E.M. van Veldhuizen

The degradation of aqueous phenol solutions by pulsed positive corona discharges

The Advanced Oxidation Process pulsed corona discharges have been utilized for the degradation of phenol in aqueous solution. The pulsed positive corona discharges are struck in the ambient gas phase over the solution. Experiments have been performed using both an air and argon atmosphere. Phenol conversion and the production of major oxidation products in the solution have been determined, using ion-exclusion chromatography with UV absorbance and conductivity detectors in series. The corona pulse energy has been measured from voltage and current waveforms using capacitive current correction. Oxidation products are polyhydroxybenzenes and carboxylic acids. Even though phenol conversion efficiencies by pulsed positive corona discharges in air and argon are similar, the degradation pathways are different.

On the formation mechanisms of the diffuse atmospheric pressure dielectric barrier discharge in CVD processes of thin silica-like films

Pathways of formation and temporal evolution of the diffuse dielectric barrier discharge at atmospheric pressure were experimentally studied in this work by means of optical (fast imaging camera) and electrical diagnostics. The chosen model system is relevant for applications of plasma-enhanced chemical vapor deposition of thin silica-like film on the polymeric substrate, from cost-efficient gas mixtures of Ar/N2/O2/hexamethyldisiloxane. It was found that the discharge can gradually experience the phases of homogeneous low current Townsend-like mode, local Townsend to glow transition and expanding high current density (?0.7Acm?2) glow-like mode. While the glow-like current spot occupies momentarily only a small part of the electrode area, its expanding behavior provides uniform treatment of the whole substrate surface. Alternatively, it was observed that a visually uniform discharge can be formed by the numerous microdischarges overlapping over the large electrode area.

The Role of Metastables in the Formation of an Argon Discharge in a Two-Pin Geometry

The breakdown process in gases is a versatile research topic. Numerous processes play more or less important roles in discharge formation, strongly depending on the gas mixture, the electrode configuration, the applied electric field, the size of the geometry, and even on the structures surrounding the active volume where the breakdown takes place. We focus our research on the breakdown process in argon at 700 mbar, in a pin-pin (point-to-point) electrode geometry, with increasing positive voltage at the active electrode. The voltage rises by 100 V/ns. We use a 2-D fluid model to examine the formation of a charged channel between the electrodes under given conditions. We find that the results describe previous experiments reasonably well. We also explore the role of excited argon atoms at (4s) metastable levels in the breakdown process, and we conclude that the ionization path with an intermediate step containing the metastables does indeed make a notable difference in the breakdown process.

Induced liquid phase flow by RF Ar cold atmospheric pressure plasma jet

The plasma of an atmospheric pressure plasma jet strongly interferes with a liquid when it just touches the liquid surface. The gas flow of the jet exerts a force on the liquid surface pushing it downward, while the plasma exerts a force that is partly counteracting the gas flow induced force. The downward force in the center of the liquid recipient causes the liquid to circulate with a circulation time of ~2 s. Due to this circulation the color change of a dye proceeds homogeneously.

Development of positive streamers in air

Summary form only given. The rough development of streamers has been studied by many and is reported well in literature. Here we will show the development of a point-plane streamer in artificial air (a mixture of 20% pure oxygen in pure nitrogen) in much better detail. This is done in a 16 cm point plane gap at pressures between 100 and 200 mbar. Positive high voltage pulses with amplitudes of 20 to 40 kV, rise times of 10 to 30 ns and 0.5 to 4 Hz repetition frequency are applied to the pointed tip. We have studied these discharges with an ICCD camera of which the gate timing with respect to the voltage pulse was varied between discharges. This was done in such a way that the gate closing was spread over the full time-domain between the start of the voltage pulse and the moment that the first streamers crossed the gap. By doing this for hundreds of images, a complete set of pictures of the streamer development as function of time was made. From each of these pictures the longest streamer channel (measured from the tip) was selected and measured by an automated computer script. This results in a streak-camera-like graph of the streamer length as function of time, similar to figure 4 in Clevis et al., albeit with a huge increase in accuracy and number of discharges (as well as a change from pure nitrogen to artificial air). Compared to a streak camera, our method has the advantage that also streamers outside the symmetry axis are taken into account. With this method we have studied the development of discharges for a variety of conditions. The early stages of the discharge are dominated by the formation of a so-called inception cloud. At higher pressure or lower voltages this inception cloud stagnates and in most cases breaks up into separate streamer channels. One of the observations we can make is that the speed of formation of the inception cloud scales with the pulse risetime, but that at a faster voltage-rise, the cloud breaks up later. Furthermore, the size of the inception cloud is very close to its theoretical maximum predicted by the applied voltage and the breakdown field.

Waste Water Cleanup by Aerosol Pulsed Corona Reactor

Summary form only given. This paper presents a study of waste water treatment by multielectrode corona reactor. A mixture of gas and polluted water aerosol flows through the 1.2-m length reactor. The flow rate is 200 l/h. A nanosecond solid state power supply (45 kV, 60 ns, up to 1 kHz) was used as a driver for the corona discharge. The cleaning experiments had carried out with a simulant and industrial waste water. Authors have investigated a simulant PEG300 to demonstrate the corona reactor in cracking of long chain organic molecules into smaller ones. As a result of the simulant treatment the ratio between the biological oxygen demand (BOD) to the chemical oxygen demand (COD) increased from below 0.01 to almost 0.5. The reactor has been used also for a treatment of a brewery effluent. The following conclusions were made: i. Treatment in the aerosol reactor removes up to 50% of the recalcitrant COD in the effluent; ii. Ammonia nitrogen is oxidized to nitrate nitrogen during treatment in the reactor; iii. The effect on phosphates is limited. Tests with concentrated waste water of a packaging recycling company have demonstrated the improvement of biodegradability. These tests showed an increase in COD removal to up to 60%, meaning that after the treatment in the corona aerosol reactor the HOD/COD ratio had increased. Thus, the aerosol corona reactor technology offers good opportunities to treat waste water that are not likely to be treated biologically at the moment.