Which thermodynamic cycle consists of two isothermal and two isochoric processes?

Which thermodynamic cycle consists of two isothermal and two isochoric processes?

• A. Stirling cycle
• B. Carnot cycle
• C. Otto cycle
• D. Brayton cycle

Answer: (A)

This cycle is defined by two isothermal processes paired with two isochoric (constant-volume) processes. In the isothermal steps, the gas exchanges heat with external reservoirs at a fixed high temperature during expansion (doing work on the surroundings) and at a fixed low temperature during compression (heat is rejected). The other two steps occur at constant volume, so no work is done there; heat transfer only changes the internal energy and temperature of the gas. A regenerator typically sits between these constant-volume steps, storing heat during the cooling phase and returning it during the heating phase, which makes the external heat transfer more efficient. That combination—two isothermal heat exchanges and two isochores with no work—matches the Stirling cycle. Other cycles mix in adiabatic or isobaric steps, not two isothermal and two isochoric ones.

This cycle is defined by two isothermal processes paired with two isochoric (constant-volume) processes. In the isothermal steps, the gas exchanges heat with external reservoirs at a fixed high temperature during expansion (doing work on the surroundings) and at a fixed low temperature during compression (heat is rejected). The other two steps occur at constant volume, so no work is done there; heat transfer only changes the internal energy and temperature of the gas. A regenerator typically sits between these constant-volume steps, storing heat during the cooling phase and returning it during the heating phase, which makes the external heat transfer more efficient.

That combination—two isothermal heat exchanges and two isochores with no work—matches the Stirling cycle. Other cycles mix in adiabatic or isobaric steps, not two isothermal and two isochoric ones.