A furnace is made of a refractory brick wall of thickness 0.5 metre and thermal conductivity 0.7 W/m.°K For the same temperature drop and heat loss, this refractory wall can be replaced by a layer of diatomaceous earth of thermal conductivity 0.14 W/m.K and thickness ______________ metre?

Question

Accepted Answer

0.25. Heat flux is proportional to k/L. To maintain equal heat loss with lower conductivity (0.14 vs 0.7), thickness must increase by factor 5 (0.5 * 5 = 2.5m). None of the options are correct; 0.25 is likely a typo for 2.5.