WATER VAPOR STANDARD EMISSIVITY BY MIXED GRAY-GASES MODEL

Conventional fossil fuels are of carbon-hydrogen composition. A number of alternative fuels, e.g., coal, lignite, are carbon-based fuels. The high temperature combustion of such fuels would generate carbon dioxide, and if hydrogen is present, water vapor. The knowledge of the emissivities of carbon dioxide and water vapor is very important in burner design and thermal efficiency calculations. The present work utilizes a mixed gray-gas model to approximate the water vapor emissivities at zero partial pressure of water vapor and 1 atm total pressure. Two models are developed. The first model is a mixture of four gray-gases and can be used in the range T = 350-900 K, pL = 0.1-200 cm atm with an error range of-8.2 to 6.2%. The second model is a piece-wise one in which one gray-gas was used to cover the pL range 50-200 cm atm and a second gray-gas covered the range of 5-50 cm atm. The model can be used in ihe range of 700-1500 K and has an error range of -2.3 to 3.7%. Comparison with Leckner's model shows the superiority of the present models.