Experimental studies on fire-induced temperature distribution below ceiling in a longitudinal ventilated metro tunnel

A series of experiments were carried out in a small-scale model tunnel with dimensions of 13m(Length)∗0.32m(Width)∗0.48m(Height) to investigate the fire-induced temperature distribution below ceiling in a longitudinal ventilated metro tunnel. The different temperature distributions with varying longitudinal ventilation velocity and fire size at both upstream and downstream side have been compared and analyzed. The relative smoke flow directions to the longitudinal ventilation flow in the upstream and downstream are different, obvious “convection shear phenomenon” occurred only in the upstream side. And it was shown that smoke temperature distribution in the upstream back layer seemed to be much more sensitive to the ventilation velocity than that in the downstream flow. Based on the experimental data, a modified coefficient 1/γ which was related to the ventilation velocity and fire size was introduced into the upstream temperature decay equation. A new modified temperature decay model for the temperature decay at upstream side of fire source was proposed. Moreover, the comparison of the modified coefficient value indicated that Tang's model underestimated the rate of temperature decay in the upstream side of fire source, the modified coefficient in his study was apparently smaller.