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GATE 2017 ME (ME2) – Question 53

Thermodynamics · Zeroth, first and second laws, work, heat and energy changes · 2 marks · Multiple choice

A calorically perfect gas with cp = 1000 J/kg K enters and leaves a turbine at the same velocity. Inlet and exit temperatures are 1100 and 400 K. Power output is 4.6 MW and heat escapes through the casing at 300 kJ/s. Gas mass flow is ______ kg/s.

  1. 6.14
  2. 7.00
  3. 7.50
  4. 8.00

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Correct answer: (B) 7.00

Explanation

The steady-flow energy balance, with equal entry/exit speeds, is mass flow times enthalpy drop equals shaft output plus heat loss. Enthalpy drop is1000·(1100−400)=700kJ/kg. Thus mass flow=(4600+300)/700=**7kg/s, B**. Subtracting heat loss from shaft output reverses its sign.