Simple Expression for the Emittance of H2O–CO2 Mixtures in Zonal Methods of Radiation Transfer Modeling

A new and simple expression for the calculation of the total gas emittance of H2O–CO2 mixtures for modeling radiation transfer in combustion furnaces is presented. Its accuracy is established by comparing the predictions with those based on the well established the model based on Hitemp database. The computational time was found to be reduced by a factor of 3 in comparison to other methods for computing the total emittance of combustion gas mixtures.

Simple Expression for the Emittance of H2O-CO2 Mixtures in Zonal Methods of Radiation Transfer Modelling

A new and simple expression for the calculation of the total gas emittance of H2O-CO2 mixtures for modeling radiation transfer in combustion furnaces is presented. Its accuracy is established by comparing the predictions with those based on the well established exponential wide band model. The computational time was found to be reduced by a factor of 10–30 in comparison to other methods for computing the total emittance of combustion gas mixtures.

A Method of Measuring the Properties of Ash Deposits in a Coal Fired Reactor

Coal is an important source of energy because of its potential for power generation and its abundance in the earth. A great deal of research is dedicated to developing cleaner and more efficient methods of generating power from coal. A major problem associated with almost all power generation processes involving coal is the formation of ash. Some of the ash that is formed is deposited on the tubes and walls of the combustion chambers. This accumulation of ash can significantly affect the thermal transport in the boiler. Modeling of the heat transfer occurring in a coal combustion process requires knowledge of the properties of these deposits. Accurate measurements of these properties will lead to better modeling capabilities and improved optimization of the design of coal fired reactors. Therefore, a method for accurate, in situ measurement of the emittance and thermal conductivity is highly desirable. This paper describes the development of a method for determining the total emittance and thermal conductivity of the deposited ash layers and analyzes the sensitivity of these properties to measurement errors.

Evaluation of Total Emittance of an Isothermal Nongray Absorbing, Scattering Gas-Particle Mixture Based on the Concept of Absorption Mean Beam Length

A general methodology to evaluate the total emittance of an isothermal, nongray, isotropically scattering particle-gas mixture is illustrated. Based on the concept of absorption mean beam length (AMBL), the methodology is demonstrated to be computationally efficient and accurate. As an illustration, the total emittance of a slab containing carbon particles and CO2 is evaluated. The nongray extinction coefficient and scattering albedo of carbon particles are calculated based on Mie theory and the available index of refraction data. The narrow-band fixed-line-spacing model (Edwards et al., 1967) is used to characterize the nongray spectral absorption coefficient of CO2. Numerical data show that the combined nongray and scattering effects are quite significant. For particles with moderate and large radius (say, ≥1 μm), ignoring the effect of scattering can lead to error in the prediction of total emittance by more than 20 percent. The no-scattering results also yield incorrect qualitative behavior of the total emittance in terms of its dependence on the mixture temperature and particle concentration. The accuracy of many of the existing predictions of total emittance of gas-particle mixtures that ignore the scattering effect is thus highly uncertain.