Numerical Simulations of Thermoplastic Burning Rate: Effect of Property Variations and the Inferred Effective Heat of Gasification
Gregory T. Linteris
The mass loss rate of Poly(methyl methacrylate) exposed to known radiant fluxes is simulated with two recently-developed numerical codes, the NIST Fire Dynamics Simulator (FDS) and the FAA ThermaKin. The influence of various material properties (thickness, thermal conductivity, specific heat, absorption of infrared radiation, heat of reaction) on mass loss history is assessed, via their effect on the ignition time, average mass loss rate, peak mass loss rate, and time to peak. The two codes predict the influence of material parameters on the MLR in the order of decreasing importance: heat of reaction, thickness, specific heat, absorption coefficient, thermal conductivity, and activation energy of the polymer decomposition. Changes in the material properties also influence the MLR curves by switching the sample from thermally thick to thermally thin. The two numerical codes are generally in very good agreement for their predictions of the MLR versus time curves, except when in-depth absorption of radiation was important. The influence of two of these parameters on the effective heat of gasification (extracted from the mass loss rate at differing external heat fluxes) is also assessed by comparing the effective heat of gasification to the heat of gasification input into the calculations; the ratio of these is highest for calculations in which the radiant energy is absorbed on the surface and the material decomposition has a low activation energy, for which it reaches 1.3, but is lower for other cases. Modifying the method used to obtain the effective heat of gasification by basing it on the net energy delivered to the polymer brings it much closer to the values input into the calculation.
Numerical Simulations of Thermoplastic Burning Rate: Effect of Property Variations and the Inferred Effective Heat of Gasification, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.TN.1929
(Accessed June 2, 2023)