Distributed temperature sensor model for linear heat detection in tunnel fires

• Developed a model of distributed temperature sensing (DTS) for tunnel fire simulations. • Linear heat detection (LHD) response is dependent on their thermal inertia and convective heat transfer. • Convective heat transfer coefficient has high values for thin objects like DTS. • The detection time of LHD correlates with HRR and airflow velocity in the tunnel. • Archived high accuracy to prediction DTS performance with Response Time Index (RTI) value equal to 90 (m/s) 1/2 . This study proposes a method for implementing distributed temperature sensing systems in tunnel fire simulations. A review of the investigations was conducted, and previous research on linear heat detection was examined. The characteristics and operational parameters of a complete DTS-based LHD system in a road tunnel are presented. A heat transfer model of the DTS sensor cable for CFD modelling was developed based on experiments in the standardised EN 54–5 wind tunnel for testing heat sensors. Based on the data analysis, substitute physical properties of the sensor cable were selected for the heat transfer model to allow implementation of the DTS model in CFD. Concurrently, an RTI value of 90 (m/s) 1/2 was approximated to compare the model with the response-time model commonly used in fire engineering analyses. To validate the model, two full-scale fire tests were carried out in a road tunnel in Świnoujście, Poland, and CFD numerical simulations were performed with the proposed DTS model. The relative error of detection time prediction was within 3% for the case with low velocity, and successfully predicted no detection in the case with high velocity (>1 m/s). The developed model allows to tracking temperature changes of the DTS sensor cable with satisfactory precision and can be applied in various tunnel fire analyses.