mechanical efficiency? Definition? Delirium of wikipedia?

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chatelot16
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mechanical efficiency? Definition? Delirium of wikipedia?




View chatelot16 » 12/11/10, 17:31

hello i am creating a new topic so as not to mix what i started to say the
https://www.econologie.com/forums/la-voiture ... -2560.html

when bernardd was doing weird calculations i just thought he was wrong, in fact he read in wikipedia the opposite of what everyone knows
http://fr.wikipedia.org/wiki/Rendement_%28physique%29

would the definition of return have changed?
if we click for the english version we fall back on the good old performance that we all know
http://en.wikipedia.org/wiki/Thermodynamic_efficiency
this new yield was introduced on wikipedia in May 2007

WHERE IS THE ERROR?

I looked for another site ... OUF everyone continues to calculate like me, no change on all the thermodynamic sites that I found, except those which are copies of wikipedia!
http://www-ipst.u-strasbg.fr/cours/ther ... incip2.htm
6.10)

* We show that the Carnot cycle is the cycle which has the maximum yield, no other cycle of a thermodynamic machine can have a greater yield.

The Carnot cycle is an ideal cycle and it is for this reason that all the other real cycles are compared to the Carnot cycle which thus serves as a reference.

We thus define the efficiency e of any cycle as the ratio of the yield of this cycle to the Carnot yield:

efficiency of a cycle: e = r / rc (with 0 <e <1)


http://www.ac-nancy-metz.fr/enseign/phy ... cours7.htm
http://www.thermodynamique.com/spip.php?article18

The relationship between the actual yield and that of Carnot has been called "energy efficiency". There is a smarter concept: exergy.

By improving this efficiency, one can increase the driving efficiency of a machine without raising the temperature difference at these terminals. This amounts to reducing friction as much as possible, avoiding disturbing the flows and banishing any thermal shock.


QUESTION? who has any information about this mess? hoax to see how long an error can remain on wikipedia, or really new vocabulary used somewhere in teaching?

as a hoax it is well done because all the pages that talk about performance were modified the same day by the same author
May 12, 2007 Kropotkin 113
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bernardd
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Re: yield change of definition? wikipedia delirium




View bernardd » 12/11/10, 17:45

chatelot16 wrote:would the definition of return have changed?
if we click for the english version we fall back on the good old performance that we all know
http://en.wikipedia.org/wiki/Thermodynamic_efficiency


And what is the translation of "efficiency" in French according to you?

Effectively, Yield is translated in English by "thermodynamic efficiency".

But the article you are quoting contains nothing, but refers to thermal efficiency.

And what does this article say?
The 'thermal efficiency' is sometimes called the energy efficiency.


There is energy efficiency.

But no more traces of performance ...

It is only in heat engines that the 2 merge.
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View Remundo » 12/11/10, 18:19

Hi friends,

The problem is that there are several meanings of the word "yield".

Traditionally, performance refers to the following ratio

useful energy
costly energy

Note: useful and costly from the standpoint of a system that receives the costly and yields the useful.

Moreover, this return is not necessarily between 0 and 1: it can exceed 1: in this case, we speak ofefficiency, the "traditional" yield being only a particular case of efficiency which cannot exceed 1. Some keep the word yield even if it exceeds 1: it is pure and hard semantics.

The other notion of "yield", less traditional and often more fuzzy, is a% deviation from an ideal thermodynamic transformation: we seek to figure in% a deviation from the real compared to the ideal

for example if an ideal isothermal trigger produces 100 Joule, and the same trigger (identical final and initial state) but taken in real conditions product 90J, we will say that the yield (or efficiency) of the transformation is 90%. In this case, the efficiency / effectiveness is perceived as the ratio of 2 performances, one which would be real, the other ideal:

Yield =
real performance
ideal performance (optimal)

What is certain ; only a case-by-case definition of what is called "yield" makes it possible to avoid confusion.
Last edited by Remundo the 12 / 11 / 10, 18: 24, 2 edited once.
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bernardd
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View bernardd » 12/11/10, 18:23

Anyway, I think you use energy for not much:

1- this is a definition. The key is to be consistent. For my part, when I talk about it for calculations, I specify the definition before, so no risk of being wrong.

2- one thing you must agree on is always, we have by definition: yield <1. It is even for this reason that we never speak of efficiency for a refrigerator, but of cop, because refrigeration engineers always want to stand out ;-)

But if they talk about cop, it's because cop> 1 (when it's done well : Evil: ) and therefore it cannot be a return.

What do you think could explain why the yield is less than 1, if you do not define the yield as a ratio between 2 efficiencies, one of which by definition is entropy, greater than the other?

