Explain Entropy? 7

[Rpsfinest]

Can someone quantify entropy for me? I am having a hard time putting the theory of entropy to something real. Can anyone explain this concept to me using a real life example, possibly a heat transfer situation?

 

[timbones]

Where did all these dirty glasses come from?

 

[mbeychok]

Latexman:

Your professor's "You can't get something for nothing" is the same as my professor's "There are no free lunches in the Universe" ... is it not? >)

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[Latexman]

mbeychok,

Absolutely!

Good luck,
Latexman

 

[timbones]

One aspect of the whole idea of "there is no such thing as a free lunch" is that it applies to closed systems. This is a key point to the whole understanding of entropy that is often missunderstood. When someone claims to defy the 2nd law of thermodynamics, by say building some sort of perpetual motion machine, they have usually violated this condition by not defining the boundaries of the situation properly.

I digress...

Why do we care about entropy in the real world is the really important question in my view? To answer this, it may be useful to look at specific examples. Let us say you want to evaluate the performance of a specific piece of equipment, say for example a steam turbine. You feed the machine a certain quantity of high pressure steam and get out the other end some low pressure steam and some power. How do you know how well that machine has done this task? One way is to look at the inlet conditions of the turbine and assume that the process to the outlet condition is reversible. In this case the entropy of the steam going in is equal to the entropy of the steam going out of the device (assume there is no energy losses to the environment due to heat transfer for the turbine casing, ie define the boundaries properly!). You can calculate how much power you could have made under this reversible and unachievable scenario, then compare it to how much power you actually made. This will give you the efficiency of the turbine and tell you how much improvement is possible. This entropy based efficiency of the device (called the isentropic efficiency) is a very useful metric.

Tim

 

[Latexman]

If the boundaries are drawn BIG enough, is the universe a closed system?

Good luck,
Latexman

 

[25362]

As long as the tendency of the energy is to run down (entropy), as for any other closed system, the answer would be: yes.

 

[ShaggyPE]

For a great sci-fi short story about entropy, read The Last Question by Isaac Asimov. Follow the link provided.

http://www.multivax.com/last_question.html

-Shaggy

 

[wfn217]

See this link:

http://www.spiraxsarco.com/resource...at-transfer/entropy-a-basic-understanding.asp