Calculation of Vibrational Relaxation Times Using a Kinetic Theory Approach

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Computational Fluid Dynamics (CFD)

Background:

• Accurate calculation of vibrational relaxation times is crucial for modeling high-temperature gas dynamics and combustion processes.
• Existing methods include experimental measurements, quasi-classical trajectory (QCT) calculations, and empirical models, each with limitations.
• Vibrational-translational (VT) relaxation times for key atmospheric molecules like nitrogen (N₂), oxygen (O₂), and nitric oxide (NO) are essential for atmospheric and aerospace applications.

Purpose of the Study:

• To develop and validate a computational method for determining vibrational relaxation times of N₂, O₂, and NO in air collisions.
• To compare the proposed method's results with existing experimental data, QCT calculations, and empirical models.
• To provide reliable interaction parameters for use in advanced computational models.

Main Methods:

• Utilized a kinetic theory definition to compute vibrational relaxation times.
• Employed various inelastic cross-section models, adjusting parameters to match experimental and QCT data.
• Calculated relaxation times for N₂, O₂, and NO in collisions with air species over a wide temperature range.

Main Results:

• The proposed kinetic theory-based method demonstrated quantitative and qualitative agreement with available experimental and QCT data.
• Adjusted interaction parameters showed good fitting capabilities across a broad spectrum of temperatures.
• The method's accuracy was validated against established VT relaxation time measurements and theoretical calculations.

Conclusions:

• The developed method provides a reliable approach for calculating vibrational relaxation times in air.
• The obtained interaction parameters are suitable for multitemperature kinetic calculations and developing state-specific models.
• Findings support the advancement of computational fluid dynamics (CFD) and direct simulation Monte Carlo (DSMC) codes for complex flow simulations.