Question Bank • QB_EXP_DFE_HEX_031 MSQ • 2 Marks

Section 7: Dairy and Food Engineering

Heat Exchangers: LMTD & NTU-Effectiveness Methods

Subtopic: Counterflow heat exchanger LMTD calculation

Question Statement:

Which of the following thermal resistances contribute to reducing the overall heat transfer coefficient $U$ in the counterflow pasteurizer shown in the diagram?

Options:

  • (A) Internal milk convective film resistance
  • (B) Plate/tube wall conductive resistance
  • (C) Milk fouling/scaling deposit layer resistance
  • (D) External water convective film resistance

Answer Key:

A, B, C, D

Step-by-Step Solution & Explanation

$\frac{1}{U A} = \frac{1}{h_i A_i} + R_{fi} + \frac{\ln(r_o/r_i)}{2\pi k L} + R_{fo} + \frac{1}{h_o A_o}$. All four components contribute.
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