A needle-water DC microplasma system working at atmospheric pressure in N2/O2 gas mixtures is used to study the fundamental mechanisms of nitrates/nitrites synthesis in highly complex and yet little-known plasma-water...
This experimental study characterized the effect of carrier gas flow on an endoscopic plasma jet. This system generates and transports helium plasma in a tube over several meters, along with a separate channel transporting oxygen to enhance plasma reactivity on site. The resulting plasma plume exiting the tube allows treatment of tissue surfaces in an endoscopic setting with a view to perform therapeutic operations in the gastrointestinal tract. In a closed cavity simulating the tract, the carrier gas flow was studied by a combined approach investigating plasma plume chemistry, fluid dynamics, and plasma effects on the surface of a hydrogel tissue model reporting oxidation. These three aspects are shown to be closely inter-related. Plasma plume length, intensity, and shape strongly depend on helium content, velocity, turbulence, and environment. Optical emission spectroscopy was used to show that the helium gas flow rate increases the amount of helium and reactive oxygen species (ROS) in the plume. Schlieren imaging was used to visualize the transition of the fluid from buoyant to laminar and finally turbulent depending on flow rate, with a backflow in a closed cavity. Finally, the frontal and radial treatment of the cavity was assessed by measuring ROS delivery to a KI-starch agarose gel model. Helium flow rate had a noticeable effect on the treatment distribution profile and treatment intensity, with different maxima for frontal and radial treatments. This combined approach, in an accurate simulation of the target configuration (i.e. a closed, cylindrical cavity), is necessary to optimize treatment, as its outcome depends on a balance between ROS production, transport, and distribution.
In this study, an atmospheric‐pressure filamentary dielectric barrier discharge plasma is produced over a deionized (DI) water surface to study the physicochemical mechanisms of plasma–liquid surface interactions for NOx synthesis. The gas‐phase plasma diagnostics are performed using optical emission spectroscopy, Fourier‐transform infrared spectroscopy, and by recording voltage–current curves, and liquid‐phase species are analyzed using ion chromatography and UV−visible spectrophotometer. The investigations indicate that the reaction pathways for reactive oxygen and nitrogen species (H2O2,
NO
2
‐,
normalN
O
3
−) formation in DI water depend on different experimental conditions. It is observed that the conversion of nitrites into nitrates is significantly influenced by reactive oxygen species. The energy yield for the total amount of NOx synthesized ranges from 1.3 × 10−4 to 3.4 × 10−3 mol/MJ.
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