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GATE 2016 ME (ME3) – Question 28

Heat Transfer · Heat exchangers: LMTD and NTU methods · 1 mark · Multiple choice

For a heat exchanger, ∆Tmax is the maximum temperature difference and ∆Tmin is the minimum temperature difference between the two fluids. LMTD is the log mean temperature difference. Cmin and Cmax are the minimum and the maximum heat capacity rates. The maximum possible heat transfer (Qmax) between the two fluids is

  1. Cmin LMTD
  2. Cmin ∆Tmax
  3. Cmax ∆Tmax
  4. Cmax ∆Tmin

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Show answer and explanation

Correct answer: (B) Cmin ∆Tmax

Explanation

The stream with smaller heat-capacity rate C_min limits transfer. Its largest possible temperature change is the inlet hot–cold temperature difference, giving **Q_max=C_minΔT_max, B**. Here ΔT_max means that maximum available inlet difference. Actual transfer is effectiveness times this limit.