No abstract

Hypoxia plays a major role in limiting the construction of the high-altitude mine. Understanding the effect and the distribution of diffused oxygen supply at different altitudes is the premise for the design of a mine with oxygen supply system and the full utilization of oxygen resources. For the optimal design of an oxygen supply mode and ventilation system, a multi-component fluid model of the diffused oxygen supply of a single-head tunnel was developed. This study reveals the variation law of the average oxygen mass fraction at different altitudes. The relationship between the distance from the heading face and the oxygen mass fraction at each altitude was fitted. The results show that the distribution of oxygen mass fraction in a single head tunnel at different altitudes presents a similar trend of increasing first and then decline. In addition, the change of the average oxygen mass fraction with the increase of altitude is not linear, and the dispersion loss is larger in high-altitude areas. The largest oxygen enrichment area is distributed at the altitudes of 4000–4500 m. This study provides theoretical support for improving the hypoxic environment of high-altitude metal mines excavation work.

To investigate the influence of surface tension and viscosity on the atomization performance of solid cone nozzles and improve their dust reduction efficiency in industrial and mining enterprises, this study employed a self-built PDPA dust-fog coupling experimental system to explore the effects of different surface tension and viscosity solutions on atomization performance from three aspects: axial, radial, and fog field distribution. The experimental results indicate that compared with surface tension, surface tension has a greater influence on droplet size and velocity in the axial direction. In the radial direction, increasing surface tension and reducing viscosity within a certain range can make the droplet size and velocity distribution more uniform. Additionally, surface tension and viscosity significantly affect the fog field distribution. It was found that a decrease in surface tension can result in a closer proximity of the droplet velocity and size expansion area to the nozzle, while an increase in viscosity can lead to a more prolonged stable area. Furthermore, optimizing the surface tension and viscosity can significantly enhance the efficacy of dust reduction for respirable dust. Consequently, the application of the aforementioned atomization principles to regulate the fog field characteristics of solid cone nozzles can effectively mitigate dust in the production process and augment the dust reduction rate of industrial and mining enterprises.

The problem of heat hazard in tunnel engineering has seriously affected the normal work of personnel and machinery. After combining the heat hazard control method of controlling the energy source and blocking the energy transfer, a technical scheme of precise thermal insulation at the working face in concert with geothermal energy extraction is proposed, forming a coupled cooling method of ventilation and partial thermal insulation. By building a scaled model test platform, the temperature field of the working area was analyzed, and the effect of factors, such as with or without a thermal insulation layer, ventilation velocity, and surrounding rock temperature on the cooling limit, was discussed. The feasibility of extracting energy and enhancing cooling through the heat exchange layer was judged. The results show that the partial thermal insulation can effectively weaken the heat dissipation of the surrounding rock and enhance the ventilation and cooling effect, which can reduce the average ventilation limit temperature of the working area by 1.6 °C. The addition of the heat exchange layer can further improve the tunnel environment on the basis of partial insulation, making the cooling limit temperature drop by another 3.1 °C, and the heat exchange layer can work for one year to extract geothermal energy 4.5 × 108 J. The coupled cooling scheme of ventilation and partial thermal insulation is practical and useful, which can provide technical ideas for improving the thermal environment of the tunnel.

Single-heading tunnels in underground metal mines have high air pollutant concentrations, chaotic airflow, and low pollutant diffusion efficiency in high-altitude areas, resulting in poor air exchange. Based on Pulang copper mine (China), a computational fluid dynamics case using the steady Reynolds-averaged Navier–Stokes equations with a k-omega turbulence model was developed to study certain factors influencing the air exchange of single-heading tunnels, and was combined with an orthogonal experimental method to simulate the mean age of air (MAA) under different working conditions. This study revealed the ranking of the importance of some factors on the air exchange via sensitivity analysis. The MAA generally increases with the increasing distance between the duct and the heading face and the increasing diameter of the oxygen supply duct. This study’s optimal distance and diameter can reduce MAA by 14.7% and 9.9%, respectively. Placing the oxygen supply duct and the duct on the same side and using an 800/1000 mm inner diameter duct can effectively reduce the MAA by 6.7% and 4.2%, respectively, in this study. The findings of this study can optimize air exchange in the Pulang copper mine, and can also be referenced for the optimization of air exchange in high-altitude highway or railway tunnels being excavated.