Because yes, the fact that the yield is less than 1 is a consequence of entropy which only goes in one direction, over time.
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View Remundo » 12/11/10, 18:29

Let us leave aside entropy (the 2nd principle). It affects the value of "returns", or even the impossibility of obtaining any return.

Regardless of all that, we can always talk about returns greater than 1 if the calculations show a possibility of this without violating the 1st and 2nd principles of thermodynamics

Simply, the practice wanted that the word yield is reserved for objects providing less useful energy than they receive costly.

I'm talking about energy, but you can change: talk about potatoes, carrots, information ...

The custom has also wanted that we speak of efficiency for "yields" greater than 1: in thermo, there is for example the cooling efficiency (refrigerator type) and calorific efficiency (heat pump type)

The COP (coefficient of performance) is a jargon of thermicians or refrigerationists who says that:
useful energy = COP x cost energy.

The useful energy is usually a thermal transfer (cold for the refrigerator or hot for the heat pump), the cost being electricity to operate the compressor ...

Note: in general, the COP is> 1 and depends on the outside or inside temperatures ...

Hoping to clear things up.

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View Christophe » 12/11/10, 18:40

No time to go into details, but I'll add Remundo to the terminology ...

In motor racing or in motor sport, it is not uncommon to hear about "good performance" for an engine which runs well in power, which makes good lap times ... It is obviously a mistake of term. Some journalists also repeat this error. It is not uncommon to read: "this car has an engine with a good efficiency because the engine goes up quickly in the revs" There too all wrong.

Now these notions have nothing to do (at least directly because we can go into the details of the specific power or specific power which are linked to the mechanical efficiency but hey ...) with the mechanical efficiency but we rather a kind of " mechanical productivity "... 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?

Also in engine mechanical efficiency is the product of several outputs (cycle, combustion, filling ...) + transmission if we talk about vehicle efficiency.
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View bernardd » 12/11/10, 18:51

To be even clearer:

- real energy efficiency, this is what is obtained by measurements;

- theoretical energy efficiency is the efficiency of what we know how to model, or sometimes of what we want to model.

- the yield, it is the ratio between the 2 real and theoretical energy efficiencies, and that gives an estimate of the losses not modeled.

Because it is very rare to forget to model gains ;-)

This is very visible for a decompression engine, because the actual mechanical work obtained is always less than the maximum possible mechanical work, which is the reversible isothermal work.

And the yield is indeed the ratio between the 2, when we are satisfied with the isothermal ideal modeling.

However, the efficiencies are calculated relative to the input energy, that in the tank. This term disappears in the calculation of yield, through the game of simplification in a report.
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View Remundo » 12/11/10, 18:57

Yes, completely Christophe : Idea:

And even in photovoltaics.

Dialogue taken from a real situation:

"what is the performance of your installation? "
// thinking of asking "what is the production of your installation"? //

I answer him "what do you mean by yield?" ...

Beennn ... The kW !!

KW is a power. Do you want to know the ratio between electric power and solar power?

No, I want to know the performance of the installation, what;

What yield?

Hey hey ... the energy it produces.

Ah, that I can tell you: X kWh / year, can power X homes of 3 people, but it is not a return.

But yes, it's the same!
-------------
: Mrgreen: Rather informative :P
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View chatelot16 » 12/11/10, 19:04

of course the word yield is used with all sorts of other meanings in other cases ... and it's already quite difficult like that to avoid confusion, but I thought that in thermodynamics and physics c was clear! if now thermodynamics gets confused with 2 opposite definitions we will never get out

I repeat my example of a steam engine
with the old vocabulary:
9% real return
theoretical yield calculated with temperature 10% (carnot yield)
proportion achieved of theoretical yield 90%

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

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

since sadi carnot explained all this in 1824 the words were clear ... except that everything was rewritten on wikipedia in may 2007!

except the page on the life of sadi carnot or he has not yet dared to change every time or there is the word output

I will therefore have to find the origin of this change which I only see used by wikipedia and bernardd while all the other sites continue with the usual notation.
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View Remundo » 12/11/10, 19:15

At one time, I tried to be an editor on Wikipedia ...

I quickly stopped.

Sagoins erase everything that you want to put important and precise, wrapped in pseudo-scientific arguments, or that what we write undermines this or is a source of controversy ...

Their only authority is that conferred on them by their status as "moderator".

Thus, I find that many scientific articles are very poor. I think people are tired of spending 4 hours on an article so that it can be erased or distorted in 3 seconds by an unknown guguss.
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