Question

A piston held by a pin in an insulated cylinder, s, contains 2 kg water at 100°C, quality 98%. The piston has a mass of 102 kg, with cross-sectional area of 100 cm2, and the ambient pressure is 100 kPa. The pin is released, which allows the piston to move. Determine the final state of the water, assuming the process to be adiabatic. 

Answer 1

C.V. The water. This is a control mass.

Continuity Eq.: m₂ = m₁ = m ;

Energy Eq.  m(u₂ − u₁) = ₁Q₂ - ₁W₂

Process in cylinder: P = P_float (if piston not supported by pin) 

We thus need one more property for state 2 and we have one equation namely the energy equation. From the equilibrium pressure the work becomes