GATE 2021 ME (ME2) – Question 54

Heat Transfer · Heat exchangers: LMTD and NTU methods · 2 marks · Numerical answer

A shell and tube heat exchanger is used as a steam condenser. Coolant water enters the tube at 300 K at a rate of 100 kg/s. The overall heat transfer coefficient is 1500 W/m².K, and total heat transfer area is 400 m². Steam condenses at a saturation temperature of 350 K. Assume that the specific heat of coolant water is 4000 J/kg.K. The temperature of the coolant water coming out of the condenser is _____ K (round off to the nearest integer).

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Correct answer: 339

Explanation

Condensation maintains a constant hot-side temperature. Water capacity rate is C=100×4000=400000 W/K and NTU=UA/C=1.5.

For this case $T_{out}=T_s-(T_s-T_{in})e^{-NTU}=350-50e^{-1.5}=338.84349$ K. **Answer: 339 K**.