Understanding Thermodynamic Cycles

Thermodynamic cycles are fundamental to the operation of heat engines and refrigeration systems. Each cycle consists of a sequence of processes that return the working substance to its initial state. Different cycles are characterized by the types of thermodynamic processes involved, such as isothermal, adiabatic, isobaric (constant pressure), and isochoric (constant volume).

Identifying the Stirling Cycle Processes

The question asks to identify a specific thermodynamic cycle based on its constituent processes. The cycle described consists of two constant volume processes and two isothermal processes. Let's examine the characteristics of the cycles provided in the options:

• Carnot Cycle: This is a theoretical cycle consisting of two reversible isothermal processes and two reversible adiabatic (isentropic) processes. It is the most efficient possible cycle operating between two given temperature reservoirs.
• Diesel Cycle: This cycle models the operation of a diesel engine. It typically consists of two adiabatic processes, one constant volume process, and one constant pressure process.
• Joule Cycle (or Brayton Cycle): Used to model gas turbine engines, this cycle involves two adiabatic processes and two constant pressure (isobaric) processes.
• Stirling Cycle: This is a closed thermodynamic cycle that operates via regeneration. A key characteristic of the ideal Stirling cycle is that it consists of two isothermal processes and two constant volume (isochoric) processes. It uses a regenerator to improve efficiency by storing and releasing heat.

Comparing the description given in the question – a cycle with two constant volumes and two isothermal processes – with the characteristics of the listed cycles, it is clear that this description matches the Stirling cycle.

Therefore, a cycle consisting of two constant volumes and two isothermal processes is known as the Stirling cycle.