The role of opened fire doors in enhanced heat exchange of long-distance utility tunnels

Abstract

Due to their distinctive structural attributes, fire compartments in utility tunnels result in regions of increased temperature concentration and thermal dissipation, notably influencing heat exchange phenomena. Investigating airflow diffusion and thermal exchange principles of fire compartments is important when optimizing heat transfer processes in extensive utility tunnels. In this study, we employed numerical simulations and rigorous experimental validation to compare velocity and temperature field attributes between conventional tunnels and those augmented with fire compartments under diverse boundary conditions. The findings revealed that substantial ventilation exchange, reduced cable-based thermal exchange, diminished wall temperatures, and incorporation of opened fire doors are effective measures in improving the thermal environment in utility tunnels. During the summer season, it was observed that the temperature prerequisites were adequately met in a 400-m-long utility tunnel featuring cross-fire compartments at a ventilation rate of 4 air changes per hour (ACH), while tunnels surpassing a length of 600 m required a ventilation rate of 2 ACH, and single-fire compartment tunnels required a ventilation rate of 6 ACH for similar thermal control. Specifically, at a rate of 2 ACH, the temperature in the tunnel exhibited an average reduction of 3.25 °C with the addition of one additional opened fire door. In comparison, a decrease of 1.91 °C was observed when maintaining a rate of 4 ACH. Finally, the airflow characteristics of tunnels with normally opened fire doors were summarized via a finite forced jet model, and the specific ranges of the potential flow core region, characteristic attenuation region and radial attenuation region were obtained.