Abstract
A 2D numerical model coupling condensed and gas phases is developed to investigate autoignition of finite thick PMMA heated by radiation in forced airflow. Six sample thicknesses (1–15 mm), four heat fluxes (30–60 kW/m2), and five airflow velocities (0–1.2 m/s) are considered to examine their effects. The model is first verified by measured surface temperatures in experiments. Then three boundary layers (BL), velocity, thermal and concentration BLs, are studied based on simulation results and BL theory. BL thickness, local and surface-averaged frication coefficients, convective heat and mass transfer coefficients at solid–gas interface are estimated and compared with analytical results. Meanwhile, Damköhler numbers (Da) in non-ignition cases are calculated to reveal their impact. The results show that the model predicts measured surface temperatures well despite some divergence for thin samples due to deformation. Simulated velocities and thermal BL thicknesses agree well with analytical ones, yielding a maximum error of 33 % for concentration BL. Numerical convective heat and mass transfer coefficients match analytical ones well, whereas large discrepancy exists for friction coefficient. Two types of Da evolution, corresponding to different controlling mechanisms of non-ignition cases, separated by 6 mm sample are identified.
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