4) The window of a large vacuum chamber is fabricated from a material of prescribed spectral characteristics. A collimated beam of radiant energy from a solar simulator is incident on the window and has a flux of 3000 W/m. The inside walls of the chamber, which are large compared to the window area, are maintained at 77 K. The outer surface of the window is subjected to surroundings and room air at 25C, with a convection heat transfer coefficient of 15 W/m.K. 0.90 0.15 0.10 0.05 0.38 1.9 2. cum) 0.38 1.9 (m) (b) (a) Determine the transmissivity of the window material to radiation from the solar simulator, which approximates the solar spectral distribution. Assuming that the window is insulated from its chamber mounting arrangement, what steady-state temperature does the window reach? (c) Calculate the net radiation transfer per unit area of the window to the vacuum chamber wall, excluding the transmitted simulated solar flux