A comparison of mathematical models of the radiative behaviour of a large-scale experimental furnace

Abstract

Three two-flux models, which had been developed previously for the approximate treatment of two-dimensional radiative energy transfer in industrial heaters, have been modified and applied to prediction of the thermal behaviour of a cylindrical large-scale gas-fired experimental furnace. Testing of the predictions has been carried out by utilising previously reported experimental values, and some zone method predictions. Cross-sectional average gas temperatures predicted using the zone and Roesler methods are found to be almost identical at any axial station, both slightly underestimating the measured values. The spherical harmonic (S-H) two-flux model distribution runs below and parallel to the Roesler predictions. The Schuster-Schwarzschild (S-S) type two-flux model with assumed plane parallel radiation (b=1) produces acceptable agreement in the first half of the furnace, and subsequent progressively increasing overestimation, whereas the same model with b=2 (isotropic radiation) underpredicts temperature in the first half of the furnace and leads to good agreement thereafter. Reasonable predictions are also obtained for the distributions of net heat flux density at the water-cooled sidewalls. The percentage errors in the predicted overall heat transfer to the water cooled walls are, with the exception of the S-S type with b=1, less than 3.5 for all the models. As the calculations involved in their use are relatively simple and economical, the Roesler, the isotropic S-S type, and the S-H type two-flux models should prove useful to designers for the approximate prediction of temperature and radiative heat flux distributions in axi-symmetrical furnaces in which one-dimensional flow, temperature and heat release patterns may reasonably be assumed.