1st & 2nd Laws for SS, SISO Systems

  • Now, let's compare a real, adiabatic process such as a pump, compressor, turbine, or a nozzle to a comparable isentropic process.
2nd Law
(Entropy Balance):
For SS, SISO Systems:
1st Law :
2nd Law
(Entropy Balance) :
  • Processes for which we use isentropic efficiency are designed to have insignificant heat transfer, so we will assume our processes are adiabatic.
  • In this course, we will usually consider processes for which ΔEK ≈ 0 and ΔEP ≈ 0 because changes in the fluid velocity and elevation from the inlet to the outlet of the process are negligible. This is not always true !
  • If you know inlet and outlet elevations, velocities and/or pipe diameters, you should include changes in kinetic and potential energies in your analysis.
When ΔEK ≈ 0 and ΔEP ≈ 0 and the process is adiabatic:
1st Law:
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Ch 8, Lesson C, Page 2 - 1st & 2nd Laws for SS, SISO Systems