## 3 Investigation of Adhesive Clogging Characteristics in Underground Coal Bunkers
### Analysis of Adhesive Clogging Characteristics of the Coal Bunker
#### 3.3.1 Influence of Convergence Angle on Adhesive Clogging of Coal Bunker  
(1) Coal flow characteristics  
The study simulated and analyzed five different bunker convergence angles \(\alpha\) (50\({}^{\circ}\), 55\({}^{\circ}\), 60\({}^{\circ}\), 65\({}^{\circ}\), 70\({}^{\circ}\)) at a coal storage height of 7 m and a raw coal moisture content of 1%. Figure 15 shows the discharge flow velocity characteristics at different convergence angles. Figure 14: Simulation of the coal bunker discharge process: (**a**) arrangement of coal bunker wall units; (**b–e**) represent different stages of the discharge process, respectively. Figure 13: Simulation of the coal storage process in the coal bunker: (**a**) free fall of coal particles; (**b–f**) represent the generation of the 1 st, 3 rd, 5 th, 7 th, and 9 th layers of particles, respectively. As illustrated in Figure 15, as the coal bunker convergence angle \(\alpha\) increases, the coal flow velocity gradually increases, and the flow pattern undergoes significant changes. When \(\alpha=50^{\circ}\) and \(55^{\circ}\), the coal particles inside the bunker exhibit slow flow velocities, with a substantial amount of coal near the bunker wall having a flow velocity close to zero, displaying a typical central flow pattern. When \(\alpha=60^{\circ}\), the coal flow velocity inside the coal bunker noticeably increases, and the flow pattern transitions from central flow to funnel flow. When \(\alpha=65^{\circ}\), the coal flow velocity inside the bunker increases significantly, and the overall flow pattern becomes more akin to mass flow. When \(\alpha=70^{\circ}\), the coal material flows downward uniformly, maintaining a high flow velocity, with the overall flow pattern distinctly exhibiting the characteristics of mass flow. (2) Adhesive clogging situation of coal bunker  
Figure 16 illustrates the adhesive clogging situation in the coal bunker at different convergence angles. When \(\alpha\) is in the range of \(50^{\circ}\) to \(65^{\circ}\), multiple layers of coal accumulate inside the coal bunker (i.e., the upper layer of coal flows out before the lower layer, and some coal adhere to the inside of the bunker), which is also consistent with the characteristics of central flow. However, when \(\alpha=70^{\circ}\), the coal bunker is primarily covered with coal adhering to the wall, which is mostly distributed in the order of coal storage, aligning with the adhesive clogging characteristics of a mass flow coal bunker. Figure 17 depicts the curve of the mass fraction of adhered coal as a function of the convergence angle \(\alpha\). It is observable that as \(\alpha\) increases, the mass fraction of adhered coal inside the bunker gradually diminishes. When \(\alpha\) is \(50^{\circ}\) and \(55^{\circ}\), the mass fraction of adhered coal in the coal bunker is \(12.57\%\) and \(10.11\%\), respectively. When \(\alpha\) is \(60^{\circ}\) and \(65^{\circ}\), this  
fraction decreases to 5.15% and 3.91%, respectively, indicating a significant improvement in the coal adhesion situation inside the coal bunker. When \(\alpha\) is 70\({}^{\circ}\), this fraction further decreases to 1.86%, which is due to the change in the coal flow pattern inside the coal bunker as the mass flow of coal results in only a small portion of coal adhering to the bunker wall. Pressure distribution on the coal bunker wall  
Based on the adhesive clogging conditions in the coal bunker, we analyzed the pressure at four locations on the bunker walls: wall-1 at the coal bunker discharge outlet, wall-5 in the middle of the coal bunker hopper, and wall-10 and wall-21 at the junction between the hopper and the vertical section. Figure 18 shows the pressure variation curves at these four locations. As depicted in Figure 18a, at the coal bunker discharge outlet (wall-1), there are frequent collisions between coal particles and the bunker wall, resulting in significant fluctuations and lower wall pressure, which makes coal agglomeration and adhesion less likely.