Stirling cycle . It is a process that allows the conversion between mechanical and heat energy .
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- 1 The cycle
- 2 Description of the cycle
- 3 Performance
- 4 Heat exchanger
- 5 Bibliographic references
- 6 See also
- 7 Sources
It is a highly ideal cycle, the practical realization of which, even roughly, involves serious difficulties. However, in recent years it has become relevant with the development of Stirling engines, which operate approximately according to this cycle.
Stirling 1 motors scheme
Stirling 2 engine diagram
An ideal Stirling cycle is made up of four reversible processes:
- Isothermal compression A → B
The gas is compressed from an initial volume VA to a final one VB, lower, maintaining its constant temperature at a value T1 (based on cooling the gas continuously).
- Constant volume heating B → C
The gas is heated from temperature T1 to temperature T2 keeping its volume fixed.
- C → D isotherm expansion
The gas expands while heat is supplied so that its temperature remains at its T2 value.
- Isochoric cooling D → A
The gas temperature is reduced back to its T1 value in a constant volume process.
In this process, heat is absorbed in isochoric heating and isothermal expansion, and it is transferred in the other two processes. The net value of the heat absorbed is
and the loan
so that performance is
being the compression ratio.
We can verify that this performance is always less than that of a reversible machine that operates between these two temperatures
being the difference
What makes the Stirling cycle special (and the Ericsson cycle, which is analogous but with isobaric rather than isochoric processes) is the presence of a heat exchanger . In gas cooling , temperature T2 is passed to T1 releasing heat. In heating, it goes from T1 to T2, absorbing heat. Since it passes through the same temperatures, it is (theoretically) possible to take advantage of the heat released when cooling without violating the second principle of thermodynamics: the heat that is gradually released at one point of cooling is transferred to the point at the same temperature at heating. Since both points are at the same temperature, the process is reversible.
- Giacosa, Dante. Internal combustion engines. Editorial Hoepli
- Automobile technique manual