GATE 2019 ME (ME2) – Question 56
A parallel-flow double-tube exchanger receives hot and cold fluids at 100°C and 15°C. Heat-capacity rates are 2000 and 1200 W/K respectively. Cold outlet is 45°C. Find log-mean temperature difference (K), to two decimal places.
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Correct answer: 57 to 58
Explanation
Heat transfer is $1200(45-15)=36000$ W. Hot outlet is $100-36000/2000=82^\circ$C. Parallel-flow terminal differences are 85 and 37 K. Thus $\Delta T_{lm}=(85-37)/\ln(85/37)=\mathbf{57.71}$ K.