Characterization of a dielectric barrier discharge operating in an open reactor with flowing helium

A dielectric barrier discharge (DBD) generated by flowing helium between the parallel-plate electrodes of an open air reactor has been characterized using time resolved optical and electrical measurements. A sinusoidal voltage of up to 5 kV (peak to peak) of frequencies from 3 to 50 kHz has been applied to the discharge electrodes. The helium flow rate is varied up to 10 litre min(-1). The adjustment of flow rate allows the creation of uniform DBDs with optimized input power equal to 120 +/- 10 mW cm(-3). At flow rates from 4 to 6 litre min(-1) a uniform DBD is obtained. The maxima in the line intensities of N-2(+) and helium at 391.4 nm and 706.5 nm, respectively, 2 under those conditions indicate the importance of helium metastables and He-2(+) in sustaining such a discharge. The power efficiency and discharge 2 current show maxima when the DBD In He/air is uniform. The gas temperature during the discharge has been measured as 360 +/- 20 K.

Time dependence of rotational state populations of excited hydrogen molecules in an RF excited plasma reactor

We report on time-dependent population distributions of excited rotational states of hydrogen in a capacitively coupled RF discharge. The common model to obtain the gas temperature from the rotational distribution is not applicable at all times during the discharge cycle due to the time dependence of the EEDF. The apparent temperature within a cycle assumes values between 350 K and 450 K for the discharge parameters of this experiment. We discuss the optimum time window within the discharge cycle that yields the best approximation to the actual temperature. Erroneous results can be obtained, in principle, with time-integrated measurements; we find, however, that in the present case the systematic error amounts to only approximately 20 K. This is due to the fact that the dominant contribution to the average intensity arises during that time window for which the assumptions underlying the analysis are best fulfilled. A similar analysis can be performed for N+2 rotational bands with a small amount of nitrogen added to the discharge gas. These populations do not exhibit the time variations found in the case of H2.

Is the flow tube reactor with NO2 titration a reliable absolute source for atomic hydrogen?

The H+NO2 titration scheme for the determination of atomic hydrogen densities within a microwave excited flow tube reactor has been investigated by laser-induced fluorescence spectroscopy in the vacuum UV. Absolute hydrogen densities are determined on the basis of calibration by Rayleigh scattering from argon. The measurement is performed at a gas mixture containing 0.5% of D2 added to the main gas H2. The ground state density of the hydrogen atoms generated in the flow tube reactor was inferred from the fluorescence radiation of the spectrally shifted optically thin D-Lyman-a transition.

Development of a slurry continuous flow reactor for photocatalytic treatment of industrial waste water

The water treatment capability of a novel photocatalytic slurry reactor was investigated using methylene blue (MB) as a model pollutant in an aqueous suspension. A pellet TiO ₂ catalyst was employed and this freed the system from the need of filtration of catalyst following photocatalysis. This configuration combines the high surface area contact of catalyst with pollutant of the slurry reactor and also offers a high illumination of catalyst by its unique array of weir-like baffles. In this work, the batch adsorption of MB from aqueous solution (10μM) onto the TiO ₂ catalyst was studied, adsorption isotherms and kinetics were determined from the experimental data. Complete degradation of MB was achieved within 60 min illumination with various loadings of catalyst (30-200 g L ^-1). A modest catalyst loading (30 g L ^-1) achieved 98% degradation within 60 min of irradiation. Experimental results indicate that this novel reactor configuration has a high effective mass transfer rate and UV light penetration characteristics. 

Novel photocatalytic reactor development for removal of hydrocarbons from water

Hydrocarbons contamination of the marine environment generated by the offshore oil and gas industry is generated from a number of sources including oil contaminated drill cuttings and produced waters. The removal of hydrocarbons from both these sources is one of the most significant challenges facing this sector as it moves towards zero emissions. The application of a number of techniques which have been used to successfully destroy hydrocarbons in produced water and waste water effluents has previously been reported. This paper reports the application of semiconductor photocatalysis as a final polishing step for the removal of hydrocarbons from two waste effluent sources. Two reactor concepts were considered: a simple flat plate immobilised film unit, and a new rotating drum photocatalytic reactor. Both units proved to be effective in removing residual hydrocarbons from the effluent with the drum reactor reducing the hydrocarbon content by 90% under 10 minutes. 

Use of a rotating disc reactor to investigate the heterogeneously catalysed oxidation of cinnamyl alcohol in toluene and ionic liquids

To evaluate the effect of mass transfer limitations in the three-phase oxidation of cinnamyl alcohol carried out in toluene and an ionic liquid (1-butyl-3-methyl-imidazolium bis(trifluoromethylsulphonyl)imide), studies have been performed in a rotating disc reactor and compared with those carried out in a stirred tank reactor where mass transfer effects are considered negligible. High catalyst efficiencies are found in the stirred tank reactor with the use of both ionic liquid and toluene, although there is a decrease in rate for the ionic liquid reactions. In contrast, internal pore diffusion limits the reaction in both solvents in the rotating disc reactor. This mass transfer resistance reduces the problem of overoxidation of the metal surface when the reaction is carried out in toluene, leading to significantly higher rates of reaction than expected, although at the cost of decreased selectivity.

Thin-zone TAP reactor as a basis of �state-by-state transient screening

Thin-zone TAP reactor is presented as a basis of the new state-by-state transient screening approach which has been proposed by the authors for non-steady-state kinetic characterization of industrial catalysts. The general thin-zone TAP reactor model is described, and its mathematical status is justified analytically. It is shown that this model provides high enough accuracy to be applicable in the wide conversion interval (up to 90%), which is an important advantage of this approach compared with the traditional differential reactor.

Computational challenges in atomic, molecular and optical physics

Six challenges are discussed. These are the laser-driven helium atom; the laser-driven hydrogen molecule and hydrogen molecular ion: electron scattering (with ionization) from one-electron atoms; the vibrational and rotational structure of molecules such as H-3(+) and water at their dissociation limits; laser- heated clusters; and quantum degeneracy and Bose-Einstein condensation. The first four concern fundamental few-body systems where use of high-performance computing (HPC) is currently making possible accurate modelling from first principles. This leads to reliable predictions and support for laboratory experiment as well as true understanding of the dynamics. Important aspects of these challenges addressable only via a terascale facility are set out. Such a facility makes the last two challenges in the above list meaningfully accessible for the first time, and the scientific interest together with the prospective role for HPC in these is emphasized.

Frequency coupling in dual frequency capacitively coupled radio-frequency plasmas

An industrial, confined, dual frequency, capacitively coupled, radio-frequency plasma etch reactor Exelan®, Lam Research has been modified for spatially resolved optical measurements. Space and phase resolved optical emission spectroscopy yields insight into the dynamics of the discharge. A strong coupling of the two frequencies is observed in the emission profiles. Consequently, the ionization dynamics, probed through excitation, is determined by both frequencies. The control of plasma density by the high frequency is, therefore, also influenced by the low frequency. Hence, separate control of plasma density and ion energy is rather complex.