Question Bank • QB_EXP_DFE_HEX_037 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 chiller diagram, hot liquid at $70^\circ\text{C}$ is cooled to $30^\circ\text{C}$ by brine entering at $0^\circ\text{C}$ and leaving at $20^\circ\text{C}$. Calculate the $LMTD$ in $^\circ\text{C}$ (round off to two decimal places).

Answer Key:

39.15

Step-by-Step Solution & Explanation

$\Delta T_1 = 70 - 20 = 50^\circ\text{C}$. $\Delta T_2 = 30 - 0 = 30^\circ\text{C}$. $LMTD = \frac{50 - 30}{\ln(50/30)} = \frac{20}{\ln(1.6667)} = \frac{20}{0.5108} \approx 39.15^\circ\text{C}$.
← Previous (QB_EXP_DFE_HEX_028) Next (QB_EXP_DFE_HEX_040) →

Practice In Authentic CBT Exam Interface

Test your skills under authentic timed conditions with live scoring and AIR percentile ranking.

Launch CBT Mock Test