A new weighted-sum-of-gray gases (WSGG) model that is based on the statistical narrow band model (SNB) RADCAL is proposed for use in computational fluid dynamic (CFD) simulations of air and oxy-combustion. When employed in conjunction with the discrete ordinates (DO) method, the model predictions compare well against line-by-line benchmark data that have been made available recently that are based on the latest spectroscopic databases. Furthermore, the model compares well against the EM2C SNB model calculations that have served as benchmark data in three-dimensional geometries. Radiative transfer calculations in these prototypical problems therefore confirm recent experimental observations that SNB RADCAL and EM2C SNB serve as good model databases to develop approximate radiative property models. To achieve an optimum balance of speed and accuracy in computationally intensive CFD simulations, non-gray formulations of the WSGG model are also employed with the P1 model and solutions are compared against those generated by the DO model. While the P1 model gave favorable comparisons when cold, black walls were present, the errors in the surface incident radiative flux predictions increased in the presence of hot, reflecting walls. Finally, in fully coupled simulations of natural gas combustion under air-firing and oxy-firing modes, the predicted incident radiative flux profiles were distinctly different between the gray and non-gray calculations at regions of high temperature gradients, while the centerline temperature predictions were comparatively unaffected. The effects of turbulence radiation interactions were also accounted for through the temperature self-correlation term. However, the magnitudes of the temperature fluctuations were small and localized within this furnace and did not significantly alter our predictions. Copyright © 2012 John Wiley & Sons, Ltd.

This study assesses the required fidelities in modeling particle radiative properties and particle size distributions (PSDs) of combusting particles in Computational Fluid Dynamics (CFD) investigations of radiative heat transfer during oxy-combustion of coal and biomass blends. Simulations of air and oxy-combustion of coal/biomass blends in a 0.5 MW combustion test facility were carried out and compared against recent measurements of incident radiative fluxes. The prediction variations to the combusting particle radiative properties, particle swelling during devolatilization, scattering phase function, biomass devolatilization models, and the resolution (diameter intervals) employed in the fuel PSD were assessed. While the wall incident radiative flux predictions compared reasonably well with the experimental measurements, accounting for the variations in the fuel, char and ash radiative properties were deemed to be important as they strongly influenced the incident radiative fluxes and the temperature predictions in these strongly radiating flames. In addition, particle swelling and the diameter intervals also influenced the incident radiative fluxes primarily by impacting the particle extinction coefficients. This study highlights the necessity for careful selection of particle radiative property, and diameter interval parameters and the need for fuel fragmentation models to adequately predict the fly ash PSD in CFD simulations of coal/biomass combustion.

Experimental and modeling based assessments of employing reflective wall coatings towards improving the effectiveness of ultraviolet germicidal irradiation in unoccupied hospital rooms were carried out. Measurements of incident radiative fluxes on different surfaces were made in a control room as well as a room whose walls were painted with a nanostructured UV-C reflective wall coating. Employing the reflective paint resulted in up to a 20% increase in the incident radiative fluxes on some surfaces that were directly exposed to the radiation and nearly a 10-fold increase on surfaces that were not directly exposed. Spatially and directionally well-resolved simulations of radiative transfer within the rooms were carried out employing the finite volume radiation model. The measured enhancement in radiative fluxes predicted numerically agreed in general with experimental observations. The volume-averaged incident radiation increased by 60% in the presence of UV reflective walls. Ray effects or the preferential streaming of radiation in the numerical calculations was more pronounced in the control room and was minimized by increasing the angular resolution of the calculations even further. However in the room with UV reflective walls, the diffuse reflections caused the intensity distributions to become more isotropic and minimized the impacts of ray effects.

New weighted-sum-of-gray-gases model (WSGGM) parameters for H₂O vapor are derived from emissivity correlations in the open literature and presented for use in hydrogen combustion simulations. Predictions employing the new WSGGM are seen to compare favorably against the spectral-line-based WSGGM on benchmark problems as well as in media conditions representative of turbulent hydrogen diffusion flames (Sandia Flame A and a model hydrogen gas-turbine combustor). The Sandia Flame A calculations were performed in a decoupled manner employing experimental measurements of temperature and gas compositions as inputs. The measured temperature variance data were employed to model the turbulence–radiation interactions. A coupled computational fluid dynamic (CFD) calculation was performed to obtain the conditions within the gas-turbine combustor geometry. The observed accuracies of the proposed set of WSGGM parameters in conditions encompassing a wide range of H₂O vapor concentrations and temperature non-homogeneities encountered in combustion media make them amenable to implementation in CFD codes. Copyright © 2011 John Wiley & Sons, Ltd.