Talk:Rankine cycle

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If anyone can get the image fit more nicely on the page, feel free. I messed with it for quite a while to get it to fit at all.

I think the Equations section could use some more clarification. Varable definitions, dot represents time derivative (I assume?).--Cmprince 21:58, 10 Dec 2004 (UTC)

Point taken. Adding variable definitions. --ABQCat 22:01, 10 Dec 2004 (UTC)
Cool. I haven't had to do any thermodynamics in years, so I'd have had to dig out a book (horrors!) :) --Cmprince 22:36, 10 Dec 2004 (UTC)
Yeah. I noticed that there was no article on the Rankine cycle after I finished with my thermodynamics course last semester, and decided (perhaps as a form of therapy to deal with the horrid subject matter?) to regurgitate what I had managed to learn and what I found useful into this article. Hopefully it'll help other people who are just as clueless as I was at points. --ABQCat 22:40, 10 Dec 2004 (UTC)

Contents

[edit] Diagram doesn't match text

The text (correctly) describes an ideal Rankine cycle as "heated at constant pressure by an external heat source to become a superheated vapor", but the diagram shows the vapor heated to the critical vapor point, not superheated.

Anyone have a better diagram handy? -- Kaszeta 15:30, 9 August 2005 (UTC)

As I recall, I picked this image because I had extracted it from a government publication. Not really feeling like creating my own image (which I may spend some time on here if a search is unproductive), I used it. Not sure if the text describing the superheating was written by me or a later contributor, but you're definitely correct about it not matching the image.
As a side note, and in case I'm perhaps being dense (despite having checked a few dusty textbooks), the equations were re-numbered recently such that heat processes were swapped for work processes. I'm quite certain I'm correct, but would value feedback here if I'm not. --ABQCat 08:17, 19 December 2005 (UTC)
Same publication has a somewhat appropriate version of the image showing superheating. I'll take a closer look, but if it seems appropriate I'll upload it and replace the current image. --ABQCat 01:13, 20 December 2005 (UTC)

The equations do not match the diagram. The subscripts on the enthalpies are incorrect, indicating that Qin and Qout are on the left and right sides of the figure, which is incorrect.

I've changed the equations, and I've also edited the image for clarity. --Dric dolphin 01:52, 5 September 2006 (UTC)

[edit] Efficiency

Some typical and maximum efficiency levels would be useful. Tobyw 12:14, 8 March 2006 (UTC)

[edit] Missing/empty link

There's an empty link, [[]], in the Regenerative Rankine cycle subsection near the bottom. I would have fixed this myself, but I don't know what it's supposed to say.

It was empty as a result of vandalism by 213.181.226.27 on 26th October 2005. I fixed it.

[edit] New graph.

I've uploaded a new vector version of the graph to the wiki commons. Image:Ts-rankine.svg Although I applied to make it almost pixel-perfect, I would like someone more confortable with this page to move on the article. As you're reading this, I will have marked the old image as superceded.
MaxDZ8 talk 16:04, 24 May 2007 (UTC)

[edit] Rewrite (and a question)

I've reworded the processes section with a new diagram, Data was plotted from IAPWS IF-97 in SI units. I'll be changing other parts of the article very soon too, equations need tidying up a little and perhaps some more info about where this cycle is used and why it is used above others. Also super heating among other things needs covering. I've also made another diagram of a schematic that I'll try to include, Ts diagrams don't mean all that much to non-Engineering/Physics students. Andrew.Ainsworth 09:40, 23 August 2007 (UTC)

The section on the reversed cycle is really a red herring. All reversed cycles are refrigeration/heat pump ones. The vapour compression cycle is really derived from the Carnot rather than the Rankine cycle. Should this section just be removed? (Donebythesecondlaw 13:28, 19 September 2007 (UTC))

[edit] Various changes.

I inflict (lecture?!) thermodynamics to undergraduates,and I have made a couple of changes to this article.

