Prediction model for pressure loss of sphere column assembly in goaf and flow characteristics of porous media

CHEN Fangxing; HAO Xiaoli; CHEN Shiqiang; ZHANG Jianwei; TIAN Feng; WU Xue

doi:10.13225/j.cnki.jccs.2024.0841

Abstract：As coal mines are mined deeper,the risk of thermodynamic disasters increases,and rapid prediction of flow loss in the goaf becomes key to precise fire prevention and extinguishing in coal mines.Considering the flow characteristics of the goaf,a physical model of the goaf porous medium assembled from spheres and cylinders with adjustable porosity is proposed,where the overall porosity of the model can be changed by controlling the angle θ.Furthermore,the model's minimum flow element is divided into 10 stages,and based on the average hydraulic radius model and a simplified ideal model of local resistance in sudden expansion-sudden contraction parallel channels,an expression for pressure loss per unit length is established.By calculating the predicted pressure loss of the model,the numerical simulation results are compared with experimental and Ergun equation calculations,and the reliability of the numerical simulation results is veri-fied.The results show that the relative error between the experimental data and the predicted values of the calculation model does not exceed 10％,proving the feasibility of the calculation model method;the dimensionless flow loss M is mainly dominated by the viscous loss term in the Reynolds number Re∈[0,10]range,with a deviation from the total loss of less than 7％.Within the Reynolds number Re∈[0,10]range,the relative error of the predicted results of the calcula-tion modelcomparedto thenumericalsimuilation calculation results is less than 10％;within the Reynolds numberRe ∈[10,1 200]range,the relative error of the Ergun equation results exceeds 20％,while the calculation model results exceed the allow-able range with a maximum of 22％when 10＜Re＜300,indicating that the calculation model can be used for predicting pressure loss per unit length.The flow state of the porous medium has a significant impact on pressure loss,and the ana-lysis of the dimensionless flow loss F indicates that as the Reynolds number increases,the flow state of the porous medi-um changes,which can be divided into four flow regions:pure laminar flow zone(0＜Re ≤ 1),laminar flow dominant zone(1＜Re≤ 10),transition zone(10＜Re ≤ 700),and fully turbulent flow zone(Re＞700).The boundaries of flow forms are divided according to the composition of flow loss,with Darcy flow when Reynolds number 1＜Re＜10 and non-Darcy flow when Reynolds number Re＞10.The research results can provide a theoretical basis for precise fire preven-tion and extinguishing in goaf engineering practice.