Excitation characteristics of pulverized coal flow under different depth of focus position
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摘要: 将激光诱导击穿光谱技术应用到煤粉颗粒流测量中，分析激光与样品流相互作用，并考察不同的聚焦焦深对等离子体激发特性的影响。在自行搭建的两相流的实验台架上，在大气环境条件下，利用激光器分别对1.0，0.5，0，-0.5, -1.0 mm焦深作用条件下的煤粉颗粒流进行击穿，同时利用光谱仪对等离子体信号进行采集。在相同的激光能量以及收光角度等条件下，改变聚焦激光的焦深，分析对比不同焦深下的等离子体温度、电子密度以及对煤元素分析中关注的C, Si和Al三个代表元素的光谱强度的变化规律。结果表明，不同的激光聚焦焦深对等离子体温度、电子密度和元素光谱强度的影响规律较为明显，三个参数整体变化规律是一致的，最优点为0 mm，其次为1.0，0.5，-0.5 mm，最劣点为-1.0 mm。Abstract: The laser-induced breakdown spectroscopy was applied to the measurement of pulverized coal flow. The interaction between laser and sample stream, as well as the effects of different focal depth on the plasma excitation characteristics was analyzed. On the self-built two-phase flow experimental bench, the coal particles flow was ablated with laser in the atmospheric environment, under 1, 0.5, 0, -0.5 and -1 mm depth of focus, and the spectrometer was used to collect the plasma signal. Under certain conditions of laser energy and angle of received light, the changes of the plasma temperature, the electron density and the spectra of C, Si and Al with laser focal depth were studied. The results show that the laser focal depth has obvious impacts on the plasma temperature, electron density and elemental spectral intensity. The overall variation of the three parameters are consistency, and the most optimum point is at 0 mm, followed by 1.0, 0.5, -0.5 mm and the worst point is at -1 mm.
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