Ericsson cycle
The Ericsson cycle (after John Ericsson ), also Ackeret-Keller cycle (after Jakob Ackeret ), is a thermodynamic cycle . The process serves as a comparison process for a gas turbine system (internal or external heating) with internal heat transfer from the turbine exhaust gas to the compressed gas (e.g. air). The ideal process has the efficiency of the Carnot process .
description
The Ericsson process consists of two isobars and two isotherms. It is shown in orange in the diagrams in the picture on the right and runs between the corner points 1-2E-3E-4E-1.
The 4 state changes are:
- 1 - 2E: isothermal compression
- 2E - 3E: isobaric heating, internal heat supply from the turbine exhaust gas (4E - 1)
- 3E - 4E: isothermal expansion with external heat input
- 4E - 1: isobaric cooling, heat dissipation internally to the compressed gas (2E - 3E)
The isobars in the Ts diagram run equidistantly (viewed in the horizontal direction!), So that the area corresponding to the transferred heat under the curve from 2E to 3E is equal to the area under the curve from 4E to 1. An ideal counterflow heat exchanger is required for heat transfer . The mean temperature of the heat supply from outside is the highest process temperature and the mean temperature of the heat dissipation the lowest, so that the efficiency is the same as that of the Carnot process (in the Ts diagram, the area enclosed by the cycle can be converted into a rectangle of equal area with the entropy difference between 1 and 2E and the temperature difference between 3E and 2E).
Real possible processes
Isothermal turbines and compressors cannot be implemented. The dwell time is not sufficient for heat transfer via the housing wall or the area is too small. Therefore, the approach to the ideal process is only possible by dividing it into different compressor and turbine stages with respective intermediate cooling or intermediate heating. The diagrams and the circuit diagram (right) show a subdivision into two levels. The internal heat exchange is now limited to the areas of the same size marked in green for heat absorption and red for heat output in the Ts diagram (also assumed to be ideal, ie without the temperature difference required for heat transfer). It can be seen from this that the approximation to the Ericsson process is the better the more steps are selected (for the ideal case an infinite number of steps would be required). The construction effort for several stages is high.
