Calculation Model And Experiment Of Gas Flow Pressure Loss In Goaf

In this paper,the pressure loss law of the gas flow in goaf is studied by combining theoretical derivation with experimental measurement.In order to solve the calculation problem of flow resistance in goaf with complex structure,three new physical model of porous media is proposed in this paper.The physical model is a three-dimensional structure surrounded by 2 times large spherical diameter cube,8 large spherical diameter,1 small spherical diameter,6 small spherical spheres and their cavities.According to the principle of equal porosity and single period flow,the minimum flow unit is constructed by cutting the physical model of porous media.Based on the assumption of average velocity,the Navier-stokes equations of fluid mechanics were applied to simplify the flow field of the minimum flow unit to one-dimensional flow,and the four-section functional expressions of the average velocity,inertial force,viscous force and pressure gradient in the minimum flow unit were derived.On MATLAB,the influence of gas viscosity coefficient on the four-stage pressure gradient is numerically calculated by using the four-stage function expression.By using the weight method of length ratio,the formula for calculating the minimum flow unit pressure loss is obtained.By means of drainage method,the porosity of goaf is measured,and a theoretical model is established which is the same as that of model test bed,which provides a similar situation for subsequent experimental verification.Through the derivation of goaf flow model and the measurement of goaf experimental model,the pressure loss law of goaf gas flow is obtained,and the comparative analysis is made.The analysis results show that the experimental results are basically consistent with the simulation results,and the reliability of the theoretical derivation method is demonstrated.The results show that the pressure loss of gas microflow in goaf satisfies the quadratic equation of average velocity,and the Forchheimer model is improved.The physical model of porous media and its minimum flow equation proposed in this paper will provide a new reference for the prevention of spontaneous combustion of residual coal in goaf.