Heat Transfer Miscellaneous
- Water (c = 4.18 kJ/kgK) at 80°C enters a counter flow heat exchanger with a mass flow rate of 0.5 kg/s. Air (c = 1 kJ/kgK) enter at 30°C with a mass flow rate 2.09 kg/s. If the effectiveness of the heat exchanger is 0.8, the LMTD (in °C) is
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ε = Ch × (th1 - th2) Cmin (th1 - tc1) ∴ 0.8 = 4.18 × 0.5 × (80 - th2) 2.09 × 1 (80 - 30)
⇒ th2 = 40°C
mhcph (th1 – th2) = mc ccp (tc2 – tc1)
∴ 0.5 × 4.18 × 40 = 2.09 × 1 × (tc2 – 30)
⇒ tc2 = 70°C
&thet;1 = θ2 = 10°C
∴ LMTD = 10°CCorrect Option: C
ε = Ch × (th1 - th2) Cmin (th1 - tc1) ∴ 0.8 = 4.18 × 0.5 × (80 - th2) 2.09 × 1 (80 - 30)
⇒ th2 = 40°C
mhcph (th1 – th2) = mc ccp (tc2 – tc1)
∴ 0.5 × 4.18 × 40 = 2.09 × 1 × (tc2 – 30)
⇒ tc2 = 70°C
&thet;1 = θ2 = 10°C
∴ LMTD = 10°C
