GATE 2021 AR – Question 65
For the wall section shown, brickwork is 100 mm on each side of a 50 mm cavity, with 10 mm plaster on each exposed face. Printed brick/plaster conductance values are 1.2 and 0.5 W/m/°C; inside/outside surface conductances 8.0 and 9.5 W/m²/°C; cavity resistance 0.17 m²·°C/W. Find U in W/m²/°C, to two decimals.
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Correct answer: MTA
Explanation
The final key awards MTA. The printed “thermal conductance” values have conductivity units, making the wording inconsistent. Treating them as conductivities, the two plaster layers contribute 0.040 m²·°C/W and the two brick leaves 0.16667. Add inside film 0.125, outside film 0.10526 and cavity 0.17. Total resistance is 0.60693 m²·°C/W, whose reciprocal is about 1.65 W/m²/°C. This is an explicit interpretation of the drawn double-leaf wall, not an enforced replacement answer.