# Second law analysis of Rankine cycle - DOC

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```					Chapter 8                                                      Lyes KADEM [Thermodynamics II] 2007

STIRLING and ERICSSON Cycles

Robert Stirling; Scotland (1790 –1878)                    John Ericsson; Sweden (1803 - 1889)

When we take a look at the ideal Otto and Diesel cycles, we can notice that they both are only
internally reversible. This is because the heat supply and rejection are not performed at a constant
temperature (isothermal process).
Therefore, for the same high and low temperatures, the ideal Otto and Diesel cycles will have a
thermal efficiency lower than Carnot efficiency (where the heat transfer is isothermal).
Hence, to approach the Carnot efficiency we have to reduce the difference in temperature between
points 2 and 3 and between 4 and 1.

This is objective of Stirling and Ericsson cycles.

How? By using a regenerator.
What is a regenerator?        It is a heat exchanger that transfers the wasted heat at (1-4) to (2-
3). As a consequence, the T 1 will increase (ideally approaches T 2) and T3 will decrease (ideally
approaches T4)

A generator induces a significant increase in thermal efficiency

Figure 8.12. The components of the Sterling and Ericsson cycles.

Gas power cycles                                                                                 23
Chapter 8                                                          Lyes KADEM [Thermodynamics II] 2007

Stirling Engine

Ericsson Engine

Figure.8.13. T-s and P-v diagrams of Stirling and Ericsson cycles.

Why don’t we use the Stirling and Ericsson cycles?
This is due to some technical difficulties. In deed, Stirling and Ericsson cycles are difficult to achieve
in practice because they involve heat transfer through a differential temperature difference (small
difference in temperature), which necessitates a long surface areas for heat transfer or allowing an
infinitesimally long time for the process.

Example

A Stirling cycle operates on air with a compression ratio of 10. If the low pressure is
200 kPa, the low temperature is 100ºC, and the high temperature is 600ºC, calculate the
work output and the heat input.

Gas power cycles                                                                                       24

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