Talk:Exergy

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Contents 1 Rewrite in progress 2 Merge 3 Comment 4 formulas 5 Availability 6 Cumulative Exergy 7 1911 Britannica 8 Free energy 9 Re: Energy quality types 10 B or ψ or Ξ or X? 11 Cold exergy

[edit] Rewrite in progress

I found one or two articles about this and emergy and energy quality that actually seem to make sense to me and seem to contain something approaching rigor. So I'm doing a rewrite starting with exergy because it's the oldest and most rigorous concept. Flying Jazz 12:00, 28 December 2005 (UTC)

[edit] Merge

I suggest that we merge the energy quality article with this article, and develop a clearer statement of the two. Sholto Maud 05:53, 4 December 2005 (UTC)

That's a really bad idea. From what I can tell, exergy has been around since the 1800s, emergy is a pretty recent concept and it might turn into an important concept, and "energy quality" relates the two using a really awful term instead of the better term of transformity. This seems like important stuff and it needs to be presented separately and presented well so that both scientists and laymen can distinguish between what's been used for power plant designs for generations (available energy=exergy) and a promising protoscience that started out being a little goofy. Flying Jazz 11:56, 28 December 2005 (UTC)

Now that I've gotten wrapped up in writing this thing, I see that energy quality might not be such a bad term. Oops. But I do think things should be presented separately. Flying Jazz 01:48, 2 January 2006 (UTC)

[edit] Comment

The sentence:

This work potential is due to either a potential due to a force, temperature, or the degree of physical disorder.

Needs rewording, but I can't figure out how to fix it.RJFJR 22:27, Feb 12, 2005 (UTC)

RJFJR, I attempted to help - Wes, Aug 15, 2005

Is there a 2nd Law of Efficiency?RJFJR 22:27, Feb 12, 2005 (UTC)

[edit] formulas

There are two fomulas listed under Exergy of heat available at a temperature, one is for heat into an object and one for heat out of an object. They both have terms that amount to T_c/T_H. Can they be combined into one formula and ignore whtehr the object is warmer or colder than the environment? RJFJR 05:27, Feb 19, 2005 (UTC)

[edit] Availability

Question: Is the exergy the same thing as the thermodynamic Availability function,

where changes in A correspond to changes in the amount of useful work that can be extracted from a system with respect to an reservoir of infinite capacity at temperature T_R, pressure P_R and chemical potential μ_R ?

(Reference: Waldram, Theory of Thermodynamics, pp. 75, 205). -- Jheald 11:24, 5 December 2005 (UTC)

Looks the same to me. The rewrite is making this clear Flying Jazz 11:56, 28 December 2005 (UTC).

When I see A, I think of Helmholtz free energy, but I think some people use F for helmholtz, and those might be the same people that use A for availability (which is another name for exergy). Just to confuse things more, the helmholtz page relates helmholtz to availability too when temperature doesn't change. Also, some people the past used B to indicate any thermodynamic potential (where I've used X). But the short answer to your question is yes. Flying Jazz Flying Jazz 22:02, 30 December 2005 (UTC)

[edit] Cumulative Exergy

I'd like to suggest that there is a separate sub-section dedicated to the concept of "Cumulative Exergy" as it is used in engineering. And then another sub-section dedication to a consideration of whether the engineering application of "Cumulative Exergy" is formally analogous to the application of "emergy" in systems ecology. Sholto Maud 03:03, 10 January 2006 (UTC)

I think the rigor of the emergy concept should be discussed in the emergy article. This article might discuss cumulative exergy eventually in a little more detail in the context of changing a reference state or unifying multiple reference states to an earlier one. In general though, cumulative exergy loss (or gain) is just like cumulative money loss/gain, cumulative weight loss/gain or cumulative heat loss/gain, so it's not worth a separate section in my opinion. Flying Jazz 16:49, 10 January 2006 (UTC)

Re: emergy... agreed.

