Ignition Modes of PMMA Under Convective Heating

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. AFRC85-1 IGNITION MODES OP PMMA UNDER CONVECTIVE HEATING by T.X.Phuoc Graduate Research Assistant and P. Durbetaki Professor School of Mechanical Engineering Georgia Institute of Technology Atlanta, Georgia 30332-0405 25~- ABSTRACT Ignition of PMMA under convective exposure Is investigated using quasi-steady approximation for the gas phase. The transient effect is accounted for the solid phase only. Both surface and gas phase chemical reactions are included simultaneously. The ignition mechanism is studied in terms of heat transfer, mass transfer and chemical processes at the surface as well as in the gas phase. The results Indicate that ignition occurs in the heterogeneous mode in a narrow range of low flow velocity and high temperature. But it switches to the homogeneous mode in a wide range of high flow velocity. NOMENCLATURE A frequency factor a potential flow coefficient c specific heat P D binary diffusion coefficient First and Second Damkohler Numbers activation energy dimensionless activation energy blowing velocity dimensionless velocity heat transfer coefficient heat of formation of species 1 thermal conductivity molar mass Nusselt number pressure Prandtl number heat of reaction gas constant Reynolds number stoichiometric ratio Schmidt number temperature time x-component velocity free stream velocity y-component velocity x and y coordinates mass fraction production rate coupling equation, Eq. (27) Lee's transformation, Eq (14)