空化水射流热效应影响煤体渗透率试验研究

Experiment study of effect of coal permeability under thermal effect of cavitation water jets

对空化水射流空泡溃灭瞬间和空化噪声声场作用产生的热效应进行了分析,得到了热效应作用下的煤体渗透率表达式,并开展了不同空化条件(泵压、空化腔围压)下的煤体温度和瓦斯渗流试验。结果表明:空化腔围压一定时,温度随泵压的增大而升高;而泵压一定时,温度随空化腔围压的增大而减小。当热应力大于平均有效应力时,煤体热膨胀出现微变形,产生的张应力使裂隙变宽、数量增多;热效应使得游离瓦斯内能增加,分子自由程大大缩短,同时吸附瓦斯解吸使得煤基质发生收缩效应,导致微孔隙及微裂隙结构产生膨胀变形,从而影响煤体渗透率。试验得到渗透率随温度升高呈指数规律增大,与理论得到的渗透率表达式描述的规律相符。

Based on analyzing of the thermal effect generated by cavitation bubble breaking moment and sound field of cavitation noise, the theoretical formulas of coal permeability under the action of thermal effect are derived. The temperature and permeability tests are performed under different cavitation conditions （pump pressure and confining pressure）. The results show that the coal temperature increases with the increasing pump pressure when confining pressure is constant; on the contrary, the coal temperature decreases with the increasing confining pressure of cavitation chamber when pump pressure is constant. When the thermal stress of coal is greater than the average effective stress, the micro deformation of coal appears under thermal expansion; and the tensile stress makes the increase in the width and number of cracks. Besides the increasing intrinsic energy of free gas causes the greatly reduces of molecular free path at the same time, due to coal matrix shrinkage effect, the coal methane desorption make the micro pore and crack structures expand, which affects the permeability. The index relationship between permeability and temperature is deduced, which is consistent with the regular pattern described by the theoretical formulas of permeability.