Non-equilibrium radio-frequency driven atmospheric-pressure plasma in He/0.6%O gas mixture has been used to study the reaction mechanism of plasma-generated oxygen atoms in aqueous solutions. The effluent from the plasma source operated with standard and O-labeled O gas was used to treat water in the presence of phenol as a chemical probe. Comparing the mass spectrometry and gas chromatography-mass spectrometry data of the solutions treated with plasma under normal and labeled oxygen provides clear evidence that O originating from the gas phase enters the liquid and reacts directly with phenol, without any intermediate reactions. Additionally, the atmospheric-pressure plasma source demonstrates great potential to be an effective source of O atoms without the requirement for any precursors in the liquid phase.

A novel lignocellulosic biomass pretreatment reactor has been designed and tested to investigate pretreatment efficacy of miscanthus grass. The reactor was designed to optimize the transfer of highly oxidative species produced by dielectric barrier discharge plasma to the liquid phase immediately after generation, by arranging close proximity of the plasma to the gas-liquid interface of microbubbles. The reactor produced a range of reactive oxygen species and reactive nitrogen species, and the rate of production depended on the power source duty cycle and the temperature of the plasma. Ozone and other oxidative species were dispersed efficiently using energy efficient microbubbles produced by fluidic oscillations. A 5% (w/w) miscanthus suspension pretreated for 3 h at 10% duty cycle yielded 0.5% acid soluble lignin release and 26% sugar release post hydrolysis with accelerated pretreatment toward the latter stages of the treatment demonstrating the potential of this approach as an alternative pretreatment method.

The Electro-Hydro-Dynamic (EHD) interaction induced in atmospheric-pressure air by a surface Dielectric Barrier Discharge (DBD) actuator has been experimentally investigated. Plasma Synthetic Jets Actuators (PSJAs) are DBD actuators able to induce an air stream, perpendicular to the actuator surface. These devices can be used in the aerodynamics field to prevent or induce flow separation, modify the laminar to turbulent transition inside the boundary layer, and stabilize or mix air flows. They can also be used to enhance indirect plasma treatment effects, increasing the reactive species delivery rate onto surfaces and liquids. This can play a major role in plasma processing and chemical kinetics modelling, where only diffusive mechanisms are often considered. This paper reports on the importance that different electrode geometries can have on the performance of different PSJAs. A series of DBD aerodynamic actuators designed to produce perpendicular jets have been fabricated on 2-layer printed circuit boards (PCBs). Linear and annular geometries have been considered, testing different upper electrode distances in the linear case and different diameters in the annular one. AC voltage supplied at 11.5 kV peak and 5 kHz frequency has been used. Lower electrodes were connected to ground and buried in epoxy resin to avoid undesired plasma generation on the lower actuator surface.Voltage and current measurements have been carried out to evaluate the active power delivered to the discharges. Schlieren imaging allowed to visualize the induced jets and gave an estimate of their evolution and geometry. Pitot tube measurements were performed to obtain the PSJAs' velocity profiles and to estimate the mechanical power delivered to the fluid.Optimal values of the inter-electrode distance and diameter have been found in order to maximize jet velocity, mechanical power or efficiency. Annular geometries are found to achieve the best performances.

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Atmospheric-pressure surface dielectric barrier discharges (S-DBDs) have been widely investigated in the past two decades for airflow manipulation due to their mechanical simplicity, electrical control capability and low power consumption [1]. In these devices, momentum transfer from charged to neutral particles results in an electrohydrodynamic (EHD) body force, a phenomenon also known as ionic wind. In its simplest implementation, the ionic wind imparts momentum to the background gas in the direction parallel to the dielectric surface [1,2]. Electrical and geometrical variations, however, can also produce fluxes in other directions [3,4].In addition to flow control applications, S-DBDs have gained renewed interest in recent years for their potential use in emerging biomedical, environmental and agricultural applications, such as hand cleaning [5], preparation of plasmaactivated water [6], ozone generation [7], seed treatment [8] and food preservation [9]. The plasma treatment in these systems is typically indirect and transport from the surface discharge to the sample being treated is normally assumed to be dominated by diffusion [6,10].Although all S-DBDs have the same underlying topology, namely two electrodes separated by a dielectric barrier, a number of different electrode designs, such as square [8], hexagonal [6], circular [11] and spiral [12] have been proposed in recent years. To date, however, limited attention has been paid to the influence of the electrode geometry on the efficacy of these S-DBDs, and here we report experimental results that demonstrate that the electrode pattern of the S-DBD can be