Kinetics and reactive stripping modelling of hydrogen isotopic exchange of deuterated waters

This work presents results of experimental kinetics and modelling of the isotopic exchange between hydrogen and water in a reactive stripping column for water dedeuteriation. The missing physical properties of deuterium and tritium isotopologues in hydrogen gas and water forms were predicted and validated using existing literature data. The kinetic model relevant to a styrene-divinyl-benzene co-polymer–supported platinum catalyst was used for modelling, by Aspen plus modular package, impact of design parameters including temperature, total pressure, gas to liquid flowrate ratio, pressure drop and flow mixing, on the separation of deuterium and further the separation of tritium. The modelling by the rate-based non-equilibrium, including design correlations of model of mass and heat transfers, chemical kinetic constants, mass transfer coefficients and overall exchange rate constants, allowed access to separation trends in a good agreement with published data. The synergy between the rates of chemical isotopic exchange and gas/liquid mass transfer, and by inference the performance of reactive stripping, was particularly sensitive to high temperatures, low hydrogen flow rates, pressure drops and internals properties. Extension to tritium confirmed a slightly slower mass transport compared with deuterium leading to potentially under-estimated design features for detritiation processing when deuterium is used instead

The characterisation of the role of BRCA1 notch signalling and differentiation of breast cells

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Screening wall effects of a thin fluidized bed by near-infrared imaging

Near-infrared (NIR) imaging was used to observe water vapour flow in a gas-solid fluidized bed reactor. The technique consisted of a broadband light, an optical filter with a bandwidth centred on strong water vapour absorptions, a Vidicon NIR camera, a nozzle from which an optically active mixture of gas and water vapour was trans-illuminated by an NIR beam and collected data of transmittance were normalized to actual optical path. The procedure was applied to a thin fluidized bed reactor with a low aspect ratio of tube to particle diameters (D-1/d(p)) in order to validate the wall effect on flow dynamics and mass transfer during the reduction of ceria-silica by hydrogen. High concentrations of water vapour emerged in the vicinity of the wall when the bed was operated at pseudo-static conditions but disappeared when the bed was run at minimum bubbling conditions. This result shows the capability of optical methods with affordable costs to 2D imaging opaque packed bed by using a spatially resolved probe located at the exit, which is of great benefit for in situ visualization of anisotropic concentrations in packed beds under industrially relevant conditions and thus for elucidation of the underlying reaction mechanism and diffusion interactions. Crown Copyright (c) 2011 Published by Elsevier B.V. All rights reserved

Flow visualization in gas-solid packed beds by spatially resolved near-infrared imaging

Conventional 'single point' spectroscopic techniques have been very convenient in helping to understand underlying phenomena in gas-solid processes, leading to concepts that rely on pseudo-homogeneous descriptions. These concepts, however, are either not sufficiently valid at different spatial scales, or mature enough to be able to describe local events since they use averaged profiles of concentration, temperature and packing structure. Nevertheless, spatially-resolved optical techniques are increasingly cited due to developments in tunable lasers, 2D array detectors and communication technology. Optical techniques allow experiments to be performed nonintrusively at high spatiotemporal resolution. The present review presents two experimental procedures based on spatially-resolved near-infrared (NIR) imaging, in order to observe temperature and concentration maps in gas-solid packed beds subjected to effects of the entrance aspect ratio and non isothermal conditions. The first technique was applied to a gas-solid fluidized bed reactor with a low aspect ratio of tube to particle diameters (Dt/dp). The technique used NIR broadband light, interference optical filters centred on absorbing and non-absorbing wavelengths of water vapour, a Vidicon NIR camera and simple back-projection of collected images. The second technique was applied to water vapour flow in a packed bed filled with a hydrophobic resin, using a tunable diode laser, focal planar array detector and tomographic reconstruction procedure. By "looking into" a thin fluidized bed, the proposed technique allowed existing models of fixed bed reactors to be extended to pseudo-static bed operations. The technique was applied to ceria-silica reduction in a fluidized bed reactor, where radial profiles of water concentration allowed the distinction between surface and bulk reduction regimes of ceria-silica packing. The tomography technique however, which observes 3D spatially resolved imaging of temperature and water vapour concentration in packed beds, revealed cold and hot spots, concentration maps and flow dynamics in the core packed bed and in the vicinity of the wall. In addition, heat uptake from the wall and mass transfer between and inside resin particles were found to be strongly affected by local concentration, temperature and packing structure profiles

Transient distributions of composition and temperature in a gas-solid packed bed reactor by near-infrared tomography

Near-infrared diffuse tomography was used in order to observe dynamic behaviour of flowing gases by measuring the 3D distributions of composition and temperature in a weakly scattering packed bed reactor, subject to wall effects and non-isothermal conditions. The technique was applied to the vapour phase hydrogen isotopic exchange reaction in a hydrophobic packing of low aspect ratio made of platinum on styrene divinyl benzene sulphonate copolymer resin. The results of tomography revealed uneven temperature and composition maps of water and deuterated water vapours in the core-packed bed and in the vicinity of the wall owing to flow maldistribution. The dynamic lag between the near-wall water vapour and deuterated water vapour compositions were observed suggesting that the convective transfer which was significant near the wall at the start, owing to high porosity, was also effective at large conversions. (C) 2012 Elsevier B.V. All rights reserved

Visualization of water vapour flow in a packed bed adsorber by near-infrared diffused transmittance tomography

This work presents a procedure based on spatially-resolved near-infrared imaging, in order to observe temperature and composition maps in gas-solid packed beds subjected to effects of aspect ratio and non-isothermal conditions. The technique was applied to the water vapour flow in a packed bed adsorber of low aspect ratio, filled with silica gel, using a tuneable diode laser, focal planar array detector and tomographic reconstruction. The 2D projected images from parallel scanning permitted data to be retrieved from the packing and above the packing sections of 12.0 x 12.0 x 18.2 mm(3) at a volume-resolution of 0.15 x 0.15 x 0.026 mm(3) and a time-resolution of less than 3 min. The technique revealed uneven temperature and composition maps in the core packed bed and in the vicinity of the wall due to flow maldistribution. In addition, the heat uptake from the packed bed and local cross-mixing were experimentally ascertained by local profiles of the water vapour composition and temperature under various aspect ratios and feed flow rates. The relative deviations in temperature and compositions were 11.1% and 9.3%, respectively. The deviation in composition, which covers the packing and above the packing sections, was slightly higher than the deviation of 8% obtained up-to-date but was limited to the exit of a packed bed adsorber

Gas Flow Visualization in Low Aspect Ratio Packed Beds by Three-Dimensional Modeling and Near-Infrared Tomography

Nonuniform local flow inside randomly porous media of gas–solid packed beds of low aspect ratios ranging from 1.5 to 5 was investigated by three-dimensional modeling and near-infrared tomography. These beds are known to demonstrate heterogeneous mixing and uneven distributions of mass and heat. The effects of the confining wall on flow dynamics were found nonlinear, particularly for aspect ratios lower than 3. High velocities were mainly observed in regions near the wall of aspect ratio value of 1.5 and those of values higher than 3, owing to high local porosities in these zones. Mass dispersion characterized both by experimental near-infrared imaging and by particle tracking showed discrepancies with literature models, particularly for aspect ratios lower than 3. Uncertainties were more significant with the radial dispersion due to bed size limits. Beyond this value, the wall affected more the axial dispersion, confirming the nonlinear impact of the wall on global hydrodynamics