the walls of an oven are made from steel sheets with insulating board betwwen them of thermal conductivity 0.18jm^-1s^-1℃^-1.if the maximum internal temperature in the ovem is 300℃and the outside surface of the oven wall must not rise above 50℃, estimate the minimum necessary thickness of insulation assuming surface heat transfer coefficients to the air on both sides of the wall are 15jm-2s-1℃0-1. assume the room air temperature outside the oven to be 25℃ and that the insulating effect of the steel sheets can be neglected.

 

열전도도가  0.18jm^-1s^-1℃^-1. 내부 온도 300 ℃ 오븐 벽 외부로50 ℃상승하면 안되고 표면 열전달계수15jm - 2 - 1 ℃ 0-1 단열효과가 무시 오븐 바깥 온도25℃