Brayton cycle in helium atmosphere with existing gas turbines?

[alexisgros]

Hello everyone,

I was wondering what would the impact be if an existing gas turbine made to run in air at atmospheric pressure was run in an atmosphere of helium (let's say in a closed loop heated through a heat exchanger). How would the power output and efficiency be impacted, and what would be the impact of the helium pressure on the system?
For example, would the power output be equivalent if the helium pressure was such that its density matched that of air?
How would the higher conductivity of helium impact the plant?

Thanks in advance for your ideas and input!

 

[BvU]

A bit hard to imagine a combustion chamber with helium only. Can you provide a sketch ?

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[alexisgros]

Yes, it would be in the case of a closed brayton cycle with a heat exchanger instead of a combustion chamber. These systems were studied for power production in spacecraft.

The reason I asked this question in the aerospace engineering forum is that I wanted to know the impact of such a cycle when using it with existing, for example aeroderivative gas turbines to be run in a helium environment.

 

[jack action]

Why don't you tell us what you find?

Here, you have all the necessary equations to evaluate a Brayton cycle.

Here, you have the physical properties of helium, and here the ones for air.

 

[BvU]

Yes, it would be in the case of a closed brayton cycle with a heat exchanger instead of a combustion chamber. These systems were studied for power production in spacecraft.

The reason I asked this question in the aerospace engineering forum is that I wanted to know the impact of such a cycle when using it with existing, for example aeroderivative gas turbines to be run in a helium environment.

I see. Your 'run in He' got me confused when opposed to 'run in air'. You mean He as a working fluid.

 

[Flyboy]

I think they already have helium working fluid Brayton turbine designs, if not necessary in hardware form then certainly as highly refined designs.

As for “aeroderivative gas turbines”, I think that’s not viable. The differences between an internal combustion gas turbine and a Brayton turbine optimized for the kind of application you’re proposing are numerous and costly enough to warrant a clean sheet design.

 

[alexisgros]

Thank you Flyboy and jack action, I have the answers I was looking for. The equations for the brayton cycle are nice but the real question is how would the efficiency of the compressor and turbine stage be affected by the use of helium, and it appears that it is affected enough to warrant redesigning the whole plant. Helium leak issues also make it challenging to reuse an existing air breathing engine.