A nongray-wall emissivity model for the full-spectrum correlated k-distribution method based on uniform media assumption

Abstract

The walls of high-temperature combustion devices are usually assumed to be black or gray in radiative heat transfer calculations to save computing resources; however, this simplification may introduce large errors. To improve the accuracy of the Full-Spectrum Correlated K-distribution (FSCK) method in calculations of nongray-wall radiative heat transfer problems without reducing the computational efficiency, a nongray-wall emissivity model for the FSCK method is proposed based on uniform-medium assumption. The accuracy of this nongray-wall emissivity model and the commonly used Planck-function-weighted gray-wall emissivity model is evaluated in 1D isothermal and homogeneous cases, 1D non-isothermal and inhomogeneous cases, and 3D flames bounded by walls coated with fly-ash deposit or soot deposit. The results show that the nongray-wall emissivity model for FSCK demonstrates much better accuracy than the gray-wall one, especially for cases of low wall temperatures. The nongray-wall emissivity model provides good accuracy over a wide range of optical depth, while the accuracy of the gray-wall emissivity model is highly dependent on the optical depth. The nongray-wall emissivity model based on the uniform-medium assumption can be applied to non-isothermal and inhomogeneous radiative heat transfer problems involving nongray walls.