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By Ignacio Vasquez-Castro
Reversible work (Wrev)
Reversible work (Wrev) is the maximum amount of Useful work (Wu) that can be produced (or the minimum amount of Wu that needs to be supplied) as a system undergoes a process between specified initial and final states.
Situation example 1: Finding Wu for the expansion of a closed system:
As system expands, work is done against the surroundings to push atmospheric air out of the way (Wsurr).
We know:
We know Wu is the work done as the system expands, as this is contained so can be recovered and used. The work done against the surroundings, Wsurr, is not recoverable or usable, so it is not a part of Wu.
Tips and illustrations
<-- This is a general definition. The Useful work (Wu) will be different in different situations, according to what the device does. See below.
From situation 1, we can deduce that for constant-volume processes, the total work is equal to the useful work, i.e. W = Wu (as the V2-V1 term in Wsurr is 0)
I is always a positive quantity since Wrev > Wu for work-producing devices and Wrev < Wu for work-consuming devices
<-- The smaller the irreversibility of a process, the more work can be produced (or less work consumed). Therefore, the performance of a system can be improved by reducing the irreversibility associated with it.
So, , where W is the total work done during the expansion.
Irreversibility (I)
The Irreversibility (I) of a process is the difference between Wrev and Wu. It is also equal to the exergy destroyed.
- for a work-producing device:
- for a work-consuming device:
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