I have put in a few more diagrams for the reheat and regenerative cycles. I have a load more, but I wanted to keep the size down.

I have moved the description to the top, to let people know what they are reading about.

I have also put in a few more technical bits about overall efficiencies and Carnot efficiencies.

I have also clarified the reverse Rankine cycle bit. This is still a bit tenuous and it migh be best to remove it entirely! (Donebythesecondlaw 13:32, 19 September 2007 (UTC))


[edit] New image

Replaced layout picture with better quality one, opinions? Andrew.Ainsworth (talk) 16:48, 29 November 2007 (UTC) I've just rewritten the description section, certain statements seemed ambiguous to me ("In general terms the Rankine cycle is similar to a Carnot cycle but with the compression process taking place on a liquid") and the order of material didn't seem to flow either. Perhaps a bit long now though, some of that text may belong in another part of the article really. I thought the picture was also best updated as now people can see where the phase change occurs. Andrew.Ainsworth (talk) 01:50, 30 November 2007 (UTC)

Fixed a mistake in the equations too: \frac{\dot{W}_{\mathit{turbine}}} {\dot{m}} = h_3 - h_4 = (h_3 - h_4,s)\times\eta_{turb} where h4,s is the enthalpy after an isentropic expansion. Andrew.Ainsworth (talk) 02:00, 30 November 2007 (UTC)

[edit] Description section

What is "heat addition temperature"? --Milkbreath 16:42, 2 December 2007 (UTC)

This whole paragraph is a bit odd, and actually contradicts somewhat the next paragraph. These should be concatenated and the numbers (such as efficiencies, 42% includes boiler efficiency) reconciled. Donebythesecondlaw 16:19, 3 December 2007 (UTC)

I have tried to sort this out. Donebythesecondlaw 11:36, 4 December 2007 (UTC)

The paragraph was a bit odd on reading again. Something about the following is what I was trying to include. Perhaps the section on alternatives to the basic Rankine cycle is where it's needed. What I meant by heat addition temperature was the average temperature of heat addition defined by:

\bar{T}_\mathit{in} = \frac{\int_2^3 T\,dQ}{Q_\mathit{in}}

In a similar way the rejection temperature is defined by:

\bar{T}_\mathit{out} = \frac{\int_4^1 T\,dQ}{Q_\mathit{out}}

and the efficiency of the cycle will be given:

1 - \frac{\bar{T}_\mathit{in}}{\bar{T}_\mathit{out}}

As the exhaust temperature is constant the only factor in increasing efficiency is increasing the inlet temperature, so superheating or feedheating would be ways to go. Andrew.Ainsworth (talk) 21:42, 7 December 2007 (UTC)

I put in the first of these equations along with a description. Can anyone shrink it a bit? Donebythesecondlaw (talk) 09:55, 21 December 2007 (UTC)

Just noticed I made a mistake above, the efficiency would be given by 1 - Tout/Tin. Andrew.Ainsworth (talk) 17:55, 22 December 2007 (UTC)

[edit] Processes of the Rankine cycle section

Last sentence: what does it mean for a Rankine cycle to be "exposed"? --Milkbreath 16:54, 2 December 2007 (UTC)

Not a clue; probably best to remove it. On a separate note, how do we get the Wikipedia credibility of this raised? It is beginning to look good. Donebythesecondlaw 16:11, 3 December 2007 (UTC)

Don't imagine for one second that I have the first clue about thermodynamics. I don't. I just bounce around copyediting, and I like things to make sense even when I don't understand what that sense is. As for raising the profile, one can submit an article for different reviews. I believe the first step is to submit for peer review. You should probably also bring this up on the talk page for WikiProject Physics. I would do it myself, but whoever does it should be able to respond to criticisms and suggestions by altering the content, and, as I said, that ain't me. --Milkbreath 18:05, 3 December 2007 (UTC)

I have tried to sort out the "exposed" sentence. It now makes sense, but may not say the right thing. Donebythesecondlaw 11:36, 4 December 2007 (UTC)