1. ENGR 2213 Thermodynamics F. C. Lai School of Aerospace and Mechanical Engineering University of Oklahoma

2. Brayton Cycles George Brayton (1870) Applications of Gas-Turbine Engines Propulsion Power Generation - The first gas turbine for electric power generation was installed in 1949 in Oklahoma. - Before 1980s, gas power plants were mainly used for peak-load power production. - It is forecast that more than half of all power plants to be installed in the future are gas power plants.

3. Brayton Cycles George Brayton (1870) Open cycle Closed Cycle

4. Brayton Cycles

5. Staedy-flow q – w = h e – h i q in = h 3 – h 2 q out = h 4 – h 1 1 2 3 4 T S Q in Q out = c p (T 3 – T 2 ) = c p (T 4 – T 1 )

6. Brayton Cycles The thermal efficiency increases with the pressure ratio. The highest temperature in the cycle is limited by the maximum temperature that the turbine blades can withstand.

7. Example 1 A gas power plant operating on an ideal Brayton cycle has a pressure ratio of 8. The gas temperature is 300 K At the compression inlet and 1300 K at the turbine inlet. Utilizing the air-standard assumptions, determine (a) the gas temperature at the exits of the compressor and the turbine, (b) the back work ratio, (c) the thermal efficiency of this cycle.

8. Example 1 (continued) Process 1-2: Isentropic compression Table A-17 h 1 = 300.19 kJ/kg p r1 = 1.386 State 1: air at the inlet of compressor, T 1 = 300 K Table A-17 T 2 = 540 K h 2 = 544.35 kJ/kg (a)

9. Example 1 (continued) Process 3-4: Isentropic expanion Table A-17 T 4 = 770 K h 4 = 789.11 kJ/kg w comp = h 2 – h 1 = 544.35 – 300.19 = 244.16 kJ/kg State 3: air at the inlet of turbine, T 3 = 1300 K Table A-17 h 3 = 1395.97 kJ/kg p r3 = 330.9

10. Example 1 (continued) w turb = h 3 – h 4 = 1395.97 – 789.11 = 606.86 kJ/kg (c) (b) q in = h 3 – h 2 = 1395.97 – 544.35 = 851.62 kJ/kg w net = w turb – w comp = 606.86 – 244.16 = 362.7 kJ/kg = 1 – r p (1-k)/k = 1 – (8) -(0.4/1.4) = 0.448

11. Brayton Cycles with Regeneration

12. Brayton Cycles with Intercooling, Reheating, and Regeneration