Directional radiation properties of an isothermal cylindrical cavity

To obtain directional properties of radiant energy streaming from an isothermal radiant cylindrical cavity, a Monte Carlo method solving the RD's value between cavity wall elements was presented. The calculations of equivalent directional emittance of cavities were performed for black body surface of undersurface and gray, diffusely emitting and reflecting side surface of tube, while the varying parameters included the emissivity of the side wall, the depth-to-radius ratios. Results of the analysis illustrate the polar angle of maximum equivalent directional emissivity decreases with the increase of the depth-to-radius ratio, and the value of equivalent directional emissivity of small polar angle increases with increasment of depth-to-radius ratio. When the ratio of depth-to-radius is bigger than 30, the polar angle corresponding to maximum equivalent directional emissivity is little than (or equal to) 2 degrees. The effect of inner wall emissivity of the elements between aperture and inner diameter of tube is remarkable when the side wall emissivity of tube is variable, and the directionality of radiation of cavity is increased at low values of the side wall emissivity.