Experimental study on upward fire spread of polyurethane foam under double fire source conditions with different restricted facade Structures

This paper examines the impact of insulation material (PU) fire spread characteristics under dual fire source conditions considering various restricted facade Structures. It is found that the merging tendency is affected by the flame inclination angle theta 1 and mapping length L. Additionally, the flame merging behavior is determined by the combined effects of the chimney effect, inter-flame air entrainment, and heat transfer changes caused by the restricted angle. The Inter-flame air entrainment lambda was introduced to confirm that there is a positive correlation between flame height and Inter-flame air entrainment in the large-angle restricted facade Structures (theta = 120 degrees, 150 degrees, 180 degrees). By introducing the hydraulic diameter D & lowast;eff to compare the experimental data with the previous flame pulsation frequency model, the proposed f = 0.5 g/D & lowast; eff model can further improve the accuracy of the prediction results. During the flame merging stage, the axial temperature field distribution on the PU board surface was compared. The study found that the restricted facade Structures resulting in a cooling effect due to fresh air entrainment at the bottom with the chimney effect. As a result, the small-angle restricted facade Structures (theta = 30 degrees, 60 degrees, 90 degrees) led to an upper-high and lower-low distribution of axial temperature.