Gas flow characteristics of a time modulated APPJ: the effect of gas heating on flow dynamics

Abstract

This work investigates the flow dynamics of a radio-frequency (RF) non-equilibrium argon atmospheric pressure plasma jet. The RF power is at a frequency of 50 Hz or 20 kHz. Combined flow pattern visualizations (obtained by shadowgraphy) and gas temperature distributions (obtained by Rayleigh scattering) are used to study the formation of transient vortex structures in initial flow field shortly after the plasma is switched on and off in the case of 50 Hz modulation. The transient vortex structures correlate well with observed temperature differences. Experimental results of the fast modulated (20 kHz) plasma jet that does not induce changes of the gas temperature are also presented. The latter result suggests that momentum transfer by ions does not have dominant effect on the flow pattern close to the tube. It is argued that the increased gas temperature and corresponding gas velocity increase at the tube exit due to the plasma heating increases the admixing of surrounding air and reduces the effective potential core length. With increasing plasma power a reduction of the effective potential core length is observed with a minimum length for 5.6 W after which the length extends again. Possible mechanisms related to viscosity effects and ionic momentum transfer are discussed.

Cold Atmospheric Pressure Plasma VUV Interactions With Surfaces: Effect of Local Gas Environment and Source Design

“…This model was developed assuming laminar flow and without consideration for heating of the flow gas. There has been work on other plasma sources that suggests that plasma heating of the flowing gas could lead to turbulent flow, especially for higher flow rates in conjunction with smaller APPJ tube size . For the kHz ring APPJ we did not observe significant gas heating and the gas velocity is lower than reported thresholds for which turbulence occurs .…”

Electrical and Spectroscopic Diagnostics of Atmospheric Pressure DBD Plasma Jet

“…Another advantage is that the size and position of the sample to be treated is not a factor and the plasma jet can be applied on the sample directly. Several parameters can control the properties (Zhang et al 2015, Ionascut-Nedelcescu et al 2008) of APDJ such as jet geometry, type of dielectric, excitation frequency, type of power source and gas composition including gas flow rate. Due to low gas temperature, APDJs do not cause thermal damage to heatsensitive biological (Stoffels et al 2006) systems such as living tissues and cells.…”

“…These application processes can be enhanced and controlled by better understanding the properties of the produced plasma. Because, the gas flow dynamics are different (Zhang et al 2015) in each type of jet due to jet structure with nozzle geometry, Reynolds number and initial velocity. The objective of this work was to develop and investigate the properties of the produced plasma jet for biological applications.…”

Polymer etching by atmospheric‐pressure plasma jet and surface micro‐discharge sources: Activation energy analysis and etching directionality

“…The APPJ has been characterized to show the flow dynamics, gas temperature, electron density, density of NO, and O . The electrical behavior of the SMD plasma source as well as the types of reactive species that it produces has also been characterized …”