Abstract: In order to study the exhaust volume enrichment coefficient of ceiling exhaust system under the influence of air leakage, a solution model of air pressure and air volume of ceiling exhaust system was established, and the accuracy of the model was verified by comparing with the full-scale test data. Based on the model, we analyzed the air pressure and air volume distribution under different design heat release rates, tunnel lengths, exhaust vent spacing and exhaust vent areas, and studied the exhaust volume enrichment coefficients under each parameter. The results show that: with the increase of heat release rate, the designed exhaust volume increases gradually, but there is no obvious correlation between the exhaust volume richness coefficient and the heat release rate. For the case of using high-tight exhaust vent, when the length of the tunnel is less than 10 km, the exhaust volume enrichment coefficient to meet the exhaust demand is below 10%. In the case of ordinary exhaust vent, the exhaust volume enrichment coefficient is almost always over 20% for both extra-long tunnels and super-long tunnels, and even over 100% when the length of the tunnel exceeds 9 km. With the expansion of the exhaust vent spacing, the exhaust volume enrichment coefficient and the designed exhaust volume show a consistent decreasing trend. With the increase of the exhaust vent area, the designed exhaust volume gradually increased, and the exhaust volume enrichment coefficient also has a similar trend, especially the common exhaust vent is more obvious. Therefore, in order to meet the demand for smoke exhaust, improving the quality of exhaust vent, expanding the spacing of exhaust vent and reducing the exhaust vent area can play a role in reducing the effect of exhaust volume enrichment coefficient.

Key words: ceiling exhaust system, air leakage, exhaust volume enrichment coefficient, air pressure and air volume distribution, tunnel fire