Stirling Cycle – Process Composition Check A Stirling cycle consists of two isothermal processes and two constant-volume (isochoric) regenerative processes.

Introduction / Context:
The Stirling cycle is a classic external-combustion, closed-cycle model employing regeneration. Understanding its process makeup clarifies how it can, in principle, approach Carnot efficiency with perfect regeneration and isothermal heat exchange.

Given Data / Assumptions:

• Ideal gas working fluid.
• Two isothermal processes at T_H and T_L.
• Two isochoric regenerative processes that shuttle heat internally.

Concept / Approach:

The Stirling sequence: isothermal compression at T_L with heat rejection to a sink, constant-volume regenerative heating, isothermal expansion at T_H with heat addition from a source, and constant-volume regenerative cooling back to T_L. The constant-volume steps store/recover heat in the regenerator matrix, minimizing external heat transfer at intermediate temperatures.

Step-by-Step Solution:

Verification / Alternative check:

T–s and p–v diagrams of the ideal Stirling show horizontal isotherms and vertical isochors; the regenerator provides internal heat interchange between those isochors.

Why Other Options Are Wrong:

Constant-pressure and isentropic legs characterize Brayton/Ericsson or Otto/Diesel cycles, not Stirling. Mixed CP/CV is not Stirling either.

Common Pitfalls:

Confusing Stirling with Ericsson (which has constant-pressure, not constant-volume, regeneration) or Brayton (adiabatic compression/expansion).

Final Answer:

two constant volume