# Lost Work

#### Lost Work

:
Watch the sign convention ! This equation applies to both turbines and compressors.
Where :
actual rate at which work is done by a real process operating between states 1 and 2.

rate at which work is done by a completely reversible process operating between the same initial and final states.

Such a process must be internally reversible and all heat exchange must be reversible as well.

Heat exchange only occurs with the surroundings, not a thermal reservoir.

Roll your mouse over this box to close.
Join Learn Thermodynamics Advantage
• Homework problem hints and answers
• Get Help from Dr. B in the LT Blog
• 120 day membership

Get it ALL for \$5 US

### Ch 8, Lesson D, Page 2 - Lost Work

• A completely reversible process operating between initial and final states 1 and 2 would produce or consume Wdot,S,rev.
• The sign convention applies.  Wdot,S,rev > 0 when the system does work on the surroundings, as in a turbine.
• A real process operating between the same initial and final states 1 and 2, produces less work (or consumes more if it is a pump or compressor). This amount of work is Wdot,S,actual.
• The lost work is the work that we did not get out of the turbine because it is not reversible.
• Alternatively, the lost work is the EXTRA work we had to put into the compressor because it was not reversible.
• Either way, the lost work is equal to the reversible work minus the actual work.
• The sign convention makes this equation work for both turbines and compressors.
• Remember, lost work is always a positive number.
• Now, let’s see if we can figure out how to calculate lost work.

 Jump to New page Show / Hide Notes