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Expansion in Steam Engines: Essentially Hyperbolic/Isothermal or an Isothermal/Adiabatic Crossbreed?

Expansion in Steam Engines: Essentially Hyperbolic/Isothermal or an Isothermal/Adiabatic Crossbreed?

Expansion in Steam Engines: Essentially Hyperbolic/Isothermal or an Isothermal/Adiabatic Crossbreed?

(OP)

Hello all, this is my first post to this forum.

I volunteer aboard a retired steamship; the following are pertinent threads I've started on the subject...

http://www.eng-tips.com/viewthread.cfm?qid=341551
http://www.eng-tips.com/viewthread.cfm?qid=342485
http://www.eng-tips.com/viewthread.cfm?qid=343198
http://www.eng-tips.com/viewthread.cfm?qid=378864

The ship's website is @ http://www.sskeewatin.com/ .

If such a rehabilitation and re-purposing as described in the above threads were ever to take place, it would be very desirable to make the facility as energy-efficient as possible within the limits imposed by not compromising the vessel's historical integrity. In consequence I'm undertaking some of the preliminary footwork so have to the right kind of info as would be needed for FEED, considering this would be a very brownfield development.

Moving on:

Numerous classic texts on the subject, and even the 1970s materials I used during my college and in-career studies, state more or less categorically that the expansion of steam within the cylinders of a steam engine is hyperbolic and/or isothermal. I find it of interest that no qualifications, codicils or caveats are appended to this assertion...

Other less-numerous sources state that in the case where steam engines harness superheated steam [the necessary lubrication, cylinder wall, piston and piston ring material considerations having been addressed], minimal heat transfer will occur between the cylinder walls and the working fluid and the expansion of the steam will in this specific type of instance be closer to the adiabatic than the isothermal.

My instincts are to believe the latter sources...but I've been wrong before, hence the wish to poll greater minds than my own.

It goes almost without saying that the answer to this query would have profound effects upon the heat balance and hence the design of the plant, whether the sizes of any of the cylinders would have to be adjusted due to the change from saturated to superheated, and perhaps even reheated, steam, to what extent this would be altered by the addition of an LP exhaust turbine in pursuit of increasing overall plant efficiency, and so on.

Any thoughts?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Expansion in Steam Engines: Essentially Hyperbolic/Isothermal or an Isothermal/Adiabatic Crossbreed?

(OP)
...hmmm...do I need to re-post in the Heat Transfer & Thermodynamics forum?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Expansion in Steam Engines: Essentially Hyperbolic/Isothermal or an Isothermal/Adiabatic Crossbreed?

Yes, I'd pull this thread and copy the body of your question over there.

You'll have more readers and commenters.

RE: Expansion in Steam Engines: Essentially Hyperbolic/Isothermal or an Isothermal/Adiabatic Crossbreed?

(OP)
Done. Thanks, racook.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

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