A study of convective heat transfer from flames

Abstract

A study of the heat transfer from highly dissociated combustion products to a cold surface has been undertaken. Convective heat transfer coefficients have been determined experimentally at the stagnation point of a blunt body immersed in the flames of several common fuel gases burning with pure oxygen. The conditions chosen result in the production of severe temperature gradients which induce correspondingly large changes in species concentrations and thermophysical properties across the boundary layer. Consequently an appreciable proportion of the energy transfer may occur by the diffusion and exothermic recombination of dissociated species. Theoretical predictions of the heat transfer have been made for the range of conditions studied experimentally. A numerical solution of the appropriate conservation equations has been obtained and a method for the modification of an established low temperature heat transfer relationship has been proposed. Both approaches enable extreme property variations and diffusion-recombination effects to be taken into account when calculating heat flux. Reasonable agreement between experiment and the numerical and semi-empirical predictions has been obtained.