Out of the following four assumptions used in the derivation of the equation for LMTD [LMTD = (Δt1 - Δt2)/ln(Δt1/Δt2)], which one is subject to the largest deviation in practice ?
Correct answer: B. Constant rate of fluid flow
- A. Constant overall heat transfer co-efficient.
- B. Constant rate of fluid flow
- C. Constant specific heat
- D. No partial phase change in the system
Explanation
The LMTD derivation assumes a constant flow rate, but density and therefore volumetric flow can change substantially as a fluid is heated or cooled. Specific heat and overall coefficient often vary too, but the flow-rate assumption commonly gives the largest practical deviation among these choices.
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