Numerical simulations of polymer pyrolysis rate: Effect of property variations

Abstract

SUMMARYThe mass loss rate (MLR) of poly(methyl methacrylate) (PMMA) exposed to known radiant fluxes is simulated with two recently developed numerical codes, the National Institute of Standards and Technology (NIST) Fire Dynamics Simulator (FDS) and the Federal Aviation Administration (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 MLR, peak MLR, 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 vs time curves, except when in-depth absorption of radiation was important.

Absorption and reflection of infrared radiation by polymers in fire‐like environments

“…The ignition time is more strongly affected: lowering a from 6000 to 1000 m −1 increases the ignition time by a factor of 3 at 200 kW m −2 and 1.5 at 50 kW m −2 . Of course, the relative effects will differ if the polymer properties vary from those in reference . It is also noteworthy that the measured broadband absorption coefficient for black PMMA in the present work (as indicated in Figure ) is outside the range of values (333 to 2000 m −1 ) found in the literature by Bal and Rien , when a sample thickness is considered in which most of the energy is absorbed.…”

“…Given the IR absorption properties of the polymers described above, the influence of absorption coefficient on the burning behavior can be inferred. Using the simulated results in reference for the modeled thermoplastic, values of a between 1000 and 6000 m −1 will have a minor effect on the shape of the mass loss versus time curve. Likewise, this increase in a lowers the average burning rate by about 9% at an external heat flux of 21 kW m −2 and raises it by about 4% at 200 kW m −2 , whereas for (50, 100, or 150) kW m −2 , the effect is only a few percentage.…”

“…Recently, the effect of infrared (IR) transmission in a polymer on the time to ignition has been calculated for a polymer slab (PMMA), of varying decomposition rates and absorption coefficients, subjected to varying radiant fluxes . For example, Figure shows the ignition time for a 25.4‐mm‐thick slab of PMMA as a function of the imposed radiant flux, with total average (integrated over all wavelengths) absorption coefficient varied from 200 to 50,000 m −1 . As indicated, this variation in the absorption coefficient gives a factor of 2 difference in the ignition time at low flux and 11 at high flux.…”

“…Ignition time as a function of the radiant flux, for a 25.4‐mm‐thick sample of poly(methyl methacrylate) with varying values of the absorption coefficient (from ).…”

A numerical study of thermal degradation of polymers: Surface and in-depth absorption

“…They found that in-depth radiation is 4 the primary cause of delayed ignition time for PMMA samples, especially at higher heating rates, which also interpreted the deviation from linearity of the ignition data at high HF. Some other researchers performed sensitivity analyses, emphasizing the sensitivity coefficients of relevant model outputs with respect to the inputs, to study the importance of absorption mode [29][30][31]. Jiang [28] and Linteris [32] measured the average absorption coefficient of several polymers that can be inputted into numerical models, and also they provided generalized techniques for other polymeric materials.…”