The gas temperature is a key parameter that affects the process of microwave plasma chemistry in industrial applications. Based on the molecular emission spectrometry of the $A^2{\mathit{\Sigma }}^{+}\to X^2{\mathit{\Pi }}_{\mathrm{r}}$ electronic system of OH radicals, the gas temperature of the atmospheric air microwave plasma core at different absorbed microwave power levels, gas flow rates, gas humidities, and volume fractions of CO₂ in air was analyzed. In the experiment, the absorbed microwave power, gas flow rate, gas humidity, and volume ratio of CO₂ in air was varied from 560 to 1750 W, 10 to 24 l min⁻¹, 30% to 95%, and 0% to 40%, respectively. Moreover, the axial gas temperature distribution of the plasma torch was measured. The experimental results showed that (i) the plasma gas temperature mainly ranged from 4000 to 7000 K, (ii) the plasma gas temperature rose with increasing absorbed microwave power but was hardly affected by the feeding gas flow rate, (iii) the plasma gas temperature decreased by ∼400 K for every 20% increase in the fraction of CO₂ in air and decreased with increasing gas humidity, and (iv) the plasma torch gas temperature decreased along the axial direction. Due to the lack of a prevailing microwave discharge theory, an in-depth analysis of the mechanisms of gas temperature variation was performed based on the heat balance equation.

中文翻译：

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大气微波等离子炬气体温度变化机理

气体温度是影响工业应用中微波等离子体化学过程的关键参数。基于分子发射光谱的${\mathrm{一种}}^2{\mathit{\Sigma }}^{+}\to X^2{\mathit{\Pi }}_{\mathrm{r}}$利用OH自由基电子系统，分析了不同吸收微波功率水平下大气微波等离子体核心的气体温度、气体流速、气体湿度和空气中CO _{2 的}体积分数。在实验中，吸收的微波功率、气体流速、气体湿度和空气中 CO _{2 的}体积比从 560 到 1750 W，10 到 24 l min ^{-1 变化}，分别为 30% 至 95% 和 0% 至 40%。此外，测量了等离子炬的轴向气体温度分布。实验结果表明：(i) 等离子气体温度主要在 4000~7000 K 之间，(ii) 等离子气体温度随着吸收微波功率的增加而升高，但几乎不受进料气体流量的影响，(iii) 等离子气体温度空气中CO ₂的比例每增加20%，温度就会降低~400 K，并且随着气体湿度的增加而降低，并且（iv）等离子炬气体温度沿轴向降低。由于缺乏流行的微波放电理论，基于热平衡方程对气体温度变化的机制进行了深入分析。