Radiative heat transfer in natural gas-®red furnaces E.P. Keramida a , H.H. Liakos a , M.A. Founti b , A.G. Boudouvis a , N.C. Markatos a, * a Department of Chemical Engineering, National Technical University of Athens, Zografou Campus, Athens 157 80, Greece b Department of Mechanical Engineering, National Technical University of Athens, Zografou Campus, Athens 157 80 Greece Received 8 April 1999; received in revised form 26 July 1999 Abstract The performance of the discrete transfer and of the six-¯ux radiation models is assessed in a swirling natural gas diusion ¯ame con®ned in an axisymmetric furnace. The predictions are evaluated as part of a complete prediction procedure involving the modeling of the simultaneously occurring ¯ow, combustion, convection and radiation phenomena. Computational results with and without radiation eects are compared with experimental data and the two radiation models are evaluated in terms of computational eciency, ease of application and predictive accuracy. The results have demonstrated that the eect of thermal radiation is important even in light ¯ames, and that the six- ¯ux model can be applied in industrial gas furnaces with relative ease, yielding accurate predictions. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Radiation; Natural gas furnaces; Six-¯ux model; Discrete transfer model 1. Introduction Thermal radiation in gaseous media can be an im- portant mode of heat transfer in high temperature chambers, such as industrial furnaces and boilers, even under non-soot conditions. Growing concern with high temperature processes has emphasized the need for an evaluation of the eect of radiative heat transfer. For example, thermal radiation aects signi®cantly the structure and extinction characteristics of a methane± air ¯ame due to the radiative cooling mechanism [1,2], as well as the NO formation due to the sensitivity of thermal NO kinetics to temperature [3]. Nevertheless, the modeling of radiative transfer is often neglected in combustion analysis, mainly because it involves complex mathematics, high computational cost, and signi®cant uncertainty concerning the optical properties of the participating media and surfaces. However, ignoring radiative transfer may introduce signi®cant errors in the overall predictions. In previously published evaluations of radiation models for gaseous furnaces, the models are tested sep- arately, that is, in isolation from other physical pro- cesses, by using prescribed radiative energy source term distributions [4±10]. In real operating furnaces though, non-uniform distributions of velocity and tem- perature are encountered and the predictive behavior of any radiation model is expected to dier from the simpli®ed case [4,11]. A numerical experiment is carried out in this paper, using two dierent radiation models to analyze the radiative heat transfer in an industrial natural-gas fur- nace con®guration. The predictions are evaluated as International Journal of Heat and Mass Transfer 43 (2000) 1801±1809 0017-9310/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0017-9310(99)00244-6 www.elsevier.com/locate/ijhmt * Corresponding author. Tel.: +30-1-772-3227; fax: +30-1- 772-3228. E-mail address: ellik@chemeng.ntua.gr (N.C. Markatos).