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[llmbs]

Lets focus on a gas turbine centrifugal air compressor and why its impossible to make it isothermal. First off, the compressor is a natural heat reservoir because when air is compressed its temperature rises. It has the least amount of variables when it comes to generating heat because all you need is a cd nozzle housing, and an impeller rotating really fast. The turbine in my opinion is not as natural a heat reservoir as the compressor cause there's more variables involved to get it going in the first place (oil needs to be processed into gas, material expansion and strength, air/fuel ratio etc.)

The point I'm getting at is in order for the 2nd law of thermo to work for us in building an isothermal centrifugal air compressor, the turbine side should be the cold sink and the compressor side the hot source (its a natural heat reservoir anyways). The major problem with this is its very difficult to find a way to have such a low temperature turbine and get high efficiency to drive the compressor. However, I think I figured out a way to do it and it works.

I wont get into detail as to how I'm doing it but here we go. The compressor I'm using is a t3-50 trim. The turbine has an inlet temp of 58 F and an outlet temp of 37 F and the amount of air exiting is about 85-90 cfm. Whats interesting is the compressor side raises its temperature 13 degrees above ambient temperature to generate slightly above 2 psi and about 100-110 cfm at 44,000 rpm. By the way, the compressor does not raise its temperature adiabatically either, I think its because of the cold sink turbine.

If you don't believe me I will be happy to email you a temperature graph I generated by sticking a thermocouple down the outlet of the compressor housing as it was running. You can also look at the t3 50 trim map and pinpoint its efficiency and use an adiabatic calculator to see just how much this compressor should have raised its temperature above ambient (its more than 13 degrees f).


So there we have it. I have a heat reservoir (compressor) and a cold sink (turbine). Based off the 2nd law of thermo, if I were to use a heat exchanger system such as an inter cooler fin heat pipe embedded inside the compressor housing and connect it to the cold sink turbine side, the 13 degree temperature rise in the compressor housing will see the cold sink turbine and travel into that direction. So now instead of the 13 degree temp rise causing resistance when compressing air, its being used to try to equalize the cold sink turbine that has a 37 F degree outlet temperature. The rpm's should also increase from 44,000 rpm as well.

If the heat exchanger system was embedded into the system I think that the compressors inlet and outlet temperature will be equal, making it an isothermal air compressor. If not, the temperature will be very, very close to each other making compressed air more easier to produce.

You have to also remember that the inter-cooler fin heat exchanger embedded inside the compressor housing can be made of diamond. Diamond will instantly transfer the heat away from the compressor housing because it has super high thermal conductivity and diffusivity.

When it comes to conventional compressors, the drive side and compressor side are both hot (although the turbine is hotter) and when air is compressed the heat of compression has no cold sink to go to. It has no direction, so all it can do is cause resistance for the next batch of air from getting compressed and now compressing air takes a lot of power.

Any arguments?

Edited by llmbs, 22 February 2010 - 03:06 PM.