Directionality of radiant energy and heat transfer efficiency of cylindrical cavity with diffuse and specular reflecting inside wall

To analyse the directional heating property of radiant energy from cylindrical tube cavity and the value of heat transfer efficiency, the finite difference method is used to solve the temperature fields of the tube wall and its inside cooling air, and radiative exchange factor in Monte Carlo method is used to obtain radiant energy of the cavity system. The study is for diffusely emitting, diffusely and specularly reflecting inner wall of tube and its bottom black body surface of a fictitious circle burner. The concept of effective directional emissivity is introduced and its values are calculated, while the changed parameters include the emittance of the inner wall of tube, the distribution of diffusely and specularly reflecting elements of the tube and the length-to-radius ratio of tube. Results of the analysis illustrate that the infrared radiant energy is collimated in a smaller polar angle range when the diffuse emittance and the length-to-radius ratio of tube are large, but the values of heat transfer efficiency is less. As the same ratio of diffusely and specularly reflecting inner wall elements, the values of heat transfer efficiency are about one or two times larger than that with all diffusely reflecting wall elements.