Closure state of CDAC device
Air flow field
To investigate the influence of the distance between the air inlet and the cutting head on the migration of the airflow field with the cone-shaped air diversion device in the closed state and to determine the minimum critical distance required to form an effective axial dust control airflow curtain. Considering the actual operational conditions of the fully mechanized mining face, the total air volumes of the air inlet and exhaust fan were defined as 300 m3/min and 240 m3/min, respectively. The distances of the air inlet from the cutting head were set at 5 m, 10 m, 15 m, 20 m, 25 m, and 30 m. When the cone-shaped air diversion device is closed, the situation is similar to when no cone-shaped air diversion device is installed. Therefore, the closed state of the cone-shaped air diversion device was used as the baseline for research before installation. The variation of the airflow field with different distances between the air inlet and the working face is depicted in Fig. 7.
Simulation results of air flow field migration at different distances from the pressure tuyere to the head. A cross-sectional analysis was conducted at the position of X = 5 m (cutting machine operator’s location). (a) 5 m; (b) 10 m; (c) 15 m; (d) 20 m; (e) 25 m; (f) 30 m.
According to Fig. 7a–f, it can be observed that as the distance between the air inlet and the mining face increases gradually from 5 to 30 m, a airflow field gradually forms flowing along the negative direction of the X-axis. With the increase in distance between the air inlet and the mining face, the axial airflow field moves further away from the mining face. When the distance between the air inlet and the mining face is between 5 and 25 m, no axial airflow field is formed, and the axial airflow field exists only at the mining face. However, when the distance between the air inlet and the mining face is 30 m, the axial airflow field begins to form, with the farthest distance from the mining face being 8.36 m, and the airflow gradually becomes more uniform. Furthermore, the minimum distance for the formation of the axial airflow field was further analyzed at the cutting machine operator’s position (i.e., X = 5 m). When the distance between the air inlet and the mining face is between 5 and 25 m, the airflow field at the cutting machine operator’s position is chaotic and unevenly distributed, unable to form a uniform and stable axial airflow field. However, when the distance between the air inlet and the mining face is 30 m, the airflow field at the cutting machine operator’s position is relatively uniform and free from turbulent flow, with the airflow velocity decreasing from a maximum of 15.7 m/s at the air inlet to approximately 0.42 m/s. This indicates that as the distance between the air inlet and the mining face increases, the injected airflow diffuses more fully and evenly in the roadway. However, as the distance between the air inlet and the mining face increases, some of the outflowing airflow begins to lose momentum, resulting in a decrease in flow velocity and a deviation in flow direction, forming a vortex airflow field and ultimately resulting in an axial airflow field flowing along the negative direction of the X-axis.
Air flow-dust particle two-phase flow field
Based on Fig. 8a–f, it can be observed that as the distance between the air inlet and the mining face increases, the aggregation range of dust particles tends to decrease. When the distance between the air inlet and the mining face is 5 m, the diffusion distance of dust particles with concentrations above 50 mg/m3 is 16.5 m. As the distance increases to 25 m, the diffusion distance gradually decreases to 11.2 m. When the distance reaches 30 m, the diffusion distance sharply decreases to 5.8 m for dust particles with concentrations above 50 mg/m3. Further analysis at the cutting machine operator’s position (X = 5 m) reveals that within the range of 5–25 m between the air inlet and the mining face, the dust concentration fluctuates between 162.5 and 237.8 mg/m3. When the distance between the air inlet and the mining face is 30 m, the dust concentration decreases to 129.8 mg/m3. This indicates that airborne dust transport simulation results are consistent with airflow field simulations. The minimum distance between the air inlet and the mining face required to form an axial airflow field is 30 m. At this point, an airflow curtain flows along the negative X-axis direction, continuously reducing the diffusion distance of dust particles with concentrations above 50 mg/m3, effectively controlling the movement of dust particles to maintain the axial airflow field. However, the cutting machine…
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