1.5 kg of steam at a pressure of 10 bar and temperature of \(250^{\circ} \mathrm{C}\) is expanded until the pressure becomes 2.8 bar. The dryness fraction of the system is then 0.9. Calculate the change of internal energy. The extract from the steam tables is as under. Assume \(c_{p s}=2.1 \mathrm{~kJ} / \mathrm{kg} . \mathrm{K}\).

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Pressure Saturated temperature Specific volume m/kg Specific enthalpy kJ/kg bar C Vf Vg h 2.8 131.2 118 0.001071 0.64604 10 551.44 179.88 2721.5 0.0011274 0.19429 2776.2