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Mechanical Engineering QUESTION #2424
Question 1
The lumped capacitance (lumped system) method for transient heat transfer is valid when the Biot number satisfies:
  • \(Bi > 10\)
  • \(Bi \geq 1\)
  • \(Bi \leq 0.1\)✔️
  • \(Bi = 1\) exactly
Correct Answer Explanation
The lumped capacitance method is valid when \(Bi=hL_c/k\leq0.1\). The temperature history is: \(\frac{T-T_\infty}{T_i-T_\infty}=e^{-t/\tau}\) where \(\tau=\rho c V/(hA_s)\) is the time constant.