A MULTI-SCALE FULL-SPECTRUM CORRELATED–k DISTRIBUTION FOR RADIATIVE HEAT TRANSFER IN INHOMOGENEOUS GAS MIXTURES Hongmei Zhang and Michael F. Modest Department of Mechanical Engineering, Pennsylvania State University, University Park, PA-16802, USA ABSTRACT. A multi-scale full-spectrum correlated–k distribution (MSFSCK) model has been developed and tested for radiative transfer calculations in absorbing/emitting molecular gases. The gas or gas mixture is broken up into different scales by separating different absorbing species and, for each specie, by collecting them into scales according to the lower level energy of their spectral lines. Like all k-distribution method as well as the full-spectrum correlated-k (FSCK) model, the new model may be used with any arbitrary RTE solver. Results for one- and two-dimensional inhomogeneous gas mixtures with varying temperature and concentration fields are presented and compared with line-by-line benchmarks and the FSCK model, showing very good accuracy in situations with severe temperature gradients and/or sharp concentration ratio changes. INTRODUCTION Radiative transfer in nonisothermal and inhomogeneous gas mixtures can be most accurately predicted by using the line-by-line approach, but LBL calculations require large computer resources and computational time. Therefore, many studies have been devoted to the development of more efficient but approximate band and global models. The correlated–k (CK) method is based on the fact that inside a spectral band , which is sufficiently narrow to assume a constant Planck function, the precise knowledge of each line position is not required for the computation since the intensity varies with gas absorption coefficient only [1 5]. Provided the medium is homogeneous or the absorption coefficient obeys the so- called scaling approximation, the absorption coefficient can then be reordered into a smooth, monotonously increasing function. Due to the presence of “hot lines”, the CK method is known to give poor accuracy in cases with extreme temperature gradients. For such situations, Rivi` ere and coworkers [6 8] developed what they called the correlated-k fictitious gas model (CKFG). Starting with a high-resolution database, they grouped lines according to the values of their lower level energy and found the k–distribution for each of the fictitious gases, making the CK method more accurate when applied to each fictitious gas separately than when applied to the real gas. They made the further approximation that the positions of lines belonging to different classes are statistically uncorrelated. Unfortunately, the method only supplies the mean transmissivity for a gas layer, i.e., it loses the most important advantages of the k–distributions, limiting its application to nonscattering media within a black-walled enclosure. The most popular global method is the so-called Weighted-Sum-of-Gray-Gases model (WSGG).