Need Help solving the following problem: As shown below, a frictionless piston i

Question

Need Help solving the following problem:

As shown below, a frictionless piston is located inside of a cylinder. The piston is free to travel between the two sets of stops. When the piston is resting on the lower stops the enclosed volume is 0.4 m3. The enclosed volume is 0.6 m3 when the piston encounters the upper stops. Initially the cylinder is filled with water at 0.1 MPa and a quality of 20%. The water is then heated until it exists as a saturated vapor. The mass of the piston is such that 0.3 MPa pressure is required to move it against atmospheric pressure. Determine the final pressure in the cylinder, the heat transfer, and the work done during the process.

Explanation / Answer

State 1: P1= 0.1MPa , x1=0.2 --> T1=100C, v1=0.34 m3/kg u1=835.07 kJ/kg

m = 0.4/0.34 = 1.176 kg

State2: x2=1, v2=0.6/1.176= 0.51 m3/kg --->T2= 140C, P2= 360kPa (>0.3 MPa OK) u2=2549.86 kJ/kg

Work done = P(V2-V1) = 0.3MPa(0.6-0.4) = 60 kJ

Q = m(u2-u1)+W = 1.176(2549.86-835.07)+60 = 2076.6 kJ (into the system)

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