A two-layer wall of equal thickness has material A with twice the thermal conductivity of material B. For a total 36°C temperature drop across the steady-state wall, the drop across layer A is ______________ °C?
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Answer: B. 12
Explanation
Thermal resistance equals thickness divided by thermal conductivity for each flat wall layer. Material A has twice the thermal conductivity of material B while sharing equal thickness. Thus material A offers half the resistance of B, absorbing twelve degrees of the total thirty six degree drop. Composite walls in series experience identical heat flux passing through every constituent layer. Temperature drops distribute across layers in direct proportion to their individual thermal resistances. Higher thermal conductivity results in lower thermal resistance and a smaller temperature drop.
Building insulation design evaluates multi layer wall temperatures to prevent internal condensation. Furnace refractory linings use materials of varying conductivities to drop temperatures safely. Steady state heat transfer analysis relies on electrical resistance analogies for composite walls. An eighteen degree drop assumes equal thermal resistances, ignoring the conductivity difference. A twenty four degree drop would occur if material A had lower conductivity than material B. A six degree drop underestimates material A's thermal resistance share within the composite wall.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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