Study of Smoke Flow of Enclosed Space Fire with Horizontal Openings
|School||Harbin Engineering University|
|Course||Thermal Power Engineering|
|Keywords||horizontal openings buoyancy-induced flow small-scale experiment FDS|
Gas exchange between the ambient and the fire room plays an important role to the fire development in case of a fire in an enclosure. The exchange channel of hot smoke and cold air channel is the opening in the wall. The building opening usually can be divided into horizontal and vertical openings. A lot of work has been dealt with the study of flow through vertical openings, but few for horizontal openings. Not only pressure-induced flow but also buoyancy-induced flow is included when smoke flow through horizontal openings. And the complicated flow mechanism needs further research.This paper described the present researches about the enclosure fire with horizontal openings and summarized the research methods, then introduces the flow model of vertical and horizontal openings. And it was pointed out the flow difference between the two models. The main factors influencing the flow through horizontal openings is the pressure difference, the temperature difference between the top and the bottom of the vent, the ratio of length and width of the vent. The purpose of this paper is to study the buoyancy-induced flow through the openings, while the influence of pressure difference was not concerned.In this paper, two flow patterns through horizontal openings were simulated by FDS software. The first case was setting pool fire as the heat source. The second case was setting heater as the heat source, and the third case was giving temperature difference between the top and bottom of the vent. The first case found that instantaneous unidirectional flow through the horizontal opening. The temperature and flow of the vent oscillates steadily after a period of time. Oscillation frequency decreases with the decrease of the heat release rate. In the second case, only bidirectional flow can happen. The temperature and flow of the vent oscillates with time but not steady. In the third case, it is simulated pure buoyancy-induced flow through a horizontal opening. The result indicated flow patterns are highly transient and unstable. The temperature and flow of the vent oscillates intermittently with time. Simulation results were agreed well with previous studies.Two small-scale box experiments are employed to study the room fire with horizontal openings. The two boxes are respectively a rectangular and cube box. The results indicated that the flame height of the pool fire in box is higher than the flame height when pool fire burns free. And a laminar-like fire was observed. Comparing with free burning, the burnt-out time of pool fire in box increases with the decrease of the vent size. In the rectangular box experiment, the pool fire at the corner is more difficult to burn than at the center. However it can form smoke layer easily. The temperature increases with height in the rectangular box. But in the cube box experiment, the temperature doesn’t increase with height. By analysis, it might be the leak of cube box. In both two experiments, the temperature of the vent oscillates with time, which indicates the unsteady smoke flow through the horizontal opening.The obtained results can provide a reference for the study of enclosure fire with horizontal openings. It has practical significance for understanding the mechanism of smoke flowing through horizontal openings.