Question Bank • QB_EXP_DFE_HEX_010 NAT • 2 Marks

Section 7: Dairy and Food Engineering

Heat Exchangers: LMTD & NTU-Effectiveness Methods

Subtopic: Counterflow heat exchanger LMTD calculation

Question Statement:

In a pasteurizer heat recovery section shown, pasteurized milk cools from $72^\circ\text{C}$ to $32^\circ\text{C}$ while incoming cold milk heats from $10^\circ\text{C}$ to $50^\circ\text{C}$. Calculate the $LMTD$ in $^\circ\text{C}$ (round off to the nearest integer).

Answer Key:

22

Step-by-Step Solution & Explanation

$\Delta T_1 = 72 - 50 = 22^\circ\text{C}$. $\Delta T_2 = 32 - 10 = 22^\circ\text{C}$. Since $\Delta T_1 = \Delta T_2 = 22^\circ\text{C}$, $LMTD = 22.0^\circ\text{C}$.
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