RADIATIVE HEAT TRANSFER AUGMENTATION IN GAS-FIRED RADIANT TUBE BURNERS BY POROUS INSERTS: EFFECT OF INSERT GEOMETRY

This article presents the results of an experimental investigation of heal transfer augmentation by porous media in a natural gas-fired radiant tube burner. The results show that significant heal transfer augmentation is possible with the use of porous ceramic inserts in both premixed and nonpremixed gas-fired radiant tube burners. Furthermore, this work has shown that geometry variations in the porous insert configuration can appreciably alter both heat transfer rates and mixing and chemical reaction rates in these systems. In the case of nonpremixed flames, the effect of variation of insert geometry is more than simple heal transfer augmentation via gas enthalpy conversion to thermal radiation by the porous medium. There is also a significant alteration of the reactive gas mixing ( and therefore chemical reaction and heal release) rates along the length of the tube. The basic mechanisms that control the mixing rate and heal release distribution in these systems are still unknown. Nevertheless, it appears reasonable to expect that optimal operating conditions ( uniform, maximum heat flux and temperature; and even minimal NOx emissions) can be achieved, at least in the diffusion burner case, solely through porous insert geometric configuration variations.