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GATE 2021 ME (ME1) – Question 33

Thermodynamics · Zeroth, first and second laws, work, heat and energy changes · 1 mark · Numerical answer

A rigid insulated tank is initially evacuated. It is connected through a valve to a supply line that carries air at a constant pressure and temperature of 250 kPa and 400 K respectively. Now the valve is opened and air is allowed to flow into the tank until the pressure inside the tank reaches to 250 kPa at which point the valve is closed. Assume that the air behaves as a perfect gas with constant properties ($c_p=1.005$ kJ/kg.K, $c_v=0.718$ kJ/kg.K, $R=0.287$ kJ/kg.K). Final temperature of the air inside the tank is _____ K (round off to one decimal place).

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Correct answer: 557.10 to 562.70

Explanation

The unsteady energy balance has no heat or boundary work and no initial tank energy. Inlet flow brings enthalpy, so $mu_f=mh_{in}$.

Thus $c_vT_f=c_pT_{in}$ and $T_f=(1.005/0.718)(400)=559.8886$ K. **Answer: 559.9 K**.