Experimental study of interlayer effect induced by building facade curtain wall on downward flame spread behavior of polyurethane

Abstract

This paper presents an experimental investigation on interlayer effect induced by curtain wall, parallel to the building exterior facade, on thermal and burning behavior of insulation material flexible polyurethane (FPU). Results show that, downward flames propagation behavior along the interlayer was determined by the coupling effects including chimney effect, constraint effect and related heat transfer variation induced by curtain wall. Firstly, comparing to the occasionally melting-dripping phenomenon without curtain wall, continuous melting-dripping liquids were generated subject to positively heat feedback by internal heat radiation to the incomplete ember layer at later combustion stage, which is more distinct for narrow curtain wall spacing. Secondly based on the analysis of heat feedback and the dripping degree, the non-monotonous relation between mass loss and spacing D was interpreted. Thirdly, flame physical variations e.g., height and stretching induced by complex turbulence were discussed with plate flow theory. Furthermore, hot gas temperature field along board surface centerline and sideline were compared. Due to the insufficient combustion and cooling of upwards air entrainment, temperature along centerline was found to be lower generally, which is different from the free burning. In addition, analysis on radiation flux development with soot blockage effect and also flame spread velocity was proposed.