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The Biot number Bi = hL/k_s appears in transient conduction. Bi ≪ 0.1 means:
A{'text': 'Conduction dominates over convection', 'label': 'A'}
B{'text': 'LUMPED-CAPACITANCE approximation is valid — internal conduction is much faster than surface convection, so temperature in the solid is approximately UNIFORM', 'label': 'B'}
C{'text': 'Radiation dominates', 'label': 'C'}
D{'text': 'Solution is unsteady', 'label': 'D'}
Answer & Solution
Correct answer: B. {'text': 'LUMPED-CAPACITANCE approximation is valid — internal conduction is much faster than surface convection, so temperature in the solid is approximately UNIFORM', 'label': 'B'}
Bi = (internal conduction resistance) / (convection resistance to environment). Bi ≪ 0.1: surface convection is the bottleneck, internal T gradients are negligible — lumped analysis valid. Body cools/heats uniformly with time.
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