Re: cumulative exergy. 1. So can we assume that the cumulative exergy concept is mathematically the same no matter whether it is used by engineers, biologists, chemists or ecologists? 2. If consequence of irreversible cycle is cumulative exergy loss, does a reversible cycle have the consequence of cumulative exergy gain? Sholto Maud 06:33, 11 January 2006 (UTC)

1. I don't know about that yet, but I suspect there won't be a simple yes/no answer to that question. 2. No. Exergy=available energy. That would mean available energy appearing out of nowhere. For a reversible cycle, there is no change in exergy. Flying Jazz 13:19, 11 January 2006 (UTC)

• Thank you for your response Flying Jazz. You might be interested in the anonymous quote I have put up at Talk:Emergy#Re:_emergy_novelty_.26_cumulative_exergy. If my anonymous source (apologies for this anonymity) is right then it seems that emergy algebra and cumulative exergy algebra are one in the same. Iff this is the case, then cumulative exergy algebra appears to address the phenomena of "coproduction". Sholto Maud 22:25, 11 January 2006 (UTC)

Cogeneration is nice. So are other coproduction methods in engineering and in nature. Your anonymous source has told you that integrals are really just like sums. There's no reason to be so strange and mysterious about any of this. If you want more people to understand exergy and emergy concepts, you are going about it the wrong way. This is not ancient Greece and we are not probing Delphic mysteries. When I wrote there probably won't be a simple yes/no answer, I meant that if someone agrees with all the assumptions made then the answer is obviously yes, and if someone doesn't agree with a single assumption made then the answer is obviously no. An encyclopedia article shouldn't make that judgement for the reader in my opinion. Please show your source what I have written under the "Applications" section. This is not yet referenced and it's a first draft, but I think I can come up with support for most of the statements I've made. I'm curious whether you or your source or others find this section to have a neutral point of view as it proceeds from engineering to the cosmological argument. Flying Jazz 00:06, 12 January 2006 (UTC)

My apologies if I am going about this the wrong way, and it seems mysterious - I have not been well schooled in diplomatic emergy synthesis. But also I don't want to make stupid errors, so I go slow. :)

• Re: Yes/No - I understand.
• Re: Show my source - I'll refer them to the section, to be rigorous, I understand it is a draft, but, as you suggest, I think that the section should be very well referenced, with actual practical examples.
• Re: Neutrality & general comments - there are a few comments which I feel hesitant about, but let me say that I think you have done some fantastic work so far, and I appreciate your contribution very much.

- Not sure if saying, "The combination of untestable hypotheses, unfamilar jargon that contradicts accepted jargon, intense advocacy among its supporters, and some degree of isolation from other disciplines have contributed to this protoscience being regarded by many as a pseudoscience." is neutral.

- Not sure if saying, "Testing this idea in living organisms or ecosystems is impossible for all practical purposes because of the large time scales and small exergy inputs involved for changes to take place. However, if this idea is correct, it would not be a new fundamental law of nature. It would simply be living systems and ecosystems maximizing their exergy efficiency by utilizing laws of thermodynamics developed in the 19th century." is neutral. I'd like to refer you to Bastianoni's article. It seems to me that k_iCE in Figure 1 is an example of exergy flow using the energy systems language in biochemistry and biophysics. And also perhaps, this book might be good read as an example of testing the maximum power hypothesis.

- Rather than say, "There has been some progress in standardizing and applying these methods." it might be better to give examples of the progress.

• The intensity of my emergy/cumulative exergy advocacy will reduce as this year proceeds. Good luck with this important work. Best Regards, Sholto Maud 23:09, 12 January 2006 (UTC)

You may be right about many of those comments. As I learn more (and relearn more of what I knew in college), I'll try to keep your comments in mind. However, your own statement about the energy systems language being important in that article does seem to support my statement that a problem many have with these fields is unfamiliar jargon to describe topics that are familiar using more standard (or simply older) language. I will consult Odum and his critics a little later after the math and engineering sections have a few examples in them. Don't worry. The guy won't be ignored when the article is done. Flying Jazz 23:11, 13 January 2006 (UTC)

[edit] 1911 Britannica

The 1911 Britannica article "Energetics" is of quite interesting historical value for this page. As well as a good survey of how the concept of Available Energy developed, clarified and then took hold during the 19th Century, particularly noting the work of Rankine and Kelvin in the 1850s, it's also of interest for showing that circa 1911 the concept of Available Energy seems to have been seen (at least by the author) as very much the best way to think about the efects of the Second Law. The original article is notably clearly written and reads very well. Unfortunately, however, none of the characters used for variables has been OCR'd at all well, which makes most of the scanned version sadly hard to follow. The original printed text is well worth looking out, however.

