Theoretical prediction model and full-scale experimental study of central smoke extraction with a uniform smoke rate in a tunnel fire

A large amount of smoke may be discharged from a smoke extraction damper located close to extraction fans in central smoke extraction systems, which greatly reduces the efficiency and increases the energy consumption. Therefore, we propose the concept of smoke extraction with a uniform smoke rate. Adjusting the damper angle can make the extraction rate uniform for each damper, so the higher temperature smoke can be discharged furthest through the damper nearest the fire. We established theoretical models according to the relationships between the smoke velocities, extraction rate, damper angle, and wind pressure for fans in traditional and uniform systems. Based on the Hong Kong-Zhuhai-Macao immersed tunnel in China, an experimental tunnel with the largest cross section size in the world is constructed. The results showed that in the traditional system, 40-60% of smoke was discharged through the damper nearest to the fan, whereas the extraction rate for each damper could be equalized by controlling the angle in the uniform system and 8-23% of the energy could also be conserved. The results suggested that the damper nearby the fire should be open and the number of dampers can be adjusted to control the smoke spread range and achieve effective energy savings.