- Author
- Chen, Y.
- Title
- Development of an Integral Model for Transient Charring Pyrolysis Process and Derivation of Material Flammability Properties.
- Coporate
- Worcester Polytechnic Inst., MA
- Report
- Thesis, January 1991, 240 p.
- Keywords
- charring | pyrolysis temperature | flammability | pyrolysis models | pyrolysis rate
- Identifiers
- heat-up process; numerical integration
- Abstract
- An integral thermal pyrolysis model for characterizing pyrolysis processes in charring material has been developed, evaluated by comparison with exact solutions and applied for deducing pyrolysis properties for charring and non-charring materials. To model the pyrolyzing material, is divided into two layers: the char layer where the material has pyrolyzed and the virgin layer where the material has not pyrolyzed yet. The two layers are separated by an isothermal interface which is at a temperature equal to the material pyrolysis temperature. At this interface, the heat of pyrolysis is absorbed by the virgin layer nd the material is converted to char and gases. One dimensional conduction heat transfer for a solid insulated at the back surface is used in this model. Different exponential temperature profiles in the char and virgin layers of a material are assumed respectively. Using these temperature profiles in the governing heat conduction equations and 0-moment method, which proved to be quite accurate, the original partial differential equations were transformed into a set of ordinary differential equations. The differential equations have been solved for the pyrolysis rate, pyrolysis depth, and surface temperature. The present model can be used for solving the transient pyrolysis processes in both charring and non-charring materials. These materials are exposed to time dependent heat flux including surface reradiation losses which are significant especially for charring materials. The results from the model have been compared with analytical results corresponding to several cases where good agreement has been obtained. The proven accuracy of the integral model together with its simplicity has allowed the deduction of pyrolysis properties for charring materials. The experimental data from previous work were obtained in an existing flammability apparatus where mass loss and surface temperature histories were measured. Material properties include for the virgin, conductivity for char as well as the heat of pyorlysis L and the pyrolysis temperature can be obtained from comparison of the integral code result and the experimental data stated above as well as the previous studies (Delichatsios et al., 1989). A methodology for obtaining these properties using both experimental results and the model is also demonstrated in this work. The present integral model for charring materials is intended to be incorporated into an upward flame spread code.