A2 m x 1.5 m section of wall of an industrial furnace burning natural gas is not insulated, and the temperature at the outer surface of this section is measured to be 80°c. the temperature of the furnace room is 30°c, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 wm2.°c. it is proposed to insulate this section of the furnace wall with glass wool insulation (k 0.038 wm c) in order to reduce the heat loss by 90%. assuming the outer surface temperature of the metal section still remains at about 80°c, determine the thickness of the insulation that needs to be used