Case Studies in Thermal Engineering (Dec 2023)
Thermal stability prediction of frozen rocks under fluctuant airflow temperature in a vertical shaft based on finite difference and finite element methods
Abstract
There are abundant coal resources in the permafrost regions of the Qinghai-Tibet Plateau. Open-pit mining is the primary method for coal extraction due to its simple technology and cost-effectiveness. However, the mining process can lead to degradation in permafrost regions. Underground coal mining has been adopted as an option to minimize the impact on the permafrost environment. However, underground coal mining in permafrost regions, along with ventilation, can disrupt the thermal equilibrium of frozen rocks around the shaft, leading to changes in the permafrost table and the seasonal thawed layer around the shaft. Therefore, it is necessary to predict the temperature field of frozen rocks under mine ventilation. Some researchers focus on the temperature of frozen rocks in respect to constant airflow temperature. In fact, the airflow temperature in the shaft varies related to shaft depth, ground temperature, ventilation amount, and ventilation time. In this study, we utilize field data to construct two numerical models for predicting the temperature regime of frozen rocks. The first model, using the finite difference method, describes airflow temperature in the shaft within permafrost regions, accounting for variations in shaft depth, ground temperature, initial rock temperature, ventilation time, and ventilation amount. A fitting equation is then determined as a third boundary condition. The second model employs the finite element method to solve the heat transfer equation with phase change. The results indicate that the maximum thaw depth of frozen rocks around the shaft of Jiangcang coal mine ranged from 3.25 to 5.3 m at various shaft depths. This maximum thaw depth occurs on September 15th and is correlated with ventilation time, stabilizing after three years. Natural ventilation offers protection to frozen rocks around the shaft, and these results can serve as references for designing support systems in underground mining within permafrost regions.
