Yield: word disaster

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Yield: word disaster




by chatelot16 » 03/05/14, 15:36

Hello

I open here to avoid the off topic elsewhere

the word performance is disastrous: it has several different meanings which renders incomprehensible certain phrase when one can not guess at what yield thinks the author

"energy efficiency": ratio between the useful energy at the output and the energy consumed at the input

"agricultural yield": number of quintals per hectare produced: it has nothing to do with the energy yield because we only count what it produces, not what it costs

if we calculated the "energy yield" of a crop by measuring the energy expended including the embodied energy of fertilizers and treatment products, we would find that the "energy yield" of a high yield crop agricultural "is completely bad

conversely, if we let grow without doing anything we have a "poor agricultural yield" but an enormous "energy yield"

"new efficiency to the con": we see in wikipedia a new definition of efficiency which renames "efficiency" the "energy efficiency" that everyone knows

with this new vocabulary a steam engine which has a theoretical carnot efficiency of 0,2 and a real efficiency of 0,1 will have a "new con" efficiency of 0,5 or 50%

this way of modifying the vocabulary known to everyone is lamentable: those who leave the school are found with a vocabulary incompatible with the previous generation
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by chatelot16 » 04/05/14, 03:34

finally i just looked at current wikipedia
http://fr.wikipedia.org/wiki/Rendement_%28physique%29

we find in the history of the pages of the big fights, but the order returned: the true performance that everyone knew has resumed its place

the "performance a la con" that I criticized was called "comparative performance" by specifying that certain author called it short yield

I do not remember when there was this controversy, or I was found lots of pretty serious courses with these new definitions
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by Remundo » 04/05/14, 09:04

the words have a precise and contextualized meaning, in particular in sciences ...

So you have to be wary of the word "performance" in particular and be aware of what people mean in the use of this word.

In agriculture, the yield is the mass of plants produced per hectare.

In thermodynamics, it's more subtle and varied, I chose the following in my lessons:
- talk about engine efficiency = mechanical power / thermal power
- talk about efficiency in general = output power / input power
- when the machines handle many energy flows: efficiency = quantity sought / cost quantity

Sometimes I add the word efficiency / effectiveness to an adjective: thermomechanical efficiency, refrigeration efficiency (for the fridge = heat sampling / mechanical work), heat efficiency (for the heat pump = thermal input / mechanical work)

solaroelectric efficiency = Pelec / Psolar

etc ... The French language is quite rich and a minimum of rigor / definition allows to remove ambiguities ... still it is necessary that the audience is attentive ... :P

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by chatelot16 » 04/05/14, 18:08

you are at an age when your lessons were clear

but how many students have been confused in the last few years by this story of yield turned into efficiency, and "stupid yield" defined as the relationship between real efficiency and theoretical efficiency?

I have seen courses with this definition and nothing to indicate that it was contradictory to the meaning used in other branches of physics
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by Did67 » 04/05/14, 18:28

More broadly, this covers two debates:

- the principle of a definition: to agree to attach a meaning to a word; we call "thing thing" what measures "thingy" ...

Ex: yield = "what it makes" (if I put so much and so much in it, or if I cultivate such and such a surface ...); It is therefore logical that there are 36 definitions of performance, depending on what each one wants to measure as "osrtie" and as "input" (which is limited, which costs, which "constrains" action ...).

And so we have to agree ... The interest of dictionaries (which evolve!) And therefore definitions ... to understand each other!

The agricultural yield (how much I get per unit area - undoubtedly the "'journal" in time, before the SI and the "usual" deviations of the meter ...) undoubtedly existed before the motor yield or the yield thermodynamic or energetic ...

- moreover, this also clearly shows a tendency in education to "standardize"; learns that "this is that"; and that's how it is ... Instead of explaining that we call yield "what I get useful by using such limited resource and which costs me" EXAMPLES - see above ... And there, if you have captured the meaning, which applies to all situations, and not the definition which evolves like the dictionary, you will find to apply it, according to the circumstances, to what someone explains to you, provided that your interlocutor formulates a sufficiently clear thought (which is, of course, not always the case!).
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by elephant » 05/05/14, 10:26

Oli 80 said:

this way of modifying the vocabulary known to everyone is lamentable: those who leave the school are found with a vocabulary incompatible with the previous generation


I'm almost 60 years old. Since my 6th grade, we have already changed the chemical nomenclature 2 or 3 times, at least once the grammatical nomenclature, once the system of physical quantities commonly used (ex: we went from cal / hour to jouleX hour exp -1).

pffffff! : Evil: : Cry:

It's Babel!
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by dede2002 » 05/05/14, 11:49

Efficiency has also become a commercial argument, for example in the case of boilers that have 110% efficiency!

Which is basically impossible, but people like ...
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by Did67 » 05/05/14, 13:52

No, not impossible, but again, a lack of precision:

1) a fuel has two "caloric powers": the lower one - the PCI (we burn and let escape all the combustion gases (including the water vapor produced by the oxidation of the H atoms contained in in the fuel which are transformed into H²0) and the higher - the PCS (we burn, we condenses water vapor and the other combustion gases are released - excluding H²0 which has condensed).

Any table gives these two values, for each fuel.

2) you know from experience that the evaporation of a liquid "produces cold" [quite exactly, "consumes calories]: getting out of a swimming pool when it is windy; rubbing yourself with ether to disinfect...

Conversely, gas that condenses into liquid gives off calories. Hence this difference between PCI and PCS.

3) In the past, there were no condensing boilers, so we got into the habit of measuring the "efficiency of a boiler" by the ratio between the calories recovered and the PCI of the fuel.

[consistent with what I wrote above: what we recover, as much as possible!)

In recent years, technology has evolved. We make condensing boilers. We continue, without specifying it, to measure the yield of calories recovered / PCI fuel.

Ex:

a) 1 liter of fuel = approximately 10 kWh in PCI
b) the condensation of the water vapor released by its combustion gives off approximately 1 kWh.
c) let's take a boiler that recovers 95% of the calories from the fire

- without condensation, it recovers 9,5 KWh; its output will be 9,5 kWh / 10 kwh (PCI) = 95%

- the same model equipped with condensation: it still recovers 9,5 kWh from the exchangers following combustion, but it also recovers the 1 kWh following the condensation of the water vapor in the condenser (it therefore "pees "!!); therefore we recover 10,5 kWh of calories; the efficiency of the boiler, since the definition has not been modified, will be 10,5 / 10 kWh of PCI = 105%


4) In fact, today, knowing that condensation exists and that we can therefore recover the heat given off by the condensation of water vapor, it would be necessary bring everything back to the PCS : the first would only have a yield of 9,5 / 11 = 86%; the second would have 10,5 / 11 = 95%

And there would be no more "incongruity"!
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by Ahmed » 05/05/14, 21:06

Yes, the absolute calorific value would be clearer than the relative calorific value ...
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by chatelot16 » 06/05/14, 02:25

when there is a change of unit you can find your way around because they have clearly different names

although there is no shortage of confusion: there was the small calorie and the large calorie, briskly mixed: distinguished only by a capital letter

1 cal = 1000 cal

so when we say that 1 cal = 4,18 joule, and that we compare with the calories in food, we are completely wrong: because it is large calories
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