Determining the optimal airflow rate to minimize air pollution in tunnels

Abstract

With the spreading of the green environmental protection concept, increasing attention has been paid to improving the tunneling environment. In this paper, the distribution characteristics of airflow fields, the diffusion laws of pollutants, and the influence of airflow rate changes on pollutants in tunnels under single-forced ventilation conditions were simulated according to the computational fluid dynamics (CFD) theory. In addition, the reliability of the simulation results was verified through field measurements. A three-stage distribution was observed once the dust concentration stabilized: we noticed areas with relatively low dust concentrations (<300 mg/m3), high dust concentrations (>500 mg/m3), and medium dust concentrations (~400 mg/m3, near the tunnel exit). Meanwhile, after stabilizing, the gas concentration was 0.67%. Properly increasing the airflow rate (Q) can effectively improve the tunnel environment: when Q reached 600 m3/min, the air in the tunnel was effectively purified. However, under a continuous increase of the airflow rate, there is a risk of pollution rebound.We conclude that, to effectively improve the tunnel environment and achieve a sustainable utilization of resources, the optimal operation airflow rate should be 600 m3/min.