A Study of Convective Heat Transfer from High Temperature Combustion Products

Abstract

The prediction of heat transfer rates from fuel-oxygen flames to solid surfaces is complicated by the wide variations in physical properties encountered in the gas phase and by the energy transfer which results from the diffusion and recombination of dissociated species. Consequently the conventional methods for the assessment of heat fluxes are found ts be inadequate when applied to combustion systems. A research programme was therefore initiated to carry out extensive experimental and theoretical studies of heat transfer from high temperature combustion products. Convective heat transfer coefficients have been measured at the stagnation point of an axially symmetrical blunt body immersed in the flames of a number of common fuel gases burning with pure oxygen. Theoretical predictions have been made for the full range of conditions covered experimentally. A numerical solution of the appropriate boundary layer conservation equations has been obtained and a method for the modification of the established relationship for heat transfer at low temperature levels has been proposed. Both approaches enable the extreme property variations and the diffusion-recombination effects to be taken into account when estimating the heat flux. Good agreement between experiment and the two prediction methods has been achieved in most cases. Because of its potential value in design calculations the suggested empirical method has been tested over a wider range of conditions. Heat transfer from stoichiometric flames to small spheres has been measured at surface temperatures ranging to 1600K. It has been found that the proposed prediction method provides quite acceptable agreement with the experimental data.