Project ForgeIn a furnace, the inner and outer sides of a brick wall (k1=2.5 W/m.K) are maintained at 1100°C and 700°C respectively. The wall is covered by an insulating material of thermal conductivity k2, whose thickness is 1/4th of the brick wall's thickness. The outer surface of the insulation is at 200°C, and the heat flux through the composite wall is 2500 W/m². The value of k2 is __________ W/m.K (round off to one decimal place).
Explanation
For the brick: q=k1(1100−700)/L1 → 2500=2.5×400/L1 → L1=0.4 m. Insulation thickness L2=L1/4=0.1 m. For the insulation: q=k2(700−200)/L2 → 2500=k2×500/0.1=5000k2 → k2=0.5 W/m.K.
Source: GATE ME 2020 Session 2 (ME-2) (2020)
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