Study On And Cavitating Water Jet Acoustic Shock Effect To The Coal Temperature

With the continuous exploitation of shallow resources will be depleted, coal mining will transfer to deep, occurrence characteristics of coal containing gas micro porosity, low permeability, high adsorption is more and more obvious, but also become the focus of many scholars to study. Domestic and foreign experts studied quite extensively for coal seam gas with high absorption and low permeable complex geological conditions of the main coal seam, strengthening measures including cavitation, hydraulic fracturing, gas injection and physical field excitation. The high pressure water jet cutting pressure relief technology is a mature technology in the field application has been more widely, including cavitation sonic effect can strengthen and promote methane desorption seepage. But now the mechanism of cavitation acoustic shock effect to strengthen and promote methane desorption gas seepage is not fully clear, such as sound is how the effects of coal, the influence to the coal body structure of transverse wave and longitudinal wave into the coal after the tensile strength of coal body, the shear strength of the impact, or thermal effect the influence mechanism has not been reported yet. In this paper, combining the domestic and foreign research status of cavitation acoustic shock effect to strengthen and promote methane desorption gas flow in coal seams, through theoretical analysis, numerical simulation and experimental verification of a combination of, the frequency characteristics of high pressure water jet cavitation acoustic, cavitation acoustic shock impact on the coal stress, and the effect on body temperature of coal the study. And through the experiment examined the effect of cavitation acoustic shock gas deal with the thermal effect of seepage. The main results are obtained:â‘ The high pressure water jet acoustic shock effects of acoustic characteristics, theoretical analysis, obtained by mechanical vibration and thermal effect of cavitation acoustic shock: alternating the role of cavitation acoustic cavitation sonic booms produced into the coal produced after tensile and shear of coal body, coal by the effective stress changes, coal matrix shrinkage; heat effect at the same time in the process of generating cavitation enhances coal temperature, coal body gas molecule is adsorbed to from the free state, the cavitation process in the higher temperature, the more gas desorption;â‘¡Analysis of the propagation process of cavitation acoustic energy into the coal, energy equation cavitation acoustic wave propagation in the coal body; attenuation on the assumption that the energy transfer process in all transformed into heat effect, the variation of coal temperature equation of coal body is affected by mechanical vibration cavitation acoustic shock after the changes in stress equation the thermal effect and cavitation sonic.â‘¢After the audio power of cavitation acoustic shock spectrum of statistical analysis, obtained under different cavitation numbers(a combination of different confining pressure and pump pressure distribution characteristics of audio). Of cavitation acoustic shock when the coal stress and temperature change of the numerical simulation, obtained the cavitation sonic, coal by distribution of cavitation acoustic sound pressure; after the earthquake, effective stress of coal increased 0.8MPa~1.2MPa, effective stress increase is positive relationship with audio, the role of mechanical vibration effect is obvious. In the cavitation acoustic shock, coal temperature rise in different forms in different audio frequency, low frequency stage in the rising speed of small to large in high frequency stage, no such trend and keep rising velocity more stable. At the same time to raise the temperature between 5~8 degrees, audio is higher, the more obvious the heat effect.â‘£ Through the combination of different confining pressure pump pressure(cavitation number) of cavitation acoustic shock test of coal body: in the cavitation vibration test experiment showed that different cavitation numbers can produce different cavitation concentrating audio, cavitation audio which mainly to coal to provide energy concentrated in between 2000Hz~6000Hz, is an important factor to influence coal temperature and stress force. The coal temperature experiment under the different cavitation numbers indicate that the temperature effect of cavitation acoustic shock effect is remarkable, the temperature increase at 4~5, the results are in agreement with the numerical simulation. On the permeability under different cavitation numbers was studied. The discovery of coal permeability on the whole are increased with the increase of cavitation number and decreased. Consistent with the theoretical deduction and numerical simulation of the results, at the same time on the cavitation number were obtained by fitting the data relation.