Determine the net work:

Q: 5 m³ of air at 2 bar, 27°C is compressed to 6 bar pressure following PV1.3  =C. It is expanded subsequently adiabatically to 2 bar. Considering two processes is to be reversed, determine the net work. Also plot the processes on T - S diagram.            

Sol: Given that:

Initial volume of air  V₁  = 5 m³

Initial pressure of air P₁  = 2 bar

Final pressure = 6 bar

Compression: Rev. Polytropic process (PV_n  = C) Expansion :Rev. adiabatic process (PV₁₄ = C) Now, work done during the process (1-2)

negative  sign shows that work input required for compression is more than work output obtained during expansion.