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Heat and Mass Transport From Thermally Degrading Thin Cellulosic Materials in a Microgravity Environment.


pdf icon Heat and Mass Transport From Thermally Degrading Thin Cellulosic Materials in a Microgravity Environment. (445 K)
Kushida, G.; Baum, H. R.; Kashiwagi, T.; diBlasi, C.

Journal of Heat Transfer, Vol. 114, No. 2, 494-502, May 1992.

Sponsor:

National Aeronautics and Space Administration, Lewis Research Center, Cleveland, OH

Keywords:

cellulosic materials; reduced gravity; thermal degradation

Abstract:

A theoretical model describing the behavior of a thermally thin cellulosic sheet which is heated by external thermal radiation in a quiescent microgravity environment is developed. This model describes thermal and oxidative degradation of the sheet and the heat and mass transfer of evolved degradation products form the heated cellulosic surface into the gas phase. At present, gas phase oxidation reactions are not included. Without buoyancy, the dominant vorticity creation mechanism in the bulk of the gas is absent except at the material surfacy by the requirement of the no-slip condition. The no-slip condition is relaxed, permitting the flow to be represented by a velocity potential. This approximation is permissible due to the combination of a microgravity environment and low Reynolds number associated with slow small-area heating by external radiation. Two calculations are carried out; heating without thermal degradation and heating with thermalo degradation of the sheet with endothermic pyrolysis, exothermic thermal oxidative degradation and highly exothermic char oxidation. The results show that pyrolysis is the main degradation reaction. Moreover, self-sustained propagation of smoldering for cellulosic materials is very difficult due to the lack of sufficient oxygen supply in a quiescent environment.