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lana
28-10-2005, 07:34 AM
Can enyone explain in a very simple manner what is the Entropy? I know the thermodynamic definition of it.
Cheers.:)

US Iceman
28-10-2005, 02:29 PM
This is a question that always generates more questions.

Try these websites:

http://www.2ndlaw.com/

or,

http://www.entropylaw.com/

These links have a lot of information and explanations that can hopefully explain this for you.

Regards,

dogma
29-10-2005, 01:49 PM
Quick question...R U in the trade?


Entropy is found on the Enthalpy chart which is the fundamental of design and fault finding in the refig industry.


Unfortunately I don't fully understand entropy myself only that it is a measure of energy and work done in the commpressor.

Don't quote me though. Google PH charts or pressure enthalpy charts.


Some one tell me if I'm wrong I'm only a 1st yr apprentice.

rbartlett
29-10-2005, 06:37 PM
Entropy entropy -they've all got it entropy !! ;-))


cheers

richard

botrous
29-10-2005, 10:15 PM
Entropy entropy -they've all got it entropy !!

Hi Richard , seems that you are very familial with the entropy concept , can you define it for us ?

Regards

botrous
29-10-2005, 10:17 PM
Lana this might be useful to :
http://en.wikipedia.org/wiki/Entropy
http://physics.about.com/cs/thermodynamics/g/Entropy.htm

dogma
30-10-2005, 11:25 AM
Entropy. 'measure of the "unavailability" of a systems thermal energy for conversion into mechanical work.'

Adiabatic Process.

Compression is adiabatic when there is no heat transfer to the cylinder wall, or from the cylinder walls during compression, so that an amount of energy equal to the work done on the vapour is set up in the vapour as internal energy, and vapour temp increases accordingly.


Australian refrigeration and air conditioning '4th ed'
West 1 services."graham boyle" 2004

This is assumed for plotting Ph charts.

Erik Detroit
30-10-2005, 03:27 PM
My quick definition of entropy is that it is a measure of the "disorder". The concept of entropy can be applied to anything, a clean and orderly house has less entropy than a messy and disorderly house.

The application to thermodynamic systems is very important, as the 2nd law of thermodynamics tells us that for any real process the entropy of everything involved (sometimes just referred to as the universe) in the process must increase. In other words, there will always be inefficiencies and perpetual motion machines are not possible.

It is possible to straighten up a house and decrease it's entropy, but the entropy that you generate in the process will be greater (you will burn energy doing the work).

For thermodynamics, the concept of entropy lets you determine the actual path that a process will take. The 1st law of thermodynamics will tell you how energy can change forms (like from kinetic energy of motion into thermal energy). The 2nd law will tell you which energy change will actually occur.

For refrigeration, entropy is very important for determining how a compressor will operate with a given refrigerant and conditions.

As you know the compression process generates both higher pressures and higher temperatures, both are forms of increased energy (or enthalpy) of the refrigerant, but how much temperature rise will accompany a given pressure rise?

Entropy lets you determine how much pressure rise will accompany the temperature rise, and vice-versa. The entropy of the compression process must increase, and since a compressor is a real device, it must have an isentropic efficiency less than 100%.

The old joke about entropy, mostly on bumper stickers of physics professor's cars is:

Entropy just aint what it used to be.

(The entropy of the universe must be increasing, since it is not possible for it to ever decrease)

I hope this point of view helps,
-Erik

wambat
31-10-2005, 01:08 AM
Can enyone explain in a very simple manner what is the Entropy? I know the thermodynamic definition of it.
Cheers.:)
A simple explanation: Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so.

lana
31-10-2005, 03:20 PM
[QUOTE=Erik Detroit]My quick definition of entropy is that it is a measure of the "disorder". The concept of entropy can be applied to anything, a clean and orderly house has less entropy than a messy and disorderly house.

:confused: Thanks Erik, it was a real simple explanation.
Regards

Lc_shi
03-11-2005, 06:37 AM
Entropy is more philosophy meaning than enthalpy. In practical work ,enthalpy is widely used. I think Entropy is the increasing function of the time. Minus entropy is needed to control the system in order and energy input needed at the same time.