Study On Smoke Movement And Mechanical Exhaust In The Main Transformer Hall Fires Of An Underground Hydropower Station

At present the hydropower resources development and construction in our country has entered a period of rapid development, and the fire safety problems of underground hydropower station appear particularly important. The main transformer halls belong to underground cavites of higher fire possibility, therefore, it is very important to study the smoke movement and smoke control in the main transformer halls.The interaction of the two factors:the fire induced buoyancy and the special configuration of the main transformer hall makes the movement of smoke induced by fire in the main transformer hall more complex than that in normal compartment. In this thesis, reduced-scale model experiments were conducted, along with FDS simulations and2DPIV tests, to study the dynamics and thermal physics of fire induced smoke movement in the main transformer hall. Through comparing with the results of the scale model tests, the accuracy and feasibility of FDS simulation and PIV technology used in the main transformer hall fires were verified. Works include:(1) This paper presented the results of physical model studies on the smoke exhaust effectiveness of the main transformer hall of underground hydropower station, as well as a comparison between experimental data and FDS predicted results. It also investigated the effect of air supply opening location and the CO concentration in the main transformer hall. The results indicated that the effects of the air supply opening location in the transformer hall are minor, but considering the real construction of transformer halls, the air supply opening should be located near the ceiling to avoid affecting the installation of the fire resisting shutters.The measured results showed t the upper layer temperature increases with higher heat release rate and was unrelatec the mechanical exhaust rate which could be obviously seen in Klote’s equation. The CO concentration reduced faster with larger mechanical exhaust rate and it would take at least about40mins for the three different mechanical exhaust rates that the staff can enter the transformer hall.(2) The fire locations in this paper were placed in the adjacent main transformer hall, not directly in the transport passage. This means the smoke spread within the passage has spilled out of the main transformer hall, and is an adhered spill plume. The characteristics of spill plume movement in the transport passage were studied with no smoke extration (Fault Condition). Results showed that temperature distribution along the transport passage of the spill plume from fired main transformer hall could fall into exponential decays.(3) The smoke movement in the transport passage under different mechanical exhaust rates was studied. It was indicated that when the mechanical exhaust rate was designed according to the standard, the smoke layer height in the transport passage could be controlled at some height by the mechanical exhaust system. It can be concluded from smoke temperature and visibility in the main transformer hall that people could escape safely. Results could provide a theoretical basis to develop guidelines for the mechanical exhaust design of the underground hydropower station.(4) The1/50th model of the main transformer hall was constructed and PIV laser particle technology was applied to investigate the smoke movement and mechanical exhaust in the main transformer hall. Results showed that due to the main transformer hall belonged to confined space; environment air would be entrainmented by the buoyancy plumes, and form large scale circulation. The velocity distribution on the height direction of the smoke plume center was found to fall into the Gaussion distribution. Air supply would affect the velocity field significantly, and as the smoke velocities at the exhaust port and air supply port were greater, clear eddy would form above the entrance of the transport passage, which would help the human evacuation.