Stirling cycle is a thermodynamic cycle consists of two isothermal and two isochoric processes. Heat rejection and heat addition takes place at constant temperature.
1-2: Isothermal compression
2-3: Constant volume cooling
3-4: Isothermal exoansion
4-1: Contant volume heating
From the p-V and T-s diagram of stirling cycle it is clear that the amount of heat addition and heat rejection during constant volume is same.
Work done = heat supplied – heat rejected