Project ForgeHeat Transfer
Heat Exchangers
GATE 2018
Hard
A hot liquid is cooled from 80°C to 50°C in a 1-1 shell-and-tube HX. Cooling water enters at 30°C, exits at 45°C. U is the same for counter-current and co-current modes. The percentage saving in heat transfer area for the counter-current option relative to co-current is (rounded off to third decimal place)
27.1 %(± 0.5 accepted)
Explanation
Counter-current: ΔT1=80−45=35, ΔT2=50−30=20. LMTD=15/ln(35/20)=26.81. Co-current: ΔT1=80−30=50, ΔT2=50−45=5. LMTD=45/ln(10)=19.54. %saving=(1−LMTD_co/LMTD_counter)×100=(1−19.54/26.81)×100=27.1%.
Source: GATE CH 2018 (2018)
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