STG-10 Gas Radiative Component in the Thermal Calculation of Tubular Heat Exchangers

P. Stehl

This report describes the causes of gas radiation and addresses the calculation of the radiative heat flux from a volume of gas whose temperature and composition are known. A polyatomic molecule has radiation potential in the range of temperatures typical in furnaces, convection sections, etc. A model is described that considers individual tubes of the bundle coated by gaseous layers. The actual bounding volume of these layers was substituted by an equivalent cylindrical bounding volume for simplification of the geometry. The authors developed a mathematical procedure using this and other assumptions to determine the gas-radiation coefficient. This procedure can be incorporated into any arbitrary program for thermal and hydraulic calculation of a tubular heat exchanger. Examples using this method illustrate that the gas-radiation coefficient distinctly increases with rising pressure, decreases with polyatomic molecule content of the flue gas, and increases with the flue gas temperature. A similar model-based algorithm for the calculation of heat flux from a volume of gas in a duct to the shield tubes or the first rows of the tube bundle is also described in this report.