A pistoncylinder device initially contains 147 kg of saturat

A piston-cylinder device initially contains 1.47 kg of saturated liquid water at 200 degrees Celsius. Now heat is transferred to the water until the volume quadruples and the cylinder contains saturated vapor only. Determine:

(a) The final volume of the tank, V in m³.

(b) The final temperature, T_f in Celsius and pressure, P_f in MPa.

(c) The internal energy change of the water in kJ.

Solution

Properties: The saturated water at 200⁰ C

Specific volume v_l = 0.001157 m³ /kg; Specific internal energy u_l = 850.46 kJ/kg

Solutions:

a) the initial volume of the cylinder = mv_l = 1.47 x 0.001157 = 0.001708 m³.

Volume at final stage = 4 x 0.001708 = 0.006803 m³

b) specific volume at final stage as it contains saturated vapour = 0.006803/1.47 0.004628 m³ /kg.

properties of the saturated vapour

T_v = 371.3 ^oC

c) P_v = 21,367kPa

u_v = 2201.5kJ/kg

total change in internal energy = m(u_v - u_l) = 1.47*(2201.5 - 850.46) = 1892 kJ