\(1.5 \mathrm{~kg}\) of steam at a pressure of \(10 \mathrm{bar}\) and temperature of \(250^{\circ} \mathrm{C}\) is expanded until the pressure becomes 2.8 bar. The dryness fraction of steam is then 0.9. Calculate the change in internal energy. [Hint: Find the value of internal energy of steam \(\left(u_{1}\right)\) at 10 bar and \(250^{\circ} \mathrm{C}\), then find the internal energy \(\left(u_{2}\right)\) at 2.8 bar as \(u_{2}=u_{f}+0.9\left(u_{g}-u_{f}\right)\) and then find \(\left.\Delta u=1.5 \mathrm{~kg}\left(u_{1}-u_{2}\right)\right]\)