Abstract
The effect of total pressure of gas mixture is included in the development of new coefficients for the weighted-sum-of-gray-gases model (WSGG). The WSGG formulation previously reported by Bordbar et al. (combustion and Flame 2014, V. 161, pp. 2435–2445), which accounts for variations of molar fraction ratio of H2O to CO2, was employed here to obtain a new total pressure-dependent WSGG model. Hence, the new model includes both the effect of total pressure and variation of molar fraction ratio. High-resolution absorption spectra of gases produced by line-by-line (LBL) calculations using the HITEMP2010 spectral database are used to produce the total emissivity databases needed for the WSGG model development and also to produce the benchmark solution of one-dimensional slab problems used for validation of the new model. The performance of the new WSGG model is studied through several test cases representing various conditions of total pressure, inhomogeneity of temperature, concentration of gas species and molar fraction ratios. In all cases, the new model exhibits a good agreement with the LBL solutions. The new WSGG coefficients allow the model to efficiently solve the spectral thermal radiation in both sub- and super-atmospheric combustion systems.
Highlights
With recent increment in computational resources, the role of numerical modeling in design process of energy conversion systems has more and more highlighted [1,2]
The main advantage of the Weighted-sum-of-gray-gases model (WSGG) model is to accurately account for spectral variation of gas mixtures with a reasonable computational cost, the model has been widely used to calculate the effective absorption coefficient used in gray gas modeling— it is, for instance, the base of the main gas radiation property model of Ansys-Fluent [66]
To assess the accuracy of the WSGG model developed here for such applications, Figure 2 compares the emissivity computed by applying the new model to Eq (7) and the emissivity directly obtained by line-by-line integration of Eq (6) using the absorption spectra extracted from the HITEMP2010 database
Summary
With recent increment in computational resources, the role of numerical modeling in design process of energy conversion systems has more and more highlighted [1,2]. Wang and Modest [25] developed a new narrow-band kdistribution database for CO2 and H2O for total pressures ranging from 0.1 to 30 bar, based on which narrow-band and full-spectrum k-distributions can be obtained for non-homogeneous mixtures Using this database, the full-spectrum k-distribution (FSK) model was applied [26] to predict the radiative heat source in twodimensional, homogeneous CO2-H2O mixtures at a total pressure of 30 atm, with maximum errors relative to the LBL solution of 11%. The present study proposes a new WSGG formulation for CO2H2O mixtures representative of high-pressure combustion This is a direct extension of the WSGG correlation for atmospheric pressure previously reported by Bordbar et al [40] to other values of total pressure (p), and, as depicted, it covers a wider range of total pressures, moleratios and temperatures than the WSGG formulation of Shan et al [51]. Spectral modeling at sub-atmospheric pressures is still a fairly unexplored subject of study, and, as far as the authors’ know, this is the first WSGG model that contemplates these conditions
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