When using turbines to extract power from any gas cycle, you can approach Carnot cycle efficiency by continuously adding more stages of turbines and/or recuperators to manage waste heat. The design of such systems goes as far as the cost of approaching the Carnot cycle matches the benefit.
For gas turbines (or steam turbines) you’ll notice that ground based systems can get quite large to maximize efficiency, where aircraft engines will attempt to minimize the size to save weight. It’s all an engineering balance of cost vs benefit.
dombar1 t1_j18r1eh wrote
Reply to Why do we use phase change refrigerants? by samskiter
To answer your bonus question:
While not technically a gas (but also kind of a gas), Supercritical CO2 is being used as a heat exchange fluid that is very efficient. Here is an example https://reactionengines.co.uk/reaction-engines-and-brunel-university-london-engaged-in-ground-breaking-project-to-optimise-supercritical-co2-for-waste-heat-to-power-conversion/
When using turbines to extract power from any gas cycle, you can approach Carnot cycle efficiency by continuously adding more stages of turbines and/or recuperators to manage waste heat. The design of such systems goes as far as the cost of approaching the Carnot cycle matches the benefit.
For gas turbines (or steam turbines) you’ll notice that ground based systems can get quite large to maximize efficiency, where aircraft engines will attempt to minimize the size to save weight. It’s all an engineering balance of cost vs benefit.