Numerical Simulation Study on Methane Diffusion Distribution Laws in Confined Spaces of Municipal Heating Underground Pipe Trenches

In order to study the diffusion distribution laws of harmful gases in municipal heating underground pipe trenches under various influencing factors, a 1:1 scale model of the municipal heating underground pipe trench was established by using CFD simulation software. This study examined the impact of closed pipe trench conditions, natural ventilation, mechanical ventilation, and gas dispersing rates on the distribution of methane diffusion in the heating underground pipe trench and was verified through on-site experiments. The findings are as follows: (1) the gas in the heating pipe trench flows violently at the bottom of the pipe trench and the examination room and the top air flow rate is small, resulting in higher top temperature and lower bottom temperature; (2) under closed trench conditions, methane gas exhibits a vertical layered distribution near the release source, with higher concentrations in the upper part compared to the lower part. This layered effect diminishes with increasing distance; (3) natural ventilation effectively reduces methane gas content in the pipe trench. Ventilation in the same direction as methane release is not conducive to gas dispersion; (4) in the closed state and natural ventilation state, with the increase of escape source rate, the growth law of methane is linear and exponential distribution, respectively; and (5) mechanical ventilation rapidly and effectively reduces methane gas content. The research results contribute theoretical insights into confined space ventilation, alarm system installations, and personnel operation, ensuring staff safety in these environments.