Experimental study on synergistic effect of exhaust vent layout and exhaust rate on performance of ceiling central smoke extraction in road tunnel fires

Abstract

In road tunnel fires, exhaust vent layout and smoke exhaust rate are two important parameters that affect the smoke exhaust performance of ceiling central smoke extraction. However, the synergistic effect between the two (cooperation of two factors) has not yet been quantitatively analysed. Reduced-scale (1:20) burning experiments were conducted in this study. Through variations in the vent area, vent width, and exhaust rate, the factors influencing the ventilation system efficiency VSE′ and ventilation system output VSO′ were analysed. It can be seen from the experimental results that for a constant vent width, the exhaust vent area has nearly no effect on VSE′ and VSO′. Furthermore, increasing the smoke exhaust rate can improve VSE′, but will reduce VSO′, whereas increasing the vent width can increase both VSE′ and VSO′. We also considered the effects of heat transfer at the tunnel wall and obtained a normalised VSE′ estimation correlation, which includes the aforementioned dimensionless influencing factors and the factor of distance between the exhaust vent and fire source. After verifying the correlation, we demonstrated its application value as a significantly useful reference for central smoke extraction design.