Current Issue : July - September Volume : 2015 Issue Number : 3 Articles : 5 Articles
This study assesses the required fidelities in modeling particle radiative properties and particle size distributions (PSDs) of\ncombusting particles in Computational Fluid Dynamics (CFD) investigations of radiative heat transfer during oxy-combustion of\ncoal and biomass blends. Simulations of air and oxy-combustion of coal/biomass blends in a 0.5MWcombustion test facility were\ncarried out and compared against recent measurements of incident radiative fluxes. The prediction variations to the combusting\nparticle radiative properties, particle swelling during devolatilization, scattering phase function, biomass devolatilization models,\nand the resolution (diameter intervals) employed in the fuel PSD were assessed.While the wall incident radiative flux predictions\ncompared reasonably well with the experimental measurements, accounting for the variations in the fuel, char and ash radiative\nproperties were deemed to be important as they strongly influenced the incident radiative fluxes and the temperature predictions\nin these strongly radiating flames. In addition, particle swelling and the diameter intervals also influenced the incident radiative\nfluxes primarily by impacting the particle extinction coefficients. This study highlights the necessity for careful selection of particle\nradiative property, and diameter interval parameters and the need for fuel fragmentation models to adequately predict the fly ash\nPSD in CFD simulations of coal/biomass combustion....
The present study explores the utilization of a porous burner for thermoelectric power generation.The porous burner was tested\nwith butane gas using two sets of configurations: single layer porcelain and a stacked-up double layer alumina and porcelain.\nSix PbSnTe thermoelectric (TE) modules with a total area of 54 cm2 were attached to the wall of the burner. Fins were also\nadded to the cold side of the TE modules. Fuel-air equivalence ratio was varied between the blowoff and flashback limit and\nthe corresponding temperature, current-voltage, and emissions were recorded. The stacked-up double layer negatively affected\nthe combustion efficiency at an equivalence ratio of 0.20 to 0.42, but single layer porcelain shows diminishing trend in the\nequivalence ratio of 0.60 to 0.90. The surface temperature of a stacked-up porous media is considerably higher than the single\nlayer. Carbon monoxide emission is independent for both porous media configurations, but moderate reduction was recorded for\nsingle layer porcelain at lean fuel-air equivalence ratio. Nitrogen oxides is insensitive in the lean fuel-air equivalence ratio for both\nconfigurations, even though slight reduction was observed in the rich region for single layer porcelain. Power output was found to\nbe highly dependent on the temperature gradient....
Biogas released from palm oil mill effluent (POME) could be a source of air pollution, which has illustrated negative effects on\nthe global warming. To protect the environment from toxic emissions and use the energy of POME biogas, POME is conducted\nto the closed digestion systems and released biogas is captured. Since POME biogas upgrading is a complicated process, it is not\neconomical and thus new combustion techniques should be examined. In this paper, POME biogas (40% CO2 and 60% CH4)\nhas been utilized as a fuel in a lab-scale furnace. A computational approach by standard k-? combustion and turbulence model is\napplied. Hydrogen is added to the biogas components and the impacts of hydrogen enrichment on the temperature distribution,\nflame stability, and pollutant formation are studied. The results confirm that adding hydrogen to the POME biogas content could\nimprove low calorific value (LCV) of biogas and increases the stability of the POME biogas flame. Indeed, the biogas flame length\nrises and distribution of the temperature within the chamber is uniformwhen hydrogen is added to the POME biogas composition.\nCompared to the pure biogas combustion, thermal NOx formation increases in hydrogen-enriched POME biogas combustion due\nto the enhancement of the furnace temperature....
Dust flames have been studied for decades because of their importance in industrial safety and accident prevention. Recently,\ndust flames have become a promising candidate to counter biological warfare. Sulfur in particular is one of the elements that is of\ninterest, but sulfur dust flames are not well understood. Flame temperature and flame speed were measured for sulfur flames with\nparticle concentrations of 280 and 560 g/m3 and oxygen concentration between 10% and 42% by volume. The flame temperature\nincreased with oxygen concentration from approximately 900K for the 10% oxygen cases to temperatures exceeding 2000K under\noxygen enriched conditions. The temperature was also observed to increase slightly with particle concentration. The flame speed\nwas observed to increase from approximately 10 cm/s with 10% oxygen to 57 and 81 cm/s with 42% oxygen for the 280 and 560 g/m3\ncases, respectively. A scaling analysis determined that flames burning in 21% and 42% oxygen are diffusion limited. Finally, it was\ndetermined that pressure-time data may likely be used to measure flame speed in constant volume dust explosions....
Measurements fromconfined, laminar oxy-methane flames at differentO2/CO2 dilution ratios in the oxidizer are first reported with\nmeasurements from methane-air flames included for comparison. Simulations of these flames employing appropriate chemistry\nand radiative property modeling options were performed to garner insights into the experimental trends and assess prediction\nsensitivities to the choice of modeling options. The chemistry was modeled employing a mixture-fraction based approach, Eddy\ndissipation concept (EDC), and refined global finite rate (FR) models. Radiative properties were estimated employing four\nweighted-sum-of-gray-gases (WSGG) models formulated from different spectroscopic/model databases. The mixture fraction and\nEDC models correctly predicted the trends in flame length and OH concentration variations, and the O2, CO2, and temperature\nmeasurements outside the flames. The refined FR chemistry model predictions of CO2 and O2 deviated fromtheir measured values\nin the flame with 50%O2 in the oxidizer. Flame radiant power estimates varied by less than 10% between the mixture fraction and\nEDCmodels butmore than 60% between the differentWSGG models.Thelargest variations were attributed to the postcombustion\ngases in the temperature range 500 Kââ?¬â??800K in the upper sections of the furnace which also contributed significantly to the overall\nradiative transfer....
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