In this work a gliding arc plasmatron consisting of a filamentary discharge rotating in a nitrogen vortex flow at low DC current (I = 100 mA) is investigated. The gas flow swirl of the plasmatron is produced by six tangential gas inlets. The Reynolds number of the nitrogen flow through these tubes at the flow rate of Q = 10 slm amounts to about 2400, which is in the intermediate range. Under these conditions, the formation of micro-vortices can be caused by small gas flow disturbances like e.g. a tube edge. The operation of the GA plasmatron at these conditions is accompanied by the production of plasma spots at the anode surface, namely near the gas inlets. Melted and solidified metal is found in erosion traces left by plasma spots at the anode surface. It is established that melting of stainless steel cannot be caused by an axial current of I = 100 mA of plasma spots and an helical current is supposed. This assumption is confirmed by microscope images of eroded traces with toroidal melting areas. These experimental results corroborate a hypothesis of previous studies, concerning the gliding arc physics, about the formation of plasma objects with an axial magnetic field by the interaction of micro-vortices with the plasma channel.
Hydrogen production via plasma methane pyrolysis is investigated using a microwave plasma torch (MPT) and a gliding arc plasmatron (GAP). The performance of the two plasma sources in terms of methane conversion, product spectrum, and energy efficiency is compared. The physical and chemical properties of the produced carbon particles are compared. The methane conversion is higher in the GAP than in the MPT. In the MPT amorphous spherical carbon particles are produced in the volume of the plasma source. In the GAP methane pyrolysis in the volume stops after the production of acetylene. The conversion of acetylene into solid carbon takes place in a heterogeneous reaction on top of the electrode surfaces instead. This leads to a lower hydrogen selectivity, higher acetylene selectivity and more platelet‐like morphology of the produced carbon particles when compared to the MPT.
Numerous studies have shown that dielectric barrier discharge (DBD) and DBD-like plasma jets interact with a treated surface in a complex manner. Eroded traces after treatment cannot be explained by conventional plasma-surface interaction theory. The mechanisms of a controlled formation of these plasma objects is still unclear. In this work, the authors show that the formation rate and characteristics of eroded traces, treating a titanium surface, can be controlled by process design and the combination of materials used. A thin (0.45 µm) layer of titanium film is deposited onto a glass substrate and is then treated in the effluent of a non-equilibrium atmospheric pressure plasma jet (N-APPJ) operated with argon or krypton flow. Plasma spots with diameters ranging from 100-700 µm are observed using an intensified digital camera on the titanium film surface. These plasma objects are strongly inhomogeneous, forming a core with a very high current density and leave erosion holes with diameters of about 1 µm. By using krypton as a working gas, effective erosion of the titanium substrate can be shown, whereas by using argon no traces are detected. For the latter case, traces can be provoked by deposition of a thin aluminum layer on top of the titanium substrate, by creation of artificial scratches or by an additional swirling flow around the discharge. Based on the experimental results presented in this and previous papers, it is assumed that plasma spots with dense cores are produced by an interaction of micro-vortices within the plasma channel and by the formation of an extremely high axial magnetic field. This assumption is confirmed by destruction of the treated surface material, extraction of paramagnetic atoms and toroidal substrate heating, which is most likely caused by a helical current of the plasma spot.
Recently, the direct conversion of methane into hydrogen using cold plasma reactors has attracted increasing attention, since hydrogen has considerable potential as a future feedstock in the steel and chemical industries. However, the simulation of plasma pyrolysis reactors is extremely complex due to the vast temporal and spatial ranges of the variables involved and steep gradients. Previously, methane pyrolysis has been meticulously modeled by 0D simulations, and 3D plasma modeling has been largely confined to Argon systems. In this paper, a systematic methodology is presented, which provides an expedient and efficient hierarchy of 0D to 3D simulations, in order to approximate the methane pyrolysis simulation of a plasma reactor in its entirety. Various simulation tools are applied in a coordinated and pragmatic manner. The results show that the proposed synergy allows simplification of the reaction set and arc characteristics, significantly reducing the runtime required for the simulations.
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