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Author
Ito, A. | Kashiwagi, T.
Title
Temperature Measurements in PMMA During Downward Flame Spread in Air Using Holographic Interferometry.
Coporate
National Bureau of Standards, Gaithersburg, MD
Book or Conf
Combustion Institute, Symposium (International) on Combustion, 21st. August 3-8, 1986, Combustion Inst., Pittsburgh, PA, Munich, West Germany, 65-74 p., 1986
Keywords
holography | interferometry | holographic interferometry
Abstract
Temperature distributions within a thermally thick slab of poly(methylmethacrylate) (PMMA) during downward flame spread were determined by measurements of changes in refractive index of PMMA using a holographic interferometry technique. The surface temperature history was measured with a fine thermocouple as a reference for the interferogram over the glass transition region. Samples with widths of 0.32, 0.47 and 1.0 cm and thicknesses of 1.5 and 2.5 cm were used. The experimental configurtion was arranged to make the phenomena two-dimensional in the direction of the laser beam. Detailed temperature and heat flux profiles, especially in the area of the immediate vicinity of the flame foot, were obtained. The results indicate that the surface temperature increases gradually from about 1 cm ahead of the vaporization front and reaches the glass transition temperature about 0.2 cm ahead of the vaporization front. Then, it sharply increases to the vaporization temperature, about 380 deg C. The visible flame front extends about 0.1 cm ahead of the vaporization front. The measured net heat flux from the gas phase to the sample surface increases sharply from about 1 W/cm2 to 7 W/cm2 within a distance of about 0.1 cm from the vaporization front. The net heat transfer rate from the gas phase to the sample is about 57% of the total heat transfer rate to the sample. It is concluded that this net heat transfer from the gas phase plays the dominant heat transfer mode to heat the thick PMMA slab instead of conductive heat transfer through the condensed phase, as was previously believed.