An experimental study on the morphology and behaviors of fire with nearby inclined surface during flame spread on building integrated photovoltaic (BIPV)

Abstract

To enhance the understanding of fire dynamics in building-integrated photovoltaic (BIPV) systems, an experimental study was performed to investigate the influence of pool fires generated by ignited PV panels on adjacent inclined unburned PV panels within an array. Experiments were conducted under 50 different conditions, encompassing a range of inclination angles (0° to 90°) and varying fire source heat release rates using a gas burner. The evolution of the flame morphology and characteristic behaviors influenced by nearby inclined surfaces was examined. The results indicate that asymmetrical air entrainment induced by the inclined surface causes the flame height to initially decrease and then increase with increasing inclination angle, while the flame tilt angle exhibits the opposite trend. Owing to the buoyancy components parallel and perpendicular to the inclined surface, the flame attachment length exhibits an increasing trend, while the distance from the flame tip to the inclined surface decreases monotonically with the inclination angle. The flame transitions from partial attachment to complete attachment mode within the range of 60° to 70°, which is a crucial factor influencing the morphology and behavior of the flame. Global correlations were established to describe the flame morphology through the force analysis of the flame. As the inclination angle increases, the flame transitions from non-attachment to intermittent attachment to the inclined surface, with the transition behavior quantified using the dimensionless heat release rate and trigonometric functions. Due to the restriction of the entrainment space, the flame pulsation frequency decreased with the increase of the inclination angle. Dimensionless models were formulated to predict the flame pulsation frequency, considering the hydraulic diameter for both free and wall flames. The morphology and characteristic behaviors of the flame predicted by the proposed model were compared with the measurement data, demonstrating reasonable agreement.