I need to aply in Flow and Thermal analysis in Femap simple radiation to environment (outer shell is radiating into environment). I know only external emissivity of 0.85. In NX Thermal there is boundary condition Simple radiation where I can set the emissivity. But I'm not sure how to make it in Femap. I set emissivity as thermo/optical material property. And than I set Thermal B.C. - Radiative, but there is only parameter Gray Body View Factor. What number to define here?