What diffrent between COP and Efficiency factor

[babieintown]

I read that to find an efficiency of device is output/input
but in many thread used COP instead.
Why we use COP to determine the Overunity ?
And what is the different between COP and normal output/input(eff.)?

Thanks

[spinner]

Hi!
Please, google or wiki,.. a "thermodynamic efficiency" and "Coefficient of performance".... Or "Thermodynamic Laws,.." etc..

In short, thermodynamic efficiency () relates to a power out / power in quotient of a closed (strictly defined) system. It's (theoretical!) limit is an "UNITY", where Pout=Pin (of course, the same is valid for energy(,...) transfers, too..).

There are cases of achieving "Unity" - (like a cryogenically cooled superconducting coils, where induced current flows "undisturbed for ages"...)
But the thing is actually a supreme proof of a "CoE" principle -  if you want to get a usefull work out of it, you' may get out only what you've put in originally...
(not mentioning an energy needed for maintaining a special environment...)
In practice - (so far) - forget about thermodynamics Unity...

Logically, By DEFINITION, it's impossible to achieve 'OverUnity' in classical thermodynamic sense (where output would be "somehow (out of nothing)" bigger than input). "Ex nihilo nihil"...
This observations (the basic Physics Laws) are still rock-solid (no matter what you read here, or elsewhere...)
Energy cannot be created, nor destructed (the Law of "Conservation of energy")...

The things became quite different if your "system" is not closed (it may have additional input(s) / or output(s)) - there may be other (known or UNKNOWN (!!!) energy transfers) - this way, it's possible to achieve "Over Unity", and physics knows a practical mechanism to describe that.

Just look at the "Heat Pumps" - the "additional input" is ambient heat, your "primary" input is electricity - the result is a device, which acts (PERFORMS) like a device which "produces" 3, 4.. times more heat than a "classical" electrical heater (the overall thermodynamic "efficiency" of a heat pump is still some 30..xx %, while the "CoP" is >3.0...). 

Consequently, a modern definition for a "Perpetual Motion Machine" (in a thermodynamic sense) - it's an impossible device (it cannot exist), because it would create energy out of nothing...
Cheers!

[babieintown]

Very very thanks Spinner.  I really really appreciate your short explanation. It help me out of the dark of fools. 

From your last paragraph i still don't understand that if our efforts is to trick the thermodynamics law or not?


Thanks in advance