Flow Mechanism And Control Strategies Of Fire Smoke In Structural Vertical Shafts

Shafts are very normal and important structures in buildings, and they could make a significant influence on smoke movement during fires. The work described in this thesis is focused on the movement of fire smoke bearing coupling effect of multiple factors in vertical shafts. The specific work in this thesis includes:smoke movement in elevator shafts with moving elevator cars, temperature distributions in ventilation shafts, neutral pressure plane in buildings and related factors.Piston effect of elevator cars on smoke movement in elevator shafts was discussed through Fluent. As the elevator cars raised, the smoke movement was disturbed and a series of swirls were generated, especially around the elevator cars and at the bottom of the shafts. As the small swirls combined and enlarged, the state of hot smoke flow was turned from laminar to turbulent. When the two elevator cars respectively raised and dropped, the effect of cars on smoke movement was the most significant; when the two cars were both still, the effect of cars was the smallest. Therefore, to make sure fire smoke could be prevented from entering the front room between the elevator shaft and the main corridor, piston effect of elevators cars should be considered when designing the smoke exhaust system.Fire smoke movement was discussed in open ventilation shafts and closed ventilation shafts respectively. According to the opening state of doors between shafts and corridors on each floor, shafts in this thesis were divided into two types:open shafts and closed shafts. In open shafts, ventilation had a considerable influence on smoke movement. The smoke flow came to a stable state in a shorter time and the velocity distribution of smoke flow in shafts tended to be more uniform. In closed shafts, a mathematical model describing vertical temperature distributions was developed and validated through a series of experiments. In this model, the heat exchange between shaft walls and smoke flow and the heat variation due to ventilation were both considered. Validation experiments were conducted on a 1/4 scale experimental platform designed and built by SKLFS-USTC (State Key Laboratory of Fire Science, University of Science and Technology of China). This platform was equipped with all essential structures, including rooms, corridors, doors, windows, shafts and front rooms. The experimental temperatures agreed well with the predicted results calculated from the mathematical model.Factors influencing neutral pressure plane (NPP) in buildings were discussed. Heat release rate (HRR) of the fire source directly influenced the flow rate while it did not make any difference to the position of NPP when it varied from 200 kW to 1000 kW. On the other hand, the position of the fire sources influenced both of the flow rate and the NPP. In cases of single fire source, the position of NPP is positively related to the position of the fire source. In cases of double fire sources, the pressure distribution and the flow mechanism of smoke were more complex and the results in cases of single fire source were not applicable any more. Generally, the NPP was located between the two fire sources. On the other hand, smoke control strategies had very significant influence on the position of NPP. This influence directly determined the efficiency of smoke control strategies.