Study on the effect of penetration enhancement and energy change of coal samples pretreated with different microwave powers
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摘要: 为探究不同功率微波下受载煤体渗透率及破坏变形能量演化特征，采用高压三维可视力学实验设备，开展不同功率微波预处理后煤样的三轴压缩渗流实验。结果表明：不同功率微波处理后煤样弹性模量呈现先降后升趋势，峰值应力与泊松比均呈现下降趋势；随微波功率增加，煤样更容易被压密，径向及体应力-应变曲线整体应变值变大，扩容膨胀现象更加显著；煤样渗透率随功率增加呈现上升趋势，符合对数函数关系；不同预处理煤样峰值应力处的总能量U与弹性能Ue总体呈下降趋势，煤样在弹性阶段积聚弹性能Ue的能力减弱；相同照射时间下相比200 W和600 W微波预处理，400 W微波预处理时各能量变化量明显变大，煤样耗散能Ud占总能量U比值最小，为24%。研究成果可为微波致裂煤层促进瓦斯抽采研究提供参考。Abstract: In order to investigate permeability and destructive deformation energy evolution of the loaded coal body under different power microwaves, the high-pressure three-dimensional visual mechanics experimental equipment to carry out the triaxial compressive percolation experiments of the coal samples after microwave pretreatment with different power. Results show that the modulus of elasticity of coal samples after microwave treatment with different powers shows a decreasing and then increasing trend, while the peak stress and Poisson's ratio show a decreasing trend; the increase of microwave power leads to easier compact of coal samples, larger overall strain values of radial and body stress-strain curves, and significant expansion; the permeability of the coal samples increases as power rises, which is consistent with the logarithmic function fitting relationship; the increase of microwave power leads to decreasing total energy U and elastic energy Ue at the peak stress of different pretreated coal samples, and the ability of coal samples to accumulate elastic energy Ue in the elastic stage is weakened. When we compare 200 W and 600 W microwave pretreatment under the same irradiation time, it is found that the change of each energy was more significant in 400 W microwave pretreatment, and the coal samples have the smallest dissipated energy Ud as a proportion of total energy U, at 24%. The study could provide references for gas extraction in microwave fracturing coal seams.
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Key words:
- microwave /
- power /
- loaded coal body /
- permeability /
- energy
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图 5 不同功率微波下煤样峰值应力变化曲线
Figure 5. Curves of peak stress in coal samples under different power microwaves
图 6 不同功率微波预处理煤样表面裂纹分布
Figure 6. Distribution of cracks on the surface of coal samples pretreated with different power microwave
图 7 微波降低煤样抗压强度原理示意图
Figure 7. The mechanism of microwave reducing the compressive strength of coal samples
图 8 不同功率微波辐射下煤样应力-应变曲线
Figure 8. Stress-strain curves of coal samples under different power microwave radiation
图 11 不同功率微波作用下煤样渗透率变化曲线
Figure 11. Variation curve of coal sample permeability under the action of microwave with different power
图 12 微波功率与煤样初始渗透率拟合曲线
Figure 12. Fitting curve of microwave power to initial permeability of coal samples
图 13 不同功率微波作用下煤样能量演化曲线
Figure 13. Energy evolution curve of coal sample under the action of microwave with different power
表 1 预处理煤样参数
Table 1. Parameters of pre-treated coal samples
微波功率P/W 质量/g 波速/(km·s-1) 煤样温度/℃ 0 235.29 1.92 23.32 200 223.72 1.86 41.37 400 219.24 1.92 62.74 600 228.32 1.94 84.46 
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表 2 煤样力学参数
Table 2. Mechanical parameters of coal samples
微波功率P/W 峰值应力σmax/MPa 弹性模量E/MPa 泊松比 0 63.056 2 878.909 0.418 200 54.580 1 979.343 0.386 400 39.156 1 785.434 0.323 600 33.229 2 129.187 0.259
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表 3 煤样峰值应力处各能量特征
Table 3. Characteristics of each energy at the peak stress of coal samples
微波功率P/W U/(MJ·m-3) Ue/(MJ·m-3) Ud/(MJ·m-3) 0 1.289 0.724 0.565 200 1.235 0.741 0.494 400 0.558 0.423 0.135 600 0.404 0.259 0.145
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