Subtopic: Steady state heat transfer in conduction, convection and radiation
Question Statement:
A cold storage chamber is constructed with 10 mm mortar, 200 mm brick, 100 mm insulation and 5 mm wood-board having thermal conductivities of 0.8, 1.5, 0.025 and 0.2 W m⁻¹K⁻¹, respectively. The resistance of 4 K m² W⁻¹ is offered by
Options:
(A) mortar
(B) brick
(C) insulation
(D) wood-board
Official Answer Key:
C
Step-by-Step Solution & Explanation
Thermal resistance of each layer, R = L/k:
Mortar: 0.010/0.8 = 0.0125 K·m²/W
Brick: 0.200/1.5 = 0.1333 K·m²/W
Insulation: 0.100/0.025 = 4.0 K·m²/W ✓
Wood-board: 0.005/0.2 = 0.025 K·m²/W
Only the insulation layer offers 4 K·m²/W. Answer: (C) insulation.
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