Theoretical Analysis and Numerical Simulation of Spectral Radiative Properties of Combustion Gases in Oxy/Air-Fired Combustion Systems

摘要

Energy efficiency is one of the major objectives which should be achieved in order toimplement the limited energy resources of the world in a sustainable way. Since radiativeheat transfer is the dominant heat transfer mechanism in most of fossil fuel combustionsystems, more accurate insight and models may cause improvement in the energy efficiencyof the new designed combustion systems. The radiative properties of combustiongases are highly wavelength dependent. Better models for calculating the radiative propertiesof combustion gases are highly required in the modeling of large scale industrialcombustion systems. With detailed knowledge of spectral radiative properties of gases,the modeling of combustion processes in the different applications can be more accurate.In order to propose a new method for effective non gray modeling of radiative heat transferin combustion systems, different models for the spectral properties of gases includingSNBM, EWBM, and WSGGM have been studied in this research. Using this detailedanalysis of different approaches, the thesis presents new methods for gray and non grayradiative heat transfer modeling in homogeneous and inhomogeneous H2O–CO2 mixturesat atmospheric pressure. The proposed method is able to support the modeling of awide range of combustion systems including the oxy-fired combustion scenario. The newmethods are based on implementing some pre-obtained correlations for the total emissivityand band absorption coefficient of H2O–CO2 mixtures in different temperatures, gascompositions, and optical path lengths. They can be easily used within any commercialCFD software for radiative heat transfer modeling resulting in more accurate, simple, andfast calculations.The new methods were successfully used in CFD modeling by applying them to industrialscale backpass channel under oxy-fired conditions. The developed approaches are moreaccurate compared with other methods; moreover, they can provide complete explanationand detailed analysis of the radiation heat transfer in different systems under differentcombustion conditions. The methods were verified by applying them to some benchmarks,and they showed a good level of accuracy and computational speed compared toother methods. Furthermore, the implementation of the suggested banded approach inCFD software is very easy and straightforward.