Question Bank • QB_EXP_DFE_HEX_022 NAT • 2 Marks

Section 7: Dairy and Food Engineering

Heat Exchangers: LMTD & NTU-Effectiveness Methods

Subtopic: Counterflow heat exchanger LMTD calculation

Question Statement:

In the counterflow diagram, milk is cooled from $90^\circ\text{C}$ to $50^\circ\text{C}$ with cooling water entering at $15^\circ\text{C}$ and exiting at $45^\circ\text{C}$. Calculate the ratio $\Delta T_1 / \Delta T_2$ (round off to two decimal places).

Answer Key:

1.29

Step-by-Step Solution & Explanation

$\Delta T_1 = 90 - 45 = 45^\circ\text{C}$. $\Delta T_2 = 50 - 15 = 35^\circ\text{C}$. $\text{Ratio} = \frac{45}{35} = \frac{9}{7} \approx 1.286 \approx 1.29$.
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