A one dimensional model for the thermal response of a decomposing polymer

A one dimensional transient model for the prediction of the temperature and pore pressure in a decomposing polymer with the capability of handling ablation at the surface is developed. The model is based on the conservation of mass, momentum and energy in a decomposing polymer. It was assumed that the pyrolysis gases and the solid are in local thermal equilibirium and therefore only one energy equation is needed for the conservation of energy. Various methods for the solution of the highly non linear pore pressure equation are outlined and one is proposed as appropriate. The effect of weakly coupled and fully coupled solution schemes as well as the use of nodelets scheme for the calculation of gas mass generation for the predicted temperature and pressure profiles are described. Although one energy equation is used, the limiting case of two energy equation, i.e., infinite and zero volumetric heat transfer coefficients between the gas and the solid is demonstrated. The effects of time stepping and effects of property variations on the in depth temperature and pressure profiles are also described. It is shown that use of sufficiently small time steps is important for the accurate prediction of the pressure and temperature profiles in the material. The effect of the Forcheimer term (inertial resistance) on the pressure solution is also shown. A numerical scheme for handling of surface recession is proposed. An algorithm for predicting the surface temperature for a chemically reacting boundary layer is suggested. Simulation of surface recession with linearly varying recession rate is also possible. The model is capable of handling multiple materials stacked one on top of the other.