b) A cylinder wall with a size of 3.0 ft thick is used as the primary lining inside the industrial furnace. The rear side of the wall is well insulated. Before the heating process starts, the wall is maintained at uniform temperature of 70 F and then it is exposed to a gas at 2800 F during heating. If the wall temperature reached 2000 F at the rear side of the furnace, the process will automatically by-passed and the safety alarm will be triggered. Use convection coefficient 3.42 btu/hr.it?..F, thermal conductivity 4.26 btu/hr.ft.F and thermal diffusivity 0.86 ft-/hr. i) Calculate the time required to attain 1450 F at a point of 1.5 ft depth from the surface furnace wall. [10 Marks [CO1, POI, C3] ii) For safety operation, justify the maximum time of the furnace can be operated continuously DEN b) A cylinder wall with a size of 3.0 ft thick is used as the primary lining inside the industrial furnace. The rear side of the wall is well insulated. Before the heating process starts, the wall is maintained at uniform temperature of 70 F and then it is exposed to a gas at 2800 F during heating. If the wall temperature reached 2000 F at the rear side of the furnace, the process will automatically by-passed and the safety alarm will be triggered. Use convection coefficient 3.42 btu/hr.it?..F, thermal conductivity 4.26 btu/hr.ft.F and thermal diffusivity 0.86 ft-/hr. i) Calculate the time required to attain 1450 F at a point of 1.5 ft depth from the surface furnace wall. [10 Marks [CO1, POI, C3] ii) For safety operation, justify the maximum time of the furnace can be operated continuously DEN