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Heat Transfer
Heat Exchangers
GATE 2010
Hard

Hot oil at 150°C is used to preheat a cold fluid at 30°C in a 1:1 shell and tube heat exchanger. The exit temperature of the hot oil is 110°C. Heat capacities (mass flow × specific heat) of both streams are equal. The heat duty is 2kW. Under co-current flow conditions, the overall heat transfer resistance (1/UA) is

  • A0.4 °C/W
  • B0.04 °C/W
  • C0.36 °C/W
  • 0.036 °C/W

Explanation

Equal heat capacity rates mean the cold fluid's temperature rise equals the hot fluid's drop (40°C), so cold exit=70°C. Co-current: ΔT1=150−30=120, ΔT2=110−70=40. LMTD=(120−40)/ln3=72.8°C. 1/UA=LMTD/Q=72.8/2000≈0.036 °C/W.

Source: GATE CH 2010 (2010)

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