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A question has been asked here before whether sliding vane compressors could be used in place of axial compressors on jet engines since they have a high compression ratio per stage (Why were rotary vane compressors never used in jet engines?), the answer being that the sliding seal would give out at the RPMs required.

What about a liquid ring pump?

It's essentially a sliding vane compressor where the seal is provided by the mass of liquid moving along the circumference. Is it possible to maintain a mass flow of the same order as axial compressors with these? Please ignore the question of cooling of the liquid for the purpose of this discussion.

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  • $\begingroup$ Liquid ring pumps are usually used for creating vacuum, which has large pressure ratio, but low absolute pressures. They less suitable for high pressures, because high pressure deforms the liquid ring more. $\endgroup$
    – Jan Hudec
    Oct 15, 2019 at 20:21
  • $\begingroup$ Also note that for a jet engine (rather than shaft engine with Brayton cycle) mass flow is much more important than compression ratio. And number of stages is not relevant, the total weight is. $\endgroup$
    – Jan Hudec
    Oct 15, 2019 at 20:29

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You said to ignore the cooling of the liquid, but that's something that cannot be ignored. With the compression ratios achieved in typical jet engine compressors, the air leaving the last stage of the compressor may be 800 - 1000 deg F. You won't find a lot of liquids that won't just completely vaporize at those temperatures. Yes you could potentially cool the liquid, but the cooling apparatus would add a huge amount of weight, as well as consume a lot of power.

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  • $\begingroup$ There are ionic liquids with boiling points around 450°C and minimal vapour pressures. $\endgroup$
    – Francis L.
    Sep 14, 2019 at 21:43
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    $\begingroup$ @FrancisL.: Which is still well below some of the temperatures he's talking about. $\endgroup$
    – Vikki
    Sep 15, 2019 at 2:52
  • $\begingroup$ It's not just cooling. It would either add a lot of weight, as the liquid carried out with the flow would have to be replaced, or a lot of complexity in separating it. $\endgroup$
    – Jan Hudec
    Oct 15, 2019 at 20:15

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