Publications (2)0 Total impact
-
[show abstract]
[hide abstract]
ABSTRACT: The effects of melt viscosity and thermal stability of a polymeric material on gasification rate under external radiant fluxes from 1.7 to 3.9 W/cm2 are studied. The effects of melt viscosity are determined by using two different initial molecular weight polystyrene (PS) samples (about a factor of 2 difference in molecular weight); the combined effects of thermal stability with melt viscosity are determined by using two different initial molecular weight poly (methylmethacrylate) (PMMA) samples (about a factor of 4 difference in molecular weight). The results show that thermal stability affects gasification rate but that the transport process of the in-depth degradation products through the molten polymer to the sample surface does not significantly affect gasification rate except at low external radiant flux. The global heat of gasification is sensitive enough to differentiate the effects of thermal stability of the sample, but its value also depends on external radiant flux; in addition, it decreases with an increase in exposure time. This indicates that the global heat of gasification is not a unique quantity for a polymeric material.
Combustion and Flame.
-
Takashi Kashiwagi
[show abstract]
[hide abstract]
ABSTRACT: The effects of sample orientation on autoignition delay times and the minimum external radiant flux for autoignition were studied using a CO2 laser and a gas fired radiant panel as external radiant sources with PMMA and red oak as samples. Ignition delay times were shorter with the horizontal sample than with the vertical one at the same external radiant flux. The minimum external radiant flux for ignition was also less with the horizontal sample. The absorption of external radiation by the boundary layer of decomposition products for the vertical orientation is significant, although its amount is less than the absorption through the plume for the horizontal orientation. Surface temperature at ignition is higher with vertical sample orientation than with horizontal at the same external radiant flux. A theoretical calculation of the surface temperature history with endothermic gasification significantly underestimates the experimental results; this raises a question of the applicability of regression rate expression derived from steady state experiments to the dynamic heating condition.
Combustion and Flame.
