Speakers
Description
3D model of a reverse-vortex flow gliding arc plasmatron
G. Trenchev, St. Kolev, A. Bogaerts
PLASMANT research group, Department of Chemistry, University of Antwerp, Universiteitsplein 1, Wilrijk, Belgium Faculty of Physics, Sofia University, 5 James Bourchier blvd, 1164 Sofia, Bulgaria
georgi.trenchev@uantwerpen.be
This study employs a comprehensive computational model for a 3D gliding arc plasma in COMSOL. The plasma arc is stabilized in the reverse-vortex gas flow of a gliding arc plasmatron. The modelling gas is argon, with a reduced reaction set. The gas flow is modeled with a RANS turbulent model. The model covers different flow rates and cathode currents. Results for the arc plasma density and gas temperature are presented. The model is based on a gliding arc plasma reactor envisaged for CO2 conversion.
Gliding arc (GA) plasma reactors are well-known atmospheric plasma sources [1, 2, 3]. They are realiable, and in general, simple to build and maintain. When used for gas conversion applications, they face an importantissue – a significant amount of gas passes outside the discharge zone, which decreases the overall efficiency. A new method of solving these common GA problems, is to stabilize the gliding arc in the center of a reverse-vortex flow. A vortex flow is produced when the gas enters a cylindrical tube through a tangential inlet. If the outlet is on the opposite side with respect to the inlet, a forward vortex is produced. If it is on the same side, a secondary reverse-vortex will result (fig. 1). The reactor geometry used in our model is illustrated in figure 2.
Fig. 1: Schematical comparison between forward (a) and reverse (b) vortex flows. [1] Fig. 2: Geometry used in the model, with a radius of 6.35 mm.
The gas flow is computed as a stationary solution with the RANS k-ε turbulent model. Flow rates between 20 and 40 L/min are considered and the gas pressure is atmospheric.
Fig. 3: Gas flow streamlines. Fig. 4: Gas velocity magnitude (top view). [m/s]
Fig. 3: Gas flow streamlines. Fig. 4: Gas velocity magnitude (top view). [m/s]
In figure 3, the gas flow streamlines are presented, and the formation of the reverse-vortex in the reactor centre can be seen. The velocity magnitude of the flow (fig. 4) ranges from 50 to 100 m/s, depending on the flow rate. The model uses a fluid plasma description within a quasi-neutral approximation, as a full fluid plasma model requires very intensive computations 3, especially in 3D. The electron impact reaction set is also significantly reduced compared to the set presented in 3, in order to lower the computation time even further. Only 3 different species are considered in the model – electrons, Ar ions and excited atoms. The average electron energy is also computed. Figure 5 shows the electrical circuit of the reactor.
Fig. 5: Electrical circuit of the reactor. A voltage of 1000V is applied between the cathode and the anode, and the current is limited by a ballast resitor. The capacitor forms a filtering circuit.
Fig. 5: Electrical circuit of the reactor. A voltage of 1000V is applied between the cathode and the anode, and the current is limited by a ballast resitor. The capacitor forms a filtering circuit.
In figures 6 and 7, the resulting arc is represented by semi-transparent isosurfaces. The arc glides in the reactor until it stabilizes in the centre, spinning around its own vertical axis.
Fig. 6: Plasma arc at initial stage (100 µs). Fig. 7: Plasma arc at a later stage (1.1 ms).
Fig. 6: Plasma arc at initial stage (100 µs). Fig. 7: Plasma arc at a later stage (1.1 ms).
In figures 8 and 9, the resulting plasma density and gas temperature in the arc are presented, at a late stage of the arc development, when it is attached to the outer edge of the outlet (1.5 ms).
![Fig. 8: Plasma density at 1.5 ms [1/m3] Fig. 9: Gas temperature at 1.5 ms[K]]5
Fig. 8: Plasma density at 1.5 ms [1/m3] Fig. 9: Gas temperature at 1.5 ms[K]
The plasma density is within the typical range for low-temperature gliding arcs at atmospheric pressure [1, 2]. The gas temperature is also typical for a low-temperature plasma source 1. As the gas flow in the reactor takes places from the walls to the centre (see fig. 3), the arc is thermally insulated from the walls, which improves the reactor efficiency.
References 1 A. Fridman, Plasma Chemistry, p. 187-207, Cambridge University Press, New York, US, 2008 2 A. El-Zein, G. El-Aragi, M. Talaat, A. El-Amawy, Discharge characteristics of gliding arc plasma reactor with argon/nitrogen, Journal of Advances in Physics, 7(1), 1316-1323, 2015 3 St. Kolev, A. Bogaerts, A 2D model for a gliding arc discharge, Plasma Sources Sci. Technol., 24, 015025, 2015
