Assessing the impact of the air speed flowing through a granular porous medium on the linear flow resistances

Underground hard coal exploitation leads to the formation of granular porous media. These media occur both in the underground parts of mines and on the surface. In the underground areas, these are the caving goaves of longwalls and the caved-in roof rocks in active mine headings. On the surface, these are most commonly the post-mining waste dumps. In both of these cases, a crucial role is played by the knowledge on the resistance of air and gases flowing through these media. In the case of underground exploitation, it is of great significance for the enhancement of production safety. It is also used for underground acid gas sequestration in inactive mine headings as well as for the storage of toxic substances in these headings and post-mining waste on the surface, or for the storage of loose substances. In the event of gases flowing through goaves with caving, treated as a granular porous medium, the resistances present during this flow affect the degree of air distribution in the goaves and the outflow of methane from the goaves into the working face of a longwall, which has a very significant impact on the safety in this region. This issue is therefore of crucial practical importance. The article presents the results of model-based tests carried out in macro-scale, aimed at determining the resistances of air flowing through a granular porous medium. The measure of this resistance is the drop in unit pressure along the layer of the medium, depending on its porosity and permeability. The tests were also conducted for various speeds of the gas flowing through this medium. They were carried out for air (as a mixture of gases). The results may be used for ventilation analyses related to fire and gas hazards in coal mines and mining waste dumps. It must also be stressed that the test methodology adopted and the numerical models developed are universal in nature and can be used for testing a variety of porous media, especially in terms of ventilation and safety engineering, including the assurance of safety in production processes.