Validation of pyrolysis model in transient heating scenarios and diverse spectral boundary conditions

Abstract

This study aims to provide a robust validation to the condensed-phase pyrolysis model approach used in the FireFOAM CFD code. Firstly, bench-scale pyrolysis tests were conducted for two engineering wood products (EWPs), namely plywood and medium density fiberboard (MDF), at three constant heat flux levels. These tests were used to derive model-effective material properties via inverse modeling and optimization approaches. For MDF, a better model fit was obtained when the virgin material density was allowed to vary along its thickness, which is consistent with its known anisotropic nature. Next, three test cases were developed for the purpose of pyrolysis model validation by subjecting the EWPs to fire-relevant dynamic heating scenarios. In two tests, the materials were exposed to transient heating conditions where the heat flux to the materials increased over the duration of pyrolysis. In the remaining test, the spectral emissivity boundary condition of the sample material was altered significantly. Very good agreement was observed between the validation experimental data and the model predictions for all three scenarios. The validation studies provide confidence that the model-effective material properties, determined using inverse modeling and optimization for constant heating conditions, can be confidently applied to fire-relevant dynamic heating scenarios and boundary conditions.