Method for determining the critical velocity of paste-like slurry filling into goaf using computational fluid dynamics

The coal mining mode of paste-like slurry fill shows the connotation and characteristics of green mining both in the resource recycle and waste reuse. Test by intelligent torque sensor, fitted by the ORIGIN software, the following relationships were obtained: (1) rheological parameters versus slurry mass fraction, (2) rheological parameters versus component ratio. Based on the relationships, the recommended ratio of paste-like slurry was determined. The mass concentration of slurry is no more than 78%, which is composed by coal gangue (diameter < 20 mm), fly ash (diameter < 30 μm), and gelling agent with the weight ratio of 8:3:1. The pipe flow dynamic characteristics of paste-like slurry have been analyzed by computational fluid dynamics (CFD) and CFD-POST. By simulating the flow behavior of the slurry at different velocities under a stable state in the horizontal pipe, the analysis of the paste-like slurry’s non-silting velocity has been done. Combined with the laboratory test data and mechanical models, the different concentrations and the velocities of the paste-like slurry in pipelines under different inlet velocities were introduced. The critical velocity is about 1 m/s corresponding to a pipe diameter of 150 mm. The results provide a better insight into the process of transportation of paste-like slurry, as well as to more cost-effective engineering designs of sustainable development of the environment and coal mines.