GATE 2022 AG – Question 64
A freezer wall comprises120 mm brick,75 mm concrete and 50 mm cork. Conductivities are .69,.76,.043 W/(m K). Outside/inside surface temperatures24 and−18°C. For1 m² wall, find steady heat transfer in W, to one decimal.
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Correct answer: 29.0 to 30.0
Explanation
The layers act in series: $R=.120/.69+.075/.76+.050/.043=1.435388$ K/W for 1 m². Surface temperature difference=42 K, so $Q=42/R=29.26038$ W, or **29.3 W**. Surface temperatures already exclude the need to add convection-film resistances.