Calculating Steam Temperature and Dryness Fraction: Thermo Tables Problem 1

[MMCS]

1 kg of steam at a pressure of 10 bar and temperature of 400°C is contained in a cylinder closed by a
piston. The steam is compressed by the inward motion of the piston until the pressure is 50 bar. The
work done on the steam is 250 kJ and the heat transfer from the steam is 700 kJ.

Calculate the final steam temperature if the final condition is superheated, or the dryness fraction if the steam is wet

equations

Q-W = ΔU
+700kj - (-250kj) = 950kj

From steam tables, state 1 at 10 bar, 400°c, U = 2957

U at state 2
U at state 1 + change in U
2957 +950= 3907
This value seems to high, is this correct? what is the next step to solve?

 

[rude man]

1 kg of steam at a pressure of 10 bar and temperature of 400°C is contained in a cylinder closed by a
piston. The steam is compressed by the inward motion of the piston until the pressure is 50 bar. The
work done on the steam is 250 kJ and the heat transfer from the steam is 700 kJ.

Calculate the final steam temperature if the final condition is superheated, or the dryness fraction if the steam is wet

equations

Q-W = ΔU
+700kj - (-250kj) = 950kj

From steam tables, state 1 at 10 bar, 400°c, U = 2957

U at state 2
U at state 1 + change in U
2957 +950= 3907
This value seems to high, is this correct? what is the next step to solve?

What should be the sign of Q if heat is transferred from the system?