Measurement of the neutral plane of an internal fire whirl using the background-oriented Schlieren technique for a vertical shaft model of a high-rise building

Abstract

Since the height of the neutral plane is related to the direction of the high-temperature smoke and airflow diffusion of fires in high-rise buildings, the identification of the neutral plane is important for both the evacuation of residents and the safety of fire fighters. As yet, there are no effective methods for directly measuring the constantly changing neutral plane position. There are complex internal fire whirl phenomena in the inner space in particular cases. In this study, the background-oriented Schlieren (BOS) technique was used to visualize the neutral plane when a fire whirl occurs in a vertical shaft with a single corner gap. With n-propanol used as the fuel, the scale modeling experiments of fuel trays 5.8cm and 7cm in diameter were tested in a 34cm (W)×35cm (L)×145cm (H) model for open and covered roof types. It is observed in the experimental process that the height of the neutral plane changes dynamically as the fire whirl is formed. The thermocouples were used to measure the temperature variation at different heights of openings to validate the measurement accuracy of the BOS technique. It is found that once a fire whirl occurs in the inner space of a high-rise building, the height of the neutral plane increases instantly. The experimental results demonstrate that the BOS technique can measure the neutral plane position of a large-scale model of a high-rise building fire scene directly, immediately and accurately.