GATE 2019 ME (ME2) – Question 57
Water flows at 1 kg/s through an electric heater, gaining specific enthalpy 2.50 kJ/kg and specific entropy 0.007 kJ/(kg·K). Electrical input is 2.50 kW. There are no other work or heat interactions. At ambient 300 K, find irreversibility rate (kW), to two decimal places.
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Correct answer: 2.05 to 2.15
Explanation
The insulated boundary carries no heat entropy transfer; electrical work carries no entropy. Therefore $\dot S_{gen}=\dot m\Delta s=0.007$ kW/K. Gouy–Stodola gives $\dot I=T_0\dot S_{gen}=300(0.007)=\mathbf{2.10}$ kW.