EFFECTS OF THE LEWIS NUMBER OF WATER-VAPOR ON THE COMBUSTION AND EXTINCTION OF METHANOL DROPS

A simplified model for the time-dependent, spherically symmetrical com bustion and extinction of methanol droplets is extended to account for a Lewis number of water vapor different from unity. A parametric stud y is performed, showing that, with water absorption and good mixing in the liquid, the burning time and extinction diameter achieve maxima f or water Lewis numbers slightly less than unity in the gas phase. At h igh Lewis numbers, the smaller diffusion coefficient reduces the amoun t of water absorbed, and at lower Lewis numbers, the larger diffusion coefficient increases the rate of water loss to the atmosphere, reduci ng the water concentration at the flame and the water absorbed in the liquid. The extent of absorption, therefore, maximizes at an intermedi ate Lewis number. (C) 1998 by The Combustion Institute.