Also relevant for the energetics page! :) Sholto Maud 06:35, 11 January 2006 (UTC)

[edit] Free energy

Would there be any merit in combining the exergy article with the free energy article? They are almost identical in their definitions? Sholto Maud 00:45, 18 February 2006 (UTC)

No. In that case they should be edited to make them more different. Exergy = Availability. Free Energy = {Gibbs, Helmholtz} Free Energy. Of course, Free Energy can be derived as a special case of the Availability function. But IMO, discussion of exergy/availability under Free Energy shouldn't go much beyond that.

The two concepts are different, and usefully treated as such. If the articles have become too close to each other then some cutting back again to separate them is required. IMHO. -- Jheald 04:54, 18 February 2006 (UTC).

I agree with Jheald. The concepts are different and are used for different purposes and exergy should be understood on its own merits instead of being merged with other concepts. That little subscript to indicate reference conditions makes a huge difference to everything! By the way, I still regard this exergy article as incomplete and messy, and I wasn't the one who removed the tag. Especially with respect to conservation issues, I think it's important that detailed and technically accurate information about this topic is "out there" online freely accesible to people. My enthusiasm for the topic hasn't decreased, but getting done the first few sections took up too much of my time and I couldn't continue at that pace. I hope to come back to this article in a few weeks and add examples and implications in text boxes and diagrams. As it is right now, this article makes a lot of statements that I'm not sure should be included as written even though I wrote it but I hope to make detailed references with a copy edit at that time too. Flying Jazz 13:05, 18 February 2006 (UTC)

Ok cool. For one, I appreciate the attempts to clarify these concepts. If I may be useful as resident fool my summary is;

• Reference conditions is what makes exergy different from free energy: exergy is applied to systems with a large scale reference environment, free energy is applied to systems with a small/no scale reference environment.?

When it says, "Unlike energy which is always conserved for a cyclic process, an irreversible cycle reduces exergy." is it correct to say that a simple electrical circuit with resistor and battery is an example of this, such that the electrical energy is conserved in the circuit/cyclic process, but the chemical energy driving electron flow is not conserved and is a non-cyclic (irreversible) process where "exergy is reduced" or lost as heat accross the resistor? Such a circuit seems to involve free energy but are the reference environments for exergy and free energy different or the same in this example? Sholto Maud 13:31, 18 February 2006 (UTC)

Didn't Socrates always pretend to be a fool at first...and then he started asking questions too... The reference conditions are what makes exergy different from every thermodynamic potential, including free energy. Exergy is applied by comparing a system to a reference environment. It says what the system can do, what work it can perform, before it can't do any more because it just blends in with a reference environment that doesn't change because the event took place. Free energy is only a property of the system and the environment is not involved in any way. Free energy doesn't compare the system to anything else. If you have a mix of chemicals in an isolated box, you can use free energy to determine whether a reaction will occur. There is a "before" and an "after" state for the contents of the box. But in order to use the exergy concept properly, there has to be something else either inside or outside the box that acts on or gets acted on by the reaction. Still, I think in many situations, free energy and available energy can be used as if they were the same thing when they are set equal to each other (see equation 6 and 7 in the current version of the article). There might be some confusion about the math as it is now because the free energies of formation for chemicals are often listed in tables with respect to forming that chemical at 25 °C from elements at the same temperature, and the subscript 0 is used to indicate a "standard state" at a certain T and P, but this is different from "reference environment" in the exergy concept. I changed the math in the article to "R" subscripts to reflect this and match the second law of thermodynamics article.

I'm not sure what you're asking exactly about the battery, but maybe the answer is in the last paragraph of the the Mathematical Description section. Flying Jazz 14:40, 18 February 2006 (UTC)

That explains alot, thanks Flying Jazz. I was really confused about the difference between this and free energy as well. So basically, free energy is the energy released during a reaction and exergy is the energy released ifa system shifted to the energy level of the surroundings? BTW, the 0 suffix is 25 degree C, 1 atm. kr5t

[edit] Re: Energy quality types

The article says that (A) "if there is an energy transformation, the second principle of energy flow transformations says that this process 'must involve the dissipation of some energy as heat'. Measuring the amount of heat released is one way of quantifying the energy, or ability to do work and apply a force over a distance".

