Multi-physics modeling of non-equilibrium phenomena in inductively coupled plasma discharges: Part II. Multi-temperature approach

TL;DR

This study compares a detailed vibrational-specific state-to-state model with a simplified two-temperature model for nitrogen plasma discharges, showing the latter can accurately replicate key plasma features under non-equilibrium conditions.

Contribution

The paper introduces a validated 2-T model derived from a comprehensive StS model, improving simulation accuracy for nitrogen ICP discharges under NLTE conditions.

Findings

The 2-T model shows excellent agreement with the StS model in plasma core predictions.

The vibrational-translational energy transfer term critically influences plasma morphology.

The quasi-steady-state assumption is validated for the plasma core region.

Abstract

This paper provides a comparison between the vibrational-specific state-to-state (StS) model for nitrogen plasma elaborated in Part I of this work and conventional two-temperature (2-T) models for simulating inductively coupled plasma (ICP) discharges under non-Local Thermodynamic Equilibrium (NLTE) conditions. Simulations are performed within the multi-physics computational framework established for ICP in Part I. Based on the findings of Part I, the quasi-steady-state (QSS) assumption is validated in the plasma core, thereby enabling the calculation of global rate coefficients under this assumption. This facilitates the reduction of the StS model to a "consistent" macroscopic 2-T model. Results from the StS model for nitrogen ICP torch exhibit considerable discrepancies when compared against predictions from the widely utilized Park 2-T model. On the contrary, the comparison between the newly proposed 2-T model, consistently derived from the original vibronic StS model, and the full StS results demonstrate excellent agreement in terms of plasma core location, morphology, and peak temperature distributions. This demonstrates the ability of the proposed 2-T model to capture the energy transfer and reactive processes predicted by the comprehensive StS model. Additionally, the study identifies the vibrational-translational (VT) energy transfer term in the 2-T model as the predominant factor in dictating plasma core morphology. This suggests a strong sensitivity of the ICP flow field to heavy-impact vibrational excitations and dissociative events.