Availability Exergy
Availability Exergy
(OP)
Thermodynamics textbooks define availability (exergy) as the max amount of work that a system can perform as it goes to equilibrium with environment and interacts with it.
They also define difference in availability (exergy) between two states. Is the difference in availability (exergy) the max amount of work achievable between the two states? Why?
If I define "associativity" of a city as the shortest distance from the city to Chicago, it does not follow that the difference in "associativity" between two cities is the shortest distance between them.
They also define difference in availability (exergy) between two states. Is the difference in availability (exergy) the max amount of work achievable between the two states? Why?
If I define "associativity" of a city as the shortest distance from the city to Chicago, it does not follow that the difference in "associativity" between two cities is the shortest distance between them.





RE: Availability Exergy
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RE: Availability Exergy
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RE: Availability Exergy
I am reviewing from a number of Thermo texts. One text (Lee-Sears) says that the difference in availability (exergy) between two equilibrium states is the max work attainable between two states. I don't see it. Other texts don't mention it.
I am a Mechanical Engineer and not familiar with Thermodynamics. I thought the question might also be of general interest to Thermodynamics.
RE: Availability Exergy
RE: Availability Exergy
RE: Availability Exergy
RE: Availability Exergy
It's something I picked up from some Thermo books. By definition, it's the max amount of work that a system can perform in coming to equilibrium with the environment. I really don't know if it's just an academic concept or something used in real world thermodynamics engineering like analysis of power plants.
RE: Availability Exergy
Based on that, the answer is also no, since entropy is included. Since you cannot make useful use of all the stored energy, unless you do directly from one state to another, there will be additional energy consumed.
TTFN
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RE: Availability Exergy
RE: Availability Exergy
RE: Availability Exergy
First Law of Thermo: The best you can do is break even.
Second Law of Thermo: You can't break even.
RE: Availability Exergy
Xdes = (Temperature of surroundings) * (change in entropy generated)
The value for Xdes is usually expressed in units of Energy per unit mass.
Hopefully that helps.
-Mike
RE: Availability Exergy
A mechanical engineer SHOULD be familiar with thermodynamics if he/she were educated in an ABET certified mechanical engineering program. The thermo text is at arm's reach at least on a dusty shelf. The school I went to required three thermo classes.
Tunalover