Non-equilibrium synergistic effects in atmospheric pressure plasmas

TLDR

Atmospheric‑pressure plasmas exhibit non‑equilibrium behavior driven by complex physical‑chemical processes that are crucial for many plasma‑based applications. This study develops a comprehensive non‑equilibrium model to uncover synergistic effects in atmospheric‑pressure low‑temperature plasmas. The model couples a thermal‑chemical non‑equilibrium fluid description of the quasi‑neutral region with a simplified sheath model, using a free‑burning argon arc as a test system to capture both equilibrium and non‑equilibrium dynamics. The simulations reveal that coupled mass, momentum, and energy transfer interactions govern the self‑consistent non‑equilibrium characteristics, and that spatial variations in the electron‑to‑heavy‑particle temperature ratio critically shape the transition between hot and cold equilibrium zones, offering guidance for predicting and controlling particle‑energy transport in AP‑LTPs.

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.