mechanical efficiency? Definition? Delirium of wikipedia?

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bernardd
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View bernardd » 12/11/10, 19:25

Well agree with you on wikipedia, Remundo: it has become a religious site.

chatelot16 wrote:with wikipedia vocabulary it will be
real energy efficiency 9%
theoretical energy efficiency 10% (carnot efficiency)
yield 90%


It's not the wikipedia vocabulary, it's the vocabulary I learned. And as I told you, my physics teacher was not a youngster himself. And very interesting :-)

chatelot16 wrote:it allows us to announce a yield of 90% which is not at all the ratio between consumption and production to which everyone is used but a ratio between real machine and perfect hypothetical machine


It is also to avoid this problem that I am careful to talk about energy efficiency: no risk of error between the two directions of yield.
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bernardd
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View bernardd » 12/11/10, 19:32

Christophe wrote:or rather a "mechanical efficiency", yes that would be fairer ... and there we join the English term "efficiency" (literal translation of performance) where can be the confusion?


Indeed, mechanical efficiency seems fair to me.

But I'm surprised you say "efficiency" is the literal translation of "yield" :-)

efficiency is therefore in your opinion closer to "yield" than to "efficiency"?

And the translation of yield is indeed "thermodynamic efficiency", as opposed to "energetic efficiency", or to other versions of the type of energy depending on the field studied: thermal, mechanical, ...

Otherwise, Christophe, I have a problem with the site: when I come back after a while, I see new posts appear between the posts I had followed live. For example this post did not appear to me when I had already read and responded to posts which are placed after ...
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chatelot16
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View chatelot16 » 12/11/10, 19:34

if it was just a fad to use the word efficiency instead of efficiency, it wouldn't matter

what is serious is to reuse the word yield for something else, this relationship between theoretical and real efficiency

Remundo have you ever seen that somewhere?
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chatelot16
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View chatelot16 » 12/11/10, 19:37

bernardd I don't allow myself to doubt what you learned, I just want to understand where this difference comes from

looking for carnot cycle with google, comes across sites that use my definition ... the only sites that I found with the definition of wikipedia are copied on wikipedia

in which class where did you learn like this? have you seen books like that?

(message I wanted to send earlier but got stuck in a corner)
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View Remundo » 12/11/10, 19:44

Yes !

for example, in machines in permanent flow, one speaks of "isentropic efficiency"

see this link page 2

This yield (defined from a report of differences in enthalpies, themselves obtained respectively from a real (losses and irreversibilities) and isentropic (ideal) evolution.

these "efficiencies" make it possible to introduce coefficients modeling the imperfections of real machines. ultimately to caculate the "real" performance of the machine, in terms of energy ratio useful / costly
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bernardd
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View bernardd » 12/11/10, 20:14

chatelot16 wrote:in which class where did you learn like this? have you seen books like that?


Math sup / math spe, but I no longer have access to my books. When I went back to thermo, I just took the references, and wikipedia said exactly what I remembered, including corrections for those who confused performance of current vocabulary and performance in thermodynamics :-)

This point had marked me, precisely as an example of the vocabulary pileups between habits and precise scientific definitions.

So no problem for me, especially since it makes sense.

Remundo's document also clearly shows the use for comparing a real situation and a model, isentropic in this case.
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chatelot16
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View chatelot16 » 12/11/10, 20:55

me in math sup math spe the book of thermo dynamic it was anequin and boutigny ... I always have it and around carnot the output is well the relationship between mechanical energy supplied and heat used

the relationship between real yield and carnot yield had not received a special name, but 2 sites that I mentioned in my first message use the word efficiency for this relationship between real and theoretical carnot

it shock me a lot to see wikipedia completely reverse the vocabulary

I often know the principles and use wikipedia to have modern notation, faster than looking in my old books ... but beware there are sometimes problems: when it's important wikipedia is as my first step which allows me to seek confirmation elsewhere

today no confirmation: all the sites I find use my vocabulary, not that of wikipedia!

the remondo pdf only talks about isentropic efficiency so don't say if they have old vocabulary or wikipedia

sadi carnot wrote his great thing in 1824, and it took long enough for everyone to understand it, and it would be a shame to change the vocabulary 183 years later
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bernardd
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View bernardd » 12/11/10, 21:45

chatelot16 wrote:the remondo pdf only talks about isentropic efficiency so don't say if they have old vocabulary or wikipedia


Isentropic efficiency in this document, it is the relationship between real efficiency and the efficiency of isentropic expansion.

Otherwise it would be output upon entry, and it is not.

Similarly, the efficiency of the compressed air motor is calculated by the ratio of actual work to isothermal work, while energy efficiency is the ratio of actual work to tank energy.
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View nonoLeRobot » 12/11/10, 22:21

Indeed I would have said like you Chatelot. In any case it would be interesting to find the "official" vocabulary if it exists.

I see that the wikipedia page is really weak and is only a draft, it would be interesting to copy a summary of your discussion in the discussion page of wikipedia.

edit:
The "National Center for Textual and Lexical Resources" says:

Ratio between useful energy and total energy consumed at the same time by a mechanism, a process. Energy efficiency. While the output of the steam engine did not yet exceed 12 percent and that of the internal combustion engine 100 percent, Diesel immediately reached 17 percent (P. Rousseau, Hist. Techn. Et invent., 100, p. 31):
... it is useful to introduce the concept of annual natural energy. It is the energy produced, in a year, in double effect, by turbines of yield equal to the unit, supposing that it is produced entirely in maximum fall. It is obviously a simple sight of the mind because turbines can never reach a yield equal to unity ... Romanovsky, Mer, source en., 1950, p. 94.


Except if other dicos do not agree, it is necessary to correct wikipedia.
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chatelot16
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View chatelot16 » 12/11/10, 23:44

I found a site which is not a simple copy which uses the vocabulary wikipedia
http://patrick.kohl.pagesperso-orange.f ... chines.htm
The efficiency of a thermal machine is equal to the ratio of the useful energy recovered by the energy spent and paid.

* The efficiency r is defined as the ratio of the efficiency of the machine to the efficiency of the corresponding ideal Carnot machine.

Attention: In the past, and the habit is still largely preserved, we called yield which is defined above as efficiency.

The word efficiency was reserved for engines and efficiency for refrigeration machines and heat pumps.


and at least that specifies it although the vocabulary has changed!

remains to know why it changed! who was able to decide such nonsense

beware in some year 2 x 5 = 7 because x will mean + ... and 2 + 5 = 10
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