Directionality of radiation for a diffusely reflecting tube of a radiant burner

To obtain directional properties of radiant energy streaming from radiant burner system, a Monte Carlo method is used to calculate the values of equivalent directional emittance for non-isothermal gray inner surface of tube with bottom fictitious black surface, while the parameters that are varied include the emissivity of the inside wall, the depth-to-radius ratios and the air velocity inside the tube. The result shows that the polar angle of maximum equivalent directional emissivity decreases with increasing of the depth-to-radius ratio. The air velocity only affects the value of equivalent directional emittance.