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GATE 2020 ME (ME2) – Question 34

Heat Transfer · Modes of heat transfer, one-dimensional conduction, resistance concept · 1 mark · Numerical answer

A furnace brick wall has k₁ = 2.5 W/(m·K), inner temperature 1100°C and outer/interface temperature 700°C. Insulation of conductivity k₂ covers it; insulation thickness is one-quarter of brick thickness, and its outer surface is at 200°C. Net heat flux through the composite wall is 2500 W/m². Find k₂ (W/(m·K)), to one decimal.

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Correct answer: .5 to .5

Explanation

Equal steady heat flux gives2.5(1100−700)/L1=k2(700−200)/(L1/4). Therefore k2=2.5×400/(4×500)=**0.5 W/m·K**. The specified2500 W/m² cancels, but independently givesL1=0.4 m,L2=0.1 m.