Study of temperature distribution and smoke movement by mobile ventilation during emergency rescue in tunnel fires

Mobile ventilation unit (MVU), as a convenient and maneuverable ventilation method, can provide forced airflow for emergency ventilation to reduce tunnel fire risk. Compared with the conventional natural ventilation and mechanical ventilation, this mobile ventilation method plays a crucial role in the current tunnel fire emergency rescue. To explore the effects of MVU on the temperature or smoke spread in tunnel fires, Compu-tational Fluid Dynamics simulation, validated by the previous experimental data, is applied in the current study. A series of tests are conducted with fire heat release rate of 1-30 MW and MVU fan flow being up to 3 x 105 m3/ h. The results show the maximum tunnel ceiling temperature presents exponential attenuation with increasing fan flow and its relational expression with fan flow and fire size is proposed. Furthermore, the temperature decay distribution between upstream and downstream area is obviously different and a new coefficient gamma is imported to represent the difference by connecting the fan flow and fire size. Moreover, the smoke backflow length theo-retical equation in the upstream area is obtained, which can provide effective guidance to tunnel fire emergency rescue with MVU.