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Jet pumps or venturi pumps are often stated as having a "terribly low" efficiency, steam jet pumps specifically are usually describes as "only justifiable when there's an abundant steam supply anyway" - however, I hardly find any numbers, and no formulas.

My question: Is there a general form to describe the work done by a (non-steam) jet pump an the pumped medium as a function of the work used to pump the working fluid (gas or liquid)

Is there a general form to describe the work done by a steam pumpe as a function of the thermal energyinput into the workng fluid?

While real-world numbers are interesting, I'm mostly after the limits posed to jet pumps by thermodynamics, not engineering.

EDIT: Can a jet pump be describes meaningfully in a p - V diagram? Put another way, can the changes of impulse in the media be expressed solely as functions of the pressures (before/after)?

Thus, can a (steam-)jet pump be described as a thermal (steam-)engine?

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This paper might have what you want: dx.doi.org/10.1063/1.1150141 –  user2963 Feb 14 '12 at 13:49
there's a paywall and it seems to bother more with engineering aspects. –  mart Feb 14 '12 at 14:18
they give an efficiency of $\eta = \frac{\dot{m_e}(P_d-P_e)}{\dot{m_j}(P_j-P_d)}$ e = entrainment j = jet d = discharge –  user2963 Feb 14 '12 at 14:20
If that's what you are looking for and you want to see the derivation, I can give you a link to the pdf –  user2963 Feb 14 '12 at 14:23
P refers to impulse, or pressure? This refers to compressible fluids also? I assume it doen'st hold true for condensing jets. I'd be interested in the derivation (so I'd know how to play this thinking in purely mechanical terms, and maybe find the solution for steam jets afterward). Thanks a lot so far, I think I need to rephrasse my question, like what's the highest entrained mass flow possible for given pressures (and why). –  mart Feb 14 '12 at 15:34

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