# H-S Diagrams

### HS Diagram

Consider an irreversible, adiabatic, steady-flow process such as the turbine shown below.
Ws = ___ kJ/s
Q = 0
1st Law:
0
Proportional to the net work for an adiabatic, steady-flow devices such as turbines, pumps and compressors.
Larger values of are associated with greater irreversibility within the system.
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### Ch7, Lesson B, Page 18 - H-S Diagrams

• We won’t use the HS Diagram quite as often as the TS Diagram, but for certain processes, the HS Diagram is the most useful.
• An example of such a process is an irreversible turbine, like the one shown here.
• The 1st Law tells us that the rate at which shaft work is produced by the turbine is just the mass flow rate times the change in the specific enthalpy.
• Therefore, the vertical distance between states 1 and 2 on the HS Diagram is proportional to the rate at which work is done by the turbine.
• We will see later in this chapter and again in chapter 8 that ΔShat or the horizontal distance between state 1 and 2 is proportional to the irreversibility in the turbine.
• If the turbine were reversible as well as adiabatic, then it would also be isentropic and the process path on the HS Diagram would be a vertical line.
• The steeper the path of an adiabatic process on the HS Diagram the closer the performance of the real process approximates the performance of an ideal, reversible process.
• So, I hope you see that, for certain processes like pumps, turbines and compressors, the HS Diagram gives some special insight into how close a real process comes to being reversible.
• That concludes our introduction to the new state variable, entropy.
• In the next lesson, we will study a very important limitation that the 2nd Law places on how entropy can change.
• Well, you know the drill by now.  Work some example problems, read the lesson summary and then try the quiz.