The entropy (second principle of energy flow transformations) article says (B) ""Ice melting" - a classic example of entropy increasing".

If A & B, then ice melting (as an example of entropy increasing) must involve the dissipation of some energy as heat. How does one measure the heat released when ice melts? (or would it be neg-exergy? Sholto Maud 05:34, 11 May 2006 (UTC)

[edit] B or ψ or Ξ or X?

These are the four letters I've seen used for exergy. I know that B is a magnetic field strength (units of tesla), so using B for exergy (units of joules) might confuse people. I want to use it anyway because my experience has been that the texts that refer to exergy most often and the most authoritatively (Szargut's "Exergy Method: Technical and Ecological Applications" is handy now) have used B and that's what I learned as a chemical engineer, so I'm reverting the introduction. E is an electric field strength (units of newtons per coulomb) and also energy (units of joules). Physicists seem used to this. The thermodynamics folks and the field folks should be used to having conflicting nomenclature by now, and these two subfields of physics don't interact often enough for it to be too much of a problem I think. Flying Jazz 06:46, 29 June 2006 (UTC)

Looks like it's called φ sometimes also. Flying Jazz 07:05, 29 June 2006 (UTC)

If I read the 2nd law article correctly and it's a thermodynamic potential, in statistical mechanics it's usually denoted as Ξ. --0SpinBoson 13:44, 29 June 2006 (UTC)

Exergy+"Statistical mechanics" receives 888 google hits. Exergy+ecosystem gets about 25,000. Exergy+physics receives about 50,000. Exergy+engineering gets about 120,000. The concept is used most often by engineers, so I'm reluctant to use the statistical mechanics variable. I also don't think putting subscripts and superscripts on a Ξ looks right but maybe that's just me. Maybe I shouldn't have asked for help on the physics project talk page after all, but I would like to have rigorous math here before writing more about less rigorous subtopics, and I'd like to put the same letter on the 2nd law page. Flying Jazz 15:12, 29 June 2006 (UTC)

As long as you're consistent, it doesn't matter much I suppose. Just one of those things, like i vs. j for electrical circuits. --0SpinBoson 15:26, 29 June 2006 (UTC)

I found a good powerpoint presentation about this issue comparing 15 textbooks (with a silly joke in the middle). Their recommendation for textbooks was to use an "E" with a different font type, like normal Roman E for exergy instead of italic E for energy. However, they didn't say whether any of the textbooks they examined did this. Flying Jazz 15:12, 29 June 2006 (UTC)

When I did thermo it was A, for Availability; but IUPAC says that now has to be Free Energy Helmholtz Energy. Ξ was the Grand Partition Function, ie the partition function for a system with a variable number of particles. I can't say I like B, because in physics there's almost always the chance of a magnetic field knocking around somewhere. So that's why I used X in the second law article -- that and the fact that it seemd a nice everyday unthreatening sort of letter, and didn't seem to be taken by anything much else. Jheald 15:23, 29 June 2006 (UTC).

All four should be mentioned in the Exergy article, and perhaps also the 2nd law page. I have no preference as to symbol. In the absence of IUPAC standard, the idea that the most used symbol (in this case engineering useage) can be a proxy-standard seems to have merit. Sholto Maud 08:52, 30 June 2006 (UTC)

What was Zoran Rant's symbolism again? Perhaps the article should track the historical development (and changes) of the symbols: who used which one for what purpose... were they trying to emphasise something different with a different symbol or were they not aware of precedent symbols

I study energy eng. in italy..we have always used the &Xi according to Kotas..

[edit] Cold exergy

The statement on "cold exergy" is incorrect.

X/Q = 1-To/T is valid even if T < To. The numerator and denominator do not magically reverse in this case. However, the signs of energy and exergy are now opposite, indicating they flow in opposite directions.

The thermal exergy of a substance below the reference temperature can have an absolute exergy greater than the energy it contains if the temperature is less than half of the reference temperature (absolute scale). Don't worry, the amount of energy flowing in at the reference temperature is still greater than the numerical value for the exergy.

If you don't get to it, i'll change it when I have time.

Wes Hermann 04:18, 3 December 2006 (UTC)