Project ForgeHeat Transfer
Heat Exchangers
GATE 2016
Hard
In a 1-1 shell-tube HX, steam condenses at Ts=135°C; cold fluid heats 20°C→90°C. ln[(Ts−T1)/(Ts−T2)]=UA/(ṁCp). Tube-side Nu=0.023Re^0.8Pr^(1/3) dominates U (shell-side/wall resistance negligible). If only ṁ (cold fluid) is doubled, the new outlet temperature (°C) is
- A80.2
- 84.2
- C87.4
- D88.6
Explanation
Original: ln(115/45)=0.938=UA/(ṁ0Cp). U∝ṁ^0.8 (tube-side dominant). New: UA/(2ṁ0Cp)=(2^0.8/2)×0.938=0.817. (135−20)/(135−T2)=e^0.817=2.263 ⟹ T2=84.2°C.
Source: GATE CH 2016 (2016)
This question is part of a 15-day revision cycle — sign in and Project Forge will bring it back the day before you'd forget it.