Chapter 6 Question 7 Answer:

(3) wf > 0 > w > ws

For an adiabatic compressor ws = -cp(DT), w = -cv(DT), and wf = R(DT). For air, cp > cv > R. Therefore wf > 0 > w > ws. This illustrates an important point regarding shaft work and flow work. For a steady flow device, what you would like to design to is the work that must be put into the shaft. If you calculate, the total work (w), you will come up short for a compressor.