Study On Smoke Movement In Vertical Shaft Of High-rise Buildings And Flame Behavior In The Fire Compartment

In the last decades, many skyscrapers have been constructed all over the world, with the fire occurred frequently which is responsible for a number of casualties and property losses. When high-rise buildings catch fire, it is difficult to put out the fire and evacuate the people. There are many vertical shafts in high-rise buildings, such as elevator wells and stairwells. These shafts may be paths for smoke spread in case of fires. Stack effect and turbulent mixing are the two physical mechanisms which are primarily responsible for vertical motion of buoyant gas within a vertical shaft. In addition, the external wind can also affect the buoyant gas move in the buildings. Statistics showed that more than80percent deaths in fire were caused by toxic gases, such as carbon monoxide. Therefore, it is important to study the motion of buoyant gas driving by these mechanisms and the motion of buoyant gas influence on the fire burning for the fire prevention and control.In this dissertation, Experimental researches, theoretical analysises were carried out to investigate the motion of buoyant gas driving by stack effect, turbulent mixing and external wind. The experiments were carried out in a1:3scale stairwell model and a1:3scale room model. Specific work includes:A set of burning experiments were conducted in a1/3scale stairwell to investigate the rise time of fire-induced buoyant plumes and the discharge coefficient of the stairwell. Results show that the time for the front of a buoyant plume to reach a given height from a fire source is inversely proportional to the1/3power of the heat release rate and proportional to the1.203, and2.129power of the height in the stairwell with top vent open and closed, respectively. The experimental results were correlated by the non-dimensional time and non-dimensional height. Results are proposed to predict rise time of fire plume fronts. Discharge coefficient of the stairwell was calculated based on the velocity at the openings of the stairwell and the temperature distribution in the stairwell. A value of0.23was proposed to be the discharge coefficient of the stairwell.Previous studies on the turbulent mixing process in closed shafts did not take into account the heat transfer from the hot buoyant plume to the boundaries such as walls. In this paper, a modified theoretical model predicting the one-dimensional turbulent mixing process in vertical shafts is proposed with the heat transfer from the hot buoyant plume to the boundaries involved. A set of small scale experiments were conducted to validate this model. A propane gas burner was used as the heat source to provide steady heat release rate. The comparison between the model predicted and experimental results show that the Cooper’s turbulent mixing model which didn’t consider the heat transfer from boundary gives higher predictions compared to the temperature data measured in experiment whereas the current modified model leads to more comparable results. Therefore the heat transfer process between the plume and the boundaries should be included in any modeling for the case of buoyant plume rising in closed shafts.A set of burning experiments were conducted in a1/3scale stairwell to investigate the characteristics of fire induced buoyant plume movement in a12-storey stairwell with three vents. Results show that the temperature of fire plume generally decreases with height in the stairwell on the steady state, and the distribution of smoke temperature in stairwell is mainly determined by the heat release rate (HRR) of fire source. The variation trends of temperature and velocity profiles measured at the middle opening were used to determine the location of neutral plane, and the determined results were confirmed by the pictures of flow field (lightened by the laser sheet). Based on the temperature distribution in stairwell and theoretical analysis, the location of neutral plane in the stairwell was calculated and the results were in good agreements with experimental results. The location of the neutral plane was mainly affected by the height of the middle opening. For cases with the same middle opening, the heat release rate of fire source weakly affected the location of neutral plane.The ejecting fire behavior from compartment with two openings under thermal forces and external wind was revealed. The experiments were carried out in a1:3scale compartment room to study the flame ejected from opening of a building compartment on the effect of thermal forces. Based on two character length of the compartment room, the ejected flame length and height are correlated by the non-dimensional heat release rate. When the flame ejected from opening of the compartment, the relationship between the shape of the opening and ejected flame oscillation frequency was revealed. Tthe impact of external wind couple with the thermal forces on the ventilation of the compartment which influence the mass loss rate of the oil pool were also revealed.