Deviations from the Ideal AS-Brayton Cycle

Ch 9, Lesson E, Page 13 - Deviations from the Ideal AS-Brayton Cycle

• Just as in the Rankine Cycle, fluid friction and mechanical friction are the main causes of internal irreversibility in the Brayton Cycle.
• Friction irreversibly converts kinetic energy into internal energy.
• There isn’t a pump or condenser, so we don’t need to worry about subcooling the pump feed in a Brayton Cycle, but all the other sources of internal irreversibility are the same as in the Rankine Cycle.
• Real heat exchangers cannot operate at constant pressure because friction causes the pressure to drop as the fluid flows though the equipment.
• Real turbines and compressors do not operate isentropically.  Fluid friction and mechanical friction irreversibly convert kinetic energy into internal energy.
• The result is an increase in entropy.
• The path for a real gas power cycle is shown in red on the TS Diagram, while the cycle path for the Brayton Cycle is shown in light gray.
• The irreversibilities tend to skew the cycle.
• Remember that this diagram is useful only to help you visualize a real gas power cycle.
• Areas are NOT equal to heat and the enclosed area is not equal to the net shaft work because this cycle is NOT internally reversible.
• Well, that concludes our discussion of gas power cycles.
• In the next lesson we will complete this chapter with a discussion of some common improvements to the Brayton Cycle.
• But for now, do the example, summary quiz routine to reinforce what you have learned in this lesson.