Study on heat allocation and temperature profile in a T-shaped branched tunnel fire with different branch slopes under natural ventilation

Abstract

Reduced scale experiments in a T-shaped branched tunnel with different branch slopes (0%, 6% and 9%) were carried out to study the variation of temperature profile beneath the ceiling under natural ventilation. Numerical simulation with branch slopes of 0%, 3%, 6% and 9% was also executed. A methodology to estimate the mass and heat flux into the branch was proposed. The results show that the branch slope has limited influence on the maximum temperature beneath the ceiling in the main tunnel when fire locates at the intersection of main tunnel. A correlation for maximum temperature beneath the ceiling in the main tunnel is proposed and agrees well with others’ experiments (in full scale and reduced scale). Higher branch slope could transport more hot smoke and heat into the branch. When the branch slope is within 0–9%, about 28–35% of the total released heat enters the branch. When the branch slope is 0%, maximum ceiling temperature in the branch can be well-estimated by Li’s model, if the heat flux into the branch is treated as the heat release rate of ‘virtual fire source’. The longitudinal temperature decay factor in the branch can be estimated based on the mass flux into the branch. This work could help to understand the flow characteristics of hot smoke of branched tunnels scientically.