Numerical study on the gas heating mechanism in pulse-modulated radio-frequency glow discharge

Abstract

The gas heating mechanism in the pulse-modulated radio-frequency (rf) discharge at atmospheric pressure was investigated with a one-dimensional two-temperature fluid model. Firstly, the spatiotemporal profiles of the gas temperature (T g ) in both consistent rf discharge and pulse-modulated rf discharge were compared. The results indicated that T g decreases considerably with the pulse-modulated power, and the elastic collision mechanism plays a more important role in the gas heating change. Secondly, the influences of the duty cycle on the discharge parameters, especially on the T g , were studied. It was found that T g decreases almost linearly with the reduction of the duty cycle, and there exists one ideal value of the duty cycle, by which both the T g can be adjusted and the glow mode can be sustained. Thirdly, the discharge mode changing from α to γ mode in the pulse-modulated rf discharge was investigated, the spatial distributions of T g in the two modes show different features and the ion Joule heating is more important during the mode transition.

Gas Heating Mechanisms in Atmospheric Pressure Helium Dielectric-Barrier Discharges Driven by a kHz Power Source

“…Figure 10 shows that around 90% of the cyclic average power consumption P CA−PFM goes to gas heating through elastic collision, ion Joule heating, and exothermic reactions considered. It is observed that elastic collision and ion Joule heating are the dominant heating mechanisms contributing 23.9% and 65.8% of the power consumption, respectively, to the heating source, which is different from the simulated results obtained in [21,22] for helium discharges excited by the radio-frequency power sources showing that elastic collision is the dominant heating source. Although a few exothermic reactions release a large amount of energy in each reaction, the exothermic reactions considered contribute only a minor amount of energy to the heating source due to the low reaction rates.…”

“…The collisions of electrons and helium atoms contribute to more than 99.9% of the heating source of elastic collision while the collisions of electrons and N 2 molecules contribute to less than 0.1% of the heating source of elastic collision since the concentration of helium atoms is much higher than that of the N 2 molecules. frequency results in a remarkable contribution to the heating source as reported by other groups [9,21,22] in atmospheric pressure helium discharges. The collisions of electrons and helium atoms contribute to more than 99.9% of the heating source of elastic collision while the collisions of electrons and N2 molecules contribute to less than 0.1% of the heating source of elastic collision since the concentration of helium atoms is much higher than that of the N2 molecules.…”

“…Figure 11 shows the contributions of elastic collisions among electrons and different background neutral gases. Although the energy exchange of each elastic collision process between an electron and a background molecule is inefficient due to large mass difference, the high collision frequency results in a remarkable contribution to the heating source as reported by other groups [9,21,22] in atmospheric pressure helium discharges. The collisions of electrons and helium atoms contribute to more than 99.9% of the heating source of elastic collision while the collisions of electrons and N 2 molecules contribute to less than 0.1% of the heating source of elastic collision since the concentration of helium atoms is much higher than that of the N 2 molecules.…”

“…The mechanisms of gas heating in atmospheric pressure helium discharges have been studied for years [9,[19][20][21][22]. The gas heating effects of atmospheric pressure helium microplasmas sustained by the dc power sources were investigated with either the 1D or 2D PFM in conjunction with the 2D gas flow model (GFM) considering ion Joule heating as the heating source for modeling the gas temperature in the discharge [9,19].…”

“…It was reported that the gas temperature plays a significant role in the discharge mode. Recently, the gas heating effects of atmospheric pressure helium discharges driven by radio-frequency power sources were studied by solving the 1D PFM with the energy equation of the background gas considering elastic collision, ion Joule heating, and exothermic reactions as heating mechanisms for obtaining the gas temperature distribution in the discharge [21,22]. It was shown that elastic collision is the dominant heating mechanism in the bulk region while the ion Joule heating and exothermic reactions are dominant in the sheath region.…”