optimization techniques. Firstly, the IFTSP method can incorporate pre-defined water policies directly into its optimization process and, secondly, it can readily integrate inherent system uncertainties expressed not only as possibility and probability distributions but also as discrete intervals directly into its solution procedure. The IFTSP process is applied to an earlier case study of regional water resources management and it is demonstrated how the method efficiently produces stable solutions together with different risk levels of violating pre-established allocation criteria. In addition, a variety of decision alternatives are generated under different combinations of water shortage.     

Reduced humic acid nanosheets and its uses as nanofiller

Leonardite is highly oxidized form of lignite coal and contains a number of carboxyl groups around the edges of a graphene-like core. A novel approach has been developed to synthesize graphene oxide-like nanosheets in large scale utilizing leonardite as a starting material. Humic acid extracted from leonardite has been reduced by performing a high pressure catalytic hydrogenation. The reaction was carried out inside a high pressure stirred reactor at 150 °C and 750 psi (~5.2×10⁶ Pa). Morphology of the as-synthesized samples showed porous platy particles and EDAX analysis indicates the carbon and oxygen atomic ratios as 96:4–97:3%. The as-synthesized material has been used as nanofiller in polyurethane. The reduced humic acid–polyurethane nanocomposite showed over 250% increase of Young’s modulus. This new approach provides a low cost and scalable source for graphene oxide-like nanosheets in nanocomposite applications.     

Optical bistability in gold nano-colloid due to thermal lensing effect

In this study, experimental results are concerning “the optical bistability due to thermal lensing effect”, in colloidal solution of gold nanoparticles (Au Nps) which has been studied under CW laser illuminations. Two different CW laser beams (He–Ne and Nd-Yag) were used to interact with a vertical Fabry–Perot interferometer, containing colloid of the Au Nps. Hysteretic loops have been observed with regard to optical bistability and the results were fitted with theoretical curves. The radiated power to the resonator was elevated up to 50 mW for both the laser beams with the same spot size. Also, new method was defined to precise evaluation of the theoretical hysteretic loop which is describing the relation between nonlinear refractive index and the beam intensity inside the resonator. This dependency is due to thermal lensing effect and numerical simulations of this effect were also performed, in order to better understanding of it.     

Optimal decay rate of the two-fluid incompressible Navier–Stokes–Fourier–Poisson system with Ohm’s law

This paper is to investigate the optimal $L^p$ ($p\ge 2$) time decay rate of global solutions to the two-fluid incompressible Navier–Stokes–Fourier–Poisson system with Ohm’s law. The result shows that the time decay rate of this system achieves the same as that of the incompressible Navier–Stokes equation, in other words, the coupling of the self-consistent Poisson equation does not change the decay rate of the incompressible Navier–Stokes equation. This phenomenon is interesting, compared to the compressible Navier–Stokes equation, whose time decay rate decreases when it is coupled with the self-consistent Poisson equation.