The role of natural convection on cool flames and autoignition

Chapek, Richard; Neville, Donna; Wu, Ming-Shin; Hehemann, David; Sheredy, William; Pearlman, Howard
January 2000
AIP Conference Proceedings;2000, Vol. 504 Issue 1, p408
Academic Journal
Slow reaction, cool flames and autoignition are discussed in the context of unstirred, static reactors at terrestrial (1g) and microgravity (μg) environments. At 1g, conductive heat transport is important when the Rayleigh number (Ra) is less than 600, conduction and convection are important when the Ra ranges from 600 to approximately 10[sup 4] and convection governs when Ra exceeds 10[sup 4]. Except for highly-diluted, weakly exothermic reactions, the Ra for all laboratory-scale, lg experiments ranges from 10[sup 3]–10[sup 5]. Hence, convection and conduction are important at 1g. Existing models, however, neglect convection, in lieu of conduction, to simplify mathematical formulation. While this assumption is not valid for most 1g cool flames and autoignitions, it is valid at μg where Ra numbers on the order of 10–100 are easily attained in drop towers and aircraft. Aboard the Space Shuttle and Station, typical Ra’s are order 1/10–1. © 2000 American Institute of Physics.


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