44 / 2021-08-17 20:49:24

Experimental Study on Gas Transport Law for Transitional Flow in Porous Media

microscopic boundary restriction,effective molecular mean free path,Maximally Stable Extremal Regions,binarization algorithm

There are many nanoscale pores in deep low permeability coal seams. The flow of coalbed methane (gas) in nanoscale pores belongs to the gas flow in porous media with medium and high Knudsen numbers. Its flow mechanism is one of the key unsolved scientific problems. In this paper, we modified the mean free path of gas molecules in nanoscale pores by considering the microscopic boundary restriction. Next, based on this restriction, we established the equation of gas transport in nanoscale pores and deduced the equivalent apparent permeability model. The Field Emission Scanning Electron Microscope (FESEM) was used to scan the nanopores of customized anodized aluminum membrane. Then, the Maximally Stable Extremal Regions (MSER) algorithm of MATLAB and the binarization algorithm were used to quantify the pore structure parameters (equivalent pore size and porosity) of the membrane nanoscale pores. Finally, PMI micro-flow permeability tester was used to carry out different rarefied degree gas penetration experiments through anodized aluminum membrane, and the derived gas transport model was verified. The results show that the mean free path of gas molecules in the nanopores is obviously decreased owing to the microscopic boundary constraint. The binarization algorithm is more accurate to quantify the mesopores, while MSER can quantify the macropores better. Compared with the traditional gas transport model, the derived gas transport model considering the microscopic boundary restriction in this paper is more similar to the experimental results. Moreover, it is suitable for describing the gas flow law in multiscale nanopores.