The Stefan-Boltzmann constant = 5.67 x 10-8 W/m K4. A cylinder of inner surface radius 12 enshrouds a smaller cylinder of outer surface radius 1. The inner surface of the large cylinder is at temperature T2 and is diffuse and grey with an emissivity of 82; the outer surface of the smaller cylinder is at temperature T1 and is diffuse and grey with an emissivity of &1. The space between the two surfaces is evacuated. (a) Determine expressions for the view factors F11, F12, F21 and F22. Cryogenic fluid flows through a tube of 30 mm diameter, the outer surface of which is diffuse and grey with an emissivity of 0.05 and temperature of -196 C. This tube is concentric with a larger tube of 60 mm diameter, the inner surface of which is diffuse and grey with an emissivity of 0.08 and temperature of 25C. The space between the two tubes is evacuated. (b) Given that the net radiative heat exchange between the two surfaces may be expressed as: 912 (T-T2) 1-5 1 1-82 + + A AF12 E2A2 Calculate the heat gain per unit length of the inner tube. (c) A diffuse and grey cylindrical thin-walled radiation shield of radius (n + 12)/2 is inserted in the evacuated space between the two tubes. The shield is concentric with the two tubes and has an emissivity of 0.04 on both sides. Draw the radiation network representation of the system and subsequently calculate the new heat gain per unit length of the inner tube.