HEAT TRANSFER PROBLEM NO18 - The configuration of a furnace can be approximate as an equilibrium triangular duct which is usually long enough so that the end effects are negligible , the hot wall is maintained at 900 k and has an emissivity e1 = 0.8 . The cold wall is at 400 k and has an emissivity , e2 =0.8 .The third wall is re-radiating zone. What is the net radiation heat flux leaving the hot wall ?