圆柱状空腔辐射能的方向性与传热效率

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

为分析空腔出口辐射能定向集中加热特性与传热效率数值,利用有限差分法求解圆管壁与管内冷却空气温度场,其中辐射换热量利用蒙特卡罗法中的辐射交换因子计算.圆管壁为漫发射、漫反射镜反射混合分布,管底部为假想的圆形黑体辐射器.引入有效方向发射率等参数来描述管口辐射能的方向分布特性,并计算了相关参数如管壁发射率、镜漫反射分布、管长与半径比变化时有效方向发射率的数值.计算结果表明:管内壁发射率以及管长与半径比较大时,管口辐射能向小角度天顶角方向集中,但传热效率较低;镜漫反射的比例相同时,比全管长漫反射时传热效率提高约1～2倍.

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.