While studying Thermodynamic Cycles like the Stirling Cycle and the Carnot Cycle, the representation of such Ideal cycles show them to have 4 distinct phases. For example, the Stirling cycle has an Isochoric heating phase which should not have any work done (no movement in the piston) but realistically we see that the piston never stops moving. I am having a hard time reconciling this theoretical ideal to the practical use. I tried looking for realistic representations of such cycles but couldn't find one.
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You can create realistic cycles. The Carnot cycle, for example, can be constructed using cylinders, pistons, and temperature baths, which you can buy at your favorite hardware store.
The primary usefulness of cycles, however, is as idealized models for real cycles that often perform less efficiently than idealized cycles.
If you want to build a Carnot cycle:
- Start with one kg of water and bring it to saturated liquid at, say 2 bar.
- Boil the liquid at constant pressure to make saturated vapor at 2 bar.
- Expand by reversible adiabatic process to 1 bar. The final state will be a vapor/liquid mixture at 1 bar.
- Condense enough vapor until you come up with the same entropy you had in state 1 (use the steam tables to find out how much vapor you need to condense).
- Finally compress by reversible adiabatic process to 5 bar. If you did everything correctly you will end uo with saturated liquid.
This is as realistic as it gets. The challenge is to make sure that the expansion and compression are done reversibly, but you can get as close to true reversibility as you want, if you don't care how long it will take you to complete the cycle.
real stirling p-v cyclegives other examples. Or see the analysis here. $\endgroup$