Abstract
Non-equilibrium is one of the important features of an atmospheric gas discharge plasma. It involves complicated physical-chemical processes and plays a key role in various actual plasma processing. In this report, a novel complete non-equilibrium model is developed to reveal the non-equilibrium synergistic effects for the atmospheric-pressure low-temperature plasmas (AP-LTPs). It combines a thermal-chemical non-equilibrium fluid model for the quasi-neutral plasma region and a simplified sheath model for the electrode sheath region. The free-burning argon arc is selected as a model system because both the electrical-thermal-chemical equilibrium and non-equilibrium regions are involved simultaneously in this arc plasma system. The modeling results indicate for the first time that it is the strong and synergistic interactions among the mass, momentum and energy transfer processes that determine the self-consistent non-equilibrium characteristics of the AP-LTPs. An energy transfer process related to the non-uniform spatial distributions of the electron-to-heavy-particle temperature ratio has also been discovered for the first time. It has a significant influence for self-consistently predicting the transition region between the “hot” and “cold” equilibrium regions of an AP-LTP system. The modeling results would provide an instructive guidance for predicting and possibly controlling the non-equilibrium particle-energy transportation process in various AP-LTPs in future.
Highlights
Non-equilibrium is one of the important features of an atmospheric gas discharge plasma
The non-equilibrium of the atmospheric-pressure low-temperature plasmas (AP-LTPs) is of great importance because we can re-distribute the input energy to other types of energies at various freedoms for their wide applications, e.g., kinetic energy in plasma flow control[5], electronically and vibrationally excited energies in plasma assisted combustion[6], energies stored in various reactive species with optimized non-chemical equilibrium spatial distributions in plasma-aided synthesis of nano-scale materials[7,8,9,10,11,12], etc
It is so difficult to describe, explain, and use such non-equilibria in the AP-LTPs since three types of non-equilibria usually appear in the same discharge
Summary
Non-equilibrium is one of the important features of an atmospheric gas discharge plasma. The modeling results indicate for the first time that it is the strong and synergistic interactions among the mass, momentum and energy transfer processes that determine the self-consistent non-equilibrium characteristics of the AP-LTPs. An energy transfer process related to the non-uniform spatial distributions of the electron-to-heavy-particle temperature ratio has been discovered for the first time. Except for the NEQ effect in plasma sheath[13,14,15], the NLCE process plays an important role among these three types of non-equilibria for various types of AP-LTPs with wide applications such as plasma biomedicine, advanced materials processing, plasma-assisted ignition or combustion, environmental protection, etc.[1,2,16,17] This is because the chemical reactions determine the spatial distributions of the species number densities and the corresponding energy transfer processes significantly. This, to some extent, indicates a mutual influence between the electron and heavy-particle subsystems
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