1. Figure Q1 shows a long equilateral triangular duct constructed with grey walls each 1 m wide at temperatures T1, T2 and T3 where its base (surface A3) is completely insulated. Au Ti = 727 C, &z = 0.33 Az, T2 = 427 C, &z = 0.50 A3, T3, E3 = 0.80 Insulated surface Fig. 21 (a) Draw a network representation of the radiation exchange in the duct. (4) (b) Determine the net radiation transfer from surface A1 per unit length of the duct in W/m. (8) (c) Determine the temperature of the insulated surface Az in C. (8) )