CFD Analysis of Gas Diffusion and Ventilation Protection in Municipal Pipe Tunnel

In order to obtain characteristics of gas diffusion in the municipal pipeline tunnel, and provide guidance on protective ventilation design, a certain municipal heating pipeline is taken as the research objects to carry out numerical simulations using computational fluid dynamics (CFD) method which mainly focuses on the distribution of the CH4 and CO2 under different conditions. Results indicate that, for the closed pipe tunnel without ventilation shaft, the gas distribution presents obvious stratification which shows in detail that light gas mainly accumulates on the top of the tunnel while heavy gas mainly accumulates at the bottom of the tunnel; besides, the gas concentration increase linearly after the gas distribution reach a stable condition. Natural ventilation in the ventilation shaft can effectively reduce the gas content within the pipe tunnel: the gas content of area over which wind flows is about one-third of that in the windless area and the total gas content in pipe tunnel is far less than that without ventilation shaft. The emission rate of the gas does not affect gas distribution in pipe tunnel, but the gas content value is proportional to its emission rate. It is easy to accumulate at dead zones where the wind cannot reach easily both in the natural ventilation and forced ventilation conditions. Thus, when designing the ventilation shaft and taking ventilation measures, areas where winds cannot reach should be avoided in pipe tunnel.