Gas-solid flow characteristics in a PDC drill bit during negative pressure pneumatic conveying

Negative pressure sampling is a pneumatic conveying technique widely used in coal mining. The structure of the PDC drill bit within a sampling system plays a crucial role in coal particle collection and transportation. To investigate the gas-solid flow characteristics inside the PDC drill bit and examine the effects of rotation speed and conveying gas velocity during negative pressure pneumatic conveying, CFD-DEM coupling simulations were conducted on a full-scale PDC drill bit model. The results indicate that as the drill bit rotated, the positions of the fluid holes alternated, leading to periodic fluctuations in the amount of collected coal particles. The particle flow patterns of swirling flow, bottom flow, and suspension flow occurred sequentially within the pipe due to variations in the gas velocity gradient. The bottom flow, which hindered particle transport, disappeared when the conveying gas velocity exceeded 30 m/s. Additionally, the distance required for particles to transition into a suspension flow pattern was negatively correlated with the conveying gas velocity and remained largely unaffected by the rotation speed.