Heat transfer from hydrocarbon-oxygen flames

Abstract

Heat fluxes from premixed methane-oxygen and propane-oxygen flames of various equivalence ratios were measured, using a transient calorimetric method. The experimental results for heat transfer to the forward stagnation point of a hemispherical-nosed probe are compared with those calculated, assuming that ( a ) recombination reactions of dissociated species are frozen in the boundary layer and the surface is noncatalytic; ( b ) equilibrium is maintained thoughout the boundary layer, but the Lewis number of all atoms and radicals is unity; and ( c ) energy transfe, by diffusion and recombination of hydrogen atoms is more rapid than heat transfer by ordinary conduction, that is, there is a Lewis-number augmentation effect. These comparisons show that method ( a ) seriously underestimates the heat transfer and that the experimental values are intermediate between those calculated on the basis of assumptions ( b ) and ( c ). Since equilibrium is assumed, negligible concentrations of hydrogen atoms exist at temperatures below 1700°K, and the Lewis number is, therefore, calculated for the outer region of the boundary layer. The Lewis numbers of other species are not high enough to affect the heat flux to any significant extent. General methods of modifying low-temperature heat transfer correlation equations to allow for recombination and diffusion are presented.